Roof Insulation Ventilation Gap

Though it s against building code to vent any kind of exhaust to an attic space many home builders have gotten away with this shortcut.

Roof insulation ventilation gap.

Residential and commercial roofing shingles slate roof ventilation roof underlayments asphaltic and tpo roof membranes. Seal any roof vents into the parts of the attic that are not heated. Of airspace between the top of the insulation and the back of the roof sheathing. Installation of this type of attic ventilation involves leaving a gap in the sheathing along the ridge and covering it with a perforated vent.

2011 code of practice for control of condensation in buildings stipulates that there should be a ventilation gap between the insulation and the bottom of the flat roof deck of at least 50mm. Duo pitch roofs greater than 200 pitch or greater than 10m span should have additional ventilation at the ridge to assist airflow through the roof void equivalent to at least a 3 mm wide continuous gap. Leave a clear space between the top of the insulation and the underside of the roof sheathing to allow for roof ventilation. Use hardware cloth metal flashing or scrap plywood to create a safety gap of at least 3 inches all around fixtures.

Roofing shingles and materials plus factory certified roofers including ratings from real homeowners from north america s largest roofing manufacturer. In a concrete deck for example this gap could be created by fixing 50x50mm timber battens at 600mm centres and attaching the insulation to underside of these battens. Then carefully seal the edges and seams with acoustical sealant. Roof voids must be ventilated in order to stop warm air condensing on cold surfaces.

However for rafters of less than 200mm dormer roofs for example it may be necessary to fix insulation boards to the lower face of the rafters. Direct all exhaust fans and vents to the exterior. Where a warm roof is required it is usually possible to install all the insulation required within the depth of the rafters while leaving a clear ventilation gap of at least 50mm below their upper edge. Condensation encourages rot and mould growth.

This is typical practice when an old fashioned black sarking felt is in place and commonly found in existing buildings. The air gap dimensions shown on the drawings are the minimum widths required for clear continuous ventilation air paths at the eaves. If the roof covering or roof membrane is a material of high moisture resistance or impermeable then the building regulations require a 50mm wide ventilation gap beneath the roofing felt and tiles. Staple a continuous polyethylene air and vapour barrier to the rafters and end wall studs.