Flat roofing – modern alternatives

You might think flat roofing is leaky and unreliable, but nowadays there are plenty of long lasting, cheaper, attractive and more effective flat roofing options - here are some ideas.

There are many new materials
available for flat roofs
C: ctd 2005 on Flickr

“Flat roofing has come a long way,” says Laurence, from I-tec Flat Roofing in Lincolnshire. “Materials are now a lot more reliable and affordable.” Traditionally, flat roofs were made up of built up layers of felt and asphalt, sometimes dangerously welded together with blowtorches and had joins that, over time, could begin to leak. As Julian Taylor, from Taylor Roofing Contractors Ltd in Wiltshire points out: “The old felt roofing, depending on how well its insulated, may start breaking down after only five years.”

What is a flat roof?

Flat roofs are an often lower cost and easier to install alternative to traditional pitched roofs. They are common on extensions, garages and commercial buildings. “Flat roofs have to be built on a fall (with a slight slope) so that water can still drain off,” explains Julian. As opposed to old built up felt roofing with joins, new single-ply waterproof membranes are now most commonly used. As the Single Ply Roofing Association (SPRA) points out, this type of flat roofing is strong, durable, completely sealed and usually lasts at least 25-30 years.

There are two types of flat roof; cold roofs and warm roofs. Cold roofs have the waterproof layer placed directly onto the roof deck and the insulation inside the roof, just above the ceiling. In this case ventilation is required and the roof can still become wet with condensation which may cause materials to decay. Warm roofs are recommended for homes; the insulation is applied above the roof deck with waterproofing on top which eliminates the need for ventilation and keeps the roof warm.

Flat roofing materials

All flat roofs are made up of a number of layers:

Roof deck – this can be made of metal, timber, concrete, composite or plywood.

Vapour control Layer (VCL) – all warm roofs need this layer inserted between the deck and the insulation; it can be made of polyethylene membrane, bitumen sheet, polymeric foil or a self adhesive sheet.

Thermal layer – this layer can be made of a cellular material such as polystyrene which traps gases in its cell structure or fibrous material like mineral wool which traps air between the fibres to insulate. “We use a fibreglass layer, which is a very good insulator,” says Laurence.

Waterproofing layer – single ply membranes made of materials like thermoplastic or elastomeric are common. “Rubber lasts longer for flat roofing because it expands and contracts with the weather,” explains Julian. UPVC or a resin type surface can also be also used. Laurence, who installs a resin coated waterproof layer, says: “Our system is so reliable because there are no seams or joins, which is where leaks usually happen.”

Surface layer – a surface layer of something like stone chippings, mineral finish or a hard resin finish is often applied to protect the waterproofing layer.

Grass roofs are becoming popular
for pitched and in particular, flat roofs

Regulations for flat roofing

When installing or repairing a flat roof, you must adhere to building regulations. A qualified roofing contractor will be able to advise on this but here are some of the main guidelines:

• There must be a slope of 1:80
• Part H of the building regulations regarding drainage state that water should drain to one or two edges
• Waterproofing should extend up the adjacent walls at least 150mm from the roof surface
• Cold roofs must have ventilation
• Warm roofs must have a VCL bonded to the deck
• Roofs must be wind resistant and strong enough to walk on
• You should consult your local authority to see if planning permission is necessary (this will usually only be if you live in a listed building or conservation area or you are making a significant change to the roof)

Flat roof maintenance

“Most types of flat roofing do not require any kind of maintenance, but you can give it a clean every so often,” says Laurence. The Flat Roofing Alliance (FRA) however, recommends that you inspect your flat roof once or twice a year. Check that drainage is working and that there aren’t any bare patches, puddles or leaves blocking the gutters.

Green roofs

Green roofs are flat roofs covered with a layer of vegetation, plants, shrubs or trees. These are layered on top of a normal flat roof structure with a root resistant and drainage layer. Green roofs insulate and cool your home naturally; according to The Green Roof Centre, a grass roof could reduce annual run off by at least 50% and increase the roof life by double.

Alex Hunt from Bright Green Homes in Brighton says: “Grass roofs look great and are good for flat roofs because they absorb water.” An intensive grass roof uses heavy plant life which requires stronger roof decking and regular maintenance. Extensive grass roofs use more lightweight, low maintenance plants.

Hiring a roofing contractor

The cost of flat roofing will vary depending on the size of the roof and which materials you choose, but Julian says: “The price of flat roofing has really come down over the past few years.” You should try and hire a professional who is registered with an association like the FRA, SPRA or the National Federation of Roofing Contractors (NFRC).

AB