A flat roof is built on joists – steel or timber – that span the width of the roof and form the load-bearing part of the structure. An insulated timber deck is then added on top of the joists. The roof can then be covered with a waterproof exterior layer. Nowadays traditional felt roofing – bitumen impregnated sheets applied in layers – is still used, but more popular are EPDM (ethylene propylene diene monomer) rubber roofing.

This depends on how badly damaged your roof is. If there are issues like small leaks, water ponding, wind damage, blisters or tears in the surface coating then a roofing contractor should be able to make repairs.

If the roof surface has suffered numerous repairs and is degrading – perhaps beginning to look a bit like a worn patchwork quilt – then a new professionally applied overlay will be the solution.

More serious damage or issues with your roof, particularly if it affects the timber base structure and the joists, are best resolved by a complete roof replacement. A roofing expert will be able to advise you.

Flat roofs are actually not flat! They should have a slight slope, known as a “fall”, so that water runs off of the lower edge. The fall should never be less than 1:80 or you risk having water pooling on the roof.

There are so many variables that it is not possible to give a figure. The cost of a new flat roof depends on things like the specification of the roofing materials; the height of the roof and access (is scaffolding required); the size of the flat roof; the amount of insulation required; whether there is asbestos in the old roof. The best thing is to engage a few contractors to survey the roof and provide you with a free no-obligation quotation so you can make an informed decision. The cheapest quote is not always the best, though. A lot depends on the standard of workmanship, so it is wise to check up on the roofers’ online reviews and testimonials from other clients. Make sure any quotation you are given includes all the required elements like the removal and disposal of the existing roofing material, any underlay required, edgings, guttering, insulation and so on. You don’t want any extras on top of the quoted price.

If it is well-constructed and well maintained the average felted bitumen flat roof and BUR (Built Up Roof – made of layers of asphalt and gravel) should last for 15 to 20 years. EPDM Rubber membrane roofing, however, has a life expectancy of at least 50 years.

You will need planning permission if you make any structural changes to an existing flat roof. If You’ll also need permission to replace more than 25% of the roofing area, and will also need to replace the thermal insulation.  As far as building regulations go, there are several for flat roofs:

• There must be a slope of 1:80 minimum
• Water drainage should occur from one or two edges
• Waterproofing should extend up the adjacent walls for at least 150mm from the roof surface
• Roofs must be wind resistant and strong enough to walk on
• Cold roofs must have ventilation
• Warm roofs must have a vapour control layer (insulation) bonded to the roof deck