Cold Deck Roof Insulation

A warm roof has the insulation above the structural deck which is thus kept warm.

Cold deck roof insulation.

There are two basic categories of roof design. Ventilation is required for these roofs. In this way the roof itself is kept cold. A cold roof is where all of the insulation is placed either between and under or completely under the joists or deck.

A cold pitched roof is where the insulation is placed either between or between and under the rafters or at ceiling joist level. Hot roofs are insulated above the rafters. A cold deck flat roof will typically require insulation to be installed between the roof joists to comply with building regulation requirements. Air sealing hot roofs is critical.

This type of insulation system can be ventilated or not ventilated. Traditional cold deck flat roof traditionally flat roofs simply consisted of a structural timber deck with a waterproof covering directly applied to the top of the deck. Cold roofs have insulation between the rafters allowing for ventilation space below your roof deck. This system is called warm deck insulation and eradicates the condensation and venting issues associated with the cold deck system.

This video shows the key features of a flat roof cold deck construction and how to draw the details to a scale of 1 10. A cold flat roof insulation requires more work taking off old boards and replacing them and the roof surface. A cold roof has the insulation placed below the structural deck which thus remains cold. Unless the joists are exceptionally deep there is also likely to be a requirement to install.

This in turn means the deck is sealed off. A cold deck roof is where the insulation is placed between the joists rafters or in between the ceiling joists in the case of a pitch roof. The waterproof layer is above the insulation and a vapour control layer is placed below the insulation. A warm deck roof is much easier to install offers great thermal performance but adds height to the flat roof.

This design dates back many years and flat roof insulation was somewhat of an afterthought with this type of roof. The layer of insulation is essentially placed outside of the roof. You only need ventilation in a cold roof. The thermal efficiency isn t as good as with warm roof insulation.

No insulation is on top.