Glossary of Terms – Flat Roofing

Flat Roof
– The formal definition a flat roof is a roof with a pitch less than 10º, however in the roofing industry flat roofs as those waterproofed with a membrane. The British Standard  for the design of flat roofs is BS 6229 :2003 Code of practice for flat roofs with continuously supported coverings. There are three main forms of construction:

Warm Roof
–  or warm deck construction has the principal thermal insulation placed above the structural deck, with a vapour control layer between the deck and the insulation.

Cold Roof – or cold deck construction has the principal thermal insulation layer below the structural deck and the concept is usually concerned with roof structures which include an independent ceiling enclosing an air space between the deck and ceiling. BRE Report BR 262 Thermal insulation: avoiding risks, 2002 states that the cold roof is considered a poor option in the temperate, humid climate in the UK.

Inverted Roof – is a form of warm roof where the principal thermal insulation is placed above the waterproof covering. This system is also referred to as a protected membrane or upside-down roof.

Built-up Felt Roofing – is formed on site from two or more layers of roll roofing. The vast majority of materials available consist of a reinforcement base of glass or polyester coated with oxidised or modified bitumen. The British Standards for this type of roofing is BS 8217:2005 Reinforced bitumen membranes for roofing. Code of practice.

Mastic Asphalt – is composed of suitably graded limestone aggregates bound together with bitumens or modified bitumen to make a dense material with no voids. It cannot be compacted, and is spread rather than rolled. The British Standard for this type of roofing is BS 8218 :1998 Code of practice for mastic asphalt roofing.

Single Ply – are flexible sheets composed predominately of synthetic polymer. Thickness is in the range 1.1mm to 2mm. Some products are homogeneous, others reinforced with glass fibre or polyester, depending upon the application. They are sealed at joints to form continuous waterproofing. There is no British Standard for this type of roofing.

Liquid Applied – generally speaking these systems are cold applied using brush, spray or roller and offer a range of specifications providing a wide variety of aesthetic finishes, life expectancy and performance characteristics. There are no British Standards covering this type of roofing.

Hot Melt –  rubberised bitumen waterproofing systems which combine the versatility and simplicity of a liquid applied system with the durability of a substantial modified bitumen membrane system. There is no British Standard for this type of roofing.