Foil insulation problems and multifoil insulation problems — what people usually mean
Searches for "foil insulation problems" and "multifoil insulation problems" almost always come back to the same three details: whether there is an air gap facing the foil, whether that gap is ventilated rather than sealed, and where the vapour control layer sits relative to the insulation and the roof structure. The product name on the paperwork — multifoil, SuperQuilt, space blanket, thermal wrap, silver foil or bubble foil — changes the specification, not the questions.
Manufacturer performance figures are achieved under specified installation conditions. Where those conditions were not met on site, the figures do not describe that roof. Whether yours meets them is answerable by inspection of your specific loft — see the foil and multifoil loft insulation inspection.
What the BBA certificate actually requires
Every multifoil product on the UK market that carries a BBA certificate has installation conditions attached to it. The certificate is not a generic stamp of approval — it is product-specific, and the performance figures (U-value, air permeability) only apply when the product is installed exactly as the certificate describes.
- A minimum air gap facing the foil — typically 25mm, sometimes more depending on the product, and ventilated where the certificate requires it
- Fully sealed joints using the manufacturer's own foil tape (not generic tape)
- A continuous vapour control layer with no penetrations breaking continuity
- A specific combined insulation buildup — multifoil + a stated thickness of rigid or mineral wool insulation — to achieve the claimed U-value
- Correct orientation, fixing centres, and overlaps
Common installation failures
The most frequent issue found on inspection is the multifoil installed tight to the rafter underside or felt with no air gap. Without the air gap, the product is essentially performing as a reflective layer with no thermal benefit, and condensation risk increases sharply. Other common failures: unsealed joints, missing vapour control continuity, and the product sold as a standalone solution where the certificate clearly requires a combined buildup.
Where foil insulation sales claims and certificate conditions diverge
Multifoil is sometimes sold as a single-product solution that 'meets building regulations on its own'. For most domestic roof applications, the BBA certificate is explicit that it does not. A combined buildup is needed. Where it was sold to you as a standalone solution, the gap between the sales claim and the certificate conditions is documented evidence for your decision, sale, or claim — whether that gives you a route is a question for a solicitor or Citizens Advice.
Where the multifoil was installed after spray foam removal — sometimes as an upsell from the same removal contractor — independent inspection becomes particularly important. The contractor has a financial interest in confirming their own work meets standard.
What the inspection produces
- Identification of the multifoil product where possible
- Cross-reference against the relevant BBA certificate conditions
- Air gap measurement on both sides of the multifoil
- Joint sealing and tape continuity check
- Vapour control layer assessment
- Combined insulation buildup vs claimed U-value
- Photographic evidence and a clear plain-English summary