All you need to know about replacing/repairing a flat roof including costs of materials, costs of labour and time frames.
Flat roofs send some people into a panic, some will not buy a house with a flat roof or will spend a fortune having it removed and a traditional pitched roof fitted - but are they really that bad? The short answer is, no! In fact a professionally sealed flat roof should last 20 years or more without leaking, so the worst case scenario for most of us would be having to replace it 3-4 times at most, with the total cost still being much less than building a pitched roof (on average you could completely replace a flat roof around 15 times to spend as much as one single pitched roof build).
But no matter how professionally a flat roof is fitted, there will come a time when it begins to fail, leaking at first, but eventually bowing in and in danger of collapse. When you see signs of leaking, you should consider repairing or replacing the roof, putting things off will not fix the problem, but will in fact make it worse and more expensive! As to whether you should repair or replace the roof, that depends on the roofing material and the amount of damage. Funnily enough flat roofs are generally built with a slight incline to allow rain water to drain off into gutters, so basically most flat roofs aren’t actually flat!
Flat roofs are made up of roofing timbers or joists which are are laid across walls at a specified distance apart, then they are covered with some sort of boards or sheeting that usually need to be waterproofed. There are many different types of flat roof materials, but felt, EPDM or rubber and fibreglass are the most popular types. Typically a repair job will involve essentially re-waterproofing a section of the roof, whereas a replacement roof means stripping away the roof covering and replacing it with a new one, which my also involve new joists depending on the damage.
When replacing a flat roof, it makes sense to fit new fascia boards at the same time, as these will have to removed anyway so you are already paying the labour for half the job anyway! In addition, a flat roof that has been leaking for some time, may also need the roof joists themselves treated or even replaced if they are damp and rotting. It obviously makes no sense to fit a new roof on top of rotting joists! So a joiner or carpenter may be required, along with a decorator to finish the interior.
Some flat roof repairs can be done on a DIY basis, there are a number of waterproofing and sealant materials which can make effective though temporary repairs, giving you time to gather quotes and save up for longer term professional repairs to be carried out. You can even buy paint on "waterproofer" which is emergency roof repair in a tin! But if damage to the roof is localised to just a small area, it may be possible to effect a permanent longer term repair, rather than replacing the entire roof. However, if you cannot fix the roof material yourself on a DIY basis, it will probably not be cost effective getting a contractor to carry out repairs, as for a little extra, you could have a complete new roof.
In many cases making repairs to a flat roof is a complete waste of money, for example if the roof timbers underneath are damaged. In addition on certain types of roofing material it is difficult to patch small damaged areas without damaging the rest of the roof, thereby making things even worse, falling through the roof when attempting repairs is not unheard of with DIY either!
The average cost of replacing a flat roof is usually in the range of £700-£1300 depending upon what materials the roofer uses, whether or not scaffolding will be needed, and the size of the roof.
Most roofers operate in pairs and will usually charge around £200-£300 per day. Usually the job will be completed within a single day, and the roofer should always come back the next day to ensure there are no leaks.
Here are a few average costs for replacing a flat roof:
|Job Size||Scaffolding?||Avg. Cost||Duration|
|Single Garage||No||£700||1 day|
|Double Garage||No||£900||1 day|
|2-storey Extension||Yes||£1200||1.5 days|
Individual costs for replacing or repairing a flat roof on a 2-storey extension - Total Cost: £1200