For further information please contact SLE Cladding Ltd. Tel. 01948 666 321. Fax.  01948 66 55 32

Felt Roofing

Coldseal and Quicktrim

Self-adhesive roofing system

Roof design & construction

Pages 4 & 5

Building Regulations	Design Considerations
It is important to be aware of the existing Building Regulations concerning the design and constructions of flat roof structures. In new constructions and some flat roof projects, It may be necessary to consult your local council Building Control office with regard to compliance with Building Regulations. For information relating to current insulation requirements, refer to Part L1 and L2.	In a flat roof the waterproofing is always supported by a structural roof deck. This is usually a timber boarding of some type which in turn is supported on joists. With the exception of garages, most roofs above habitable parts of the house require insulation. The most common method is where the insulation is located immediately above the ceiling. This is known as a cold roof. (See Fig. 5). In cold weather the roof could be prone to condensation if adequate through ventilation is not provided. Refer to BS 6229: 1982. Alternatively, the insulation may be placed above the roof deck. This is known as the warm roof design (See Fig. 6). The insulation used must be of a urethane/plywood composite board with the plywood face on the top surface.
	Deck materials It is important that the right materials are chosen for constructing or strengthening a flat roof deck. Below are some suitable materials OSB 3 conditioned decking Oriented Strand Board (OSB) should be a minimum thickness of 18mm and be manufactured in accordance with BS EN 300: Part 3: 1992. As with plywood you should check with your supplier that it is suitable for your particular roof structure.
Timber Boarding Where an existing deck comprises of close boarded tongued and grooved timber, it is recommended that a 6mm plywood overlay deck should be installed to provide a smooth homogenous surface for the self-adhesive membrane to bond to. Concrete. Common in roofs to blocks of flats and some pre-war houses, concrete is a stable and reliable deck material. If it needs repair, provision should be made for drying out before any priming or waterproof covering is laid. Chipboard. Although frequently used for residential flat roofs, it is not generally suitable unless the roof has no ceiling, for example, as in a garage. If chipboard is used it should conform to British Standard 5669; Part 2: 1989 Types C.3, C.4 or C.5. Note: Pre-bituminized decks are also suitable. Protection from condensation Cold roofs should have adequate through ventilation in the void space (see Fig. 5) All insulated roofs require a a vapour control layer. Protection from the wind All roofs should be constructed to resist wind forces.	Essential for a successful flat roof. Like any part of a building's exterior, flat roofs should be constructed to withstand natural and human forces with the minimum of attention. Protection from rain and snow  The finished roof should have a slope of at least 1 in 80. It is best to drain the roof to one or two edges. Conventional eaves gutters are better than internal outlets Internal outlets should be adequately sized to deal with storm conditions and be fitted with clamping rings, leaf and gravel guards. The waterproofing should extend up adjacent walls at least 150mm from the finished roof surface in all situations. The top edge of felt should be protected by a cover flashing. Protection from sun and frost It pays to insulate: heating bills are lower and rooms are cooler in the Summer. Insulation of new flat roofs must satisfy the Building Regulations, Part L1 and L2. Protection from people. If the use is changed, the structure may have to be strengthened. Damage is often caused by service trades such as window cleaner, for example