GET Draft ISSB Construction Manual (Final_2)

35
Interlocking Stabilised Soil Block Draft Construction Manual Double Interlocking Rectangular Blocks for House Construction Part I: Planning, Setting-out and Construction [Part II: Building Services, Finishes and Maintenance] April 2009

Transcript of GET Draft ISSB Construction Manual (Final_2)

Page 1: GET Draft ISSB Construction Manual (Final_2)

Interlocking Stabilised Soil Block

Draft Construction Manual Double Interlocking Rectangular Blocks for House Construction

Part I: Planning, Setting-out and Construction

[Part II: Building Services, Finishes and Maintenance]

April 2009

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Good Earth Trust Draft ISSB Construction Manual - Part I April 2009 i

CONTENTS

A. PREFACE ...................................................................................................................................... ii

B. DISCLAIMER.................................................................................................................................iii

C. ACKNOWLEDGEMENTS ..................................................................................................................iv

D. INTRODUCTION ............................................................................................................................ 1

D.1 Building Plan........................................................................................................................... 1

D.2 Good Quality ISSBs ................................................................................................................. 1

E. SUB-STRUCTURE.......................................................................................................................... 3

E.1 Introduction ............................................................................................................................ 3

E.2 Site Clearance ......................................................................................................................... 3

E.3 Setting Out ............................................................................................................................. 4

E.4 Excavations............................................................................................................................. 5

F. FOUNDATION STRIP ...................................................................................................................... 6

G. FOUNDATION PLINTH.................................................................................................................... 7

G.1 Introduction............................................................................................................................ 7

G.2 Mortars .................................................................................................................................. 7

G.3 ISSB Parts .............................................................................................................................. 8

G.4 Single Wall ............................................................................................................................. 8

G.5 Double Wall ............................................................................................................................ 9

G.6 Plinth Wall Construction......................................................................................................... 10

G.7 Ground Slab ......................................................................................................................... 11

H. WALLING.................................................................................................................................... 13

H.1 Introduction.......................................................................................................................... 13

H.2 Corners/Wall Intersections..................................................................................................... 13

H.2.1 the “L” Junction.............................................................................................................. 14

H.2.2 the “T” Junction.............................................................................................................. 15

H.2.3 the “+” Junction ............................................................................................................. 16

H.2.4 the “Y” Junction.............................................................................................................. 17

H.2.5 Stopped Ends, Door and Window Openings ...................................................................... 17

H.3 Super-structure Wall Construction .......................................................................................... 18

H.3.1 Layout, Door Openings and First Course........................................................................... 18

H.3.2 Raising the Walls ............................................................................................................ 19

H.4 Ring Beam / Bond Beam and Formwork .................................................................................. 19

H.5 Finishing the Wall.................................................................................................................. 21

H.6 Scaffolding/Platforms ............................................................................................................ 21

I. ROOFING .................................................................................................................................... 24

I.1 Introduction........................................................................................................................... 24

I.2 Roof Structure ....................................................................................................................... 24

I.3 Connecting the Wall Plate and Trusses..................................................................................... 25

I.4 Roof Cover and Rainwater Harvesting ...................................................................................... 26

J. APPENDIX ................................................................................................................................... 27

J.1 Some Design Considerations................................................................................................... 27

J.2 Typical Low-Cost Home Plans.................................................................................................. 28

J.3 Sample Building of Costs ........................................................................................................ 30

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A. PREFACE

ISSB (interlocking stabilized soil block) is an alternative and appropriate building material for East Africa

with proven success for a wide range of housing types from simple buildings such as latrines to more

involved and sophisticated single-rise and storied residential, institutional and commercial structures. The

technology has been in use in East Africa for over twenty years but scanty specialized technical

information is available for potential users of the technology. It is against this background that this Draft

ISSB Construction Manual has been prepared by Good Earth Trust (GET) primarily targeting the informal

and small-scale formal building associations and companies in the region. Nevertheless, fully-fledged

establishments may also find it useful.

The main objective of the Manual is to provide trainees and potential users of the ISSB technology with

simple but sufficiently detailed and well illustrated ISSB construction guidelines for easy assimilation and

effectual adoption and use of the technology on any construction site without the need for further

information. Detailed sketches and lists of relevant tools/equipment which may be manufactured or

available locally are provided. In the few instances where the available information is not sufficient, the

reader may obtain additional technical details from any credible source available or contact the nearest

Good Earth Trust office for assistance.

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B. DISCLAIMER

The construction techniques presented here are derived from the best practices in East Africa where the

initial target audience is based. However, it is assumed that the potential users of this Manual are trained

persons who already are familiar with the conventional building practices. Therefore, Good Earth Trust

reserves the right not to be responsible for the topicality, correctness, completeness or quality of the

information provided in this Manual. Liability claims regarding damage caused by the use of any

information provided, including any kind of information which is incomplete or incorrect, will thus be

rejected. Information in this document might be extended, changed or partly or completely deleted

without prior notice. [To be edited]

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C. ACKNOWLEDGEMENTS

The Good Earth Trust teams in Uganda, Kenya and the UK for every support and facilitation, Technology

for Tomorrow (T4T) (Uganda) for the invaluable training expertise, Makiga Engineering Services Ltd.

(Kenya) – the manufacturer of the block press.

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D. INTRODUCTION

D.1 Building Plan

All building projects must have relevant drawings (of sorts) usually produced by competent person(s) or

group(s) thereof. As this manual is based on building construction using the straight double interlocking

stabilized soil block, a simple 2 bed-roomed ISSB building plan is provided below, Fig. D.1, which will

therefore be used throughout the manual for illustrations (detailed architectural models of low-cost

homes are included in the Appendix to this Manual). Other related features such as cross-sections and

elevations will be derived and used as and where necessary. Note that the building dimensions are ISSB-

specific (see Section D.2 below for the block dimensions).

D.2 Good Quality ISSBs

For best results, good quality interlocking stabilized soil blocks (ISSBs) (see Fig D.2 for dimensions)

should have been produced while carefully considering the following points: (1) adoption of optimum

proportions of soil, stabiliser (usually cement (OPC)), and water, taking into consideration the

characteristics of local soil; (2) careful mixing of the various components of stabilised soil blocks; (3)

application of an adequate compaction pressure to the moist soil/cement mixture in order to obtain dense

and strong building blocks with well-shaped surfaces and edges – by the correct use of the block press as

detailed in its operational manual; and (4) allowing blocks to cure sufficiently before usage to minimise

the risk of damages to the blocks and cracks in the finished structure as well as give an excellent finish to

Fig D.1 Ground Plan

REAR

SID

E (

2)

FRONT

SID

E (

1)

STORE

BEDROOM

PORCH

BEDROOM

LIVING ROOM

7.82 m

6.7

5 m

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Good Earth Trust Draft ISSB Construction Manual - Part I April 2009 2

a wall surface. Obtaining a smooth block surface can further permit their use without rendering or with a

minimum use of rendering materials if required.

