Cavity wall insulation cost calculator: what the job involves and who is registered to do it

How cavity wall insulation cost calculator works

1. Measure the external wall area. Perimeter multiplied by height, minus windows and doors. That is the number every per square metre rate multiplies, and you can check it with a tape.
2. Get the cavity inspected. A borescope inspection tells you the cavity width, whether it is clean, whether it is already filled and whether debris is bridging it. Any of those changes the answer, and none is visible from outside.
3. Weigh the exposure. Walls facing prevailing wind and rain in exposed parts of the country can carry moisture across a filled cavity. This is the main reason a competent surveyor sometimes says no, and it is a reason worth hearing.
4. Ask about the guarantee. Cavity wall insulation installed under the recognised schemes carries an independent guarantee. Ask who provides it, what it covers and how a claim is made, because that is what you have if the wall gets damp.
5. Check the funding before you pay. Government backed schemes fund this measure for qualifying households and the qualifying rules change. Establish whether you qualify first, since the route in is through an approved installer.

Insurance and paperwork

Common questions

Is cavity wall insulation ever a bad idea?

Yes, in an exposed wall with a narrow or dirty cavity, or where the outer leaf is in poor condition. Filling those walls can carry water inward, which is why the survey rather than the calculator decides.

What if my cavity is already filled?

Then the question is whether the existing fill has slumped or is holding water, which needs inspection rather than a top up. Extraction and refill is a real and separate job.

How do I know a wall has a cavity at all?

Wall thickness and brick bond are the first clues and a borescope is the proof. Solid walls need a different measure altogether, internally or externally applied, at a different price.

Registered contractors by region

• Registered roofers in the East Midlands postcode area
• Registered roofers in the East of England postcode area
• Registered roofers in the London postcode area
• Registered roofers in the North East postcode area
• Registered roofers in the North West postcode area
• Registered roofers in the Scotland postcode area
• Registered roofers in the South East postcode area
• Registered roofers in the South West postcode area
• Registered roofers in the Wales postcode area
• Registered roofers in the West Midlands postcode area
• Registered roofers in the Yorkshire and The Humber postcode area