Re-roofing a house is straightforward when the underside of the roof is bare timber. When it has been coated in spray foam, the job changes. The foam is stuck to the roof felt, to the battens and sometimes to the backs of the tiles themselves, so you cannot strip the covering without deciding what happens to the foam. The order of work, the cost, the waste and the way the new roof will be insulated all follow from that decision. This guide explains the problem, the options, how the job runs, and what to ask a roofer before you agree to a scheme.
Why foam complicates a re-roof
On a normal re-roof, the old tiles or slates come off, the felt and battens come off, the rafters are checked and any repairs made, and a new underlay, battens and covering go on. Each layer is separate and lifts away from the one beneath. With spray foam on the underside, the layers are glued together. The foam is sprayed up against the underside of the felt and battens, sets, and bonds them to the rafters. If you pull the battens off from above, the foam may tear the felt, snap the battens along their length or lift in lumps still holding wood fibre. The old tiles may be held to the battens in turn. You end up with a loose, heavy and uneven mess, and nowhere to put it.
The foam also hides what you most need to see. When a roof is stripped, the timbers are inspected, because leaks and condensation over the years may have rotted the rafter tops, the battens or the ridge board. Where foam covers the rafters, that inspection cannot happen until the foam is gone. RICS advice to homeowners, published in 2023, makes the same point: the wood can appear dry on its visible face and be damp behind the foam. A re-roof is the moment when the truth becomes visible, and it is better to find out deliberately than to cover it with a new roof.
There is also a regulatory side. A re-roof that affects over half of the roof, or over a quarter of the building envelope, normally needs a building control application, and the insulation across the roof may have to be brought up to current standards. How that interacts with existing foam is a question to put to your building control body at the start.
The three options
Option 1: remove the foam first, then re-roof
This is the cleanest route. The foam is taken out from inside the loft by scraping, cutting and shaving it from the rafters, with dust protection and extraction. The timber is cleaned back to bare wood, inspected and repaired. The roof is then stripped and re-covered in the normal way, and the roof is insulated afterwards. It takes longer and costs more because there are two stages, but it gives a sound base and the timber has been checked before it is covered. Our page on spray foam removal sets out the process in detail.
Option 2: strip the covering, then take the foam out from above
Once the tiles or slates, battens and felt are off, the foam sits exposed on top of the rafters. It can then be cut or scraped away from the outside, or in lumps with the battens attached, and the timber inspected from above. This route can be quicker where the covering is being replaced anyway, because the roofer has direct access and no overhead working. The cost is that the roof is open to the weather for longer, so the sequence has to be planned around the forecast and protected by temporary sheeting. It also puts a lot of waste on the scaffold. It suits a whole-roof replacement and not a partial one.
Option 3: leave the foam and re-roof over it
Occasionally a new covering is laid with the foam left in place. It is the cheapest in the short term and the one most likely to cause trouble. It buries the problem, it leaves the timber unseen under a roof that has just been renewed, and a surveyor or lender can still ask the same questions about the foam. We would only consider it where the foam is demonstrably sound, the timbers are accessible for checking elsewhere, the installation was done under a proper guarantee and the roof was designed as an unvented warm roof from the start. Even then, we would say what the risks are. Our page on spray foam over roof felt explains one of the commonest awkward cases.
What the job looks like, step by step
- Survey and moisture check. We look at the roof from outside and the foam from inside, photograph what is visible, and take readings in accessible timber where the foam has been cut back or does not reach.
- Decide the sequence. Based on the survey, we recommend one of the options above, with a reason.
- Scaffold and protection. A full scaffold goes up, and the loft floor and contents are protected. Foam waste is bagged on site.
- Foam removal. Done in the agreed order, with dust control and suitable respiratory protection for the operatives.
- Timber inspection and repair. Rafters, battens and the wall plate are checked, damaged wood is cut out and replaced or treated, and any leaks that caused the damage are traced.