The Kenya Standard Specification (KS 02-1070: 1993) and Draft Uganda Standard (DUS 849: 2009)

provide the following (minimum) physical characteristics of stabilized soil blocks necessary for good

building construction:

• Dry Compressive Strength of blocks at 28 days 2.5 N/mm2;

• Wet Compressive Strength of blocks at 28 days 1.5 N/mm2;

• Rapture Strength of blocks at 28 days 0.5 N/mm2;

• Water Absorption of blocks 15 per cent of the original mass;

• [Dry] Density of blocks 1600 Kg/m3;

• Weathering loss of mass 15 per cent of the original mass;

• Shrinkage cracks 0.5 mm wide and 50 percent of the parallel block dimension; and

• Visibly free of broken edges, honeycombing, and other defects that would impair quality.

Please note that determinations of the above parameters are beyond the scope of this Manual therefore

the reader is advised to refer to relevant local authority for detailed procedures.

Fig D.2 ISSB Dimensions

STRAIGHT DOUBLE INTERLOCKING BLOCK

Format Size: 290 x 140 x 115 mm

Coordinating Dimensions: 266 x 140 x 95 mm

(Order: Length x Breadth x Height)

Courtesy of Makiga Engineering Services-2009

115 mm 95 mm

266 mm 140 mm

290 mm

SIDE

PLAN

END

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E. SUB-STRUCTURE

E.1 Introduction

Sub-structure generally includes all the components of a building that bear directly onto the ground (see

Fig E.1 below). The usual order of the activity sequence in its construction is: (1) Site Clearance, (2)

Setting Out, and (3) Excavations – as preliminary operations; (4) Foundation Strip (plain concrete), (5)

Foundation Plinth (double ISSB wall), and (6) Ground Slab (usually a composite structure consisting

of 25 mm cement/sand screed on 100 mm mass over-site concrete (plain or reinforced) on rubbles or

“hard core” on well compacted formation). Each operation is described in more detail hereafter.

E.2 Site Clearance

Vital Tools/equipment: Hoe, Spade, Pick axe, Wheelbarrow. Others: Axe, Rake, Machete, and Bow-

saw. These can readily be obtained from the local hardware shops and the specific types and numbers

will depend on the nature of the proposed building site and the number of operatives to be deployed on

the job – depending on the availability and cost of labour at the project site.

Start by clearing the site of any obstacles such as trees, rocks, vegetative cover etc. using the building

plan in Fig D.1 above and providing 0.5 m as width of the foundation trenches and 0.6 m clearance

around the walls, a minimum area of about 9 m long by 8 m wide (72 m2) should be stripped of the top

vegetative soil to an average depth of 150 mm from the existing ground level. Vegetative soil is not good

for use in construction, so remove and deposit the spoil away from the building area but in a place where

it can eventually be used for gardening purposes.

Fig E.1 Typical Sub-structure Detail

Stripped ground level

Foundation strip

Backfill

Plinth wall

Ground slab

Finished floor level

Super-structure wall

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E.3 Setting Out

Vital Tools/equipment: Pegs & profiles (4x2 timber or 60 mm poles cut to 1 m), Nylon strings, Claw

hammer, Hoe, Long tape ( 30 m), Steel tape ( 5m), Water level, Spirit level, Bow saw, Wire nails

(assorted). Others: Plumb bob, Machete, Sledge hammer, Crow bar, white (pit) sand or ash for marking,

Mortar pan. These can readily be obtained from the local hardware shops. Note that “vital tools” are necessary

for a proper setting-out operation to be conducted while “others” are optional tools that may be improvised.

The building is set-out for excavation by use of profiles fixed clear of the trenches by at least 1 m so as

not to disturb the lines by excavation activities or bury the profiles in the heap of excavated soil (Fig

E.3a). All profiles should be established to a fair level (using a water level) and set off the ground by at

least 0.5 m (Fig E.3b).

Fig E.2 Site Clearance Plan

9 m

8 m

FRONT

REAR

SID

E (

1)

SID

E (

2)

Fig E.3a Setting Out Plan

7 m

6 m

FRONT

REAR

SID

E (

1)

SID

E (

2)

Profiles

Lines/Strings

Keep profiles clear

of excavation ( 1m)

0.5

m

0.5

m

0.5 m 0.5 m

2.7 m

0.7 m

2 m

2.5 m

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E.4 Excavations

Tools/equipment: Hoe, Spade, Pick axe, Machete, Wooden rammer. Others: Wheelbarrow, Watering

jar.

Excavate strip foundation trenches 500 mm wide (Fig. E.4) using the simple hand tools listed above, to a

depth usually determined on site where uniform and stable soil is encountered, but 0.5 m. Heap the

excavated soil within the building area – clear of the trenches – to be eventually used for backfilling.

Ensure that the sides of the trenches are fairly vertical if in stable soil by trimming with machete;

otherwise if the soil is seen to be unstable then the sides should be cut to a suitable slope outwards to

avoid the ground caving-in and causing accidents to the operatives. Depending on the general nature of

the local terrain, the foundation trenches may be stepped for safety and economic reasons. Level the

trench bottom and compact with a wooden rammer (see Section E.5 below) and if required, apply anti-

termite treatment to the bottom and sides of the trenches by sprinkling the solution with a watering jar.

Note that a strip foundation may not be suitable for use in unconsolidated landfills, marshes and other

unstable ground conditions in which case specialist advice must be sought.

Fig E.4 Strip Excavation

500 mm

Stripped ground level

100mm vertical to receive concrete

500 mm

A: Stable soil (vertical sides)

B: Unstable soil (reposed sides)

Fig E.3b Profile Set-up

Peg: 4"x2" timber or 60mm pole sharpened on one end

350 mm 350 mm

Profile: 4"x2" timber or 60mm pole 1m long nailed to fair level on pegs 5

00

mm

Ground level

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F. FOUNDATION STRIP

Tools/equipment: Hoe, Spade, Jerry-can, Bucket, Wheelbarrow, Wooden rammer, Wire nails, Claw

hammer, Water level, Nylon string. Others: Porker vibrator, Water reservoir, Gauge box (Fig. F.3),

Timber (12”x1”), 100mm Diameter eucalyptus poles – platforms for pushing the wheel barrow in case of

soft ground (rain & loose soil).

Materials: Cement, Sand (both coarse and fine if available), ” Aggregate (ballast), Water (clean).

The footing is usually plain concrete of class C10 – C15 commonly associated with a volume mix ratio of

1:3:6 (cement: fine aggregate (or sand): ” coarse aggregate (or ballast)). Note that sand for concrete

is not normally sieved. Use the same gauge box or bucket to measure all the ingredients including

cement and mix concrete on clean platform using clean water; pour 50-100 mm thick in trenches.

Compact concrete with a porker vibrator or manually using a wooden rammer (Fig F.1) to a fairly level

finish and cure by wetting the strip twice daily for at least 2 days to allow concrete to harden reasonably

well before setting and constructing the plinth wall.

