Pitched Roofing

7/27/2019 Pitched Roofing

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DOW CONSTRUCTION PRODUCTS(a division of the Dow Chemical Company Ltd)

INSULATED PITCHED ROOFING

Welcome to this RIBA approved CPD self tutorial.

First some information about the Dow Chemical Company itself:

US origin, 100 years old.2nd largest chemical company in the world

Produces: chemicals, plastics, agrochemicals.

Annual sales: 18 billion.

Employs: 45,000 globally (Europe 8,000)

Dow in the UK

STYROFOAM* production since 1969 : polystyrene produced at Barry,Wales; extruded foam insulation produced in Kings Lynn.

Dow Construction Products offers the STYROFOAM range of blue

extruded polystyrene foam insulation:

Floors - Floormate* 200,350,500 and 700

Cavity Walls - Wallmate* CW

Walls internally - Styrofoam* IB

Structures below ground - Perimate* DI

Pitched Roofs - Roofmate* PR, RL

Inverted Flat Roofs - Roofmate* SL, LG

Conventional Flat Roofs - Deckmate* CM, FF

* Trademarks of the Dow Chemical Company


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Dow Construction Products

Insulated Pitched Roofing

This self-tutorial seminar covers all aspects of the so called Warm

Roof Concept at rafter level pitched roof insulation.

You will discover

The insulation options

The advantages of the warm versus the cold roof

How a warm roof is constructed

The general design considerations, relevant codes of

practice and applicable standards to adhere to

The role and selection of the various components with

particular emphasis on the insulation, the underlay,

fasteners and methods of securement

The relevance and importance of the building physics

issues, thermal insulation, condensation and ventilation

The ins and outs of detail design: eaves, ridge, valley,

hip and roof penetrations

How the warm roof concept has been put to the test in

the field


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INTRODUCTION:

It is estimated that today around 10% of new pitched

roofs are insulated atrafter leveland that this

figure is increasing.

Various insulation solutions are available which aredependent on the type of insulation used and its

location ( ie above, between or below the rafters or a

combination of these ), and the type of underlay

used. Although the insulation of pitched roofs cannot

be considered a new application it is now the subject

of much debate both in the technical press and within

the industry itself - indeed the BRE, NFRC and BSI

are all actively involved.The aim of this seminar is to review the application

from an insulant manufacturers point of view.


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Insulation options Advantages of an insulated

roof structure

TheWarm roof concept

Design considerations

Roof build-up: the components

Building Regulations: requirements

Case study

Detailing

Conclusions

CONTENT


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Roof structure: uninsulated

attic/loft

space

insulation at

ceiling level

insulation at ceiling / joist level- mineral / glass

fibre normally used

attic / loft space ventilated (vents provided at eaves

and at ridge)

Note: Could adequate ventilation be prov ided by a

water vapour permeable (breather) underlay and

thus do away wi th providing vents at eaves and

ridge level ?


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Roof structure: insulated

room in

the roof

insulation at

rafter level

Insulation can be a) above,

b) between

c) below the rafters

or a combination of these Warmroof

insulation above rafters

sometimes referred to as sarking insulation (see BRE Thermal insulation: avoiding risks BR262

Hybridroof : insulation between and/or under rafters.

Note: Focus of this seminar will be on the warmpitched roof as this is the

optimum( and perhaps the most challenging ) of the insulation options.


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ADVANTAGES : INSULATED VS

UNINSULATEDROOF STRUCTURE

Increased living /working space for same

footprint

Additional space at lower cost

Added value

Allows room to grow

Cost of providing additional space in the attic can be less than

50%of the standard floor cost.

plus-----

with a warmroof:

- reduced risk of condensationon structural membranes.

- thermal movementof roof structure reduced.

- roof structure kept dry- no need for timber

preservative treatment.


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THEWARM PITCHED ROOF

Rafter

Tiling batten TilesCounterbatten

InsulationVapour permeable

underlay

- roof build up

Insulation shown above and betweenrafters

Vapour permeable underlay(breather type) can be laideither in direct

contactwith the insulation( as shown ) or over the counterbattens

Suitable for new bui ld or where the roof covering is to be replaced(

note increase in roof height ! ) and where it would be difficult to provide

eaves ventilation

Note: Need for a vapour control layer (VCL) ? YES for areas exposed to

high humidity levels e.g swimming pools, kitchens, changing

rooms.

