This guide is intended for homeowners who are considering alternatives after loft spray foam removal, or who want to understand what lender-friendly options look like before committing to any insulation product. All costs below are guide ranges — a site survey gives a fixed price.
Quick Answer: Breathable, Lender-Accepted Options Exist
The core reason spray foam causes problems for lenders is that it is permanently bonded to the roof structure and prevents inspection of the timber beneath. Every alternative listed on this page shares a crucial characteristic: it can be lifted, removed, or inspected without damaging the structure. That is what makes them acceptable to mortgage lenders, RICS surveyors and equity-release providers.
There is no single “best” alternative — the right choice depends on your roof type, the condition of existing felt, your budget, and whether you want a cold-roof or warm-roof system. If you are re-insulating after foam removal, our vetted partner contractors will advise on the most appropriate option during the site survey.
Why Breathability Matters to Lenders — and to Your Roof
A traditional UK pitched roof is designed as a breathing structure. Warm, moist air rises from the living space below, passes through or around insulation, and any residual moisture is ventilated away via eaves and ridge vents. When this moisture path is blocked — as it is by spray foam bonded directly to the underside of the felt — condensation builds up within the roof structure.
From a lender’s perspective, the risk is twofold. First, hidden moisture accelerates timber decay, meaning the structural integrity of the property cannot be guaranteed. Second, the foam physically prevents a RICS surveyor from inspecting the rafters, so the valuer cannot certify the property as suitable mortgage security. Breathable alternatives avoid both problems: they allow moisture to dissipate and they can be removed or moved aside for inspection.
Mineral Wool: The Most Common Choice
Mineral wool — sold under brand names including Knauf, Isover, Rockwool and Earthwool — is the most widely used loft insulation in the UK. It comes in two principal forms:
- Glass wool: made from recycled glass, lightweight, flexible, and available in rolls and batts. Thermal conductivity (lambda value) typically 0.032–0.044 W/mK.
- Rock wool (stone wool): made from volcanic basalt rock; denser, more rigid, with better acoustic and fire performance. Lambda typically 0.033–0.040 W/mK.
Mineral Wool: Pros and Cons
| Pros | Cons |
|---|---|
| Lowest upfront cost of any option | Can settle and compress over time |
| Fully breathable; does not trap moisture | Can irritate skin during installation |
| Accepted by all UK mortgage lenders | Not suitable as the sole layer in a warm-roof system |
| Non-combustible (Class A1 fire rating for rock wool) | Loses performance if it gets wet (needs to dry out) |
| Widely available; easy to install and replace | Lower acoustic performance than natural fibres |
Guide cost: £5–£12 per m² for supply and installation in a cold-roof loft (laid between and over joists). Total for a 50 m² loft: approximately £300–£700.
Natural Fibre Insulation: Sheep’s Wool, Hemp and Wood Fibre
Natural fibre insulation has grown in popularity as homeowners seek more sustainable materials. It performs exceptionally well in breathable roof systems and is fully accepted by lenders.
Sheep’s Wool
Sheep’s wool is naturally hygroscopic, meaning it absorbs moisture vapour and releases it again without losing thermal performance. This makes it particularly forgiving in older properties where moisture management is critical. It is soft, non-irritating to install, and sustainably sourced. Lambda values are typically 0.035–0.040 W/mK.
Guide cost: £10–£25 per m² supplied and fitted. Higher than mineral wool, but the moisture-management properties often mean fewer secondary problems.
Hemp Insulation
Hemp batts and rolls are made from natural hemp fibres, typically blended with a small proportion of polyester for structural stability. Hemp is breathable, has good thermal mass, and is carbon-negative in production. Lambda values are typically 0.038–0.042 W/mK.
Guide cost: £8–£20 per m² fitted.
Wood Fibre
Wood fibre boards (such as Gutex or Steico) are suited to warm-roof and sarking applications where rigid insulation is required. They are vapour-permeable, have excellent thermal mass properties (reducing summer overheating), and are straightforward to assess and inspect. Lambda values are typically 0.038–0.050 W/mK.
Guide cost: £15–£35 per m² fitted, depending on thickness and specification.
Rigid Insulation Boards (PIR/PUR)
Rigid polyisocyanurate (PIR) or polyurethane (PUR) boards — brands include Kingspan and Celotex — offer very high thermal performance in a slim profile. They are commonly used between and below rafters in warm-roof systems. Unlike spray foam, rigid boards are mechanically fixed or friction-fitted and can be removed for inspection.
A critical requirement when using rigid boards in a pitched roof is maintaining an adequate ventilation gap between the board and the underside of the roofing felt (typically 50 mm) to allow moisture to escape. When correctly installed with this gap, rigid boards are acceptable to lenders and surveyors. Lambda values are typically 0.022–0.028 W/mK — among the best available.
- Pros: very high performance per millimetre; slim profile; rigid, easy to handle
- Cons: more expensive than mineral wool; requires careful installation to maintain ventilation gap; not suitable for every roof type
Guide cost: £15–£40 per m² fitted, depending on thickness and system specification.
Multifoil Insulation
Multifoil insulation consists of multiple thin layers of foil, wadding and reflective membranes compressed into a relatively thin product (typically 25–50 mm). It works by reflecting radiant heat rather than trapping it in a solid matrix, and is lightweight, easy to handle, and suitable for certain roof and wall applications.
In the UK, multifoil products must be tested and certified to demonstrate equivalent thermal performance before they can be accepted in Building Regulations calculations. Well-known brands include YBS SuperFOIL and TLX Gold. When certified and installed correctly — with the required air gaps — multifoil is lender-acceptable. However, it is not appropriate as a standalone solution in all configurations; always check the product’s tested performance certificate.
- Pros: very thin profile; lightweight; quick to install; suitable where space is constrained
- Cons: requires air gaps on both faces to perform correctly; performance claims vary — check certification; not suitable in all roof types as a standalone product
Guide cost: £8–£20 per m² fitted.
Choosing the Right Option After Spray Foam Removal
After foam is removed and the timber inspected, the choice of replacement insulation depends on several factors:
| Factor | What it points to |
|---|---|
| Cold-roof (insulation at joist level) | Mineral wool most cost-effective; sheep’s wool if moisture a concern |
| Warm-roof (insulation between/below rafters) | PIR boards with ventilation gap; wood fibre for breathable warm roof |
| Listed building or conservation area | Natural fibre or breathable boards; check with local authority |
| Budget priority | Mineral wool offers lowest installed cost |
| Sustainability priority | Sheep’s wool or hemp; wood fibre for rigid applications |
| Space constrained (slim rafter depth) | PIR boards or multifoil (check certifications) |
| Older property with moisture history | Sheep’s wool or hemp; avoid any vapour-impermeable product |
Our partner contractors assess the roof structure during the post-removal inspection and can recommend the most suitable product. Re-insulation guide costs range from £300–£1,500+ depending on area, method and product choice.
If you are still at the stage of deciding whether foam needs to be removed at all, please read our loft spray foam removal guide and our information on the independent inspection process before proceeding.
For general background on why spray foam causes problems, see our spray foam problems guide.
This is general information, not financial advice. Insulation choice may affect your EPC rating and future mortgage applications — consult a qualified assessor and mortgage broker for advice specific to your property.