Installer ceased trading: a 25 mm air gap was designed and sold, but not reliably built

What was measured

• Gap behind the foam where visible: 70, 32, 19 and 6 mm, against 25 mm sold; in other places the card lay flat on the felt or was missing.
• Eaves packed with foam at fifteen places; six still open to daylight; no ventilation at the ridge.
• Ten timber readings, 15.5% to 19%, mean 17.5%, none at 20%; the installer's survey recorded 8%.
• Loft air 1.0 g/kg wetter than outside, rising rather than clearing during the visit.

What it means

Vapour passing through this foam meets felt that the installer's own calculation rates far more vapour-resistant than any other layer; the ventilated gap was designed to carry it away, and that calculation only passes with it. Where the gap is missing, moisture would be trapped on the coldest surface, behind the foam, where no instrument reaches. Nothing is rotting, but timber the installer's survey put at 8% now reads 15.5–19%.

What happened next

First, notify the insurance-backed warranty's administrator in writing within its deadline; no work on the foam until the insurer replies. Without waiting, an electrician for cables buried in the foam at four places. A solicitor alongside; then a choice: correct, remove, or re-measure in winter.