Use plasterboard (13 mm) to cover exposed XPS insulation.


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THE WARM PITCHED ROOF CONCEPT

rigid insulation over (and between)rafters

plus

a water vapour permeable (breather)underlay

Note: Where proprietary products are to be specified,

manufacturers recommendations should be followed.

Designers should satisfy themselves that the performance of

these products and the given recommendations have been

proven by relevant experience in use or by test data based

on the conditions and methods of application in equivalent

and appropriate internal and external climatic conditions.


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THE WARM PITCHED ROOF

First thatched roofing !

Developed from Scottish sarking - early 80s

Agrment certification - mid 80s

Thousands roofs, millions sq metres installed

Includes all insulation types

Minimal condensation problems

No securement problems

Note: Thatched roof- really is a breathing warm roof

Sarking - originated in Germany / Scandinavia refers to a sheet or

underskirt of boarding.

- traditionally in Scotland 25mm thick close timber boarding at

underslating level.

- helps reduce effect of wind uplift on slates.


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Design considerations

! BS 5268 : Part 7 : 1990 Roof

construction - rafters & purlins

(Approved Document A : 1994 )

! BS 5534 : Part 1 : 1997 Slating & tiling

! BS 6399 : Part 1 : 1984 Dead loading! BS 6399 : Part 2 : 1995 Wind loading

! BS 6399 : Part 3 : 1988 Imposed &

snow loading


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ROOF BUILD-UP - THE COMPONENTS

Rafters

Vapour Control Layer

Insulation

Underlay

Battens

Fasteners


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RAFTERS

Consider:

Roof slope

Cut vs trussed

Dimensions (and tolerances)

Spacing

Bracing

Note:

Must assume that insulation does not contribute to

the racking strength of roof structure.


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VAPOUR CONTROL LAYER (VCL)

Usually a membrane (eg 500 gauge polyethylene

sheet)

Substantially reduces transfer of water vapour

Installed on warm side of insulation

A VCL reduces water vapour transfer through any building component in

which it is incorporated.

(BRE document BR 262: Thermal insulation - avoiding risks specifies a

minimum water vapour resistance of 200 MNs/g. BS 5250 refers to the useof 500 gauge polyethylene with a range of 200 to 350 MNs/g, typically 250

MNs/g.)

The VCL should be installed on the warm side of the insulation. ( Note that a

VCL at ceiling level will require increased ventilation below it during the wet

trade phases of construction.)

Performance of a VCL also is dependant on workmanship and build ability -

see Clause 9.2 of BS 5250.

It is essential that it is adequately lapped and sealed so as to maintain its

integrity.

Particular care should be given to detail design and installation around

penetrations through the VCL (e.g services, compartment walls) and to the

sealing of punctures caused by fasteners.


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INSULATION

Location

- above / between / below (or any combination)

Selection

- thermal performance

- water vapour permeability

- water resistance (absorption) - user friendliness

Thickness

Installation

- thermal integrity - convection tight

Location:

(a) over the rafters

(b) between the rafters(c) under the raftersor any combination of these

Note : Option (a) is sometimes referred to as a warm roof construction or assarking insulation.

All options can be used for new roof constructions or where the roof is to be

replaced from rafter level up.

Only options (b) and (c) can be used in situations where the roof covering cannot

be removed or replaced.Selection:

Rigid, semi-rigid and flexible insulants can be used. Each has its own specific

physical characteristics as regards performance and installation requirements -

the manufacturers recommendations should be followed. cont ->


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Thickness:

The thickness of the insulation will be determined by the required thermal

performance as well as by the roof construction (see Approved DocumentL). It is important to ensure the continuity of the thermal insulation. If this

is broken eg by the rafters and /or penetrations through the roof, the

resulting thermal bridges can increase the risk of localised condensation

and pattern staining of ceilings at rafter line.

Note: Building Regulations require the effect of thermal bridging to be

taken into account when calculating the thermal performance (U-value) of

the roof. Refer to BS 5250 Section 9.6 and BRE Document 262: Thermal

insulation - avoiding risks.

Installation:

Thermal integrity is essential.

