Buying a house with spray foam
Buying with old foam on the slates: the lowest reading came from failed timber
Stockport · Recent inspection · Spray Foam Inspection
The house
Three-storey detached solid-brick house under natural slate, with two turret roofs over the front bays. One loft in three compartments; the rafters sit on a stub wall about 1 m high, with no soffit.
The foam
Closed-cell foam sprayed directly onto the slates over 83.7 m², with nothing between at any point seen. Said to be more than twenty years old; nothing documents that. It is heavily discoloured and has fallen away in many places.
The paperwork
None: nothing naming the installer, and no contract, invoice, product approval document or warranty. The install date rests only on the owner's account.
Why they called
The buyer instructed the inspection after spray foam was found in the roof during the purchase.
What was measured
- Excluding the wall plate, fourteen readings from 16.3% to 20.6%, in a sealed loft in summer, when roof timber would ordinarily be at its lowest.
- The wall plate read 11.6%, the lowest of the day, yet pieces lay loose on the brickwork and more came away under light finger pressure.
- Near the eaves where the wall plate had failed, a dew point of 17.6 °C, about 4 °C higher than elsewhere.
- No eaves ventilation: only two gable windows, one small slope opening and the hatch.
What it means
The reading that mattered most was the lowest. A moisture meter shows how wet timber is on the day, not how strong it is. Timber that decayed in the past and has since lost its moisture can read low with no strength left. Here the 11.6% came from the timber the rafters sit on. That is why a structural engineer comes before anyone prices anything.
What happened next
A chartered structural engineer for the wall plate first; not optional. Then a timber decay specialist, the solicitor's enquiries for paperwork and repair records, and three roofers pricing the same measured schedule.
For other homeowners
If you are buying, a low moisture figure on its own does not show the timber is sound. Make sure someone looks closely at the timber the rafters sit on.
Read the guide: Buying a house with spray foam: step by step · Should you buy a house with spray foam insulation?
The honest limit
A warm summer day with no rain, so whether water is still getting in could not be told. Only parts of the 23.6 m wall plate could be seen, so how far the failure runs was not established. Timber behind the foam could not be seen, and the covering was viewed from the ground only.