Why are flat roof’s on properties especially extensions which are a later addition?

The answer is simple, it generally boils down to cost. There are other reasons such as roof height restriction’s but cost is the controlling factor.

Comparing the cost of a pitched slate or tile roof, a flat roof can be installed for a fraction of the cost.

By implication, as the materials are less durable and the structural detailing is less conducive to pass water away from the roof covering, flat roofs have a shorter lifespan; as little as 10 years!

What are the main types of flat roof?

1) The most usual is built-up felt. Timber decking is laid then built-up felt layers are installed which are over-lapping to provide the watertight roof covering. The quality of felt can vary greatly but in some cases is very poor.

2) The other common type of flat roof covering is asphalt. This is a mixture of bituminous pitch with a gravel or sand aggregate. It is quite durable but can be prone to cracking.

3) There are other proprietary roof coverings such as elastomeric coverings. These are less common.

What are the pitfalls?

The first thing is to know what to look for and the tell-tale signs that the roof may be failing:

1) Worn or weathered upstands, these are the rolled over coverings at the edges of the roof.

2) Ponding of water.

3) No dedicated drainage.

4) No solar protection, i.e. chippings or solar paint.

5) Bubbling or cracking.

6) Poor flashings at abutments.

7) Internal staining.

8) In the event that the roof covering has failed and water is passing through to the interior, it is likely that the decking will be affected. This is the timber structure underneath the flat roof covering. Internal finishes such as plasterboard to ceilings can also be adversely affected. If the leak is serious, this can lead to complete failure and the collapse of the ceiling.

What should I do?

1) Carry out a good general inspection of any flat roof areas if visible.

2) You may be able to see flat roofed areas from higher windows that will often give an indication of the general condition of the roof. If the roof is at high level, this may not be possible in which case you would only see the upstands. These do generally give a reasonable indication of the condition of the rest of the roof.

3) You should check if there is any documentation relating to when the roof was covered or recovered.

4) Make enquiries with the vendor to gain as much information as possible.

If in doubt regarding the integrity of the flat roof, you should engage the services of a roofing contractor for professional advice.

BLOG provided by R Pearson (MRICS)

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