The Mad Surveyor

We often receive enquiries across the pond from our US friends although there is quite an established spray foam industry there. One such enquiry was about what one spray foam contractor had done and whether or not ventilation was necessary after the foam had been installed. The answer is not always. We explained and wrote:

Ventilation is typically required to minimise condensation. If the design structure has a proven low propensity to condensation then ventilation is not required. Why vent and lose expensive energy from a building if condensation is not going be a problem?

Ventilation is not required if the spray foam application creates what is known as a ‘warm roof’ or ‘warm deck’ solution since the ‘warm’ to ‘cold’ movement of air is prevented and any moisture in the air is not released as condensation if the installation maintains temperature above the dew point of air. ‘Warm roofs’ in the UK by definition do not require ventilation. Any cold bridging points might be a problem though and still cause condensation unless controlled for.

We are spray foam contractors and the requirement to vent an attic (loft in the UK) space after installing polyurethane foam is not a concern if the job is done properly. We are moving to sealed envelope solutions in the UK for building design (I believe the US is similar on this point) and ventilation is only introduced where the condensation risk cannot be solved by any other method. Condensation needs to be avoided since long term this destroys the fabric of the building, leading potentially to wet and dry rot in timbers, reduces its energy efficiency as wet insulation, particular fibre glass or mineral wool loses all its insulation qualities, and can cause bad air quality which may negatively impact upon the occupants of the building, produce mildew and mould growth etc. Ventilation may help control condensation but only adds to the energy loss of a building which clearly is to be avoided if at all possible.

If you sit in the car without the ventilation open and without allowing fresh air in it is usually not long before the windows mist over which are the coldest surface inside the car. Merely winding a window or two down by a fraction allows sufficient ventilation to avoid this misting or condensation. However, if the windows were coated with polyurethane (not recommended by the way!) then no misting would occur. The air in the car would go stale but ventilation in buildings in areas not used by people (e.g loft spaces) is more about avoiding condensation than promoting fresh air although both are clearly desirable.

The original installer should have the technical specifications of the foam installed which might further answer your question which really is all about the likelihood of condensation occurring in an unvented space (not withstanding the fact that condensation can still occur in vented spaces especially under still air conditions).

From the pictures you have sent, though the installation looks rather ugly by our company standards it should not detract from its fitness for purpose as long as a minimum depth in line with the foam’s specification/performance parameters has been met. That looks to be the case from the pictures. I would not think condensation will be a problem save in very unusual circumstances.