How to tell if a house already has cavity insulation
Look for a regular pattern of small patched holes in the mortar joints, often about a metre apart. Check the EPC, which may say 'filled cavity'. Ask the seller for a guarantee. The reliable answer is a borescope check, because patched holes can be from a fill that was later removed and EPCs are sometimes wrong.
Tracing a guarantee
Many cavity fills carry a 25-year guarantee from the Cavity Insulation Guarantee Agency (CIGA). CIGA can confirm whether a property is covered and can issue a duplicate guarantee for a fee; at the time of writing that fee is £60 including VAT, and proof of ownership is required.
What is included
- Borescope checks
- Visual check of walls and patched holes
- Damp signs inside and out
- Guidance on tracing a guarantee
- Short written report
Existing insulation and guarantee check prices
| Existing insulation and guarantee check guide prices | Guide price |
|---|---|
| Existing insulation and guarantee check | £145–£245 |
This work is not insulation, so it is normally standard-rated for VAT. Guide prices include VAT where it applies. Guide ranges only: the fixed price is confirmed in writing before any work starts, and anything that could not be seen at survey is agreed with you first.
Rules and funding by nation
The building regulations route and the funding schemes differ between England, Wales, Scotland and Northern Ireland. The local pages for your area explain the rules where you are; in short:
- England: Filling a cavity is notifiable building work and needs a building notice or competent-person self-certification.
- Wales: Filling a cavity is notifiable work under the Building Regulations as they apply in Wales, usually self-certified through a competent person scheme.
- Scotland: No building warrant is needed for insulation within a wall, but the work must meet the building standards.
- Northern Ireland: Inserting cavity wall insulation needs a building control application to the council before work starts.
Sources: Energy Saving Trust: cavity wall insulation; Planning Portal: cavity wall insulation and building regulations; Welsh Government: building work competent person schemes; HMRC: VAT on energy-saving materials (Notice 708/6).