PurAcell vent cards which are branded PurAvent are required when applying PurAcell spray foams to the underside of pitched roofs. The PuraVent card maintains a 50mm air gap which is required for compliance with NSAI certification and also a requirement of the building regulations in Ireland . Despite claims by some system designers that they can apply spray foam directly onto a membrane or felt there is no product certified in Ireland for direct application . To claim their is is simply untrue and misleading . The only exception to this rule is where the roof is counter battened on the outside which allows for airflow on the external side of the felt or the membrane. what does this vent card do that it is so important ? The vent card not only maintains the required 50mm air gap but also retains the ‘drape’ of the membrane and stops the felt from being pushed up against the slate or tile which could possibly cause condensation issues. NSAI have indicated their preference for a cardboard type card as opposed to plastic as cardboard offers more porosity than plastic and if a leak occurs in the roof it is more likely to become obvious with a cardboard type card and remedial works can be carried out by the homeowner . With the plastic card the leak will not become obvious as the plastic will retain the water and guide it towards the eaves and eventually the chute, however water lying continuously on the roofing timbers for long periods will lead to rotting of the timbers and damaging the integrity of the roof structure. Anybody considering having spray foam applied to their existing home or new build should ensure that firstly the spray foam system is certified by the NSAI and secondly that the system is installed in compliance with the certificate.