- New underlay, battens and covering. Laid in the usual way, with ventilation detailed to match the new insulation plan.
- Insulation. Fitted after the roof is watertight, in a form that suits the roof; see below.
- Clear-up and handover. Waste goes with us and the site is left clear.
Living in the house while it happens
Foam removal is noisier and dustier than an ordinary re-roof. Scraping and cutting foam from rafters sends fine particles into the air, and although sheeting and extraction keep most of it in the work area, the loft hatch and the rooms below need protecting. Bedrooms directly under the roof are best emptied of bedding and clothes, and anything stored in the loft is moved out first. Pets and young children are better elsewhere on the removal days. A good contractor sets out these arrangements in advance, not on the morning.
The weather needs planning too. Work that opens the roof is scheduled for a settled spell, the opened area is kept small, and the covering goes back on before the next forecast of rain. Neighbours with shared walls or close boundaries should be told about scaffold, noise and the delivery of materials. Ask whether any bats or nesting birds use the roof, because protected species can mean work has to wait or be surveyed first.
Warning signs that point to a re-roof with foam removal
Some roofs do not give you a choice. If you can see daylight at the eaves where the foam has pulled away, if tiles have slipped because the battens beneath have lost their grip, if the ceiling below shows stains that return after rain, or if there is a musty smell in the bedrooms under the roof, the covering and the timber behind the foam are probably unwell. A surveyor's report that flags damp readings behind foam, or a lender who refuses to proceed until the foam is dealt with, points the same way. In each case the cheapest course usually combines the foam removal and the re-roof under one scaffold, so the work is done once. Our guide to spray foam insulation problems explains the symptoms in more detail.
Insulating the new roof
When the foam has gone, the roof needs insulating again, and the house should not lose its thermal performance. For a ventilated cold roof, mineral wool or similar insulation goes on the loft floor, with the roof space kept cold and ventilated. For a warm roof, rigid boards are fitted above or between and below the rafters with a vapour control layer, designed so the timbers stay dry. The choice depends on whether the loft is used and on the energy rules for the work. Our page on how to insulate after removing spray foam sets out the alternatives, and the comparison of warm and cold loft insulation explains the trade-offs.
Cost and what moves it
Costs are best understood as two parts. A published guide puts the typical UK cost of re-roofing a three-bedroom semi in concrete tile at £6,500 to £10,500, and slate costs more. Removal of spray foam is on top: professional removal is reported at £40 to £80 per m², or £2,000 to £4,500 for a standard three-bedroom loft, with a lower estimate of £20 to £50 per m² elsewhere. The two jobs sharing one scaffold is cheaper than doing them years apart, which is the main argument for combining them. The firm price comes after the survey, and it will separate the foam removal, the timber repairs, the new covering and the insulation so you can compare each line.
Several things move the price: the thickness and type of foam, how well it has bonded, whether the covering is being replaced anyway, the amount of timber repair, the size of the roof, and whether the loft is accessible. Open-cell and closed-cell foam differ in removal effort, as our comparison of open-cell and closed-cell foam explains.
Questions to ask a roofer
- Will the foam be removed, and by what method? Who does the removal, and how is the dust controlled?
- How will the timbers be inspected, and what happens if rot is found?
- How will the new roof be insulated and ventilated, and who has designed it?
- Does the quote separate the foam, the timber, the covering and the insulation?
- Will building control be notified, and who deals with it?
- How is the roof protected from the weather while it is open?
A roofer who talks only about the covering and says nothing about the foam has not understood the job.
How we approach it
Our free survey includes the loft, with photographs of the foam, the rafters and any damp or staining, so the report shows your own roof. We explain the options in plain terms, say which we would choose, and give a fixed written price. Where the foam can safely stay, we say so. Ten years of written guarantee cover our workmanship, and we arrange the building control side where it is notifiable. See spray foam insulation assessment and removal in Basingstoke for the rest of our work in this area, or telephone 01256 213956 or open a WhatsApp chat when you are ready for a survey.
