First, a breathable card membrane/ Vent card is installed between the rafters.
Then a 50mm ventilation gap is left between the vent card and the roofing felt to prevent the buildup of moisture, allowing it to dissipate to the outside.
Next, the foam is simply sprayed onto the vent card to the desired thickness. It's as simple as that.
Here spray foam insulation is being applied above the eves in an attic. First a breathable vent is fitted 50 mm from the roofing felt allowing a continuous air flow which removes moisture from the attic and allows your timbers to breath, then the foam is applied giving your attic a continuous airtight seal.
What is unique about spray foam insulation in comparison to traditional insulating materials, such as rock wool, fibre glass or cellulose, is that it expands into ever nook and gap of the roof space, providing an airtight seal which prevents the infiltration of damp cold air and more importantly wind.