The roof void should be completely insulated. For example gable end

walls will need to be insulated to their full height.

The designer should take care to ensure that there are no gaps or breaks

in the insulation envelope.

The insulation should be installed to fit tightly at ridges, at eaves andaround penetrations. Seal if necessary with flexible (polyethylene) or PU

foam.

Insulation boards should fit tightly together with no gaps around them.

Rigid board joints should be correctly positioned so as to shed any likely

incoming external water. Some types of board will require their joints to

be sealed with tape - refer to the manufacturers instructions.

Special care needs to be taken with rebated boards designed for over and

between rafter installation e.g Roofmate PR to ensure that the rafterspacing is accurately set out so as to avoid gaps or unnecessary cutting of

boards.

Convection tight /airtight:

A roof system in which the free movement of air through any section of the

construction is prevented by use of airtight joints and seals is said to be

convection tight or airtight.


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INSULATION

- typical physical properties

XPS EPS PUR MF

Thermal conductivity W/mK 0.025 0.036 0.024 0.036

Water vapour resistance

(relative to MF)

- 140 60 80 1

Water vapour resistivity MNs/m 1000 300 600 5

Water absorption % vol 0.3 6 3 ?

Compressive strength kPa 300+ 190

max

175

max

120

max

Density kg/m3 30 15-30 30 180

XPS - extruded foamed polystyrene

EPS - expanded foamed polystyrene (bead board)

PUR - polyurethane/polyisocyanurate

MF - mineral fibre

Thermal conductivity

XPS, EPS measured at 90 days (after equilibrium reached) - long term value.

PUR measured immediatelyafter production ie before equilibrium

reached - short term value.

Water vapour resistanceDetermined relative to MF(air) for equivalent U-value thicknesses (XPS=50mm)

Water absorption

Be sure to take into account likely effect on thermal conductivity !


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ROOFMATE* RL, PR

- physical characteristics

PR RL

Density kg/m3 34 34

Thermal conductivity W/mK 0.025 0.025

Compressive strength kN/m2

300 300Water absorption % vol 0.3 0.3

Water vapour resistivity MNs/gm 940 940

Board size mm 2500 x 600 2500 x 600

Thickness mm 80, 90, 120 35, 50

Edge profile - rebated tongue &

groove

Roofmate RL

Tongue and groove on all sides.

Board should be laid so the tongues in horizontal joints face up the slope.

Roofmate PR

Available with edge flanged to suit 38 and 50mm rafters - type 38 and 50

respectively.Boards should be laid so that horizontal lap joints (i.e top and bottom of boards)

point down the slope so that boards higher up the roof overlap those further

down (boards are marked so as to facilitate this e.g with an arrow pointing up the

slope of the roof).


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UNDERLAYS-REQUIREMENTS

- TRADITIONAL

Keep water (snow, dust) out

Air tight

Adequate strength

- WATER VAPOUR PERMEABLE (Breather)

As Traditional

plus water vapour permeabil ity

Keep water etc. out- secondary defense against wind driven rain,

snow and dust.

Air tight - to reduce wind load on primary roof covering.

Adequate strength - tensile, tear strength (for nails), extensibility

(reduce movement under wind pressure).

Working temp. range - 20 to + 80 deg C.

Water vapour permeability

- Traditional underlay e.g BS747 Type IF felt These are defined (BS5250) as having a water vapour resistance in

excess of 50MNs/g - Water vapour permeable (breather) underlay

BS 4016 : 1995Flexible building membranes (breather type)

- max. water vapour resistance 0.6MNs/g BRE Thermal Insulation : Avoiding risks- specifies 0.1 - 2.0 MNs/g.


