People ask for a spray foam assessment for different reasons. Some have a buyer's surveyor asking questions. Some have a lender that wants evidence. Some have noticed a damp patch, a smell or a stain and want to know whether the foam is to blame, and some simply put the foam in some years ago and are no longer sure what was done. Whatever the reason, the job is the same: to look at the roof as a system and to report what is there, in terms you can pass to a solicitor, a lender or a buyer. This guide walks through what an assessment covers, in the order we work, what the readings mean and what the written findings should contain. It also says what a survey cannot tell you, because a report that claims to see through foam without opening it should be treated with care.
What the assessment is for
An assessment has three aims. The first is to identify what has been sprayed: which kind of foam, how thick, over how much of the roof. The second is to judge the condition of the roof beneath it, particularly the timbers, which are the part that foam hides. The third is to give you a clear recommendation, whether that means leaving it alone, keeping watch on it, or stripping part or all of the foam.
It is not a sales visit for removal. If the roof is dry and sound, the report should say so openly, and a good report of that kind is useful in its own right when you come to sell. If there is a problem, the report should say where it is, how far it reaches and how urgent it is. Either way you leave with a record of the roof as it stood on the day, backed by pictures taken on your own roof.
Typical UK costs are worth knowing before you book. MyBuilder's spray foam removal cost guide (2026) puts an assessment at £100 to £200. That is a national range reported by a third party, not our price, and the price of any work that follows is set out in a fixed quote after the survey.
You may also see the word survey used for a general roof inspection. The typical UK range for those, reported in MyBuilder's roof inspection guide (2026), sits between £150 and £500 depending on the type of inspection. A foam assessment is narrower than a full roof survey, though it often touches on the same things.
From the outside first: covering, flashings and gutters
We usually begin outdoors, because water that enters from above can look exactly like condensation from below, and the two need telling apart. Up on the slopes, we check the covering for pieces that have slipped, cracked or gone. Around chimneys, walls and valleys the flashings and lead get a close look. We check the gutters and downpipes for blockages and leaks that could be soaking the eaves, and the ridge and hips for loose or cracked pieces.
Flashings are strips of lead or another metal dressed over a joint so that water runs off, and a valley is the internal gutter-line where two slopes meet. If either has failed, water enters at that point and runs down the foam or along the timber. Where the underside is sprayed, the water cannot show itself as a drip, so it can sit unnoticed for a long time.
Why start here? Because the cheapest cure is often a simple repair above. A cracked slate or an open flashing found now is a small job. Found only after the timber has been wet for a season, it can be much larger. We photograph what is visible from the ground and, where it is safe, from the roof, so the detail we saw is in front of you too.
Inside the roof space: the foam itself
Inside the loft, the foam gets examined before anything behind it. We note whether it is open-cell or closed-cell, which affects how moisture behaves in and around it. We note its thickness where we can measure it, and whether it covers the rafters entirely or only the spaces between them. We look at where it stops, at the eaves, the ridge, the gable ends and around the chimney breast, because edges are where problems tend to show first.
Surface condition tells us a good deal. Foam that has cracked, shrunk away from a rafter or sagged between supports leaves a gap that moist air can reach. Staining, white deposits or mould at the edge of the foam suggest moisture. Foam sprayed over wiring, pipes, extractor ducts or recessed lights raises other questions that we flag in the report, including heat build-up and access. Where the foam has been applied over an old roof covering, we check whether it has crept through the gaps between slates.
Identifying the foam type is not always simple. We explain how it is done in our page on how to identify the type of spray foam, and the type affects both the risk and any removal plan. The difference between the two is covered in open versus closed cell foam.
The timbers: readings, probing and inspection openings
The timbers are the heart of the assessment. Rafters, purlins, wall plates and battens carry the roof, and if they have been wet for long they can lose strength. Foam hides most of their length, so we work from the places we can reach: exposed ends, sections beside the foam edge, and the wall plate at the eaves.
The main tool is a moisture meter, which measures how much water the wood holds. A reading by itself is not a verdict. Wood in a roof space is rarely perfectly dry, and what matters is whether readings are high, whether they are rising in the places most exposed to cold, and whether they match the signs we see: rusted nail heads, staining and softness under a probe. We press a probe or a small awl into the wood to test for softness, which shows decay that a reading can miss.
When a small opening is justified
If the evidence suggests a problem but the foam blocks the view, the next step is a small inspection opening. A small window is cut through the foam at a chosen spot, the timber behind it is examined and tested, and the result goes in the report. Doing so does not commit you to removal, and we agree where we will cut before we start. The opening is patched or noted in the report afterwards. For older houses, where we want to disturb as little as possible, we discuss the choice with you first, and our guide to older and listed Bath houses with foam explains why.
Ventilation and the house beneath
Moisture in a roof comes from the house, so the assessment looks downwards as well. We check the bathroom and kitchen for extractor fans that work and vent outside, not into the loft. We look at the landing and bedroom ceilings for stains, and at the loft hatch for a tight fit. A house that makes a lot of moisture and holds it in will test any roof harder.
We then look at what air paths remain in the roof itself: eaves vents, ridge ventilation, gaps at the verges. Manufacturer guidance built on BS 5250 expects continuous ventilation along the eaves of a cold roof, with the opening size varying by pitch and underlay. If foam has closed those paths, the roof has lost the means of drying that it was designed with. If the foam was installed as a sealed warm roof, the question is instead whether it is airtight and whether the house is managing its own moisture. Both are matters of fact that a survey can establish, and we set them out in our guide to condensation behind foam.
We also record signs of damp elsewhere that might be mistaken for a foam problem. Our page on spray foam and damp deals with the ways damp can arrive and how to tell one from another.
What the written findings should say
A good report is readable by someone who was not in the loft. At the least it should record:
- The foam type, approximate thickness and the areas covered, with photographs.
- The condition of the roof covering and the main flashings, noting any defects found.
- Moisture readings and where they were taken, with a note on the weather and the state of the house at the time.
- The condition of the timbers that could be seen or tested, and anything that could not be examined.
- The ventilation arrangements, and whether the foam appears to have changed them.
- Signs of past or present leaks or condensation.
- A clear recommendation: leave, monitor, repair, remove in part or remove in full.
A report should be honest about its limits. We cannot see through closed-cell foam, and a survey that does not open it up gives only a partial picture. Where we have not seen something, the report says so, rather than implying it is sound.
The report is yours. Lenders and buyers often ask for something in writing, and a clear record is more use to them than reassurance. Our page on the RICS position on spray foam explains the consumer guidance published in March 2023, which is the standard many surveyors have in mind when they raise foam.
After the survey: choices and costs
If the survey finds dry timbers and sound foam, the likely recommendation is to leave things as they are, keep an eye on the loft each winter and look again if anything changes. If it finds damp or decay, the options widen. Removing foam from one slope, from one section, or from the whole roof are all possibilities, and which one fits turns on where the damp sits and what caused it.
Costs depend on the area and the condition. MyBuilder's 2026 figures show a typical UK range of £20 to £50 per square metre for removal, averaging about £1,500, with disposal at £150 to £400. Repairing or replacing timbers, re-insulating and any work to the covering come on top, and the price you pay is the fixed figure we write down after the survey.
Once the foam is off, the roof needs insulating again. There are several ways to do this that avoid the concerns lenders have raised, and we set them out in our guide to alternatives to spray foam. Our wider foam work is gathered under spray foam insulation.