Airtightness

Leaving Certificate Revision Notes

Airtightness

Common air leakage paths 5

2.1 Descriptions of air leakage paths1 Suspended floors (timber and concrete beam and block):

! Gaps between floorboards or concrete blocks around the perimeter of thedwelling/junction between floor and walls.

! Large gaps left around services that penetrate through the floor (eg soil vent pipes).

2 Gaps left between floorboards or blocks and also gaps around services (eg pipesand cables).

3 Window/door components:

! Windows and doors that do not close tightly resulting in large air leakage paths.

4 Joists that penetrate into wall construction:

! Masonry walls: Gaps left around joists that penetrate into the inner leaf ofexternal walls. Air leakage from the cavity into the upper floor void leaking intothe dwelling through gaps between flooring and through any penetrations inthe ceilings, eg recessed lights and ceiling light roses.

! Timber frame construction: Gaps left around joists, where they penetratethrough the air barrier, allowing air leakage into the dwelling throughpenetrations in the walls and ceilings.

5 Window sills and reveals:

! Air can leak directly to the outside or into the cavity through gaps between thewindow frame and wall reveals.

! Gaps around window casements (component air leakage).

! Gaps between doors and frames.

! Gap at bottom of door across threshold.

6 Gaps between dry lining and ceilings:

! Gaps and insufficient sealing at the wall to ceiling junction allowing air to leakinto, and out of, the unheated loft void.

7 Internal partition walls:

! Air leakage can occur through internal partitions if the detailing or location of the air barrier leaves a pathway between indoors and outdoors. Gaps in the airbarrier allowing air into the partition which then leaks through penetrations such as light switches and power sockets.

8 Loft hatches:

! Loft hatches that do not fitproperly (prefabricated lofthatches can become twistedas they are installed) (Fig. 2).

! Inadequate seals betweenthe hatch and the frame.

(Note: condensation can be anissue if the loft hatch does notfit – warm moist air from thedwelling rises into the loft andcondenses on cold surfaces,such as roof timbers and roofunderlay.) Figure 2 Air leakage through gaps around a loft hatch.

Air leakage paths, which are commonly found in dwellings, can be easily avoided bycareful design and good quality construction practice (Fig. 1).

2 Common air leakage paths

4 A practical guide to building airtight dwellings

Figure 1 Potential air leakage paths (the numbered points in section 2.1 give a description foreach path).

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AirtightnessIntroductionAirtightness is a key principle in energy efficient home design. The idea is quite simple: houses lose a lot of heat when warm air leaks out of the house. We usually think of draughts as bringing cold air into a house from the outside. This is true, but air also leaves the house - taking warmth (heat energy) with it.

BenefitsThe benefits of making a home airtight include:• reduces heat loss,• reduces the energy required to heat the house,• it improves thermal comfort - an even temperature is achieved throughout the house,• reduces greenhouse gas emissions,• reduces energy bills.

The aim of making a building airtight is to seal the external envelope (floors, walls, roof, windows, doors) to prevent the unwanted movement of air.

Achieving a reasonable level of airtightness is important for the energy efficiency of dwellings and the comfort of the people living in the home.

The benefits listed above are lost if warm air can leak out of a building and cold air can leak in.

Making a house airtight:Concrete cavity walled house:The inner surface of the walls are parged* to ensure there are no gaps in the blockwork. Then the entire surface is thoroughly plastered from floor to ceiling and into the corners.* parge coat = a thin coat of cement based mortar

Complying with checklist qualifies builder to claim value in Table 3 of IP 1/06 and Table K1 of DEAP 2006

!