Fig F.1 Placing Foundation Concrete (trench in stable soil)

500 mm

Stripped ground level

Foundation concrete

100 mm

Wooden rammer

300 mm

6"x2" or 4"x2" timber firmly nailed on end of pole

1200 mm

60 mm pole

Fig F.2 Gauge Box for Measuring Materials

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G. FOUNDATION PLINTH

G.1 Introduction

Tools/equipment: Builders tools (trowel, square, plumb bob, spirit level, water level, building lines),

Machete, Hoe, Spade, Jerry-can, Wheelbarrow, Mortar pan. Others: Gauge rod (Fig G.4c below), Water

reservoir, Gauge box (Fig. F.2 above), Metal saw, Timber (12”x1”), 100 mm Diameter eucalyptus poles –

platforms for pushing the wheel barrow in case of soft ground (rain & loose soil). Personal Safety Gear:

Overall, Boots, Helmet, Gloves, Goggles.

Materials: Good quality ISSBs (see Section D.2 above), Mortar (see Section G.2 below): Cement, Sand

(both coarse and fine if available), Water (clean). Others: 1.2 mm Flat bars (mild steel), Weld mesh

(8'x4').

Foundation plinth or plinth wall is the block-work that is usually buried in the ground and on which the

ground slab or the superstructure rests. It is therefore the means of permanently fixing a building to the

Earth's surface; as such it should be made sufficiently stable to be effective. For this reason, it is

recommended that the outermost plinth walls and those underlying load-bearing walls of low-rise

buildings be made of double ISSB block-work as explained in Section F.5 below. Where necessary, other

internal plinth walls can be made of single ISSB block-work provided that they are mortared at every

course and adequately secured with hoop iron at wall intersections or corners.

G.2 Mortars

The tools/equipment and materials are listed under Section G.1 above.

Mortars are used primarily to accommodate slight irregularities in size, shape and surface finish of blocks

thus providing uniformity and stability to a wall. In doing so any gaps between blocks are also closed,

preventing wind and rain from passing through the wall. Mortar has a further purpose in that it improves

both the shear and compressive strengths of the wall. Mortars have some binding characteristics which

improve the shear resistance but do not add significantly to the tensile strength of a wall.

For ISSB construction, cement/sand mortars of different mixes are normally used for different strength

requirements. For instance, a 1:3 (cement: sand) mortar is expected to be stronger than a 1:4 mix – the

former often used in foundations whereas the latter in superstructure walling. Two types of sand are

normally used to achieve good results; these are pit/plaster sand with very fine grains or particles and

washed (lake/river) sand having coarse grains. More of pit sand to washed sand is used (say 2:1 in a 3-

part mortar sand, and 2.5:1.5 in a 4-part mortar sand) for improved workability and bonding

characteristics of mortar.

The oversize material in the sand for mortar must always be removed by sieving as a separate operation.

This is because course particles in mortar will distort the alignment of blocks both horizontally and

vertically – giving a poor finish to the walls as well as weakening the interconnection between the blocks

and the wall at large. Just enough mortar to last for a maximum of 1 hour at a time should be mixed on a

clean platform using clean water.

The simplest sieving device is a wire mesh screen, nailed to a supporting wooden frame and inclined at

approximately 45° to the ground (Fig. G.2). Sand is thrown against the screen, the fine material passing

through and the coarse, oversize material running down the front. Alternatively, the screen can be

suspended horizontally from a tree or over a pit. This latter method is suitable in cases where most

material can pass through in windy conditions; otherwise too much coarse material is collected, and the

screen becomes blocked and requires frequent emptying thus more labour/cost required.

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G.3 ISSB Parts

The ISSB parts shown in Fig G.2 below are not standard names but used herein this document for

descriptive purposes. The orientation of the block is as it comes out of the block press and the various

parts are: (1) “head” – the depressed cross-sectional end; (2) “tail” – the protruded cross-sectional end;

(3) “top” – the depressed longitudinal bed; and (4) “bottom” - the protruded longitudinal bed. For

dimensions of the ISSB block, refer to Section D.2 above.

G.4 Single Wall

The tools/equipment and materials are listed under Section G.1 above.

ISSBs are self interlocking and therefore can either be dry-stacked (e.g. in a small family latrine of say

2–3 m2), mortared in say every 3rd or 4th course (e.g. in a 2-roomed residential house) or mortared in

every other course (e.g. in foundations and large walls) depending on the size, structural and

environmental requirements of the walls in question. It is recommended that foundation walls be

mortared in every other course for greater strength and efficient supporting system.

However, for economic reasons and to achieve greater benefits of the interlocks, the mortar should be

limited to just about 5 mm – which can practically be controlled by using a gauge rod (Fig G.4c below).

Fig F.2 Simple site screen to remove coarse particles from mortar sand

Fig G.3 ISSB Parts (side elevation)

"Top" (depressed)

"Bottom" (protruded)

"Head" (depressed)

"Tail" (protruded)

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Note that ISSB vertical joints are not normally mortared and the blocks should always be stacked in such

a way to avoid the vertical joints in adjacent courses coinciding or being too close to each other (Fig G.4d

below).

The blocks are usually laid on their bottom face and running tail-wise from a corner outwards (see Fig

G.3 above for the block parts). For the first course (often sitting directly on the foundation strip or the

ground slab), the protrusion is ripped off using a machete (panga knife) so the blocks can stably bed in

mortar. Ripping of the protrusion also helps to control the amount of mortar used at that level (Fig G.4d

below). The first course must be carefully set to good level using water and spirit levels and building line

as subsequent courses will generally assume this level. The overlying courses can be controlled using a

gauge rod, building line and plumb bob and levelling tools to ensure uniform levels and verticality of the

wall. A builder’s square must always be used to check right angles as shown in Fig G.4a below.

G.5 Double Wall

The tools/equipment and materials are listed under Section G.1 above.

An ISSB double wall is achieved by laying two single walls adjacent to each other (Fig G.5 below) using

the same tools, materials and procedures described earlier under Single Walls. However, the interface

between the two walls must be mortared and metal strips used to secure the wall leaflets as detailed in

Section H.2 (Corners/Wall Intersections) below. Fig G.5 is the layout of the plinth wall for the building

plan shown in Fig D.1 above. Note that no internal plinth walls are used because of the relatively small

size of the building and that a great deal of the slab is directly sitting on the ground, as detailed in Fig E.1

above.

Fig G.4 Typical ISSB Corner Detail

1st

(d) Elevated Wall

2nd

Mortar on DPC

Trim dotted portions

3rd

5th

4th

6th

Spirit level

(a) 1st, 3

rd, 5

th, 7

th … Course Plan

95mm

95mm

95mm

95mm

95mm

95mm

95mm

95mm

95mm

95mm

105mm

(c) ISSB Gauge Rod

7th

8th

Builder’s square

(b) 2nd

, 4th

, 6th

, 8th

… Course Plan

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G.6 Plinth Wall Construction

The tools/equipment and materials are listed under Section G.1 above.

Raise the plinth wall to a minimum height of 200 mm above the stripped ground level – the idea is to

have the finished floor level at least one foot (300 mm) above the stripped ground so that storm water

cannot run into the house. Backfill the excavated subsoil around the plinth wall in layers not exceeding

200 mm ensuring that both sides of the walls at any point are filled to the same level every time. This

ensures balanced earth pressures on either side of the wall thereby eliminating the risk of buckling or

cracks in the plinth during compaction of the backfill and thereafter (see Fig G.6 below).

