Taking foam off a roof leaves bare, cleaned timber, and nothing between the loft and the tiles or slates except air. That is a good moment to decide what insulation suits the building, because the choice is wider than the one that was made last time. The aim is to hold heat without sealing the structure against the damp that every roof meets sooner or later.
Here we look at the two basic roof arrangements, the breathable materials that suit each, how ventilation is worked out, and which of the Building Regulations questions come up. We also cover VAT and the sequence of work. If your worry is about warmth rather than materials, read the answer on whether the house will be colder after removal. For the wider service, see spray foam insulation removal.
Cold roof or warm roof: the decision that comes first
Before choosing a material, you need to know what kind of roof you have. There are two ways to arrange the insulation, and they ask for different products.
Cold roof
With a cold roof, the quilt sits flat on the loft floor, directly over the bedroom and landing ceilings. Everything above it stays unheated, and air moves through that space so that damp drifting up from the house can escape. This is the classic loft arrangement, and the insulation is usually rolls or boards laid between and over the ceiling joists. Foam was often sprayed under the roof in a cold-roof loft to turn it into a warm space, which is how many of these problems began.
Warm roof or room in the roof
If the loft is used as a room, or the owner wants the full volume of the roof pulled inside the heated part of the house, insulation follows the slope of the roof between and under the rafters. Then the rafters, the covering and the underlay all have to be considered together, because there is no cold void to carry moisture away.
Why the foam question helps
With the foam gone, the old decision is open again. Some owners go back to a plain cold roof and recover the loft for storage. Others fit insulation between the rafters with a breathable arrangement. The right choice comes from the survey, the roof covering and what you want to use the space for. We write that into the quote. A narrow loft with a low ridge, for instance, may leave little height for deep quilts, while a steep Victorian roof with deep rafters has room for a layered build-up.
Breathable insulation: what the term means and what the options are
A breathable build-up lets water vapour pass through it and out into the air instead of stopping it at a barrier. Timber can then stay in balance with the air around it. The idea matters most on old roofs and on stone, clay or slate coverings, which were never designed to be sealed from below.
Fibre insulation
Mineral wool in batts or rolls is the familiar choice. It is open to vapour, sits between rafters or joists and is widely available. Sheep wool and recycled fibre products work the same way, and are chosen by owners who prefer natural materials. These fit well in cold roofs and between rafters, provided the airflow is maintained above them.
Wood fibre boards
Rigid wood fibre boards go over or between rafters and are valued for their vapour openness and thermal mass. They suit period buildings where the owner wants a continuous layer without a plastic barrier. They are thicker and heavier than some alternatives, so the rafter depth and the weight on the roof need to be considered. Cutting them tight to the rafters matters, because a gap down the side of a board is a path for moving air, and moving air carries moisture to cold timber.
Matching the layer above
Whatever goes in, it works together with the underlay and covering above it. A breather membrane under the battens, a gap where air can move and a vapour control layer below the insulation, where the manufacturer asks for one, all work as a set. Mixing products from different systems without checking compatibility is a common cause of the dampness we are asked to look at. Tape, sealant and fixings belong to the system too: a vapour layer with unsealed laps, or a membrane punctured by a stray staple, lets moist air through at the very points where it does most harm. Where a plan calls for a new membrane, see our answer on breathable membranes after spray foam.
Ventilation: the other half of the answer
Insulation keeps heat in; ventilation lets moisture out. A roof needs both. BS 5250 is the British Standards code that deals with moisture control in buildings, and the airflow needed over a cold loft is normally read from it. Marley, the tile manufacturer, publishes a digest of its figures.
The figures
Under a solid, non-breathable underlay, Marley asks for a 25 mm slot running the whole length of the eaves when the pitch is 15 degrees or shallower, easing to 10 mm on steeper roofs. A further 5 mm continuous gap near the top is added for pitches over 35 degrees and spans beyond 10 metres, and for any roof that is a lean-to or a mono-pitch. Fit a breather underlay over an airtight ceiling and an air-permeable covering and the sums change: 3 mm of leakage through ordinary eaves detailing can be enough, or alternatively 5 mm at the ridge. Treat these as starting points and check them against the data sheet for the product you are using.
