Selling a house with spray foam
Selling with foam on bare slates: the wettest timbers were at the valley and chimney
near Chester · Recent inspection · Spray Foam Inspection
The house
Detached house with a hipped natural-slate main roof laid without felt, and a rear wing.
The foam
Closed-cell foam sprayed straight onto the slates and old lime torching in the main roof, with nothing between; the rear wing has none. Installer, product and year unknown. Roughly ½ in to 2¼ in thick at four measured points, against rafters about 3 in deep.
The paperwork
None: no invoice, product document, warranty or grant paperwork. The foam was said to pre-date the current owners; neither of the property's two EPCs records rafter insulation, which does not prove it absent but leaves the date unknown.
Why they called
The house was for sale with foam in the loft and no paperwork. The owner wanted independent evidence before deciding.
What was measured
- 15 timber readings, 5 at or above 20%: highest 22.0% against the south chimney breast, where the timber is soft; lowest 17.0%.
- Main loft air 9.5 g/kg against 7.6 g/kg outside, a gap of 1.9 g/kg; the unfoamed rear part was 3.7 g/kg above outside.
- Dew point 13.6 °C, coldest surface 16.9 °C: a 3.3-degree margin on a sunny autumn morning.
- Foam covers only about 5–10% of the eaves line, but no vent for the main loft was found and the gaps between slates are sealed.
What it means
A leak typically leaves a trail, worst directly beneath the fault. All five readings at or above 20% were on water-stained timber at the valley and the south chimney breast, where loose and slipped slates and torn felt were found. So a leak could not be ruled out, nor the foam named as the cause: the roof covering has to be checked first.
What happened next
A roofing contractor first, for the slates, valley, chimney flashings and torn felt, and the purchase file searched for paperwork. Then checks on the extract ducts and the soft timber. Only then decide on the foam: keep it with designed ventilation or remove it, and whether the cost is reflected in the sale.
For other homeowners
Selling with foam and damp timber? Have the roof covering checked before pricing removal: taking the foam off first can destroy the evidence of where water gets in.
Read the guide: Selling a house with spray foam: step by step · Selling a house with spray foam: what to tell buyers (including the TA6)
The honest limit
Timber and slate undersides behind the foam could not be seen, stored belongings limited the view of the far hip, and the roof was seen from the ground only.