Spray Foam Insulation 2026: What Homeowners Must Know

Spray foam insulation is one of the most divisive home upgrades in the UK right now. It can be effective in specific situations, but it causes mortgage and survey problems far more often than the installers will admit. Most homeowners are better off with other insulation types. Here's what you actually need to know before spending £2,000 to £5,000 on something that might devalue your home.

Why Spray Foam Is So Controversial

Let's start with what the aggressive Facebook ads won't tell you.

Spray foam insulation, specifically the closed-cell variety applied to the underside of roof tiles, has become one of the biggest headaches in UK property transactions over the past few years. Mortgage lenders including Halifax, Nationwide, and Santander have all flagged properties with spray foam as potential risks, and some surveyors will automatically downvalue a home if they spot it in the loft. The reason isn't that spray foam doesn't insulate well. It does. The problem is that it can trap moisture against timber, hide structural defects from surveyors, and in some cases make it nearly impossible to inspect or replace a roof without ripping the whole lot out first.

That's a serious issue if you ever plan to sell.

The Royal Institution of Chartered Surveyors published guidance in 2021 warning that spray foam applied directly to the underside of roof tiles can conceal problems like broken tiles, failed felt, and timber decay. When a surveyor can't see the roof structure, they can't assess its condition, and when they can't assess its condition, they flag it as a risk. Mortgage lenders then get nervous. And nervous lenders either refuse to lend or demand remediation work that costs thousands.

So here's the honest bit: spray foam insulation isn't inherently bad. But the way it's been marketed and installed across the UK over the past decade has created real problems for real homeowners.

Open-Cell vs Closed-Cell: The Difference That Matters

Not all spray foam is the same, and this distinction matters more than most installers will explain.

Open-cell spray foam is softer, more breathable, and less likely to cause the moisture-trapping issues that surveyors worry about. It expands significantly when applied, filling gaps and irregular spaces effectively. It's generally cheaper too, typically £15 to £25 per square metre. The trade-off is that it offers lower insulation value per inch compared to closed-cell, and it absorbs water if it gets wet, which means it's not suitable for areas prone to leaks.

Closed-cell spray foam is the dense, rigid type. Better thermal performance per inch. Acts as a vapour barrier. More expensive at £25 to £50 per square metre.

But it's also the type that causes the vast majority of mortgage and surveying problems, because when it's sprayed directly onto roof tiles or rafters, it essentially glues the roof together into a solid mass that nobody can inspect without destructive removal.

Here's what we see regularly: homeowners who had closed-cell foam sprayed onto their roof tiles five or six years ago, thinking they were making a smart energy-saving investment, now discovering they can't remortgage or sell without paying £3,000 to £8,000 to have it professionally removed. That's not a theoretical risk. It's happening right now across the UK.

When Spray Foam Actually Makes Sense

Right, so is there ever a good reason to choose spray foam?

Yes. In specific situations.

Spray foam works well in places where traditional insulation can't easily reach or stay put. Irregularly shaped cavities, areas with lots of pipes and obstructions, or spaces where you need a very thin layer of high-performance insulation can all be reasonable candidates. Some commercial and industrial buildings use it extensively without issue. And open-cell foam applied between rafters (not directly onto tiles) in a properly ventilated warm roof construction can be perfectly fine, though you'd need a specialist who actually understands building physics rather than someone who just bought a spray rig.

The key question isn't whether spray foam insulates well. It does.

The question is whether it's the right choice for your specific situation, and whether the long-term risks outweigh the benefits when cheaper, less problematic alternatives exist. For most standard UK homes with accessible lofts, the answer is no. Mineral wool loft insulation at 270mm depth will get you to a similar thermal performance for a fraction of the cost and none of the mortgage headaches.

What It Actually Costs

£2,000 to £5,000 for a typical three-bedroom semi. That's the range we see quoted most often for spray foam loft insulation.

Breaking that down:

Look at that table for a moment. Mineral wool costs a fifth of what closed-cell spray foam costs and carries zero risk to your property's mortgageability. There are situations where spray foam's gap-filling properties justify the premium, but for a standard loft? We'd struggle to recommend it.

And here's a number the spray foam companies definitely won't mention: removal costs. If a surveyor flags your spray foam during a sale, professional removal runs £3,000 to £8,000 depending on the area and the type of foam. Some homeowners have reported quotes over £10,000 for particularly stubborn closed-cell installations. That's potentially more than you paid to have it installed in the first place.

Can You Get Grant Funding for Spray Foam?

Short answer: almost certainly not.

The main insulation grant schemes in the UK, ECO4 and the now-closed Great British Insulation Scheme (GBIS, which ended in March 2026), have historically focused on established insulation methods. ECO4, which is still open until December 2026, primarily funds cavity wall insulation, loft insulation with mineral wool, and in some cases external or internal wall insulation. Spray foam doesn't typically appear on the approved measures list.