Ensure wall insulation is installed at least 225 mm below top of floor

Floor insulation to tightly abut blockwork wall

Detail applicable:- Ground-bearing floor; raft foundation; in-situ suspended ground floor slab; pre-cast suspended ground floor; concrete and screed. Insulation below slab

Seal all penetrations through air barrier using a flexible sealant

Seal between wall and floor air barrier with a flexible sealant OR seal gap between skirting board and floor with a flexible sealant

Ensure partial fill insulation is secured firmly against inner leaf of cavity wall

Ground Floor - Insulation below slab


DETAIL 1.02b, JULY 2008

The wall insulation installed below the wall DPC must be fit for purpose with regards to water absorption

Keep cavities clean of mortar snots and other debris during construction

AIR BARRIER - CONTINUITY

AIR BARRIER - OPTIONS

THERMAL PERFORMANCE

(1) WALLS:- INSULATION IN CAVITY

Complying with checklist will help achieve design air permeability

GENERAL NOTES

ACCEPTABLE CONSTRUCTION DETAIL

CHECKLIST(TICK ALL)

CHECKLIST(TICK ALL)

OPTION(TICK ONE)

Masonry inner leaf with wet-finish plaster, or

Inner leaf with plasterboard on dabs, with continuous ribbon of adhesive tape around all openings, along top and bottom of wall, and at internal and external corners, or

Masonry inner leaf with scratch coat, and finished with plasterboard, or

Airtightness membrane and tapes

225 m

m m

in

Install perimeter insulation with a min. R-value of .75 m K/W2

Ensure block with a maximum Thermal Conductivity of .20 W/mK in the direction of heat flow is used and that block is suitable for use in foundations in all conditions. Block is to be installed so to avoid any effect of moisture on thermal conductivity.

Timber frame house:This is done by installing an airtightness barrier (also called an airtightness membrane) throughout the entire structure. This barrier prevents the movement of air from inside to outside (and outside to inside). This keeps the heat energy in the house.

Installing an airtightness membrane depends on a very high quality of workmanship. Every joint in the membrane must be carefully sealed to ensure it is airtight - this usually involves using a very sticky tape designed specifically for this purpose (it’s blue in the image to the right).

The joints are overlapped by 150mm and sealed with tape.

Every possible air leakage route must be carefully sealed.

!Complying with checklist qualifies builder to claim value in Table 3 of IP 1/06 and Table K1 of DEAP 2006

Ground Floor - Insulation below slab DETAIL 4.02, JULY 2008


Detail applicable:- Ground-bearing floor; raft foundation; in-situ suspended ground floor slab; pre-cast suspended ground floor. Insulation below slab

Seal all penetrations through air barrier using a flexible sealant or tape

Seal between wall and floor air barrier OR seal gap between skirting board and floor using a flexible sealant

Floor insulation must tightly abut concrete block inner face

To improve air tightness, ensure sole plate DPC turns up behind and laps with vertical vapour control layer/vapour control plasterboard

If sole plates are packed to level, ensure any gaps are sealed

Floor slab perimeter insulation to have a min. R-value of 0.75 m K/W2

AIR BARRIER - CONTINUITY

AIR BARRIER - OPTIONS

THERMAL PERFORMANCE

(4) TIMBER FRAME

Complying with checklist will help achieve design air permeability

GENERAL NOTES

ACCEPTABLE CONSTRUCTION DETAIL

CHECKLIST(TICK ALL)

CHECKLIST(TICK ALL)

OPTION(TICK ONE)

Internal lining, for example, plasterboard, or

Airtightness membrane and tapes




















8 Loft hatches:




Air leakage paths, which are commonly found in dwellings, can be easily avoided bycareful design and good quality construction practice (Fig. 1).

2 Common air leakage paths


Figure 1 Potential air leakage paths (the numbered points in section 2.1 give a description foreach path).

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8 Loft hatches:





9 Ceiling roses and recessed ceiling lights:

! Holes made through the upper ceiling for lights creating air leakage paths intothe loft space.

10 Gaps around soil and vent pipes and flue stacks:

! Gaps in ceilings around soil vent pipes and passive flue stacks allowing airleakage paths.

11 Gaps around extractor fans and cooker hoods:

! Poorly fitted extractor fans and cooker hoods allowing air leakage through gapsleft between the wall and the ventilation duct.

12 Gaps around service pipes (these gaps can often provide the largest air leakagepaths in dwellings) (Fig. 3):

! Gaps left around service pipes, cables and ductsthat pass through the dwelling’s external fabriccan be a major contributor to poor airtightness.

! Large holes often created for much smallerdiameter pipes to pass through.

! Gaps and holes around service penetrations often hidden from view behind baths, vanity units and kitchen units.

