Existing dwellings - improving air tightness
To upgrade existing dwellings, the same constructional elements need to be considered. In
some instances, the methods will be the same as in new buildings, for example gun-applied seals around service
penetrations and the gaps around windows and doors.
However, in many cases it will be difficult to access the air leakage points to apply sealants without removing
fixtures and fittings e.g. kitchen units, bathroom fittings, skirting boards, ceilings, boxed-in pipework/services
A list of suggested airtightness techniques that can be used to improve the performance of existing dwellings is
Improving airtightness in an existing dwelling
• Use sealant materials to fill the gaps around windows and doors to prevent air leakage from the reveals and
• Apply an external mastic seal to all window and door frames.
• Apply a bead of mastic to seal any internal gaps between the wall reveals/window boards and window units or
• Repair any damage to window frames and ensure the casements, sashes and top-lights close firmly. It may be
necessary to replace closing mechanisms.
• Apply draught proofing to gaps around window opening casements, sashes and top-lights.
• In dry-lining applications, inject continuous ribbons of expanding polyurethane foam between the plasterboard
sheets and the inner leaf blockwork: this will prevent air leakage into this space from the void between the ground
floor ceiling and first floor, or from internal partition walls. Drill small holes (approximately 9mm) at regular
intervals (approximately every 100mm) around the edges of the plasterboard to allow the foam to be injected into
• Make good damage to mortar joints and fill any holes in the external walls. If the dwelling has been extended
and the kitchen/bathroom has been moved to a new location, make sure there are no holes through the external walls
where service pipes were previously located.
• Ensure the loft hatch fits into its aperture and apply draught stripping between the hatch and the frame.
• Seal gaps around service pipes and the cables that pass through external walls, ceilings and ground floors. It
may be necessary to remove baths, kitchen units, boxing around service pipes, washing machines, etc, to gain access
to these pipes and cables.
• Ensure there is a good seal around boiler flue pipes where they pass through the external wall/ceiling. Check
the performance of the sealing material to ensure it will not be affected by heat.
• The airtightness of suspended timber floors can be improved by laying hardboard sheeting over the top, to
cover any gaps between the floorboards. Seal around the edges of the rooms and make good any gaps in the floor
around service pipes (it is advisable to check for holes behind baths and under shower trays). Do NOT use plastic
sheeting to cover timber floors as this may cause the timber to rot.