The Warm Homes: Local Grant scheme, run through local authorities, also tends to fund conventional insulation types. Amounts vary by council, but we haven't seen any local authority specifically offering spray foam as a funded measure.

If you're on a low income and your home needs insulation, you're far more likely to get it fully funded through ECO4 using mineral wool or rigid board than you are with spray foam. And honestly, that's probably a better outcome anyway, given everything we've covered about mortgage risks.

For homeowners looking at broader energy improvements, it's worth checking what your EPC rating currently is. Homes rated E or below often qualify for more grant support, and there are usually cheaper insulation upgrades that'll shift your rating more effectively than spray foam would.

Better Alternatives for Most Homes

So what should you actually do instead?

For loft insulation, 270mm of mineral wool is the gold standard for most UK homes. It's cheap, effective, easy to install (many people DIY it over a weekend), and no surveyor will ever flag it. If your loft currently has less than 100mm of insulation, topping up to 270mm is one of the single best energy upgrades you can make. We're talking about £300 to £600 for a typical house, and it's often enough to improve your EPC by a full band.

For walls, cavity wall insulation is the obvious first step if your home has unfilled cavities. It costs around £500 to £1,500 privately, or nothing at all through ECO4 if you qualify.

What about if you're converting your loft into a room and need to insulate between the rafters? This is the one scenario where spray foam advocates have a genuine point, because fitting rigid insulation board between rafters is fiddly and time-consuming. But rigid PIR board (brands like Celotex or Kingspan) achieves excellent thermal performance, doesn't cause mortgage issues, and can be removed or inspected without drama. It costs roughly the same as spray foam installed professionally. The only real advantage spray foam has here is speed of installation and its ability to fill irregular gaps, which matters in older properties with wonky rafters.

Honestly, for 90% of homeowners reading this, mineral wool or rigid board will do everything spray foam does without any of the downsides.

What to Do If You Already Have Spray Foam

This is the section nobody wants to read.

If you already have spray foam installed in your loft, don't panic. Not every installation causes problems, and the severity depends on several factors: what type of foam it is, where exactly it was applied, whether ventilation pathways were maintained, and the current condition of your roof.

Here's what we'd suggest:

First, find out what you've got. Open-cell foam applied between rafters with maintained ventilation is generally less concerning than closed-cell foam sprayed directly onto the underside of roof tiles. Your installer's paperwork should specify the type, though we know plenty of homeowners were never given proper documentation. If you can't tell by looking, an independent surveyor can identify it.

Second, get a RICS surveyor's opinion before you need one. If you're planning to sell or remortgage in the next few years, it's worth paying £300 to £500 for a survey now rather than discovering a problem during a sale when you're under time pressure and the buyer has all the leverage.

Third, if remediation is needed, get multiple quotes. Removal costs vary wildly. Some companies will quote £8,000 for work that another will do for £4,000. And in some cases, a surveyor might accept the installation if you can provide evidence of a proper ventilation strategy and a guarantee from a reputable installer.

One slightly tangential point worth knowing: there's been talk in the surveying industry about developing clearer standards for assessing spray foam, which could eventually reduce the blanket caution that currently exists. The Building Research Establishment has been working on guidance. But that's a separate issue, and it doesn't help you if you're trying to sell your house this year.

The Installer Problem

We can't write about spray foam without mentioning this.

The spray foam industry in the UK has a quality control problem. The barrier to entry is low. Someone can buy a spray rig, do a short training course, and start marketing themselves as an insulation specialist. There's no mandatory certification equivalent to the MCS scheme that covers heat pump and solar installers. Some spray foam installers are excellent, experienced professionals who understand building physics and moisture management. Many are not.

The result has been thousands of substandard installations across the country, homes where foam was applied too thickly, where ventilation was blocked, where the wrong type of foam was used for the application, or where no assessment of the existing roof condition was done before spraying.

If you do decide spray foam is right for your specific situation despite everything, insist on an installer who is a member of the National Insulation Association (NIA) or the British Urethane Foam Contractors Association (BUFCA), who provides a proper survey before installation, who gives you a written guarantee backed by an insurance-backed warranty, and who can show you examples of similar installations they've done. If they can't tick all four boxes, walk away.

Our View

Spray foam insulation has its place. But that place is much smaller than the industry wants you to believe.

For the vast majority of UK homeowners looking to insulate their homes, conventional methods are cheaper, equally effective, grant-fundable, and carry zero risk to your property value. The aggressive marketing around spray foam, particularly the door-to-door and social media campaigns, often overpromises and underdelivers.

If your home genuinely has an unusual insulation challenge that only spray foam can solve, do your research, use a properly accredited installer, and get everything in writing. But if you're just looking to cut your energy bills and improve your EPC rating, start with the basics: loft insulation, cavity walls, draught-proofing. They're boring. They work. And no surveyor will ever give you grief about them.