Retrofitting Airtightness into an Existing Home (Brush)
Most of the UK’s housing stock is leaky, draughty and expensive to heat. Retrofitting airtightness is one of the highest-impact upgrades you can make — but it has to be done without trapping moisture in old walls.
Why retrofit airtightness matters
Existing homes leak air at junctions, around services and through tired fabric. That wastes energy, causes draughts and cold spots, and makes heating systems (and heat pumps) work harder. Cutting air leakage is often the most cost-effective step in a fabric-first retrofit — paired, as always, with adequate ventilation.
Do it without trapping moisture
Retrofit standards such as PAS 2035 stress moisture safety. Solid and older walls need to dry, so the airtight layer should be vapour-open — stopping air movement while letting the structure breathe.
The solution: Passive Purple Retrofit (5kg Brush)
Passive Purple Retrofit (5kg) is a brush-applied, vapour-open airtight membrane made for existing buildings. It seals leaky junctions and details by hand while letting old walls breathe — cutting draughts and heat loss without the mess of stripping back.
How it is applied
- Identify leak paths (a smoke test helps)
- Prepare and prime the substrate as needed
- Brush the membrane into junctions, reveals and around services
- Pair with controlled ventilation
Benefits
- Vapour-open — safe for older walls
- Brush-applied for retrofit detailing
- Cuts draughts and heat loss
Frequently asked questions
Will it cause condensation? No — being vapour-open, it avoids trapping moisture; always pair airtightness with ventilation.
Big project? Use the spray grade to cover large areas fast.
See the method in How to Retrofit Vapour Control Without the Mess.