Gransnet forums

House and home

Flat Roof

(29 Posts)
Countrylife Fri 07-Jun-19 14:16:45

We are considering a flat roof on our large extension to avoid cutting into original cottage and allow a slight slope leaving us with minimum of 2.4 internal ceiling height.

Anyone got any recommendations or nightmares to share. Reading up on this is so confusing. It’s a large area and some materials I’ve read about aren’t recommended for large roofs. Ours will be about 17x7 metres.


varian Fri 07-Jun-19 14:21:58

There are many ways of constructing a flat roof and the best advice is to consult a good architect. (Check that he or she is registered with the Architects Registration Board

Countrylife Fri 07-Jun-19 14:30:11

Why didn’t I think of that. Ta!

jusnoneed Fri 07-Jun-19 14:30:21

Don't have one on our house but I used to work somewhere that had an elderly one, a couple times we had to have repairs on leaks. A friend has one on her kitchen and has had a couple of leak repairs over the last couple of years - again an old one.
One of my neighbours has one on her kitchen extension and they have been happy with it so far, about 10 years old. Her hubby gets up and cleans it off every now and then, usually after the birds have chucked moss etc off the house roof.
I think as long as it's done by a good company and you keep checking the seams occasionally they are alright.

FlexibleFriend Fri 07-Jun-19 15:23:46

Part of my house was designed with a flat roof, when it inevitably leaked we had it replaced with a fibreglass roof and so far so good, it has a lifetime guarantee in reality 25 years but was no more expensive than the alternatives and I'd certainly have the same thing again. Ours is about 15 years old and the only maintenance is sweeping moss etc off and it can be walked on etc without causing damage. It's much better than felt or rubber.

Eglantine21 Fri 07-Jun-19 15:51:50

Just to say I am looking at houses to buy and won’t even consider ones with large flat roof extensions.

Even the best only last twenty years or so and then it’s a major expense. A flat roof extension is unlikely to hold its original value because of that.

It depends whether you need the cheaper option now or whether ease and price of resale is important.

Nonnie Fri 07-Jun-19 15:58:44

Generally you get what you pay for. I don't know how long they last but it used to be about 10 years. I'm sitting under one right now as my study is part of an extension before we bought this house. It is pouring with rain, which is quite noisy but if it ever leaks through we will just get it repaired or replaces as necessary. Suggest you get proper advice .

varian Fri 07-Jun-19 15:59:06

That is incorrect. There are many types of flat roof covering which will be guaranteed for thirty years or longer.

varian Fri 07-Jun-19 15:59:52

My post was to Eglantine

J52 Fri 07-Jun-19 16:05:38

Our last house, modernist design, had a large flat roof. We replaced it when we moved in with the then conventional roofing for flat roofs. It was still going strong after 30 years.
However, flat roofs on period properties can look out of place, also check with you house insurers, some don’t like insuring flat roofs.

M0nica Fri 07-Jun-19 16:42:19

We have a flat roof extension to our listed house. It measures approx 15 metres by 2.4 metres. It was buit in the 1960s.

When we moved in over 20 years ago it had the standard felt roof - bit like a shed and there had been leaks. We replaced with a product that looks like a large sheet of black plastic. It has been in place for about 20 years and has never leaked.

However I am not sure I would want a flat roofed extension as large as you are planning, Countrylife. Would it not be possible to have a roof that slopes on all four sides with a roof lantern or similar at the apex?

HildaW Fri 07-Jun-19 16:42:43

My DH is a retired Structural Surveyor and he would always advise against flat roofs as they had far more problems than any other type. When he was working and regularly doing structural surveys 9 time out of 10 a property with a flat roof had problems with it. The usual faults were the actual covering itself you basically get what you pay for. The other was pooling due to poor construction and drainage. Its quite technical to get the water to come off the roof. You really need to track down good roofing specialists - and not those with a one type fits all attitude.

petra Fri 07-Jun-19 16:54:01

We have the High-Tech ( tm) system. This is the same system that was used on the uk Olympics swimming pool.
Not cheap but well worth it. It's guaranteed for life.

