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Warm deck or cold deck roof?

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There are two main types of flat roof – cold deck roof and warm deck roofs, do you know the difference?

Cold deck roof:

The insulation in a cold deck roof is installed at ceiling level, therefore the void is at a colder temperature than the room below during colder weather. This poses a risk of condensation forming within the void or on the underside of the roof slab. This can lead to rotting timbers, damp ceiling and ineffective insulation. Consequently, it is important that the void is well ventilated. This was the traditional way of flat roof construction and as insulation has increased over the years, the warm deck roof is now the commonly used method of construction.

Warm deck roof:

The insulation in a warm deck roof is installed immediately below the roof membrane on top of the roof deck, usually with a vapour control layer underneath the insulation. Contrasted with the cold deck roof, this construction has a much lower risk of condensation as the void will be of a comparable temperature to the roof. Ventilation is also not required with this type as the design works by conserving heat. Furthermore, an Inverted roof is a different type of warm deck roof, where the insulation is installed above the membrane and so no vapour control is needed. This then means that the roof void or deck are at a similar temperature to the room below.

 

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