Roof Insulation Ventilation Gap

Condensation encourages rot and mould growth.

Roof insulation ventilation gap.

The air gap dimensions shown on the drawings are the minimum widths required for clear continuous ventilation air paths at the eaves. This is typical practice when an old fashioned black sarking felt is in place and commonly found in existing buildings. Residential and commercial roofing shingles slate roof ventilation roof underlayments asphaltic and tpo roof membranes. Roof voids must be ventilated in order to stop warm air condensing on cold surfaces.

Staple a continuous polyethylene air and vapour barrier to the rafters and end wall studs. Seal any roof vents into the parts of the attic that are not heated. Static vents often protrude from roofline thanks to. 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.

Leave a clear space between the top of the insulation and the underside of the roof sheathing to allow for roof ventilation. Direct all exhaust fans and vents to the exterior. Then carefully seal the edges and seams with acoustical sealant. 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. 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. The code calls for a minimum of 1 in. 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.

Use hardware cloth metal flashing or scrap plywood to create a safety gap of at least 3 inches all around fixtures. 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. 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. 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.