Selling a house with spray foam
Checked before listing: water ingress indicated at the rear slope, and a rotted purlin
North Wales coast · Recent inspection · Spray Foam Inspection
The house
A 1930s semi-detached house: clay-tiled roof, two chimneys, a roof window in the rear slope.
The foam
Rigid closed-cell foam, fitted in 2019 and paid for by credit card, sprayed directly onto the battens and tiles with no felt behind it. Depth not measured but visibly uneven: in places it buries the rafters, in others it sits nearly flush.
The paperwork
Unusually complete: order form, receipt, a thirty-year warranty that excludes wood, terms and brochure. The felt-repair line was struck through; the brochure said eaves ventilation is left, yet every eaves point reached was filled. Not provided: anything naming the product, and the installer's pre-spray inspection report.
Why they called
Preparing to sell, the seller wanted to know the state of the roof and installation before listing.
What was measured
- 67.6%, taken twice, where a purlin meets a rafter on the rear slope: above the range where a meter gives a reliable percentage, so it indicates free water now. 32.6% beside the chimney breast.
- 15 positions, five at or above 20%, clustered at the roof window and rear chimney; elsewhere 16% to 20%, lowest 16.3%.
- Loft air 1.4 g/kg wetter than outside; the landing below 0.7 g/kg, a normal household level.
- Dew point 13.3 °C, coldest surfaces 17.6 °C: a 4.3-degree margin. Eaves filled solid wherever reached on all three runs, where guidance expects around 0.2 m² of opening.
What it means
Condensation typically spreads along cold surfaces; a leak typically leaves a trail. Here staining ran down the rear chimney breast from the top and sat both sides of the roof window, where the wettest timber and a purlin rotted through were, while the front chimney breast on the same wall was clean. That pattern indicates water getting in at the rear slope, held in by unfelted foam and sealed eaves.
What happened next
First, a roofer on the outside of the rear slope: chimney flashings and pointing, roof window flashing and collar. Then a structural engineer or chartered building surveyor for the purlin. Only then a decision about the foam.
For other homeowners
Selling? Have the loft checked before you list: with a structural timber involved, the answer is then yours rather than a buyer's.
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
One mild afternoon. Timber behind bonded foam could not be read, so most of it is unknown; foam depth was not measured, and the rear flashings were seen from the ground only.