Eglantine21 Fri 07-Jun-19 17:12:31

Yup, looking it up I see that some are guaranteed for thirty years. Provided they have have had regular inspection and maintenance.

I still wouldn’t buy anything with a large flat roof though. The Institute of surveyors warns that roofing problems are three times more common with flat roofs and that they should have a detailed inspection twice yearly to nip those problems in the bud.

Insurance is more expensive and some building societies won’t lend on a large flat roof.

Why would you buy a potential problem? Unless costs aren’t important to you.

But the initial reduction in building cost might be more important to the OP than maintenance or resale. I can see that 😀

kittylester Fri 07-Jun-19 17:17:13

but at least we are keeping the roofman in business.We live in a period property with a very small bit of flat roof between two sloping roofs. It leaks! Probably about once every 5 years

M0nica Fri 07-Jun-19 17:44:46

Hilda sometimes there is no alternative, which is what has happened in our case. About 150 years ago our house was divided into four cottages, all of which had at various times had ramshackle single storey outhouses added to them. When it was returned to one house and renovated in the 1960s, the renovator was allowed to demolish the outhouses but any replacement had to match the footprint of the outhouses and be one storey. The first floor windows are so low that a roof with a pitch steep enough to tile was not possible. Hence the long thin shape of our flat roof (15m x 2.4m). But its pitch is sufficient for water to drain off and make pooling very unlikely.

FlexibleFriend Fri 07-Jun-19 19:04:49

I wouldn't say it's that expensive to replace a flat roof ours is about 2mtrs x 8mtrs and cost approx.£1500. If I have to pay that every 25 years that's hardly the end of the world.

HildaW Fri 07-Jun-19 20:52:19

MOnica, I am sure you are right.....was just reiterating the sort of comments he used to make. I think many of the really dodgy flat roofs date from the 1970s era when they were seen as a cheap alternative but were installed without much thought as to maintenance and longevity. As I said if anyone wants to go down this route they really need to do their research and go with an expert.

Coolgran65 Fri 07-Jun-19 20:54:25

We have been quoted £7500 to repair/replace the flat roof of our chalet bungalow. It has to be done as we have a leak into the bedroom. It was done about 10 years ago with 30 year guarantee material. However only as good as the construction Company!!

petra Fri 07-Jun-19 21:22:03

Our roof done by the company I quoted is 26 x12 ft.
It cost £6,000 3 years ago.

JessK Fri 07-Jun-19 21:39:48

You also need to check with your buildings insurance. If the flat roof is more than a certain percentage of the total roof area it will put your premiums up with most insurers.

FlexibleFriend Fri 07-Jun-19 21:58:43

usually over 10% for the above

M0nica Sat 08-Jun-19 20:18:02

Replacing our flat roof with a special plastic roofing sheet cost £6000 in about 1998. It has needed no attention since. The 20 year guarantee it came with has now expired.

We also have a long garden workshop. Approximatedly 9m x 2.4m. That is a standard roofing felt roof. It was last refelted about 10 years ago and cost about £1,500.

Willow500 Sat 08-Jun-19 20:37:04

Our house already had a flat roof extension over the garage when we bought it in 1986. We added a further extension at the back about 20 years ago and the builder added another roof over the existing one which also covered the new part. There was nothing wrong with the existing one but he felt it would be extra insulation. So far we have not had any problems with it (touch wood). However having said that we had the house up for sale a few years ago and no one came to view - the agent said it could be the flat roof putting people off. Not a lot we can do about it - there is no way a pitched roof could be added to it.

crazyH Sat 08-Jun-19 20:44:38

Flat roofs are nightmares. We had one on our kitchen extension in the previous house. I used to dread a shower forecast - I am talking of 40 years ago. I’m sure designs and materials have improved since then. However if I were you , I would have a pitched roof extension if that’s possible .