Warm Roof Deck Insulation

A warm deck roof is where the insulation is placed on top of the rafters joists and the roof covering is then placed over the insulation.

Warm roof deck insulation.

The layer of insulation is essentially placed outside of the roof. The vapour control layer is above the decking but below the insulation. The best method of insulating a flat roof is by using a warm deck flat roof construction method. Effectively placing the deck inside making it completely free from the dangers of condensation and the associated rotting commonplace with cold roof insulation.

There are two basic categories of roof design. To use epdm for a warm deck flat roof construction solid closed cell roof insulation such as kingspan or celotex should be placed on top of the roof deck rather than in between the rafters. This system is called warm deck insulation and eradicates the condensation and venting issues associated with the cold deck system. A warm flat roof or a built up roof bur is one where all the insulation is above the joists deck making them part of the warm fabric of the building.

The insulation can be adhered mechanically fixed or loose laid. In a warm roof construction the principal insulation layer is placed above the structural decking resulting in the structural deck and support structure being at a temperature similar to that of the building interior. No ventilation is required for these types of roofs. Warm flat roofs do not need to be ventilated as the insulation is above the structure.

A flat roof where the insulation sits below the waterproof membrane and above the structural deck is a warm roof deck. The main advantage of a warm deck construction versus a cold deck construction is that there is no need to include a ventilated cavity in the warm deck construction. This in turn means the deck is sealed off. The waterproof layer is above the insulation and a vapour control layer is placed below the insulation.

A warm roof has the insulation above the structural deck which is thus kept warm. A cold roof has the insulation placed below the structural deck which thus remains cold. Cold flat roofs are typically avoided as you d need to install ventilation which can prove problematic for many reasons relating to space labour costs etc. It also provides better thermal performance and makes it easier to eliminate thermal bridging.

Warm deck flat roofs can be constructed on most modern construction material types such as concrete timber and timber based sheets.