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Flat Roof Insulation

Rigid PIR insulation boards, such as Quinn Therm QR boards, are generally the preferred roof insulation materials for flat roofs for a number of reasons. They are lightweight, easy to fit and come in a range of thicknesses. More importantly, they have excellent thermal properties and compressive strength, which makes them ideal for flat roof insulation. Specifiers can achieve excellent U-values when choosing these Quinn Therm roof insulation boards, thanks to their low thermal conductivity of 0.022W/mK.

Given the elevation of the roof and the resulting exposure to wind, rain and cold, and the fact that warm air is naturally pushed up by falling cold air, installing high performance roof insulation is now deemed an essential construction element of any building and a key part of retrofit and refurbishment projects which involve flat roof construction.

There are significant advantages to insulating the roof, not least of which is the reduction in heat loss, improved comfort levels and resulting improved energy efficiency of the building.

Warm Roof or Cold Roof Insulation

When insulating a timber deck flat roof, the positioning of the insulation can make a significant difference to the performance. Warm roof, or warm deck construction, positions the insulation boards above the timber rafters, directly below the roof’s weatherproof membrane. This warm deck construction method is generally accepted as the best method of insulating this type of flat roof and is the standard method of installing roof insulation in most new builds.

In cold deck construction, the insulation boards are placed below the timber joists, leaving the deck cold. This method of roof construction is found more in older buildings and is a consideration mainly for retrofit and refurbishment projects. 

Considerations for Insulating a Flat Roof

Other important factors to consider when insulating a flat roof are:

  • Ventilation: Dependent on the positioning of your roof insulation boards, it may be necessary to ensure a ventilation gap in the construction detail to avoid deterioration of the construction materials and ensure the performance of your insulation.
  • Loading: Ensuring your insulation has the appropriate strength to take the anticipated load and adhere to Building Regulations is essential. Rigid insulation boards are strong in nature and designed to bear the relevant loads specific to each application.
  • Condensation: Cold roofs can be more prone to condensation in colder weather where there is not adequate ventilation, which can cause decay or distortion of the materials.

Further details on installing roof insulation and these important considerations are included in our Quinn Therm Product and Installation Guide, or you can contact or Technical by Quinn team directly at technical@quinn-buildingproducts.com.

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Need technical support?

For help and advice on any of our products and how they might fit your needs please contact our Technical by Quinn team.

  • Floor Insulation
  • Pitched Roof Insulation
  • Flat Roof Insulation
  • Wall Insulation