If the backfilled soil is not moist (especially during very dry weather), sprinkle some water onto the soil

using a watering can – the amount of water used should just be enough to make a lamp of soil squeezed

in the palm stick together the same way water content is tested in the soil-cement mixture for making

the stabilized soil blocks. Compact both layers of soil on either side of the wall at just about the same

time (it is better to have at least two people compacting at the same time, one on each side of the wall).

Repeat the backfilling and compacting operations, each time in layers not exceeding 200 mm, up to the

level of the stripped ground. Once done, your foundation is then ready to receive the ground slab.

Fig G.5 Foundation Plan

3000mm 1640mm

2000mm 7250mm

7850mm

61

50

mm

67

50

mm

SID

E (

1)

SID

E (

2)

300mm 300mm

30

0m

m

30

0m

m

FRONT

REAR

1000mm

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G.7 Ground Slab

The ground slab is usually a composite load-bearing structure comprising two or more layers of different

materials. The most common detail includes 1 inch (25 mm) cement/sand screed; on 2, 3, or 4 inches

(50, 75, or 100 mm) plain or reinforced concrete; on 4, 6, or 8 inches (100, 150, or 200 mm) stone base

(commonly referred to as ‘hardcore’); on well compacted backfill or formation (Fig G.7 below).

Fig G.6 Backfilling around the Plinth Wall

Backfill in layers not exceeding 200mm & compact up to this level

200 mm

200 mm Stripped ground level

300 mm Part of plinth wall above stripped ground level

500 mm

Foundation concrete

Backfill

100 mm

Fig G.7 Typical Low-Cost Ground Slab and Weathering Detail

Stripped ground level (Or Formation level)

Foundation strip

Backfill

No “splash apron” but part of plinth wall to be rendered to serve the same purpose

Gro

un

d s

lab

Finished floor level

Super-structure wall to be rendered externally to at least 900 mm above formation level

300 mm

1ft “ring” of hardcore along the plinth walls

150mm Backfill

75mm Ballast

50mm Concrete

25mm Screed

300mm Seal the top of the backfill and the vicinity with big stones to prevent run-off water from entering the foundation

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In constructing the slab, it is always important to bear in mind the final or finished floor level and the

design or construction detail (that is, the materials and thicknesses to be used and therefore the

sequence of placing them into the slab). It is good practice to always mark the various depths of the

flooring materials on all sides of the slab against the corresponding plinth walls before commencing with

the slab construction. These levels should be coordinated with a water level and always referred to when

laying the floor materials.

In the case of a low-cost slab (Fig G.7 above) and after backfilling around the plinth walls as described

earlier, start by compacting the stripped ground within the plinth walls using stamping rods and

sprinkling water where necessary. Pack a “ring” of hardcore at least 1' (300 mm) wide and up to 8" (200

mm) high along the plinth walls, on the inside part of the house. This hardcore “ring” acts to reduce soil

pressure against the plinth walls during compaction and thereafter. Backfill the “basin” so created with

plain excavated soil (sprinkle water onto the soil if necessary) to a depth of about 7" (175 mm) and

compact with stamping rods – the soil will hopefully settle at 150 mm above the formation level. Spread

a thin layer of 3" (75 mm) crushed stone and level with strings and sledge hammers if necessary.

Prepare concrete (1:3:6) with 1" (25 mm) aggregates or ballast and cast, compact and level to an

average depth of 2" (50 mm) above the stone base. Note that this level should also be approximately 11"

(275 mm) above the formation level.

Cure the concrete adequately by soaking it in a pool of water or by pouring water onto the slab at least

three times a day (morning, noon, and evening) for a minimum of seven consecutive days before

proceeding to set and raise the walls (Section H below). After walling, the house is then roofed, plastered

internally if required and eventually the floor finished off with a thin layer of about 1" (25mm)

cement/sand screed, which must also be cured for at least 7 days before painting and applying any other

internal finishes.

Note also that Fig G.7 above does not have the traditional independent “splash apron” but the exposed

part of the plinth wall external to the house is rendered with 1:3 mortar to serve as splash guard or

“boot” of the house in rainy conditions. Top of the backfilled portion of the foundation trench is then

adequately sealed with closely packed boulders to prevent run-off water from entering the foundation.

Depending on the local terrain, suitable storm water drains must be provided to ensure water does not

pool around the house after a heavy downpour.

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H. WALLING

H.1 Introduction

Tools/equipment: Builders tools (trowel, square, plumb bob, spirit level, water level, building lines),

Machete, Hoe, Spade, Jerry-can, Wheelbarrow, Mortar pan. Others: Gauge rod (Fig G.4c above), Water

reservoir, Gauge box (Fig. F.2 above), Metal saw, Timber (12”x1”), 100 mm Diameter eucalyptus poles –

for scaffolding and platforms for pushing the wheel barrow in case of soft ground (rain & loose soil).

Personal Safety Gear: Overall, Boots, Helmet, Gloves, Goggles.

Materials: Good quality ISSBs (see Section D.2 above), Damp proofing material (bituminous felt or

G1000 polythene sheet) Mortar (see Section G.2 above): Cement, Sand (both coarse and fine if

available), Water (clean). Others: 12 mm steel bars, 5 or 6 mm round bars, 1.2 mm flat bars (mild

steel), 60 mm Diameter hollow steel pipes, Door/Window frames.

The superstructure wall is set directly onto the ground slab, and for a small residential house such as the

one shown in Fig D.1 above single walling with the 140 mm wide ISSB mortared in every course is

sufficient. The wall will ultimately be plastered internally and skirted externally up to the window level

and around the corners to improve its structural and environmental performance (see Appendix Section

for drawings). Mortar for this purpose is of mix 1:4 (cement: sand). Both pit and washed sands must be

used at the ratio 2.5:1.5, and remember that sand for mortaring ISSBs must always be sieved.

H.2 Corners/Wall Intersections

The tools/equipment and materials are listed under Section H.1 above.

Room

Room

Lobby

1

3

2

4

5

Fig H.2 Common Wall Intersections / Junctions

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Corners or wall intersections are critical sections of walls as they help to increase the lateral stability and

load carrying capacity of the walls. In ISSB construction, special corner details are involved which are not

often met with ordinary bricks or blocks. However, the cardinal principle in assembling all sorts of

building units is to avoid straight joints or locating vertical joints above or very close to each other to

eliminate potential lines of weakness where cracks can develop in the wall. In severe cases of loading and

differential settlements, the wall can even open-up or collapse.

Five (5) different scenarios of wall intersections or junctions often encountered in ISSB construction will

be considered: (1) the “L” junction, (2) the “T” junction, (3) the “+” junction, (4) the “Y” junction, and

(5) the stopped end (see Fig H.2 above). If dry-stacking the narrow (140 mm) blocks or not mortaring

every course, remember always to use mortar in the vertical joints at the corners because there are no

vertical interlocks there.

