Air Sealing Gaps And Cracks

What this is

Air sealing means finding the unintended openings in the shell of a house and closing them with a material that stays flexible. It is not the same as insulation. Insulation slows heat moving through a solid layer; air sealing stops air carrying heat straight past that layer. A wall can be well insulated and still feel cold if air moves freely around the insulation, which is why sealing is usually the first thing worth doing.

Telling whether your home needs it

The openings are rarely obvious. They collect where different materials meet: around loft hatches, at the top of internal walls, behind skirting boards, where pipes and cables pass through, around recessed light fittings, and at the frames of windows and doors. On a cold, windy day you can find many of them by moving the back of a hand slowly along those junctions. Dust staining on insulation or carpet edges marks places where air has been moving for a long time.

What the job involves

Work from the top of the house downwards, because warm air leaves highest. Larger gaps get a backing material pushed in first so the sealant has something to grip. Narrow cracks take a flexible sealant; wider openings around pipes take an expanding filler cut back flush once cured. The loft hatch itself is usually worth treating as a small door, with a compression seal around the rebate and insulation fixed to its upper face.

Things to watch

A house needs a controlled supply of fresh air, so sealing should go together with keeping deliberate ventilation clear: trickle vents, extract fans and air bricks stay open. Never seal an air brick serving a room with a fuel-burning appliance. Around flues, chimneys and recessed fittings that get hot, use a material rated for high temperature rather than a general-purpose filler.