When a house with spray foam in the roof comes up for sale, somebody has to look at what is under the foam, and that somebody is usually a surveyor. Owners often dread the visit because they do not know what is being checked or what the surveyor can and cannot conclude. This guide explains what an inspection of a foamed roof covers, the tools used, what gets written in the report, and how to prepare so the process goes smoothly, whether you are the seller, the buyer or an owner who simply wants to know.
Who inspects a foamed roof, and why
Three kinds of person tend to look. A buyer's surveyor works for the purchaser and reports to them, and a mortgage valuer works for the lender and assesses the property as security for a loan. A roofer or timber specialist works for whoever hires them and can be asked to dig deeper. The different jobs matter. A general surveyor often notes the presence of foam, flags the risk and recommends further investigation, because the roof timbers behind the foam cannot be seen from the loft. Further investigation is where a roofing survey fits.
Behind that sequence sits the RICS consumer guide on spray foam, published in March 2023, which explains that foam can trap moisture against timbers and make a roof hard to inspect, and which is the reference many surveyors work from. The professional bodies and lenders have also discussed an inspection protocol for surveyors, and lenders mainly want certainty that the foam was properly installed and that someone is accountable for it. Our page on spray foam and mortgages covers the lending side.
What an inspector looks at from the outside
The outside of the roof comes first, because tiles and flashings show symptoms that the loft hides. From the ground, with binoculars, and from a ladder or scaffold where access is safe, the inspector looks at the following points.
- The tile courses, for slipped, cracked or lifted tiles that might signal weakened battens or foam gripping the tile back.
- The ridge and hips, for sagging lines that suggest rafters or the ridge board have moved.
- Valleys, chimney flashings and abutments, for the failed details that let water in.
- Gutters and fascias, for overflow staining that sends water under the first course of tiles.
- Eaves, for any sign that foam has been pushed out to the edge and smothered the ventilation path.
- Moss and algae patterns, which show where the surface stays damp for longest.
A drone can make this safer on steep or high roofs, and photographs taken give you something to keep. Cost guides put a domestic drone roof survey at about £200, although that figure is a national average for orientation only.
What goes on in the loft
Inside, the inspector asks first how and when the foam was applied. Then the inspection turns practical. The visible surface of the foam is checked for cracks, shrinkage, gaps at the eaves, debonding from the rafters and staining. Edges around the chimney breast, the gable walls and the water tank are looked at closely, because those junctions often hide trouble. Any vents, spotlights or extract ducts are noted, since foam sprayed over a vent defeats it.
The key measurement is moisture content in the timber. A pin-type moisture meter pushes two small probes into the wood, and the reading shows how wet it is. Pins cannot reach through foam, so a surveyor either works from exposed timber at the gable, ridge or hatch edge, or cuts small inspection openings in the foam, with the owner's permission, and takes readings through them. Several readings across the roof tell more than one. A thermal camera can show cold or damp patches on the foam surface, but a thermal image points to where to look, and it cannot prove what is behind the foam.
What the report should say
A useful report is plain about what was seen, what was measured and what could not be checked. It should state the type of foam where known, the area covered, the condition of the foam, the readings and their positions, any signs of decay or staining, and the access limits that applied. It should then give a clear recommendation: leave and monitor, open up and investigate further, remove in part, or remove entirely. Reports that merely say "foam present, further investigation advised" leave the owner exactly where they started.
When we survey, you receive the photographs, the readings and a written explanation in everyday language, followed by a fixed written quote if work is recommended. If the roof is dry and the foam is behaving, we say that and do not suggest work for the sake of it. A buyer's surveyor or lender may want their own report, and the one we write can sit alongside it as supporting evidence.
Why a survey cannot give a guarantee
Even a thorough inspection has limits. The inspector can test only where they can reach, and they cannot see behind every inch of foam. A dry reading today does not promise a dry roof next winter if a bathroom fan starts venting into the loft or a gutter blocks. Equally, a high reading in one spot does not prove the entire roof is rotten. Good reports describe the condition seen on the day and explain the reasoning. Anyone who promises more than that is overselling.
Making sense of the moisture readings
A moisture meter reports the water content of the wood as a percentage of its dry weight. Dry softwood in a heated building sits at a modest level. A roof timber that reads well above that, and stays high over repeat visits, is wet enough for decay to take hold. Between those two zones sits a grey area, and the reading is judged alongside the temperature, the season and what the surface of the timber looks like. A rafter that reads high near a leaking flashing but normal elsewhere points to a local leak. A roof where every reading is elevated points to a general condensation problem. Meters also read differently on treated timber, and a competent inspector allows for it and records the instrument and settings used.
Readings are only half the picture. Probing with a bradawl or screwdriver tells you whether the surface fibres have softened, and a sound-looking rafter that feels spongy at the foot is a worry. Photographs of each reading position let anyone reading the report match numbers to places. Where we cut into the foam, the openings are labelled on the photographs and listed in the report, so a later surveyor can find the same points and compare.
Defects that foam hides
Several roof faults go unnoticed under foam for years, and an inspector looks for clues to each. A failed lead flashing round a chimney lets water run behind the foam, and the first symptom may be a brown stain on the chimney breast two floors down. A missing or slipped tile leaves a patch of foam rained on from above. Rusted clout nails and corroded wire ties show on the surface where foam has pulled away. Cracked rafter feet show as a gap where foam splits along the line of the wall plate. Birds, wasps and mice can also nest in gaps behind loose foam, which is a tell that the foam has parted from the roof. None of these is unique to foam. The difference is that without foam a torch and a few minutes would have found them early.
Surveys on commercial and outbuilding roofs
The same approach applies to non-domestic roofs, though the scale is different. Garages, outbuildings, barns and extensions are sometimes foamed on the underside of sheeting or boards, and moisture can be as much of a problem there as in a house. Cost guides put commercial drone roof surveys in the region of £750 to £1,000, with the usual caution that these are national figures. On a flat or low-pitched roof the inspector also checks falls, outlets and the membrane, since foam on the underside of a deck can hide a leak from above as easily as from the pitched kind. Our team treats every roof as its own case, and the survey is arranged around what is actually there.
How to prepare for the visit
Preparation saves time and money. Clear a route to the loft hatch and, if the loft is boarded, move boxes away from the eaves. Gather every document from the original installation: invoice, product data sheets, any guarantee and the installer's details. Note the date of the work, and any previous leaks, stains or smells. If the house is being sold, ask the agent what the buyer's side has already requested, so you can answer the right question the first time. And if you do not know whether the foam is open-cell or closed-cell, the guide to open-cell and closed-cell spray foam explains how to tell.
What happens next
The report leads to one of four outcomes. Dry timbers and sound foam mean you keep the report with the sale paperwork. Marginal readings mean a re-test after a wet spell and a plan for improving ventilation in the house. Damp but undamaged timbers mean removing the foam so the roof can dry, which our page on spray foam removal describes. Decayed timbers mean repair as well as removal. For a first look at your own situation, or to arrange a survey, start from the spray foam assessment and removal page. If the foam was fitted after a doorstep sale, our page on spray foam mis-selling may also help.
Surveys for buyers and sellers
Sellers gain from acting early. A survey commissioned before the house goes on the market gives you time to deal with any findings and the paperwork to answer a buyer's questions without a rushed negotiation. Buyers gain from asking the seller for any survey that already exists, and from commissioning their own if foam is mentioned on the particulars or found by the valuer. In both cases, the sooner the roof is understood, the less the foam is likely to disrupt the sale. Our page on selling a house with spray foam looks at the seller's side in more detail.
