General Flat Roofing

Condensation: Conversion of water vapour to liquid water

Interstitial Condensation: Condensation which occurs within or between layers of a roof system

Surface Condensation: Condensation which occurs on surfaces visible within the building

Dew Point: Temperature at which air becomes saturated with water vapour and condensation occurs

Vapour Resistance: Resistance of a material to the diffusion of water vapour

Air & Vapour Control Layer: Continuous layer of low permeability material to control the movement of air and water vapour

Water Flow Reducing Layer (WFRL): Robust vapour permeable layer to restrict the flow of water in an inverted roof system

Breather Membrane: Continuous layer of highly vapour permeable, but air impermeable, material to permit the movement of water vapour in cold roof constructions

Waterproof Layer: Layer of impermeable flexible material

Thermal Bridge (Cold Bridge): Part of a roof with thermal resistance significantly lower than that of the surrounding construction

Flat Roof: Roof with a weathered surface at no more than ten degrees (10˚) to the horizontal

Warm Roof: Roof in which the principal thermal insulation is placed above the roof deck and a vapour control layer, and immediately below the roof waterproofing

Inverted Roof (Inverted Warm Deck Roof, Upside-Down Roof, Protected Membrane Roof): Roof in which the principal thermal insulation is placed above the waterproof covering

Cold Deck Roof / Cold Roof: Roof in which the principal thermal insulation is at or immediately above the ceiling

Access Roof: Roof used to provide access to plant or equipment

Terrace Roof: Flat roof for use as an amenity area

Zero Fall Roofs: Roofs with a slope which lies between 0 and 1:80

Root Resistant Material: Membrane that permanently protects the roof’s waterproof covering by preventing plant roots or rhizomes from growing into or through it

Roof Deck: Support structure of profiled metal or timber, part of the roof construction which supports the waterproofing system, including as appropriate the vapour control layer and insulation

Roof Slab: Support structure of in situ or pre-cast concrete

Substrate: Surface or layer upon which reinforced bitumen membrane roofing is laid

Top Layer: Uppermost layer of reinforced bitumen membrane that requires the application of surface protection

Capsheet: Uppermost layer of reinforced bitumen membrane that incorporates a protective finish

Bonding Bitumen: Oxidized bitumen or other suitable bitumen compound melted and used hot

Hot Melt: More generally referred to as Hot Melts, these products are based on hot-applied polymer-modified bitumen, usually applied in two layers incorporating a polyester reinforcement. Hot Melts as a system are also covered by EAD 030065-00-0402 'Composite Roof Waterproofing Kit'. Both EAD's will be used when assessing a system's performance.

Full Bonding: Use of a continuous coat of bonding to adhere a layer of reinforced bitumen membrane roofing

Partial Bonding: Use of a controlled and regular quantity of bonding, so as to provide adhesion over a proportion of the total area of the substrate

Flat Board: (No description provided)

Tapered Insulation: Insulation of varying thickness to create or augment drainage falls

PIR: Polyisocyanurate

PUR: Polyurethane

XPS: Extruded polystyrene

EPS: Expanded polystyrene

PMMA: Polymethyl Methacrylate

GRP: Glass Reinforced Polyester

SMP: Silane Modified Polymers

Reaction to Fire: Reaction fire measures how a product behaves when exposed to fire, and how the product continues to contribute to a fire as it decomposes as a result of that exposure. Products are classified according to BS EN 13501-1. From best to worst, the classifications are: A1, A2, B, C, D, E and F. A designation of NPD means ‘no performance determined’, as the product has not been tested. Classifications A2 to E have a designation for the production of smoke and/or flaming particles added.

Cricket: Wedge of material (usually thermal insulation) to divert the flow of rainwater on a roof. A tapered insulation wedge, usually thin, designed to promote flow along a parapet edge or a flat gutter line, or around obstacles such as a rooflight kerb, to reduce or prevent standing water (ponding).

Firrings: Battens intended to provide drainage falls or ventilation of a roof void.

Blue Roof: Roof designed to attenuate the rate at which rainwater is drained from the roof and is allowed to enter the drainage system.

Green Roof: A roof or deck onto which vegetation is intentionally grown or habitats for wildlife are established, including: extensive, intensive and biodiverse roofs; roof gardens; biodiverse roofs; brown roofs; public and private amenity spaces.

Biodiverse Roof: A roof designed to create a desired habitat that will attract a particular flora and fauna.

Biosolar Roof: A system of using green roof materials to hold solar photovoltaic panels in place.

Brown Roof: Refers to a self-established green roof. No longer considered best practice (see Biodiverse Roof).