H.2.1 the “L” Junction

These are usually found at the extreme ends of a rectangular shaped house. Note that an ISSB crossed

on top of another will not key-in or sit in good alignment with the rest of the blocks at that level because

of the bottom protrusion, which should therefore be carefully trimmed with a machete prior to laying the

block (Fig H.2.1c). A double “L” corner is derived by laying two single “L” corners adjacent to each other

and adequately securing them with mortar at the interface and metal strips (flat bars) on every third or

fourth course as illustrated in Fig H.2.1d and Fig H.2.1e below.

Mortar

Fig H.2.1d 1st & 3rd Course Plan

Mortar

Mortar

Mortar

Metal Strips (Flat Bars)

Mortar

Fig H.2.1e 2nd Course Plan

Mortar Mortar

Mortar

Use mortar here

Fig H.2.1a 1st Course Plan

Use mortar here

Fig H.2.1b 2nd Course Plan

1st

Fig H.2.1c Joining Corner Blocks

2nd

Mortar on DPC

Trim dotted portions

3rd

5th

4th

6th

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H.2.2 the “T” Junction

The “T” is an extension of the “L” corner and must always be made to coincide with a vertical joint of the

running (main) wall. In order to avoid straight joints, the adjoining blocks (i.e. the blocks forming the

cross on the “T” in the main wall must be cut to reduce their lengths in such a way that the established

block pattern in this wall is not interrupted. Note that the narrow ISSB length (266 mm) is not an exact

multiple of its width (140 mm) therefore never cut the block in two equal halves. When laying corner

blocks, always remember to trim portions of the bottom protrusion as described earlier so the blocks can

sit neatly on those underlying them. A double “T” corner is constructed as detailed in Fig H.2.2c and Fig

H.2.2d below, adequately secured with mortar at every interface and tied with metal strips (flat bars) on

every third or fourth course.

3rd

5th

1st

Use mortar here

2nd

3rd

6th

5th

4th

1st

Fig H.2.2b 2nd Course Plan & Wall Elevation

Full blocks

Main wall

2nd

4th

Mortar

Fig H.2.2a 1st Course Plan & Wall Elevation

Mortar

75mm

Cut tail

75mm

Cut head

Cut

Fig H.2.2c 1st Course Plan

Cut

Mortar Metal Strips (Flat Bars)

Mortar

Cut

Fig H.2.2d 2nd Course Plan

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A further extension of the “T” junction is a pier, which is a buttress-like reinforcing section of a very long wall

– usually of more than 3 m – commonly found in perimeter walls and large institutional buildings such as

classrooms blocks, halls, dormitories, etc. As there are usually no close junctions in such walls, piers are

introduced at intervals not exceeding 3 m so as to stiffen the walls and enhance their structural integrity.

H.2.3 the “+” Junction

The “+” or cross Junction is similar to the “T” junction where blocks in the main wall have to be cut to

reduce their lengths to create room for the intersecting wall, without altering the established block

pattern in this wall and avoiding vertical joints. Note that the blocks should always tie at the centre of the

cross. However, one has to decide which one of the two walls is the “main wall” as it will always have the

“tie block” (see Fig H.2.3a and Fig H.2.3b below for illustration).

Fig H.2.2f 1st Course Plan

Mortar

Maximum 3 meters

Fig H.2.2e Plan of Long Wall with Piers

Pier Wall

Fig H.2.2g 2nd Course Plan

Mortar

Use mortar here

Fig H.2.3b 2nd (& even Nos.) Course Plan

Tie block

Main wall

Mortar

Fig H.2.3a 1st (& odd Nos.) Course Plan

Mortar

75mm

Cut head

Mortar

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H.2.4 the “Y” Junction

The “Y” junction is ideally an “L” junction where the interior angle is greater than 90o. However, the

corner blocks have to be cut to the required angle with a hack (metal) saw prior to laying the blocks.

H.2.5 Stopped Ends, Door and Window Openings

Walls are usually stopped to create openings such as doors and windows. Given that vertical joints are

always staggered for succeeding courses in a wall, cutting of the blocks to create a regular vertical edge

is inevitable. It is recommended that an opening or a stopped end be introduced just after full blocks in

alternate courses (see Fig H.2.5b below). This implies that doors or window frames to be used in ISSB

construction should have breadths in multiples of a unit ISSB length (i.e. 266 mm) so the frames can fit

nicely in place and the blocks can connect perfectly well above the frames. Note also that for good

stability of the walls, maximum recommended breadth for any opening into ISSB walls without extra

reinforcements at the stopped ends is 1.2 m. Furthermore, if cut neatly using a metal saw, the two block

pieces should always fit properly in the gaps adjacent to the opening – this ensures non-wastage of the

blocks and cost saving.

In ISSB construction, it is recommended that any door or window frames be installed during construction

of the walls because some difficulty may be encountered when installing them later. Installing the frames

in the traditional way (after the wall has been constructed) often requires nails or anchors of some sorts

on the sides that normally involves cutting out the wall in those locations whereby the walls may be

damaged if the operator is not very careful or does not have the right tools for the job. Subsequently,

large amounts of cement mortar or concrete will be required to secure the frames onto the walls.

Use mortar here

Fig H.2.4a 1st Course Plan Fig H.2.4b 2nd Course Plan

Use mortar here

Cut off

Cut off

Fig H.2.5a ISSB Window Frame with Wall Anchors

Flat bars attached to a window frame at strategic positions to coincide with horizontal ISSB wall joints

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Properly cured and treated wooden frames are safe to use in ISSB construction and they are preferred for

low-cost housing for ease of adaptability and relatively low material and fabrication costs (as compared to

steel frames). For better anchorage, the frames must be made with grooves to accommodate the ISSB

keys (protrusions) and metal strips such as flat bars nailed onto the frame at strategic positions to

coincide with horizontal ISSB wall joints (Fig H.2.5a above).

During construction, a frame is raised to its final position in the wall and supported with long poles fixed

to the ground. As the wall is raised, the metal strips on the frame are slotted into the ISSB channels and

secured with small-sized nails before applying mortar and laying the succeeding courses. Provisions

should be made for ultimately screwing the shutters onto the frames; avoid nailing the shutters into place

as the hammering impacts may damage the wall.

H.3 Super-structure Wall Construction

The tools/equipment and materials are listed under Section H.1 above.

H.3.1 Layout, Door Openings and First Course

Once the ground floor is done and set, arrange strips of plastic sheet or bituminous-felt membrane

(commonly referred to as DPC) on the slab following the proposed layout of the superstructure walls. The

entire house should be laid out on the first course including the door openings to ensure that the blocks

tie up above the door lintels.

Fig H.2.5b Stopped End / Opening in ISSB Wall

10th

Cut Cut

Mortar Mortar

PLAN VIEW

1st

Trim dotted portions

1st

7th

8th

10th

9th

11th

Cut block Cut block

Window Opening in ISSB Wall

Mortar on DPC

9th

Mortar Mortar

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Before continuing with the second course, check that the base or first course is level and that all corners

are square. Once this is completed the blocks of the door areas should then be removed and door frames

inserted and supported as described earlier. Note that the first course is always laid in mortar (even

where the blocks are to be dry-stacked) with the ISSB top upwards and the bottom protrusion trimmed

as described before.