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UNDERLAYS

WATER VAPOUR RESISTANCE

Traditional MNs/g

BS 747 Type IF felt 50 - 270

Monarfil* 250 420

Breather

Permo* 0.20

Tyvek* HD - Soft 0.24Tyvek* 2001 - Pro 0.16

Roofshield* 0.08

Monarperm* 450 0.11

Insulation

XPS - 90mm 85

PUR - 80mm 46

MF - 115 mm 0.6 * Tradenames

Monarfil 250 - reinforced polyethylene (0.25mm)

Permo - laminated spunbond polypropylene

Tyvek Soft - spunbond polyethylene (0.19mm)

Tyvek Pro - spunbond polyethylene / polypropylene

laminate (0.42mm)

Roofshield - spunbond polypropylene laminate (0.60mm)

Monarperm 450- spunbond polypropylene (0.45mm)


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BREATHER UNDERLAYS

Performance criteria should reflect real life roof

conditions

Water vapour permeability + water resistance - working conditions

- compatibility

- tenting

- blinding

Installation

Roof conditions: - 20 to +800C, 0 to 100% RH, seasonal, daily,

hourly changes

Compatibility - specifically with timber preservatives - water ( surfactants ) vs solvent based ( swelling )

cause loss of performance.

Tenting - a problem with the early materials. Underlay

leaks when touching surface below.

Blinding - by dust, ice (?)

Installation - laid direct on insulation (common practice in

North)

- can cause noise (ie wind flutter ) ?

or

- supported on counterbattens(common

practice in South)

- userfriendliness => slipperiness underfoot

for roofer!


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BATTENS

Tiling, counter

Dimensions

Location of underlay

Securement

When the insulation is installed over the rafters, counter-battens will

be required to secure the insulation to the rafters and to provide

drainage under the tile battens - refer to BS 5534 Part 1 Section

3.6.3.2.

Care should be taken to ensure that the construction techniques

employed provide for adequate and accurate location of the fixings

used to secure the battens and counterbattens to the rafters.

Width determined by diameter of fasteners (10 - 11 x diameter)

Thickness determined by method of securement

Underlay can be in direct contact with surface of insulation or

located above the counter battens

Who installs what ?

Carpenter - up to and including counterbattens

(rafters, insulation)

Roofer - above counterbattens

(underlay, tile battens, tiles)

or from the rafters up

(insulation, battens, underlay,tiles)


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SECUREMENT

- need to secure tiles/slates, underlay and

insulation against dead wind and imposed

loads

Insulation

consider:-thickness (over rafters), physical properties

Fasteners

egBS 1202 nails, Helifix Inskew, Proctor PR nails

consider:- penetration, pull-out strength, deflection under load - ease and accuracy of installation

Refer to manufacturers for advice


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When the insulation is installed over the rafters the fasteners securing the

counter battens or battens through to the rafters must be of sufficient strength

and length and correctly spaced so as to resist dead, wind and imposed

loads.

The following should be considered:

Site locality - the assessment and determination of wind and imposed loads

Roof Construction - roof pitch, rafter spacing, depth and width, insulation

thickness; batten/counter batten length, width and depth; fastener diameter,

length and spacing.

Materials and related properties - slate/tile weight; rafter and

battens/.counter battens: timber specification; fasteners: pull-out and pull-

through strengths, shear strength and deformation under load characteristics.

Consideration should also be given to the deflection and possible

overloading of the fasteners under load down the slope of the roof. It isrecommended that the deflection should not exceed 3mm. A fastener must

be capable of withstanding the dead and imposed loads vectored down the

slope of the roof i.e its maximum allowable bending stress must not be

exceeded - refer to the fastener and insulation manufacturers for advice. It

may be necessary to provide stronger and larger diameter fasteners (with a

corresponding increase in batten and rafter dimensions) or a reduced

spacing and/or stop battens (i.e parallel to the eaves/ridge)

Note : The trend towards increased thickness of insulation with reduced

U values (June 2000 proposals to change Approved Document L).

SECUREMENT cont


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Securement cont

! BS 6399 : Part 1 : 1996 Deadloads

! BS 6399 : Part 2 : 1995 Wind uplift

! BS 6399 : Part 3 : 1988 Imposed Loads

! BS 5268 : Part 2 : 1996! BS 5534 : Part 1 : 1997

! BS 1202 : Part 1 : 1994

use above to determine fastener size

and density ( per m2

)

Note:

Designers must take into account the two loading conditions for

the fasteners:

Wind uplift on the roof.Resistance to slip (deflection of the fastener) down the slope -

dependant on the pitch of the roof and the dead and imposed

loading. Insulation should not be considered to be a structural

material.

Refer to manufacturers l iterature for the specialist fasteners.


