Spray foam insulation: assessment and removal in Bath

Spray foam insulation is a two-part chemical mix that is sprayed on to the underside of a roof, where it expands and sets. In a pitched roof it is usually applied between and over the rafters, so it clings to the back of the slates or tiles, to the underlay if there is one, and to the timbers themselves. The idea is to insulate and seal the roof in one pass, turning the loft into a warm space. For some roofs, in the right hands, that works. For others it has caused problems that only appear years later, and more owners are now finding out about it when a surveyor writes it up during a sale.

The trouble with foam on the slates is that you cannot see what is behind it. A slipped slate, a rusted nail or a damp batten all sit under a rigid skin of foam, and the foam itself can grip the slate so hard that lifting one risks breaking it. That is one reason we start any job with a careful look at the roof from outside as well as from the loft. Slipped, cracked or missing slates tell us where water may have been getting in, and the foam can hide the staining that would normally give the game away. If your roof is slate, the page on whether spray foam can damage slates and tiles sets out what we look for.

Where the RICS stands

The Royal Institution of Chartered Surveyors published a consumer guide on spray foam in March 2023. It warns of uncontrolled condensation and damage to parts of the property, and it advises owners to check with their mortgage provider whether the lender's policy allows such products to be installed. You can read it on the RICS consumer guide page. Our own page on the RICS position on spray foam explains what the guide says and what it leaves open. It does not say that every spray foam roof is a problem, and neither do we.

Lenders and sales

A BBC investigation reported in November 2024 that some lenders say they will not lend on a property with spray foam in the roof, while others look at each case on its merits. We mention the date because lender policy changes and you should always ask your own lender or broker for the current position. In practice, it is a buyer's surveyor who usually raises the issue, and a sale can stall until it is dealt with. Two pages cover this side in more detail: spray foam insulation and mortgages and selling a house with spray foam insulation.

Removal is a decision, not a default

Whether foam must come out is a question for assessment, not for a slogan. A roof where the timbers are dry, the ventilation is sound and the lender has no objection might be left alone. A roof with damp timbers, trapped moisture or a buyer's surveyor who has flagged a concern is a different matter. Our answer on whether you should remove spray foam insulation goes through how we weigh it up, and there is a separate page on partial removal for owners who want to open up only part of the roof.

What matters most is usually what the foam is hiding. In the next chapter we look at the rafters, battens and wall plates beneath it, and how they are checked without wrecking a sound roof.

The eaves are where the rafters meet the wall at the foot of each slope. On many pitched roofs, air is meant to enter here through vents in the soffit board or through gaps left at the top of the wall, pass up under the covering and leave at the ridge or through tile vents. That small current of air carries away moisture and keeps the timbers dry. It is the quiet job that a cold roof does, and it stops working if something blocks the way in.

Spray foam is applied to the full depth of the rafters, and in the process it often pushes right into the eaves, closing the gap between the rafters and the wall plate and covering any vents. Sometimes the installer left vents on the outside but sealed the roof space behind, so the vents lead nowhere. Sometimes the soffit has been blocked in the roof void with a lump of foam. We check by looking from outside for the vent, from inside for a clear path behind it, and if needed with a smoke pencil or a torch held at the soffit.

Why a warm roof still needs a plan

A well designed warm roof can work without eaves ventilation, because the insulation sits tight to the underside of the covering and the roof space is part of the heated house. That design relies on the right materials and details, including a vapour control layer to keep house air out of the build-up. It also relies on an air-tight, continuous installation. A foam roof that was sprayed into an older roof without that thinking can fall short. Where that is the case, one answer is removal and a return to a ventilated cold roof; another is a redesigned warm roof, with proper detailing, done by someone prepared to take responsibility for it. Our page on spray foam, condensation and roof ventilation goes through how the two approaches differ.

Restoring ventilation after removal

Once foam has been taken out of the eaves, we look at what the original ventilation was. Soffit vents are cleaned or fitted, a continuous eaves ventilator may go in, and eaves trays or tile vents can be added where the roof structure and the covering allow. We take care to keep a clear air path above any new insulation, using rafter ventilation battens or tray vents so that the insulation cannot slump and block it. Ridge and high-level vents complete the path on a roof that needs them.

Many people ask how long this part takes, and the answer depends on the roof. A simple roof with open eaves is quick. A complex roof with several hips, valleys and dormers has more eaves to clear and more air paths to check. Our answer on how long spray foam removal takes gives a sense of what affects the time.

If you have noticed condensation on the inside of the roof covering, a musty loft or mould on the ceilings of rooms below, the ventilation is the first thing worth checking. A roof inspection can confirm whether the airflow is working before you decide what else to do, and our roof inspection service covers that.

Air movement at the eaves is half of a dry roof. The other half is the layer directly beneath the covering, which has to let moisture out while keeping rain from getting in.

Taking the foam out leaves a bare roof, and most owners want it insulated again. The first question is whether the loft is a living space or just storage. If nobody lives up there, the simplest and most reliable approach is usually to insulate at ceiling level and let the roof space above stay cold and ventilated. If the loft is a bedroom or a study, the insulation has to follow the slope of the roof, and then the detailing gets more careful.

Insulating between and under the rafters

For a sloping ceiling, fibrous insulation such as mineral wool or wood fibre batts can be fitted between the rafters, with a clear ventilation gap kept above them, beneath the underlay. Rigid boards of foam or wood fibre can then be added across the underside of the rafters, which cuts the cold bridge where heat would otherwise leak through the timber. A vapour control layer sits on the warm side and is taped carefully, then plasterboard finishes the surface. The ventilated gap is not an optional extra. It lets any moisture that does reach the timbers dry out. Our page on re-insulating a roof after spray foam removal compares the main routes and what each demands of the rafters, and the broader guide to loft and roof insulation alternatives to spray foam sets them against each other.

Building Regulations and the thermal element

Replacing the insulation in a roof can bring Building Regulations into play. The Planning Portal notes that re-covering or altering a roof above the usual thresholds can mean upgrading the thermal element, and Approved Document L sets limits for new fabric. Whether foam removal and re-insulation counts as a notifiable job is a question for your registered building control approver or the council's building control. Our answer on whether spray foam needs Building Regulations approval covers the thinking, and we always suggest you check before work starts instead of afterwards.

On a listed home, the choices narrow. The materials have to suit the historic fabric, and consent may be needed from B&NES for changes to a listed roof. Breathable insulation, such as wood fibre, is often preferred because it lets the structure handle moisture in the old way.

Who is responsible

If foam was installed recently and went wrong, you may have a claim against the installer or the company behind it. Legal advice is for a solicitor, but we can give you a report of what we find, with photographs, to support a conversation. The answers on what to do if spray foam was mis-sold and on whether a spray foam guarantee is worth anything explain the practical side. Do not rely on a certificate you were handed at the time without reading what it covers.

Saving energy is the other reason people choose foam in the first place. Our answer on whether spray foam saves energy explains what it can and cannot do once the roof has been judged as a whole.

Not every roof needs insulation on the slope. The last part of the picture is the loft floor, where the simplest and most forgiving insulation in a house is normally laid.