A roof is classed as a flat roof if the pitch is less than 10°. Flat roofs can be classed as either cold deck or warm deck which relates to where the insulation is located in the roof build-up and can be finished in a range of different products including multiple layer mineral felt systems, mastic asphalt systems and single-ply membranes.

Cold & Warm Decks

In a cold deck roof, insulation is laid between the ceiling joists above the ceiling finish, which acts as a vapour control layer. There is then a small void between the insulation and roof deck which is ventilated and prevents moisture build-up and condensation. With a warm deck roof, the insulation is located above the ceiling joists and deck and is laid on top of a vapour control layer. The flat roof finish is then installed directly onto the insulation. The main advantage of installing a warm roof over a cold roof is it is more efficient at keeping the building cool in summer and warm in the winter, helping to reduce energy costs.

Types of Flat Roof Coverings

Below are some examples of the most common waterproof coverings we come across when surveying flat roofs:

Bitumen Felt Covering

This is the traditional method for covering a flat roof and involves applying multiple layers of bituminous felt to the deck which provides a waterproof finish to the roof. Traditionally, hot bitumen is poured onto the insulation or lower layer of the system and layers of bitumen felt are rolled into it. It is more common today to apply a bitumen felt covering using ‘torch-on’ methods. The felt is produced in roll format and is heated as it is rolled onto the roof which bonds it to the surface below.

Mastic Asphalt Covering

Mastic asphalt is a dense mixture of course and fine aggregate with a bitumen binder and additives. Blocks of mastic asphalt are heated up on site into a molten state and poured onto the roof in two layers. Prior to pouring the asphalt, an isolating membrane is loose laid onto the roof. Asphalt roofs need a solar reflective covering applied, usually in the form of stone chippings, to prevent heating and cooling which leads to cracking.

EPDM & Single-Ply Systems

Single-ply membranes are durable, flexible and resilient sheet materials, composed of mainly synthetic polymers. Ethylene Propylene Diene Monomer (EPDM) is a type of single-ply system which can be installed without the need for joints, or any naked flames. The rubber system is simply glued to a clean roof decking. This is generally a more cost effective waterproofing solution than torch-on felt coverings, however they can be easily punctured and seams are vulnerable to leaks.

If you are experiencing issues with a flat roof, Bradley-Mason LLP are well equipped to provide you with the necessary advice in terms of potential remedial works and specification for repair and replacement roof projects.

Please contact us at www.bradley-mason.com if you require assistance in this area.