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Fasteners

- method of securement

Tile battens

nailed to counter battens

Counter battens nailed torafters through insulation

Rafter thickness

Figure above shows a method of securement for insulation laid

over and between the rafters, in this case Roofmate PR.

Counterbattens 32 mm thick secured with galvanised slab

nails 100mm long x 3.35 mm dia spaced at 200 and 150 mm

centres for duo and mono pitched roofs respectively - refer to BS

5268 : Part 2 : 1996.

Tiling battens are secured with galvanised slab nails at the

required gauge - refer to BS 5534 : Part 1: 1997.

Tiles


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BUILDING REGULATIONS

Reasonable provision shall be made

for the conservation of fuel and power

in buildings by limiting the heat loss

through the fabric of the building

Building Regulations 1991, amended 1994

- Requirement LI : Conservation of Fuel and Power


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Approved Document L : 1995 U-

values

Approved Document L

Maximum U-values(W/m2K)

DWELLINGS

SAP 60

Cold roof 0.20 0.25 Warm roof 0.20 0.35

OTHER BUILDINGS

Cold roof 0.25

Warm roof - residential 0.35

- others 0.45

If roof slope is greater than 70o then max U = 0.45 W/m2K

For building classification see Approved Document B

Building Regulations specifymaximum allowable U-values -

the optimum cost effective U-values are in fact lower eg:

W/m2K

Floors 0.35

Roofs 0.20 - 0.25

Walls 0.30 - 0.35


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CONDENSATION

Approved Document F:1995

Adequate provision shall be made to prevent excessive

condensation in a roof

but . Is based on traditional underlay experience

therefore ..

refer to:

BRE Thermal insulation : avoiding risks 1994

- see Section 2.7 - 2.10 Sarking insulation

BS 5250 1989

-see Clauses 9.1, 9.2 and 9.3


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CONDENSATION - it s prevention

Short, long term concerns

Insulation

- continuity, convection tight, performance

Underlay

- choice, performance

Roof covering (tiles/slates)- air permeability (?)

Ventilation

YES - between underlay/roof covering

YES - between insulation/traditional underlay

NO - between insulation/breather underlay

Control of condensation is of particular concern for those roof

systems where a breather underlay is used without a ventilated

airspace between it and the insulation. It is recommended that a

condensation risk analysis is undertaken - refer to to BS 5250.

Use of the criteria for condensation build-up within the roof system

as detailed in BS 6229 : 1982 (Section A.2.5.5.) is recommended.

The roof system below a breather underlay should be designed

and installed so as to be convection tight as is possible throughout

its design life.

Consideration should be given to installing a VCL on the warm

side of insulation if the insulation has a low water vapour

resistance - refer to the insulation manufacturer for advice.

cont ->


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For buildings with high internal temperatures and humidities it is

recommended that a VCL be installed and for exceptional conditions,

as may be experienced in say swimming pools, laundries, that the

advice of a design specialist be sought.Ventilation

- defined as the controlled movement of air

There are two air spaces to be considered:

Between the underlay and the insulation

Fortraditional

underlays ventilation should be provided in

accordance with the recommendations given in BS 5250 and

Approved Document F2 (1990). For breatherunderlays ventilation is

not normally required.

Between the roof covering and underlay

Where a traditional underlay is used it is not normally necessary to

provide ventilation.

Where a breather underlay is used without ventilation between the

underlay and insulation it will be necessary to ensure that there is

adequate ventilation. This may be provided through the slate/tile

assembly. Apertures for ventilation can be provided at the eaves,

ridge or incorporated into the slate/tile assembly - refer to BS 5250 for

ventilation aperture sizes.

NOTE: Ventilation through the slate/tile joints may not be sufficient

due to the close fitting of the slates/tiles. There may also be a risk

that the joints become blocked by vegetation or dust over the lifespan

of the roof. Additional ventilation inlets or outlets may, therefore, be

required. Particular attention should be given to long span roofs to

ensure that adequate ventilation is provided.


