In essence achieving an air tight building should not be too difficult. Identifying potential air paths is fairly straightforward and addressing them is often not complicated or may be already dealt with by measures to achieve acoustic or fire requirements, as well as achieving the basic finish that is likely to be expected by the occupants.

Basically, the objective is to create a continuous air barrier between:

• Inside and outside
• Conditioned and unconditioned spaces ie apply the same principles to barriers between heated and unheated areas eg plant rooms, stair wells
• Adjacent units eg flats or attached houses are tested individually so, as far as the test is concerned, air leakage into neighbouring units is still leakage.

Creating this air barrier is the SHARED responsibility of:

• The designer
• The contractor – namely the construction manager and/or the site manager
• The subcontractors – notably those that are responsible for creating the air barrier eg plasterers, timber frame erectors and those that may penetrate it eg plumbers and electricians

Therefore communication is important. Ensure workers and sub-contractors are aware of the important areas and the impact of their work. Place responsibility on ‘subbies’ to maintain the air barrier and require them to pay remedial or re-test costs if found to be their responsibility. It may be helpful, having established the air barrier, to identify it on drawings so the site manager is made aware of critical areas and therefore operations.

Areas to focus on:

1. Where elements of the air barrier meet eg wall to floor, wall to structural ceiling (suspended ceilings are permeable), cladding to roofing, eaves details, etc. For dwellings these details comprise the ACD and are focussed on achieving a good internal finish. In more complex constructions it may be helpful to identify the air barrier – which must be continuous. Typically the air barrier will be external or party walls, ceilings and floors plus elements bordering ‘unconditioned areas’ (eg plant rooms, garages and cold roof spaces). Sometimes detailing around partition walls and floors may also present an air path into cavities or voids that link to an external space. Extensions can create particular difficulties where contractors are trying to seal against the external face of an existing building as well as running services and allowing access between the new and old areas.
2. Where components meet eg block work joints, joints between beam and block flooring, where cladding systems overlap or meet blockwork.
3. Where penetrations interrupt the air barrier:

• Doors and windows - ensure door and window fitters produce a good seal between the building and the product (ensuring air cannot escape outside or into the cavity) – eg board out the aperture.
• Loft hatches – some of the plastic hatches may distort; preferably they would close against a lip rather than be suspended so that gravity helps to seal them.
• Piping – especially soil piping, sealing where pipes enter boxing and/or where they exit eg into unconditioned loft spaces.
• Electrical fittings – resealing behind sockets and switches is preferable on external/party walls eg taping or putty pads in extreme cases. Down-lighters in party ceilings can present a problem.
• Trickle vents – these are closed but not sealed during testing so it is important they create a good seal and are not damaged/distorted.
• Ventilation – although the face of vents for extraction and air supply systems are sealed during testing, you still need to make sure they are well fitted

Generally, air should not escape in great quantities through walls, floors and ceilings themselves (plaster is an excellent seal) but it is worth checking the permeability of certain materials eg:

• the density of block work effects its permeability (large expanses may need painting)
• mineral wool is permeable and therefore continuity of insulation does not necessarily guarantee air tightness
• perforated acoustic products obviously will not provide an air barrier on their own

Finally, be aware of concealed areas to avoid an ‘out of sight, out of mind’ mentality, eg:

• Above suspended ceilings
• Below raised floors
• Behind bath panels and shower trays

These may mask unsealed penetrations or other problems so site managers and agents will need to be vigilant when signing off sub-contract work

On site, basically:

1. Can you see any holes?
2. Are they supposed to be there?
3. If not, where would air go that passes through them?
4. If it is likely to escape outside, seal it at one end or the other.

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