What this means in practice
Foam often covered the eaves, closed the gaps and blocked the flow. Part of the work after removal is to clear those routes, fit eaves vents or tray vents so insulation does not choke them, check that the loft hatch and pipe penetrations are sealed from below, and make sure the ceiling below is well sealed against the warm, damp air of the house. Whether extra ventilation could be an alternative to removal is dealt with in the condensation guide and its linked answers.
Part L: when new insulation has to meet a standard
Part L is the section of the Building Regulations about saving fuel and power. Approved Document L Volume 1 (dwellings) in its 2021 edition, with the 2023 amendments, has applied in England since 15 June 2022. Its figures are U-values, which measure how fast heat passes through a building element in watts per square metre per degree of temperature difference; a lower number means a better insulator.
Three ideas to hold on to
First, a new or replacement roof element should reach 0.15 W/(m²·K) under Table 4.2. Second, one route into the rules is stripping a layer down to the rafters and building it up again, which Approved Document L treats as renovation of a thermal element. When over 50% of the element's surface is renovated, or the job is a major renovation touching more than 25% of the envelope, the whole roof is to be improved to 0.16 under Table 4.3, the existing-element table, where 0.35 is the threshold figure. Third, note 3 to that table allows a lesser standard where meeting the number would cut head room.
Does removal on its own trigger it?
Not necessarily. Removing foam and then fitting new insulation inside an existing build-up is a different job from stripping and rebuilding the roof. Whether the job falls into that category is for building control to say, and the answer turns on how much of the surface is touched. Stroud District's service is the Gloucestershire Building Control Partnership; a registered building control approver is the private alternative. If the job needs approval, we explain what is involved and send the notification ourselves. Where foam removal is bundled into a re-roof, the thresholds in our guide to Building Regulations for foam removal also apply.
Listed and period homes: the extra layer of care
A listed house brings extra checks. If a change to the roof insulation alters what makes the building special, listed building consent comes into play. Stroud's planners say the legal protection reaches every grade and the whole building, while RICS calls foam not reversible and unlikely to gain consent on a listed home. Those points favour products that can be lifted out again, such as fibre quilts and boards, when the roof is insulated for a second time.
The council's conservation team can say what applies to your property, so ring them before drawing up the work. There are 41 conservation areas across the district, with Article 4 Directions in five. The council does not state whether those reach roof work, so ask them directly.
Breathable choices for older roofs
On older roofs the usual advice is to favour vapour-open products: wood fibre, wool or mineral fibre, with the roof able to breathe through its covering and eaves. We cover the planning side in our answer on spray foam in a listed home. Our approach to like for like on older roofs means that the covering we put back matches what came off: stone stays stone, slate stays slate.
Cost, VAT and the order of work
MyBuilder's 2026 spray foam removal guide puts repairs and new insulation at £500 to £3,000 nationally, in addition to removal. That is a broad range because the price depends on the floor area, the product, the depth needed and how much timber repair is involved. Your own quote covers each of these.
VAT
Most roofing work carries the standard 20% rate. Insulation fitted to the roof or loft of a house is zero-rated up to 31 March 2027, with the 5% reduced rate following, according to the government's VAT notice on energy-saving materials. Your quote shows VAT. For jobs that mix several kinds of work, ask for the VAT treatment to be spelt out.
Sequence
The order matters. The foam comes off first. The timbers are then cleaned and, if needed, repaired. If the covering is going to be replaced, that happens before the new insulation, so the roof is watertight and the loft is not exposed. The underlay and ventilation follow, then the insulation, then the ceiling or lining below.
Do not insulate over timbers you have not seen dry. If the inspection was skipped before the foam came off, ask for readings on the cleaned wood first.
When we finish, the loft and garden are left tidy, the waste goes with us, and a 10-year workmanship guarantee is written out for you.