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FIRE

APPROVED DOCUMENT B : 1992

EXTERNAL FIRE SPREAD - B4

BS 476 : Part 3 : 1958 AA (best) rating - tile/slate roofs

- unaffected by insulation

INTERNAL FIRE SPREAD - B2

BS476 : Part 7 : 1971 Class O rating - 13mm plasterboard

BS476 : Part 7 External fire exposure roof tests

BS476 : Part 1 Surface spread of flame test

- lists Classes 1 (highest) to 4; XPS is unclassifiable

Class O is not identified in BS476. However, it can be achieved by materials of limited combustibility

e.g plasterboard or a Class 1 material which has a fire

propagation index (I) < 12 and a sub-index (I,) < 6.

For useful information on aspects of XPS in building

applications see BS 6203 : 1989


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In summary:

Warm roof concept

15 + years proven track record

minimal condensation problems secure

Design for the total system

Pay attention to the design of details*

Take care in installation

The issues:

Insulation - location, selection, installation

Underlay -selection, performance, installation

Condensation -its prevention

Securement

* see end of tutorial for typical details


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CaseCase study- Hospital- Hospital

Extension - 2600m2insulated pitched roof

Architects: Watkins, Gray International

Main contractor: J Longley & Co.

Insulation installer: NH Etheridge Ltd

Roofer: Cobsen, Davies

Location: Conquest Hospital, Hastings,

East Sussex

Project: BUPA extension - completed 1998


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Case study - Hospital

! Insulation: Roofmate* PR Type 50 (90mm)

! Roof space for services - heating,

ventilation


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! Underlayer:: TyvekTyvek 2001-B Pro2001-B Pro

(over(over counterbattenscounterbattens))

!! SecurementSecurement:: Helifix InscrewHelifix Inscrew600600

fasteners - 110mm longfasteners - 110mm long

!! Tiles:Tiles: MarleyMarleyModernModern


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U-value calculations

Tiles

Tyvek 2001-B Pro

Roofmate PR

U-value = 0.25 W/m2K

Vented airspace

Unvented airspace

Plasterboard

Thickness Thermal Resistance (mm) (m2K/W)

Outside surface resistance - 0.020

Concrete tiles 8.00 0.007

Vented airspace - 0.120(between tiles and sarking)

Tyvek 2001-BPro - -

Unvented airspace - 0.180

Roofmate PR 90.00 3.600

Unvented airspace - 0.180

Plasterboard 13.00 0.081

Inside surface resistance - 0.100


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Notes:

Element: Pitched roof, ceiling at rafter line, warm pitched roof

Exposure: exposed

Internal surface emissivity: high

External surface emissivity: high

Building use: hospital

Environmental conditions Summer Winter

Internal temp C 25 25

External temp C 18 5

Internal humidity % 60 60

External humidity % 65 95

Construction Thickness (mm) Vapour Resistance (MNs/g)

Outside surface resistance - -

Concrete tiles 8.00 0.91

Vented airspace - -

(between tiles and sarking)

Tyvek 2001-BPro - 0.16

Unvented airspace - -



Umvented airspace - -

Plasterboard 13.00 0.68

Inside surface resistance - -

-10 0 10 20 30Red : Actual temperature profile

Blue : dew point temperature

Condensation occurs where red and blue lines touchor cross


Condensation risk

analysis

U-value: 0.25 W/m2K

Condensation build up

winter 0 g/m2

summer 0 g/m2

annual 0 g/m2

Temperature C


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Warmpitched roof construction

- detailing

7

6

5

4

3

2

1


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Warm pitched roof construction

Rafter

Tiling battens TilesCounter battens

Vapour permeable

membrane

Type A - insulation over and between

rafters - Roofmate PR

Roofmate PR Insulation


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A1- Eaves detail

Ensure continuity

of insulation

Set rebated edges of insulation

over rafters


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A2 - Hip detail

Cut insulation

to line of hip and set over

support battens

Hip rafter


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A3 - Roof window detail

Cut insulation to fit tight against roof

window trimmers and seal with gap fillerRoof window

Counter batten


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A4 - Valley detail

Cut insulation boards to

line of valley. Form rebate

to set over valley boards

Discontinuous edge batten to

allow drainage and ventilationGutter lining on

separating layer

Set valley boards

between rafters


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A5 - Ridge detail

Cut insulation to fit

tight at ridge and seal

with gap filler

Nail counter

battens to rafters

Nail tiles to

battens

Nailtiling battensto counterbattens


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A6 - Abutment detail

Fix batten in

gap between insulation

and wall

UnderlayInsulationoverand

between rafters


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A7 - Verge detail

Insulation set over and

between rafters BargeboardFlying rafter


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Warm pitched roof construction

