Cold Flat Roof Construction Detail

The 3 most common materials used for flat roof construction.

Cold flat roof construction detail.

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. Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading. The construction of the flat roof is similar to that of the timber upper floor. Hot tar and gravel.

Cold deck roof 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. There must be an adequate void minimum 50mm between the deck and the insulation traditionally mineral wool to allow free movement of air and to prevent moisture vapour being transmitted from the building outwards where it could condensate in the roof. Warm cold and inverted. It must provide adequate protection against the elements keeping the buildings structure and interior dry.

Warm roof build ups can be installed on most modern construction material types such as concrete timber and timber based sheets. The membrane is then attached to the insulation. Flat roof design guide. For that reason cold flat roof construction needs to keep in mind the need for unblocked airflow.

In case of warm roofs they have an insulation above the roof deck in this way it keeps the deck warm. Cold bridging through the system is easier to eliminate or control as ordinarily there are no breaches from the structural supports as there is in a cold roof construction. No ventilation is required for these types of roofs. A flat roof must be strong durable and stable throughout its lifetime.

It is usually the most acceptable type of construction for domestic possessions and belongings as it avoids the need for aeration of the roof construction. Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls. In a cold roof construction the sarnafil membrane is installed directly to the structural decking usually timber with firrings to fall. There are several methods and materials for the design of the exterior surface of a warm or cold flat roof.

In the case of cold. A roof is defined in bs 6229 as a flat roof if it has a pitch of 10 degrees or less.