✓ Plain-English Reference — Free to Use
The Spray Foam Glossary
Every term you’ll meet in surveys, quotes and lender letters about spray foam insulation — explained in plain English, with links to the full guides. Journalists and publishers are welcome to reference this page with credit to National Spray Foam Advisory.
Definitions are general guidance, not advice about a specific property. Terms are listed roughly in the order homeowners meet them: the foam, the survey, the mortgage, the removal.
- Open-cell spray foam
- The softer, spongy, breathable type of foam, usually white or yellowish. It allows some moisture vapour movement and is generally the easier of the two types to remove. How to tell which you have: identifying your foam.
- Closed-cell spray foam
- The rigid, dense type of foam. It sets hard, adds stiffness, resists moisture movement — and typically bonds firmly to whatever it was sprayed against, which is why it is the harder case for removal and often the bigger concern for surveyors.
- Retrofit installation
- Foam installed into an existing roof (usually from inside the loft), as opposed to foam applied during construction. Most lender concern in the UK relates to retrofitted foam.
- BBA certificate
- Certification from the British Board of Agrément confirming a product was assessed against its stated use. The certified figures — not brochure claims — are what surveyors and lenders give weight to.
- Sarking / roof membrane
- The layer directly under the roof covering (traditional sarking felt or a modern breathable membrane). Whether foam was sprayed onto the membrane or directly onto tiles/battens affects both risk and removability.
- Breathability / vapour permeability
- How readily moisture vapour can pass through a material. Roof spaces need a route for moisture to escape; sealing one without managing ventilation is how condensation problems start.
- Condensation risk
- The risk of airborne moisture condensing on cold surfaces — including hidden timber faces. This is one of the three things surveyors check where foam is present.
- Interstitial condensation
- Condensation forming inside a construction build-up (for example between foam and timber) rather than on a visible surface — invisible until investigated, which is why surveyors flag what they cannot see.
- Roof timbers / rafters
- The structural wood of the roof. The central question in most spray foam cases is the condition of the timber behind the foam — see timber rot behind the foam.
- RICS surveyor
- A surveyor regulated by the Royal Institution of Chartered Surveyors. What they look for around spray foam is covered in our surveyor guide.
- HomeBuyer survey (Level 2) / Building survey (Level 3)
- The two common depths of pre-purchase survey. Either can flag spray foam; a Level 3 goes further into condition. A flag is a recorded limitation or risk, not automatically a defect — see what a flagged survey really means.
- Mortgage valuation
- The lender’s own check that a property is suitable security for the loan. Not a survey for your benefit — but it is where spray foam often first surfaces in a purchase or remortgage.
- Lender criteria
- Each lender’s own rules on what it will lend against. Spray foam criteria differ significantly between lenders and change over time — tracked in our lender-by-lender guide.
- Equity release / lifetime mortgage
- Borrowing against a home in later life. Currently the most restricted corner of the market where retrofitted spray foam is present — see the notes and sources in the lender guide.
- Product transfer
- A new mortgage deal with your existing lender rather than a new application elsewhere — often relevant because it may not involve a fresh physical valuation. Covered in the remortgage guide.
- Day-one sampling
- Testing a section of foam at the start of a removal to confirm it comes away cleanly before committing to the whole roof — a standard worth insisting on, especially with closed-cell foam.
- Making good / reinstatement
- The finishing work after removal: waste cleared, any agreed insulation reinstated, and the roof space left inspectable.
- Completion certificate
- The removal company’s own paperwork saying the job is done. Useful — but it is the company marking its own homework, which is why lenders prefer the next item.
- Independent sign-off
- Inspection of the finished removal by someone who didn’t do the work — typically a chartered surveyor. The document that carries weight with lenders, buyers and their surveyors. See choosing a removal company.
- Cold-call sale
- A sale that begins with the company contacting you — the single biggest red flag in this market. What to do if it has happened: mis-sold spray foam.
Spray foam in the UK — the key numbers
250,000UK homes estimated to have spray foam insulation
35%of 500+ inspected properties had at least one defect
~25%of mortgage lenders will lend on retrofit spray foam
£2,000–£8,000typical professional removal cost (≈£4,500 for a three-bed)
Who will lend where spray foam was retrofitted?
Mortgage lenders willing to lend
Equity release providers willing to lend
Inspected properties with at least one defect
Sources: House of Commons Library briefing CBP-10658 · PCA & HomeOwners Alliance joint letter (May 2025) · BBC research (Nov 2024) — full detail on our spray foam statistics page.
Met a term that worries you in a real survey or quote?
An independent adviser will tell you what it means for your property — free, no pressure.
Looking for the numbers rather than the words? See our UK spray foam statistics & key facts, with sources.
Worried about spray foam problems in your home? Call us free on 0800 494 7163 or leave a message about your situation and we will give you the advice you need to resolve it — and a full understanding of the guidance around spray foam and how it applies to your home. We are a free, independent advisory service and we carry out no removals ourselves.