by Mark Row

Best solutions for insulating pitched roofs

For pitched roof insulation most commonly used materials are glass or rock wool, and PIR insulation boards. Innovative eco products such as hemp and local British sheep's wool insulation, for example ThermaFleece Eco Rolls and ThermaFleece Original Slabs (available in different lengths, widths and thickness), are also well suited for roof insulation and have multiple benefits both for the homeowners and the environment.

Roof of the building is an element that is most exposed to external influences. It is also the most exposed part of building through which heat transfer occurs in substantial amounts. For that reason it is very important to have adequate roof insulation in order to achieve thermal stability in the building.

Measuring the width and depth of the rafters

To determine the thickness of the insulation materials needed, you must measure the distance between  rafters (inside dimensions) and the depth of the rafters. If the depth is not optimal for the right thickness of insulation, it is necessary to put extra battens on the face of the rafters to create the required depth. Modern roofs typically already have a breather membrane, like DuPont Tyvek Housewrap Breather Membrane, and there is no need for a background ventilation. This type of roof configuration is called a warm roof. In other roofs without this membrane (cold roofs) you have to strictly follow the special guidelines about vapor treatment.

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Insulation installed above and between rafters

Membrane should be placed over the rafters and insulation if the insulation completely fills the depth of the rafters, with counter battens nailed into the rafters.

On the inner (warm) side of the insulation a vapor layer should be installed.

It is not necessary to put in place any additional ventilation below the breather membrane. With concrete or clay tiles moving air above the membrane there is no need for additional eaves and ridge ventilation.

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Insulation installed at rafter level with timber sarking

This pitched roof insulation design requires the use of timber sarking which has a high resistance to the passage of water vapor.

It is not recommended to use sarking boards (OSB) without additional ventilation. But if using 150mm wide timber planks with a 2mm gap between them, there is no need to have additional ventilation under the breather membrane.

When either slates or tiles are installed on battens, the use of counter battens above of the membrane is a must.

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