Open-Cell Spray Foam Insulation: What It Means For Your Mortgage and Your Loft

Why "it's only open-cell" isn't the reassurance it sounds like

Quick Answer

Open-cell spray foam is a softer, more flexible spray insulation applied to roof timbers or loft joists, cheaper to install (roughly £20-£35 per m²) than closed-cell (£40-£60 per m²). Being told you have open-cell rather than closed-cell is not necessarily better news for a mortgage application: most UK lenders don't distinguish between the two when they decline or restrict lending, because the problem is that foam of either type prevents a surveyor inspecting the roof timbers underneath. Around 70-80% of the mortgage market declines outright regardless of which type is installed.

Key Takeaways

Open-cell spray foam is softer and cheaper to install (£20-£35 per m²) than closed-cell (£40-£60 per m²), but that difference is about the product, not about mortgage risk.
Most UK lenders don't distinguish between open-cell and closed-cell foam — around 70-80% of the market declines outright on either type.
The reason is structural: foam of either type, applied to the underside of the roof or across loft joists, stops a surveyor inspecting the timbers underneath.
Removal costs are driven mainly by property size and access, not by foam type, and typically run from £3,000 to £8,500.
If you've been told your foam is open-cell as reassurance, it's worth checking who told you that and why — it doesn't change the lending picture on its own.

If someone has just told you that your loft has open-cell spray foam — a surveyor, an estate agent, the seller, maybe a broker trying to soften bad news — you may have been told it in a reassuring tone. "It's only open-cell, that's the fine one." It's worth pausing on that, because it isn't quite right, and believing it can cost you time you don't have if you're mid-sale or mid-remortgage.

This article answers the question the general open-cell-versus-closed-cell comparisons don't: what does having open-cell specifically mean for your mortgage, your survey, and your next decision. Short version — less than you'd hope.

What actually is open-cell spray foam?

Open-cell spray foam is a lighter, more flexible foam formed from cells that aren't fully sealed, which is what gives it its softer, spongier texture compared with closed-cell foam. It costs roughly £20-£35 per m² to install, against £40-£60 per m² for closed-cell — a meaningful difference for installers and for anyone who had it fitted. In UK homes it's applied in the same places closed-cell is: the underside of the roof, against rafters, tiles or slates, or across the loft joists. That's the detail that matters for everything else in this article — where it goes, not what it's made of, is what causes the trouble.

Does being open-cell make your situation better than closed-cell?

Not in the way most people assume. The distinction between open-cell and closed-cell is a real one for insulation performance and installation cost, but it isn't the distinction that drives a mortgage decision. Most UK mortgage lenders decline or restrict lending on properties with spray foam insulation because the foam — whichever type — sits between the surveyor and the roof timbers they need to inspect. A softer, more open foam doesn't restore that line of sight any more than a denser one does.

If someone has told you open-cell is "the fine one" for lending purposes specifically, ask them where they got that from. It isn't a distinction the lending market broadly makes.

Will a lender or surveyor treat open-cell differently?

Around 70-80% of the UK mortgage market declines outright on properties with any spray foam insulation present. A smaller number of building societies and specialist lenders will consider an application, but usually with conditions — a specialist survey, a reduced loan-to-value, a higher rate. Nothing in that process depends on the foam being open-cell rather than closed-cell; the trigger is the presence of foam obstructing the timber inspection, not its chemistry.

That's a hard thing to hear if you were hoping the type of foam in your loft was a get-out. It isn't proof that every lender treats the two identically in every case — underwriting varies, and you should always get a current answer from your own broker or lender rather than relying on general market behaviour. But you shouldn't walk into that conversation assuming open-cell gives you an easier ride.

If you're weighing up whether to buy a property with foam already in place, our guide on whether you should buy a house with spray foam insulation goes through the decision in more detail.

What does removing open-cell foam involve, and what does it cost?

Removal cost is driven far more by the size of the property and how accessible the loft is than by which type of foam is up there. Across the UK, professional spray foam removal typically costs between £3,000 and £8,500. A smaller property, or one where only part of the roof was foamed, tends to sit at £3,000-£5,000. An average three-bedroom semi-detached property is more commonly £5,000-£7,000. A large or detached property, with more roof area and often trickier access, sits at the top of the range, £7,000-£8,500.

Most three-bedroom properties take 2-5 days to complete, again depending on roof complexity and access rather than on the foam type itself. Open-cell's softer structure can make it easier to strip in some cases, but that isn't a saving you should bank on before getting quotes — get a specialist to look at your specific roof.

Is open-cell foam actually good insulation — and does that matter right now?

It can be, and that's a genuinely separate question from the one you're probably dealing with today. If your only concern were thermal performance, the cost difference between open-cell (£20-£35 per m²) and closed-cell (£40-£60 per m²) would be a straightforward value calculation, and plenty of installers will make that case to you. But if a survey has flagged the foam, or a lender has queried it, the insulation performance isn't what's being assessed. What's being assessed is whether the roof structure underneath can be inspected — and neither type answers that question in the foam's favour.

For more on what the foam does to the roof itself, including the ventilation and moisture questions surveyors ask about, see our guide to spray foam loft insulation.

What should you actually do next?

Start by confirming, rather than assuming, what you've been told. If a surveyor's report says "open-cell," ask how they identified it — visual inspection alone isn't always reliable, and getting it wrong in either direction could shape a decision you make about removal or disclosure. Then talk to your mortgage broker about where your specific application currently stands, because lender policy on spray foam shifts and individual underwriting varies. If removal is on the table, get quotes from more than one specialist, because the range between £3,000 and £8,500 is wide enough that your actual figure depends heavily on your property, not a rule of thumb.

NSFA doesn't carry out removals. What we can do is help you understand the situation clearly enough to have a straight conversation with whoever quotes you next.

How common is this, and are you the only one dealing with it?

You're not. An estimated 250,000 UK homes have spray foam insulation installed, split across open-cell and closed-cell products fitted over several decades, often before the mortgage-lending consequences were widely known. If you've only just found out your loft has it, you're joining a large group of homeowners working through exactly this same set of questions.

Frequently Asked Questions

Is open-cell spray foam easier to get a mortgage with than closed-cell?

Not reliably. Most UK lenders decline or restrict lending on properties with spray foam insulation regardless of type, because the foam obstructs inspection of the roof timbers underneath. Always confirm current policy with your broker or lender rather than assuming open-cell is treated more leniently.

How do I find out whether my loft has open-cell or closed-cell foam?

A specialist inspection is the reliable route, since visual identification alone can be uncertain and the consequences of getting it wrong — for disclosure, removal quotes or a mortgage application — are significant. If a surveyor's report already states a type, it's reasonable to ask how they determined it.

Is open-cell spray foam cheaper to remove than closed-cell?

Removal cost is driven mainly by property size and roof access, with UK costs typically running from £3,000 to £8,500 depending on those factors. Foam type can affect how the job is approached, but you shouldn't assume a saving before getting quotes on your specific property.

Does open-cell spray foam cause damp or timber problems?

Spray foam of either type is applied to the underside of the roof or across loft joists, which is why it prevents the visual inspection surveyors rely on to check timber condition. This article can't tell you the condition of your own roof — that's what a specialist inspection is for.

If I remove the open-cell foam, will my mortgage application be approved?

Removal restores a surveyor's ability to inspect the roof timbers, which addresses the objection that caused the original decline or restriction. Whether a specific lender then approves your application depends on their own underwriting and the rest of your circumstances, which is outside anyone's ability to promise in advance.

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Published 14 September 2026 by National Spray Foam Advice.