How To Ventilate A Pitched Roof

For the best results place roof ventilation near the roof s peak and soffit vents in the eaves.

How to ventilate a pitched roof. It is important that air movement occurs and is not impeded by any framing members of the home. The code also allows for air permeable insulation such as fiberglass or cellulose to be used under the roof deck as long as rigid foam is used above the roof sheathing. Unfortunately these slates are exceptionally thin and flat and the mortar torching pointing prevents any air beneficial movement. A ridge vent is a ventilation strip that is placed along the ridgeline of the home.

Prior to installing the ridge vent a 1 inch wide strip of roof decking is cut out along both sides of the ridgeline to allow for air movement through the vent. Air flows in through the soffit vents and out through the roof vents. However there are many other critical steps that we need to master in order to make roof ventilation an efficient process. Bs 5250 sets out the minimum requirements for roof space ventilation.

Alternatively an unventilated pitched roof may be designed. Condensation control is most often accomplished by installing rigid foam above the roof deck or by installing air impermeable spray foam insulation directly against the underside of the roof deck. For example in the average house with a cold loft there should be a minimum of a 7mm continuous ventilation gap at eaves when using a vapour permeable underlay with a normal unsealed ceiling. The principle applied here is warm moist air rising from below is allowed to permeate through the roof membrane removing the need to fully ventilate the roof.

Damp in roof space as a general rule of thumb slated or tiled roofs without underslaters felt tend to breathe and ventilate through natural gaps in the slate. The enclosed void of a warm pitched roof may not require to be ventilated but this is usually subject to the requirement to install a fully sealed air and vapour control layer avcl in conjunction with an air open roof covering.