Spray foam insulation in the loft: problems and removal

What spray foam is

The Energy Saving Trust (EST) describes spray foam insulation as a liquid polyurethane foam that installers apply with a spray gun; it sets to form an insulating layer. Because it is sprayed, it can reach awkward areas quickly. It is used on roofs, walls and floors, and in a loft it is usually sprayed onto the underside of the sloping roof, instead of laying mineral wool on the loft floor.

There are two main types, and the difference matters:

The problems, according to the Energy Saving Trust

Timber rot. Spraying foam directly onto the underside of the roof partly seals the timber. If rainwater from a leak collects there, it will eventually cause the timbers to rot. Even without a leak there is a risk of condensation doing the same. The EST says this risk should be much lower with open-cell foam.

Repairs. Timbers coated in foam are harder to replace. So are tiles or slates, if there is no roofing felt or other layer between them and the foam.

Permanence. Spray foam is considered a permanent installation. If you decide to remove it later, you may also need to replace the structure it was applied to.

False claims. The EST records two sales lines it treats as problems in themselves: that foam will fix a leaking roof (no insulation should go onto a leaking roof), and that existing mineral wool no longer complies with regulations and must be replaced (misinformation used to increase sales).

Mortgages and selling

The headline worry for many owners is selling. The EST’s view is that mortgage refusals were possibly true for a while, when lenders reacted to concerns about damp and repairability, but that progress in assessing whether a house is at risk means there should be less of an issue for homes where spray foam was installed correctly. In practice, a buyer’s surveyor may ask to see the loft and any paperwork. Keep the installer’s details, the product used and any guarantee together.

Removal: when and how

Removal is not automatically the answer. Start with an independent look at the roof:

1. Is the roof dry? Check for leaks, damp patches, staining or a musty smell. Any leak must be repaired regardless.
2. What type of foam is it? Closed-cell foam carries the higher moisture risk.
3. What condition are the timbers in? A surveyor can check for decay where the foam allows.
4. What will replace it? Once foam is removed, the loft needs insulating properly, usually with mineral wool at joist level, with the eaves ventilated.

If removal is recommended, get more than one quote, make sure each one covers repairs to timbers or felt that removal may reveal, and ask how the loft will be insulated afterwards. The EST suggests getting multiple quotes from accredited installers, such as TrustMark-registered businesses.

The lower-risk alternative

For a normal pitched roof with an accessible loft, the EST describes mineral wool at joist level as one of the lowest-risk options for insulating the loft. It keeps the roof timbers ventilated and inspectable, can be laid by a competent DIYer in a dry loft, and is the method behind the EST’s own cost and saving figures. See loft insulation depth for how it is laid and warm roof vs cold roof if you need the loft space warm.