Cold Flat Roof Construction Detail

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

Cold flat roof construction detail.

The membrane is then attached to the insulation. 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. 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. It must provide adequate protection against the elements keeping the buildings structure and interior dry.

In a cold roof construction the sarnafil membrane is installed directly to the structural decking usually timber with firrings to fall. Flat roof types. A flat roof must be strong durable and stable throughout its lifetime. 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 are three recognised designs of flat roof construction. Flat roof design guide. In case of warm roofs they have an insulation above the roof deck in this way it keeps the deck warm. Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading.

Warm cold and inverted. 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. 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. Warm roof build ups can be installed on most modern construction material types such as concrete timber and timber based sheets.

Hot tar and gravel. Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls. The 3 most common materials used for flat roof construction. In the case of a flat roof insulation is usually in the form of either a rigid board above the deck or a fibrous quilt immediately above the ceiling depending on the type of roof construction.

For that reason cold flat roof construction needs to keep in mind the need for unblocked airflow. There are several methods and materials for the design of the exterior surface of a warm or cold flat roof.