Roof, moisture and ventilation questions

Describe the whole roof build-up

Record the roof covering, underlay or felt, structural timbers, foam location, ceiling-level insulation, ventilation paths and any vapour-control layer where they can be established. RICS advises considering the building components together because a retrofit can change how they perform.

Sources for this section: RICS consumer guide to spray foam insulation

Separate observations from concealed areas

Ask what was inspected internally and externally, what access was available, which timbers or junctions remained concealed and whether any reading has a recorded location and context. Foam can restrict inspection from within the roof space.

Sources for this section: RICS consumer guide to spray foam insulation

Ask focused moisture and ventilation questions

• Where can water enter from outside?
• How is water vapour controlled through ventilation and layers?
• What signs or readings were observed, where and under what conditions?
• Does existing ceiling-level insulation alter the intended build-up?
• What further access or monitoring would answer a remaining question?

Sources for this section: RICS consumer guide to spray foam insulationUK government moisture-risk study

Keep the modelling inside its limits

The government study investigates theoretical moisture and timber-degradation risk for modelled combinations of foam, underlay resistance, vapour control and climate. Its reported results vary by scenario. It applies to England and is not a certificate, inspection result or conclusion about an individual roof.

Sources for this section: UK government moisture-risk study

Next steps

1. Gather records describing the roof build-up, installation, repairs, ventilation and prior moisture evidence.
2. Ask an appropriate independent assessor what can be inspected safely and what remains concealed.
3. Use published modelling to frame questions, then rely on property-specific findings for the decision.