Drainage Layer / Reservoir Board: A layer of material to aid water removal or detention.

DIN Standards: Deutsches Institut für Normung, which means “German Institute for Standardization.” DIN Standards are the published results of DIN’s work.

Extensive Green Roof: A lightweight, low-maintenance roof system.

Filter Fleece / Filter Layer: Prevents fines and sediments from being washed out of the green roof into the drainage system.

FLL: Forschungsgesellschaft Landschaftsentwicklung Landschaftbau’s (German Landscape Research, Development and Construction Society).

Green Roof Plants: Plants chosen and cultivated for their resistance to the harsh conditions of a roof environment.

Green Roof System: The component layers of a green roof build-up.

GRO: Green Roof Organisation: The Trade Association for green roof, blue roof, and biosolar roof development and promotion in the UK.

Growing Medium/Substrate: An engineered lightweight soil replacement specifically designed for green roofs.

HSE: Health and Safety Executive.

Hydroseeding: Spraying a specially designed blend of seeds and growing medium.

Inspection Chambers: Enclosed container that allows access for inspection and maintenance.

Intensive Green Roof: High maintenance version of a green roof, sometimes called a roof garden.

Modular Green Roof: Green roof system consisting of off-site constructed and grown identical trays/panels/cassettes, which can be laid directly onto suitable waterproofing.

Protection Layer: Layer designed to protect the waterproofing during construction and function of the green roof.

Root Barrier: A layer (membrane) designed to prevent roots from penetrating the waterproofing layer and building fabric.

Sedum: A genus of about 400 species of low-growing, leafy succulents that are wind, frost, and drought-tolerant, found throughout the northern hemisphere. Not all species are suitable for roofs.

Stewardship: The long-term care of a green roof as an environmental asset.

Substrate/Growing Medium: An engineered lightweight soil replacement specifically designed for green roofs.

SuDS: Sustainable Drainage Systems.

AOV: Automatic Opening Ventilators for smoke ventilation in the event of fire. Opening rooflights adapted for this purpose with smoke-sensor operated opening mechanisms are available.

Argon: An inert gas commonly used to fill cavities in double or triple glazed rooflights. Argon provides an additional barrier to heat transfer.

GRP: Glass Reinforced Polyester, commonly referred to as ‘fibreglass’. GRP is a lightweight, translucent material that is widely used for profiled rooflights for industrial and agricultural buildings, warehouses, and other applications.

G-value: The coefficient commonly used to measure the solar energy transmittance of transparent and translucent materials.

In-plane Rooflight: A flat or profiled rooflight that is installed in the same plane as the roof itself. Conversely, out-of-plane rooflights protrude above the plane of the roof, as in a lantern light or dome.

Light Tube (or Light Pipe): These are generic names for rooflights supplied with and fitted above a tube made of reflective material, designed to provide natural light to rooms under roofs where a loft cavity exists.

Low E Glass: Low emissivity glass designed to improve thermal insulation. Low E glass has a heat-reflecting transparent metal oxide film applied to one side.

Lumira®: Lumira® (formerly Nanogel) is a granular aerogel material offering unsurpassed thermal insulation, as well as light diffusing and sound reduction properties. Lumira-filled multiwall polycarbonate rooflights provide extremely high insulation values, making them a popular choice for projects where energy efficiency is paramount.

Out-of-plane Rooflight: A rooflight which protrudes above the plane of the roof upon which it is installed. Domes, pyramids, barrel vaults, and lantern lights are all examples of out-of-plane rooflights.

Sinusoidal Profile: ‘Wavy’ profiled sheets typically used in agricultural and utility buildings. GRP rooflights are available to match most sinusoidal profiled sheets. Some sinusoidal profiles are also available in polycarbonate.

Trapezoidal Profile: Angular profiled sheets typically used in factories, warehouses, and commercial premises. A wide range of trapezoidal profiles are available. These give a more modern appearance than sinusoidal profiles. GRP rooflights are available to match most sinusoidal profiled sheets. Some sinusoidal profiles are also available in polycarbonate.

U-value: The measure of heat loss in building elements such as roofs and floors. It can also be referred to as an ‘overall heat transfer coefficient’ and measures how well parts of a building transfer heat. A higher U-value means worse thermal performance, while a low U-value usually indicates high levels of insulation. U-values are useful for predicting the composite behavior of an entire building element rather than individual materials.

Ud-value: The U-value of a rooflight based on the developed area of the complete rooflight assembly, including any frameworks or upstands. It is this value which should be checked against limiting values in The Building Regulations.

Walk-on Rooflight: A glass rooflight with a laminated glass load-bearing outer pane, allowing safe pedestrian access.