"Understanding Your Home" by Building Inspector Mark Visser
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Continuous ridge vent


Insulating Cathedral Ceilings
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The thermal resistance (or RSI) value is a measure of a material's ability to resists heat flow. The higher the R value, the better the material insulates.
In a cathedral ceiling the rafters are sometimes exposed to the living area. It is possible to fill the space between the joists with insulation and to install a continuous ridge vent. The depth of insulation can be increased by adding strapping to the bottom of the rafters. Install a ventilation system to allow free air movement over the insulation to the continuous ridge vent. The minimum space for air circulation is 3" (75mm) between the top of the insulation and the underside of the roof.

You can add more insulation to an existing finished cathedral ceiling by nailing strapping over the old ceiling finish. The old ceiling and vapour barrier has to be punctured to prevent air from being trapped between two layers of vapour barrier. After this is done you can add the insulation, new vapour barrier and ceiling finish.

WARNING. All styrofoam (or ridged board) insulation is a fire hazard if not properly protected by a non-combustible material such as drywall.
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