Flat Roof Cold Deck Construction

A cold deck is constructed as follows.

Flat roof cold deck construction.

In a cold weather such roofs are inherently prone to condensation which can cause material decay and deterioration. Thickness varies according to the manufacturer s specifications. It is universally recommended that cold deck flat roof construction should be avoided. There are three recognised designs of flat roof construction.

When building a flat roof it is vital that a degree of falls is built into the construction to ensure rainwater run off. The insulation material is placed immediately above the ceiling between the rafters. Ashford building services can quickly and economically convert any cold deck flat roof to a warm deck insulated flat roof particularly where problems have been tackled sooner rather than later. This arrangement allows the deck to become cold.

Where the existing roof deck is in satisfactory condition and of a suitable material e g. Building regulations state that a ventilation gap of at least 50mm must be in place between the insulation and the underside of the flat roof deck. Others would treat even steeper pitches as flat roofs. The definition of a flat roof according to bs 6229 is having a pitch less than 10 o to the horizontal however some in the industry would consider up to 15 o as their definition of a flat roof.

Flat roof design guide. Flat roof u value 0 18 w m2k 2 warm deck flat roof the type of insulation for this is usually of a rigid type and the thickness will vary depending on the manufacturer s specifications. Where the insulation is placed above the structural deck warm deck and either above or below the waterproofing. For both a warm and cold flat roof a vapour control layer must be installed.

Less thermally efficient than a warm roof construction cold roof construction remains the most common form of construction for existing flat roofs. 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. This is placed over the roof joists and a board normally external ply is laid on top. Warm cold and inverted.