Worried about damp or condensation
Hoping to keep the foam: why vents at the top would not fix filled eaves
Rochdale · Recent inspection · Spray Foam Inspection
The house
Detached two-storey modern house, rendered, with interlocking concrete tiles on trussed rafters and four small gable projections. Soffit vents outside, open.
The foam
Open-cell, sprayed in 2022 onto a breathable membrane, with mineral wool left on the loft floor. Rafters mostly buried (about 100 mm at two tape points, about 50 mm at one); some slope areas bare; at the roof pipe, membrane folded back, foam sprayed onto the tiles.
The paperwork
Contract, quotation and a manufacturer's safety sheet, the only document the contract lists as supplied. Not supplied: any pre-installation survey, ventilation assessment before the eaves were filled, product documentation stating the required thickness, or the quoted warranty documents.
Why they called
The homeowner hoped to keep the foam and asked whether ventilation could be improved without removing it.
What was measured
- Loft air 2.3 g/kg wetter than outside: above 2.0, the report's working band for moisture with nowhere to go.
- 14 timber readings, 11.6% to 18.3%, none at 20%. Timber outside the foam averaged 11.9%; timber in the foamed zone, read at gaps, 17.2%: 5.3 points higher, same morning, same meter.
- Dew point 16.8 °C, coldest timber 19.6 °C at the eaves: a 2.8-degree margin with 18.6 °C outside.
- Bathroom air 1.4 g/kg above outside, read as normal; but some ceiling bays had no insulation, with gaps where pipes and cables cross.
What it means
A traditional loft draws air in low at the eaves and lets it out high. Here the soffit vents are open, but foam fills the eaves behind them wherever examined: air can enter the soffit, not the loft. Top vents would give air a way out and no way in, moving very little. Getting ventilation back would mean clearing the eaves, which is partial removal.
What happened next
First, a roofer at the roof pipe and above the water-marked joist, before any foam decision. Then confirm what the pipe is and where the extract fan discharges. If the foam stays, repeat the same readings yearly.
For other homeowners
Keeping your foam? In this loft, the advice that needs no removal is to cut the moisture rising from the house: fill empty insulation bays and seal round pipes and cables.
Read the guide: Does spray foam cause condensation or rot roof timbers? What the evidence says · Living with spray foam: should I worry?
The honest limit
One mild morning, not a midwinter night. Timber encased in foam could not be read, the extract duct's end was not traced, and staining on the membrane was not sampled.