H.3.2 Raising the Walls

With the base course established and all door frames in place (and for whatever reason, one may as well

raise the walls without first installing the door frames), the next courses can then be continued. The

corners are first raised to about five courses high at a time and every corner level must be coordinated

using a water level (Fig H.3.2 below). A string is then fixed along a given course and blocks are laid from

the corners towards the middle of the wall. Depending on the orientation of blocks from either corner, the

tying blocks are likely to meet head-on-head or tail-on-tail and in this case mortar will be required in the

vertical joint and for the latter scenario the tail protrusions will need to be removed (Fig H.3.2). This joint

should be staggered for subsequent courses as the wall grows in height and the corners should be

checked regularly for square and vertical alignment. Note that if the layout on the first course was

correct, the blocks should fit into the wall without trimming.

Generally for the entire building, wall construction should proceed in an organized fashion with all walls

raised at fairly the same rate in order to maintain the overall stability of the structure. On reaching the

windows level, install the window frames and support adequately to the ground using long poles and

continue raising the walls around the frame as described earlier. Once again, for whatever reason, one

may raise the walls without first installing the window frames although this procedure is not

recommended. Note that checking the vertical alignment using a plumb bob as illustrated in Fig H.3.2 is

very important as the walls gain height and the window openings create breaks in the structure.

H.4 Ring Beam / Bond Beam and Formwork

The bond beam (commonly referred to as “ring beam”) is an important part of the structure as it ties the

walls together at the weak openings. Traditionally, 150 – 200 mm in-situ (cast-in-place) reinforced

concrete of mix 1:2:4 (cement: sand: ballast or stone aggregates) is used for this purpose. This normally

requires formwork to be fixed all over the walls just above the openings for moulding the concrete.

Fig G.3.2 Raising the Walls

1st 1

st

2nd

3rd

5th

4th

Blocks meet here, so mortar this joint

Mortar on DPC

Use a string to fill-in blocks

Use a water level to set opposite corners

Check verticality of wall using plumb bob

Blocks are laid towards middle of wall

Use a water level to set opposite corners

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However, nailing into ISSB walls is not recommended where the walls will not eventually be plastered or

rendered. The nails usually damage the surface of the blocks with the risk of cracking them and rendering

the blocks vulnerable to moisture attacks especially in rainy weather. Therefore, the best way to do

formwork in ISSB construction is to use pre-fabricated moulds normally assembled on the ground and

lifted into place. Reinforcement wire is then installed (often 4 mild steel bars of 10 or 12 mm in the beam

section). Concrete is cast and carefully compacted using tamping rods (Fig H.4a). Separate strips of tying

wire (say 5 or 6 mm round mild steel bars (or 1.2 mm mild steel flat bar)) should be secured to the

reinforcement cages and allowed to stick out of the bond beams with sufficient lengths to hoop around

the top of the wall at strategic locations to ultimately tie the wall plates or the roof structure firmly onto

the walls.

ALTERNATIVELY, for a properly designed small low-cost house (say up to 45 m2) using the narrow (140

mm ISSBs) having a light roof structure, NOT IN AN EARTHQUAKE PRONE AREA, and in which the door

and window frames have been installed during construction of the walls, the walls can adequately be tied

just above the openings with 12 mm diameter mild steel bars placed in the ISSB channels and running all

over the walls in pairs secured in 1:2 (Cement: sand) mortar. In this case, the overlying block should

have the bottom protrusion removed to create room for the reinforcement/mortar matrix (Fig H.4b

below). Note that this method avoids the time and cost of moulding concrete thereby speeding up

construction; and ultimately, the “ring” of concrete usually visible around the house is not there even

when the house is not rendered externally.

Fig H.4a ISSB Ring Beam Formwork in Cross-section

200 mm

100 mm

140 mm

50x25x140 mm timber struts, 600 mm apart

ISSB Wall

Use 3" nail here

300x25 mm (12"x1") timber board

Reinforcement wire (Y10 & R5)

50x25 mm timber ties, 600 mm apart

Tying wire/bar protruding out of beam

Use 3" nail here

Fig H.4b Alternative ISSB Wall Tie in Cross-section

140 mm

Pair of reinforcement wire (Y12) in mortar & sitting on the R5 bars as spacers

Tying wire/bar protruding out of joint for tying the wall plates ( 900 mm on either side)

Note that the bottom protrusion of this block has been removed

Maintain a regular joint & key-in neatly if wall is not plastered

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H.5 Finishing the Wall

Where specialised trusses are to be used as the main load-bearing roof components, it is recommended

that the house is roofed when all the walls are at the level of the wall plate for easy installation of the

roof trusses. Once the roof cladding (or cover e.g. iron sheets) is installed, the walls should then be

extended up to the cladding especially where there is no ceiling to be fixed – to provide privacy and

security in each room of the house. However, appropriate vents must be provided in these walls to allow

for proper air circulation across the house.

Otherwise where a simple roof structure that sits directly on the walls is to be used, the walls should be

fully raised before roofing the house. In this case, it is important to follow the correct slope of the roof

when finishing off the walls and all walls at the same level must be coordinated using a water level.

H.6 Scaffolding/Platforms

When constructing walls at levels above the chest (normally between 1.0 – 1.5 m from a standing

position), it becomes increasingly strenuous to lay the blocks and difficult to level and plumb the wall.

Therefore, the block layers should always keep elevating their working positions by using appropriate

scaffolding systems or platforms. Simple, low-cost and safe scaffolds can be constructed at the site using

lower-grade timber and poles. For elevations up to 300 mm and where the ground is stable and fairly

level around the walls, two 12"x1" timber boards sitting directly on dry-stacked ISSB blocks at intervals

not exceeding 1 m is a safe and inexpensive accessibility means (Fig H.6a below).

Fig H.6a ISSB-stack Platform

1000 mm

Ground level

1000 mm 1000 mm

200 mm 200 mm

300 mm ISSB stacks 2 Pieces of 12"x1" timber

Stick this block firmly into the ground

Fig H.5 Finishing the Wall

Wall finished

following the roof slope

Roof truss

Wall plate (4"x3" timber)

Wall plate level

Proper ventilation in party wall

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For elevations between 300 mm and 1 m, another inexpensive platform similar to the one above uses 60

mm poles (eucalyptus or bush type) instead of the ISSB stacks. Two poles are buried in the ground

adjacent to each other about 0.4 m apart and a cross-pole nailed onto them; bracing poles may be

required across the supports when the elevation is above 600 mm from the ground. The platform should

be clear of the wall (Fig H.6b below).

There is also an option of a mobile platform that uses pole-framed tripods instead of the fixed supporting

poles (Fig H.6c below). A tripod has two long legs that are supported on the ground and a short leg that

is supported against the wall. Note that this system is only suitable to use on double walls or where

single walls are adequately mortared at every course. Allow the supporting portion of the wall to set

adequately before using the tripod system.

