Roofs

7.1Flat roofs, terraces and balconies

This chapter gives guidance on meeting the Technical Requirements for flat roofs, terraces and balconies.

Definitions for this chapter

Air and vapour control layer (AVCL)	Continuous layer of impermeable material to prevent the movement of air and water vapour.
Balcony	Accessible external amenity platform over an open space above ground level, with direct access from a building. Balconies may take the form of: ■ projecting – cantilevered from the external wall line of a building. ■ inset – recessed inwards from the external wall line of a building. ■ open – has guarding but no other form of vertical enclosure ■ enclosed – protected from rain by a roof or balcony above and walls or weather screens to the sides, (sometimes referred to as a ‘winter garden’). ■ access balcony – Providing pedestrian access to two or more dwellings. (Sometimes referred to as a ‘walkway’ or ‘access deck’). ■ freestanding – fully, or partially, supported independent of the building structure.
Biodiverse (brown) roof	Surface often of rubble, site excavated soil, sometimes with the inclusion of logs and rocks etc. to replicate the ecology of the local area and seeded or left to self-seed.
Blue roof	Roof installation designed for temporary attenuation of rainwater to delay entry into the urban drainage system and prevent flooding (Blue Roofs are not for water storage use).
Cold roof	Insulation below the deck with a ventilated void between the deck and breather membrane supported on the insulation.
Deck	The structural substrate, including timber boarding or sheeting, profiled metal sheeting on joists/ purlins or, the upper surface of in situ or pre-cast concrete and any applied screed.
Design fall	The fall that a roof should be designed at to accommodate initial and long-term deflection and achieve at least the required ‘finished fall’ in use. The ‘Design fall’ is normal taken as twice the ‘Finished fall.’
Finished fall	The minimum fall that should be achieved on the waterproofing layer once the roof has been installed and fully loaded.
Firring	A tapered batten which creates a fall to a timber deck.
Flat roof	A roof with a maximum slope of 10 degrees from the horizontal.
Flat roof build-up	The roof components above the deck including, as applicable, AVCL, insulation, waterproofing layer, and surface finish/topping.
Fully supported hard metal roofing	Flat hard metal sheeting forming the weather skin and fully supported on a deck.
Fully supported soft metal roofing	Soft metal sheeting (lead) forming the weather skin and fully supported on a deck.
Green roof - extensive	Roof topping of a shallow growing medium supporting plants such as sedums, grasses, wildflower species etc. Generally low maintenance and access for maintenance only.Green roof - intensive
Green roof - intensive	Roof topping of a growing medium to support trees, shrubs, lawns etc. and may include hard land- scaping, and used as an amenity space (sometimes referred to as a Roof Garden).
Interstitial condensation	Condensation that occurs within or between layers of construction.
Inverted warm roof	A roof with Insulation placed directly above the waterproofing layer.
Paving/Decking	A protection layer on which people walk, above the waterproofing layer, on a balcony or terrace.
Profiled self-supporting metal deck	Profiled metal deck, spanning between structural supports e.g. purlins, and supporting the flat roof build-up.
Profiled self-supporting metal roofing	Profiled metal sheeting forming the weather skin and spanning between structural supports e.g. purlins.
Terrace	External surface for amenity use, above an internal space, above ground level and with direct access from a building. For waterproofing and thermal purposes, a terrace is treated as a flat roof. Terraces may take the form of: ■ private Terrace – for the use of a single dwelling. ■ access Terrace – providing pedestrian access to two or more dwellings (Sometimes referred to as a ‘walkway’ or ‘access deck’). ■ raised podium – A terrace, other than an access terrace, above ground level, over a non-habitable area(s) such as a car park or plant room(s). The podium itself may provide hard and/or soft landscaped amenity areas. ■ buried podium is a roof structure at, or below, ground level with hard and/or soft landscaping and sometimes vehicular access for emergency vehicles or parking. Waterproofing to the podium is linked to the tanking of the basement structure below, as described in Chapter 5.4
Warm roof	A roof with Insulation placed directly below the waterproofing layer.
Water flow reducing layer (WFRL)	A vapour permeable loose laid layer, resistant to water, UV, and rot, used to reduce the flow of water and fines into the insulation layer in an inverted warm roof system.
Waterproofing layer	Layer of impermeable flexible material forming the primary barrier to water ingress.
Zero fall roofs	Roofs with a finished slope which lies between 0 and 1:80 and which achieve a finished drained surface that has no back falls or ponding.