Type B - insulation over rafters Roofmate RL

Tiling battensCounterbattens

Vapour

permeable

membrane

Tiles

RafterRoofmate RL

Insulation


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B1 - Eaves detail

Ensure continuity

of insulation


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B2 - Hip detail

Cut insulation

to line of hip and set onto

support battensHip rafter

Support

battens


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B3 - Roof window detail

Cut insulation to fit tight against

roof window trimmers and seal

with gap fillerRoof window

Counter batten


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B4 - Valley detail

Cut insulationboards to line of

valley and set over

valley boards

Discontinuous edgebatten to allow

drainage and

ventilation

Gutter lining onseparating layer

Set valley boards

between rafters

Valley rafter


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B5 - Ridge detail

Cut insulation to fit tight at ridge

and seal with gap filler

Nail counterbattens to rafters Nail tiles to battens

Nail tiling battens to

counterbattens


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B6 - Abutment detail

Plasterboard

ceiling

Nail battens to counter

battens

Lay insulationboards

over rafters

Nail counter

battens to rafters


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B7 - Verge detail

Plasterboard ceiling Bargeboard

Make up piece of insulationset

over gable wall


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Summarising:

WarmRoof: 15 years proven

experience ! minimal condensation,

securement problemsDesign for total system

Attention to detaildesign

Care in installation

Issues :

Insulation selection, performance,

installation

Underlay selection, performance,

installation

Condensation: its prevention

Securement


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If the following questionnaire is successfully completed and sent to Dow ConstructionProducts, 2 Heathrow Boulevard, 284 Bath Road, West Drayton , Middx UB7 0DQ

Fax Number 0208 917 5413 a CPD certificate will be forwarded to you.

1. In the warm roof concept the insulation is placed

above the rafters

between the rafters

above and between the rafters

between the rafters

2. If a pitched roof is insulated at rafter level (and the loft space is to be utilised)

What are the maximum allowable U-values

0.25 0.35 0.45

Domestic Buildings (SAP>60)

Non-Domestic

- Old Peoples Home

- Office

3. What is the difference between a traditional and breather underlay

Water tight

Air tight

Tear Strength (nails)

Tensile properties

Water Vapour permeable

4. Where would you provide ventilation in a pitched roof construction insulated at rafter

level if a) a traditional or b) a breather underlay is used ?

(a) (b)

Below rafters

Below insulation

Between insulation and underlay

Between underlay and tiles/slates


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5. Which properties are of particular importance for breather underlays ?

Water resistance

Water vapour resistance

Compatibility with timber preservatives

Tear strength

Tearing resistance

Slipperiness

Blinding resistance

Colour

Air tightness

6. In designing a pitched roof which standards should you refer to for

1 2 3 4 5

General design - slating/tiling

Wind loads

Design - timber structure

Dead loads

Imposed loads

1 = BS 6399 : Part 1

2 = BS 6399 : Part 2

3 = BS 6399 : Part 3

4 = BS 5534 : Part 1

5 = BS 5268 : Part 2


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7. Where would you go for advice on how to avoid condensation in a pitched roof ?

BS 5250

Approved Document L

Approved Document F

BRE 262 Thermal Insulation : avoiding risks

BS 5534

Insulation manufacturers

8. In a warm roof construction what issues did you need to consider to avoid/reducethe risk of condensation. ?

Use of a vapour control layer Water vapour permeability of insulation

Convection tightness of insulation layer

Type of underlay

Location of underlay

Where to ventilate

Air permeability of primary roof covering

Drying our of building structure

Attention to details e.g. at eaves

Securement of underlay

9. What factors must be considered when selecting and specifying fasteners ?

Length

Diameter

Pull-out strength (from timber)

Bending stress

Ease and accuracy of installation

Deflection under load

Width of battens, rafters


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10. Which of these should be considered when selection of insulation for

installation or rafter level ?

Location

Compressive strength

Rigidity

Water vapour permeability

Water resistance

Thermal conductivity

Ease of installation

Fire resistance

Nail ability

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Pitched Roofing

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