! Cuts and holes in vapour control membranes(used as air barrier for framed construction) made to accommodate pipes, cables and ductsas they penetrate through the dwelling’s externalwalls resulting in large air leakage rates.

13 General air leakage through walls (Fig. 4):

! Gaps in mortar joints (or in some cases missing mortar joints) between concreteblocks on the inner leaf allowing significant air leakage from the cavity (Fig. 5).

! Figure 5 shows cold external air beingdrawn in through gaps and missing mortar joints in the blockwork wall behind the dry lining. Draughts will be felt at the base of the wall (underskirting boards), through electricsockets, around light switches and light roses/recessed light fittings.

Figure 3 Gap around soil pipe atback of toilet.

Figure 4 Air permeability through gaps in a blockworkwall.

Figure 5 Air leakage through gaps andmissing mortar joints in a blockwork wall.


9 Ceiling roses and recessed ceiling lights:

! Holes made through the upper ceiling for lights creating air leakage paths intothe loft space.

10 Gaps around soil and vent pipes and flue stacks:

! Gaps in ceilings around soil vent pipes and passive flue stacks allowing airleakage paths.

11 Gaps around extractor fans and cooker hoods:

! Poorly fitted extractor fans and cooker hoods allowing air leakage through gapsleft between the wall and the ventilation duct.

12 Gaps around service pipes (these gaps can often provide the largest air leakagepaths in dwellings) (Fig. 3):

! Gaps left around service pipes, cables and ductsthat pass through the dwelling’s external fabriccan be a major contributor to poor airtightness.

! Large holes often created for much smallerdiameter pipes to pass through.

! Gaps and holes around service penetrations often hidden from view behind baths, vanity units and kitchen units.

! Cuts and holes in vapour control membranes(used as air barrier for framed construction) made to accommodate pipes, cables and ductsas they penetrate through the dwelling’s externalwalls resulting in large air leakage rates.

13 General air leakage through walls (Fig. 4):

! Gaps in mortar joints (or in some cases missing mortar joints) between concreteblocks on the inner leaf allowing significant air leakage from the cavity (Fig. 5).

! Figure 5 shows cold external air beingdrawn in through gaps and missing mortar joints in the blockwork wall behind the dry lining. Draughts will be felt at the base of the wall (underskirting boards), through electricsockets, around light switches and light roses/recessed light fittings.

Figure 3 Gap around soil pipe atback of toilet.

Figure 4 Air permeability through gaps in a blockworkwall.

Figure 5 Air leakage through gaps andmissing mortar joints in a blockwork wall.


The infrared image in Figure 6 shows the effect of cold air leaking in behind the drylining. Cold air has been drawn in through missing mortar joints. (Coldness shows upas dark coloured patches in this image). The cold dots that can be seen are theplaster dabs used to fix the plasterboard to the blockwork.

The reasons for the air leakage may be:

! Gaps left around the service pipes.

! Air barriers (vapour control membrane – timber frame or dry lining – steel frame) that have been cut to allow services to penetrate through the wall creating air leakage paths into the dwelling.

! Cuts in membrane are often unnecessarily large for service penetrations makingsealing difficult afterwards.

! The wrong tape may have been used to seal the membrane material. Sometapes may not provide a robust seal and could peel off soon after being applied.

Figure 6 The effects of cold air behind dry lining attributed to air leakage.

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14 Gaps between walls and solid ground floors:

! Gaps left between the sole plate of a frame and the ground slab due toundulations in the concrete surface.

Standards & testing:The Building Regulations set a standard for airtightness in newly built houses in Ireland:

10 m3/h.m2 at 50 Pa.(ten cubic metres of air change per hour for every

square metre of floor area when the difference in air pressure between inside and outside is fifty pascals.)

A house is usually tested by carrying out a door blower test:door blower test (also known as: air tightness test or pressurisation test or permeability test)

the test:• install the door blower fan in the doorway of the principal entrance to the dwelling, • seal all fans, flues, chimneys, vents etc.• turn on the fan,• measure the air flow rate required to maintain an excess pressure of 50 Pascals (Pa) above outdoor air pressure.

Airtightness

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