Fig H.6b Pole-framed Platform

1000 mm

Ground level

1000 mm 1000 mm

200 mm 200 mm

1000 mm

60 mm poles

2 Pieces of 12"x1" timber

Plant poles firmly into the ground

END VIEW SIDE VIEW

Use 4" nails here

Bracing

400 mm

Wall

Platform clear of wall

Fig H.6c the Tripod System

2000 mm

Ground level

2000 mm

200 mm 200 mm

1000 mm

END VIEW SIDE VIEW

Tripods made of 60mm poles

600 mm

Wall

Tripod supported

on wall

600 mm

Temporary bracing poles

nailed on tripods Tripods supported

on the ground

Timber planks

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For higher elevations ( 1 m), the usual eucalyptus pole framed scaffold can be used. It is similar to the

pole-framed platform described above but has the vertical members extending to greater heights and

multiple braces at intervals of about 1 m (Fig H.6d below).

It is recommended that all scaffolds used in ISSB construction should be independent systems and not

involve opening up sections of the wall for support. This implies that high level scaffolds should stride

walls and have lateral members passing through window or door openings. Use 4" nails to secure the

poles in place.

Fig H.6d Eucalyptus-framed Scaffold

2000 mm 1500 mm

END VIEW SIDE VIEW

1000 mm

Ground

Scaffold a-stride

wall

Wall

Scaffold

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I. ROOFING

I.1 Introduction

Tools/equipment: Carpenter’s tools (hand saw, bow saw, Claw hammer, wood chisel, square, nylon

strings, and spirit level). Others: Water level, Plumb bob, Pencil, Knife, Metal saw, Machete. Personal

Safety Gear: Overall, Boots, Helmet, Gloves, Goggles.

Materials: Timber (various sizes and quantities as described in the BoQ), Roof cladding (e.g. iron sheets

and matching ridges/valleys), Wire nails (assorted sizes), Roofing nails, Rubber washers. Others: Hoop

iron, Rain gutters and accessories.

Roof design and construction details are normally influenced by the local weather and available materials,

and ISSB roofs are constructed following the traditional systems. The roof of a house primarily serves

both functional and aesthetic requirements i.e. protecting the interior of the house from the elements

(rain/cold and sunshine) and adds "beauty" to the house. In ISSB construction where external walls are

not to be rendered fully (for aesthetics and economic reasons), the roof has an additional function of

protecting the exterior wall surfaces from severe rain impacts – often achieved by providing a sufficient

roof over-hang (usually 2' or 600 mm in plan view) in addition to at-least 600 mm high above the ground

external rendering to the wall (Fig I.1 below). Where rainwater is to be harvested, then most claddings

are suitable except grass thatch. The adopted roof design must therefore be able to fulfil these

requirements using locally available materials.

I.2 Roof Structure

Roof designs are often a component of the approved building plans required for every project. Given that

every project is unique, there are several designs and techniques of constructing roof structures ranging

from simple rack-forms in small buildings where girders directly bearing on the walls carry the purlins

and roof cover – to sophisticated roof trusses bearing on specialist beams or structural walls in large

buildings.

Fig I.1 ISSB Roof Requirements

Sufficient roof over-hang

600 mm

Window

Plastered wall section

Roof

Open ISSB wall

Incident rain

600 mm Ground level

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I.3 Connecting the Wall Plate and Trusses

The tools/equipment and materials are listed under Section I.1 above.

Often 4"x3" timber profiles, the wall plate is usually the first roof element to be installed, it serves as a

load transmission or distribution facility between the roof trusses or rafters and the bearing walls; the

wall plate also provides easy connection between the roof and walls of a house. It is normally a

continuous system thus timbers must be joined to the required lengths using suitable connection details

(see example in Fig I.3a below). Metallic roof anchors must have been connected to the wall ties or ring

beam (see Section --- above) at convenient locations where the roof trusses or rafters are to sit on the

wall. The wall plate is then fastened to the wall using these anchors as shown in Fig I.3b below. Note that

the channel in the last ISSB course is filled with mortar to flush with the top of the blocks.

Fig I.3a Wall Plate Connection

X

Wall plate (side elevation)

DETAIL AT X 100 mm

75 mm

3" Nails

100 mm

Fig I.3b Roof Construction and Wall Connection Detail

ROOF TRUSS

Rafter

Tie Beam

Tying wire wound around

wall plate & truss / rafter

Wall plate

ISSB wall

Tying wire

flat on wall

Mortar here

Roofing nail

Roof cover (Iron sheet)

Rain gutter

Fascia board

Purlin

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The length of construction wood in the market (Uganda) is anywhere between 10' (3 m) to 14' (4.2 m).

For large buildings therefore, there will be need to join timber for roof elements, and in this case try to

join the pieces accurately and tightly. Steel bands (commonly referred to as hoop iron) can be used to

splice together timber members. These bands should be well secured with 2" wire nails. The usual

sequence in constructing the roof detailed in Fig I.3b above is as follows: wall plates, roof trusses,

purlins, fascias, covering, and rain gutters.

I.4 Roof Cover and Rainwater Harvesting

The tools/equipment and materials are listed under Section I.1 above.

One of the main uses of ISSB is to construct rainwater harvesting tanks. Water tanks made from ISSB

prove to be low-cost, more durable, and safely store water without contamination. ISSB water tanks can

be built both above and below ground: above ground ranging from 2,000L to 30,000L and below ground

ranging from 10,000L to 200,000L. Compared to plastic tanks, ISSB tanks can generate significant cost

savings (more than 50 percent) for larger tanks. Please refer to the Rainwater Harvesting Water Tank

Manual for guidelines.

The main rainwater harvesting elements of a roof are the roof cover and gutters. Most roof covering

materials in East Africa are suitable for rainwater harvesting with the exception of thatch and asbestos.

The gutter should be installed with a slight slope towards the collection point. Other than using strings to

establish the profile, the gutter slope can be achieved by fabricating the brackets with an ascending

hanger-length. The collection piece of gutter should have an outlet for connection to rainwater descend to

the tank. In use, the water can either be drawn directly from the tank, which is cheaper, or by plumbing

to serve the kitchen, toilet, and washroom. Please refer to ISSB Construction Manual - Part II for

guidelines on plumbing

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J. APPENDIX

J.1 Some Design Considerations

While making design choices, keep in mind that “more”, “bigger” or “stronger” mean “more cost” but not

necessarily “better!”

The following are some of the architectural design aspects to be considered when developing ISSB

building plans:

1. How many rooms required? Therefore, how big should the house be? Note that room layouts should

maximize the functional use of the house with minimum redundant spaces.

2. Do you want to construct a separated kitchen? (And washroom / toilets?) Or would you like these in

the main house? The concept of having an open kitchen within the main house (as presented in

both home plans in this Section) is relatively cheaper than a closed-in (within the main house) or

separated kitchen.

3. Do you want to include in-built fuel efficient cooking devices in the kitchen? Options are for “rocket”

and equivalent stoves, bio-gas systems, etc.

4. Do you need a rainwater harvesting tank? If so, then suitable roof cover should be used to collect

the rainwater. We recommend a 5,000 litres tank for a typical (Ugandan) home.

5. What roof shape do you prefer: gable-ended or heaped roof? The former is usually relatively

cheaper to construct whereas the latter is prettier!

6. What door/window materials to use? The choice is usually between metal and timber, the latter

being relatively cheaper and more adaptive for use with ISSB construction.

7. Do you require roof ceiling? This is greatly influenced by cost and the type of roof cover – a tin

(iron sheet) roofed house without a ceiling can be uncomfortable to stay in during a heavy

downpour.

8. What finishes (both internal including floor and external) to deploy? Refer to ISSB Construction

Manual - Part II for guidelines.

9. Do you need to install building services (plumbing, sewerage, electricity, etc)? Refer to ISSB

Construction Manual - Part II for guidelines.

The following are some of the structural aspects to be considered when developing adequate and

durable ISSB buildings:

1. Interlocking stabilized soil blocks are recommended permanent building material, although they

may take proper training and experience to use properly.

2. Structurally sound blocks must be produced in accordance with the Block Making Manual and

training guidelines – where appropriate soils are chosen and recommended quality measures

maintained throughout the block production process.

3. No vertical joint should be positioned above another vertical joint.

4. Appropriate and strong ties or ring beams around the entire perimeter of the house at the top of

the major wall openings (windows and doors) which will prevent collapse at these locations.

5. A light-weight roof relative to the entire structure and adequately secured to the tie or ring beams.

6. Relatively small and uniform openings such as windows and doors that are no more than 30 percent the

wall length, and these openings should not be too close to or at corners if not necessary.

7. Good quality materials and workmanship, including plumb walls for guaranteed structural integrity.

8. Uniform thickness of mortar between joints – 5 mm is sufficient and use a suitable gauging device.

9. In large buildings, interior walls in both directions which are load bearing and similar in construction

detail as exterior walls.

10. Properly constructed foundation – double walled plinths are recommended for the narrow ISSBs.

11. Good external protection of the wall: sufficient roof overhang, splash protection on the base of the

wall and good drainage around the house.

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J.2 Typical Low-Cost Home Plans

Fig J.2.1 - 1 Bedroom ISSB Model Home

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Fig J.2.2 - 2 Bedroom ISSB Model Home

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J.3 Sample Building of Costs

PROJECT : PROPOSED 57SQM LOW-COST ISSB MODEL HOME [2 beds + kitchen]

ISSB DEMAND : 6,360 BLOCKS [foundation - 1,320; super wall - 5,040]

CLIENT : FOUNDATION FOR RURAL HOUSING - UGANDA

SUBJECT : ITEMISED COSTING

DATE : MAR. '09

COMPILED BY : DAN A.; CHECKED BY : LISA B.

Item Description Unit Quantity Rate Amount Comments

A Preliminaries 281,500

1 Tools and equipment required Item 1 150,000 150,000 provisional sum

2 Site clearance m2 75 500 37,500 do

3 Setting-out facilitation Item 1 50,000 50,000 do

4 Trench excavations m3 11 4,000 44,000 do

B Cement 2,599,000

1 Cement for concrete (foundation strip) Bag 5 23,000 115,000 100mm thick, mix 1:3:6

2 Cement for concrete (ground slab) Bag 10 23,000 230,000 50mm thick, mix 1:3:6

3 Cement for mortar Bag 15 23,000 345,000 approx. 5mm, mix 1:3

4 Cement for internal plastering Bag 10 23,000 230,000 approx. 10mm, mix 1:4

5 Cement for rendering (external plastering) Bag 8 23,000 184,000 approx. 10mm, mix 1:5

6 Cement for screed & other finishes Bag 12 23,000 276,000 approx. 20mm, mix 1:4

7 Cement for block making (6,360 blocks) Bag 53 23,000 1,219,000 120 blocks per 50kg bag

C Stones and Aggregates 1,060,000

1 1/4" Agg. for concrete (foundation strip & floor top) Trip 2 120,000 240,000 50mm blinding on hardcore

2 3" (75mm) crushed stones for slab conc. base Trip 2 100,000 200,000 placed on compacted fill

3 Hardcore Trip 2 100,000 200,000 300mm wide around plinth

4 Coarse sand (concrete, mortar, plaster) Trip 2 120,000 240,000

5 Pit sand (concrete, mortar, plaster) Trip 2 90,000 180,000

D Reinforcements 365,000

1 Y12mm m/s (for tying wall) Bar 9 20,000 180,000 (no ring beam in the wall)

2 R5mm m/s for tying roof to wall Bar 0 6,000 0

3 1.2mm Flat bar (for tying roof to wall) No. 5 15,000 75,000 1 ring halfway in the wall

4 1.2mm Flat bar (in plinth wall) No. 0 15,001 0 2 ring halfway in the wall

5 Binding wire Kg 5 5,000 25,000

6 8'x4' Weld mesh (on top of plinth wall) No. 5 17,000 85,000

E Roofings 2,307,000

1 Wall plates (4"x3"x14' timber) No. 10 10,000 100,000 (hardwood timber)

2 Ridge Rafters (4"x3"x14' timber) No. 10 10,000 100,000 do

3 Under-purlin (4"x3"x14' timber) No. 6 10,000 60,000 do

4 Valley Rafters (4"x2"x14' timber) No. 2 6,000 12,000 do

5 Girders / Secondary Rafters (4"x2"x14' timber) No. 15 6,000 90,000 do

6 Purlins (3"x2"x14' timber) No. 36 4,500 162,000 do

7 Fascia boards (8"x1"x14' timber) No. 10 10,000 100,000 do

8 10 Ft long G30 iron sheets No. 54 21,000 1,134,000

9 6 Ft long G30 ridges No. 13 8,000 104,000

10 Valley Gutters No. 2 8,000 16,000

11 Wire nails (assorted) Kg 10 4,000 40,000

12 Roofing nails Kg 25 6,000 150,000

13 Rubber washers Pkt 3 8,000 24,000

14 Rain gutters (complete with accessories) m 15 10,000 150,000

15 Hoop iron for connecting timber Roll 1 65,000 65,000

F Scaffolding 60,000

1 12"x1" timber ("kirundu" ) for platforms

2 2"-3" Eucalyptus poles Item 1 60,000 60,000

3 Assorted wire nails

G Doors & Windows 1,335,000

1 Standard solid timber door No. 4 150,000 600,000

2 Standard solid timber window No. 5 120,000 600,000

3 Vents No. 3 45,000 135,000

H Miscellaneous Items 550,000

1 DPC (bituminous felt) Roll 2 10,000 20,000

2 Lime for plastering Bag 5 20,000 100,000

3 Hollow steel pipes (60x2mm) No. 2 40,000 80,000

4 Painting m2 140 2,500 350,000

I TOTAL 8,557,500

1 Labour (20% of Total less preliminaries) Item 0.2 8,276,000 1,655,200 2 General Contigency (5% of Total less prelim.) Item 0.05 8,276,000 413,800

J GRAND TOTAL 10,626,500

5,000Lts ISSB Water Tank Item 1 750,000 750,000 750,000

1-Stance VIP Latrine Item 1 1,770,000 1,770,000 1,770,000

OVERALL COST 13,146,500