Rear extension - flat roof or pitched?

[Bumblebee46]

Hi all
Just hoping for some advice. We're planning a single storey rear extension to 1930's house. Just getting an architect to draw plans.
Does anyone have any advice, pros/cons on whether we should have flat roof or pitched roof? Especially interested in cost difference if anyone has any knowledge?

Thanks

We had this exact dilemma, also for a 1930s house! Haven’t built yet but have done planning permission drawings.

Some of it is about aesthetics. We didn’t want a modern box on the back of the house but a lot of people like that look and if that’s what you want, they often have a flat roof.

We wanted a pitched roof, partly because I have never heard anything good about flat roofs and partly because we think it will look better from the garden (next door have a pitched roof extension) and means we can have skylights and a sloping ceiling in some of it. We have had to leave a small area of the roof flat because of how it will fit around the rear bedroom window, if that makes sense. But most of it will be pitched.

If you want a flat roof, I’d do some research and also see whether it affects your buildings insurance if more than a certain percentage of the property’s roof is flat. I’d also have a look on Pinterest to get an idea of what it will look like inside.

Cost: not sure - I suspect flat is cheaper in the short term but I might be wrong.

Pitched if at all possible. Last year we reroofed both our pitched roof and a very small flat roof. The pitched roof had lasted over 100 years the flat roof about 20. The pitched roof was ten times the area of the flat roof and cost only double the flat roof to replace.

If we had had enough scope to do so we would have added a pitched roof but the window in the room above is very low and it just wasn't possible.

Our flat roof also leaked after it was replaced which cost even more to fix. We thought we had made every choice possible to ensure it wouldn't leak but it still did.

Pitched roof every time. Flat roof construction still isn’t long lasting and cannot match up to tiles etc. A pitched roof with tiles matching the rest of the house is the best solution.,

Pitched, without a doubt, far superior longevity, more aesthetically pleasing - makes the extension look more like part of the house.

Although having said that, I have an orangery kitchen with a glass roof. That’s another option but not a cheap one!

I had a flat roof on my kitchen extension on the back of my house, until 7 years ago when I had it re-done and a pitched roof put on. I deeply regret it now as I have solar panels on the main roof and it is practically impossible to get them cleaned now. I needed some work doing to the main roof (slipped slates and chimney pointing), and the work cost almost twice as much because scaffolding had to be factored into the quote; whereas when I had the flat roof work could be done from the flat roof using ladders. Getting my gutters replaced also cost more due to scaffolding being needed.
The reason I had it changed was to let more light into my kitchen as there are now 3 velux windows in it.

Alternative view. We had plans for both drawn up. But whatever we were going to have to have either all flat roof or half and half because of where it was going.

We've gone for all flat - partly to avoid 'joins' , partly as its a very distinct difference from the 1908 house. We'll have the sliding doors look - basically a full glazed corner... rather than french windown.

There was little difference in cost.

I liked the look of the pitched design and the extra roof height. And it would have blended into the house well.

Flat roofs have a poor reputation based on experience of older flat roofs, but construction has changed hugely in the past few years. A flat roof covered in fiberglass/GPM is a completely different beast from the old felted or bitumen roofs (and even felt has improved a lot). So don’t choose based on past experience or bad reputation.

With a pitched roof you will need to consider how it works on the back wall. If you start it too high it will impinge on your upper windows. If you start it too low it will end up with low head height at the garden end. Flat roof makes it easier to have decent ceiling height in the whole extension without impeding upper windows.

With a pitched roof you will also have a sloping ceiling in the extension which can cause issues if you want to fit a kitchen or light fittings in that area. However if you want the extension to be just a sitting area for example then this isn’t such a problem.

As a pp said a sloping roof with Veluxes in can be more effective at getting light into the back area of the extended room. And if you want your skylights to open, Veluxes are probably cheaper than opening flat skylights.

Aesthetically it’s a matter of opinion. Pitched roofs perhaps blend in better with the original house (if it’s a period house) whereas flat roofs look more modern.

Much prefer the increased ceiling height of a pitched roof, makes the room feel lighter and airy. But does depend on the position of first floor windows.

I work in insurance - flat roofs are a bit of a hassle to cover as they have a lot of potential issues!

We went for shallow pitch to fit under first floor window, give more ceiling height and avoid leaks. I’d go as pitched as you can. But your architect should advise you?

@PresentingPercy

Pitched roof every time. Flat roof construction still isn’t long lasting and cannot match up to tiles etc. A pitched roof with tiles matching the rest of the house is the best solution.,

Totally agree. If you're planning on staying there long term then go for a pitched roof, altho it is a lot more expensive. That said, a roofer-man told me that if your flat roof is in the shade then they will last a lot longer.

Even fibreglass has a 20-25 year life span. They are not suitable for larger areas and can shrink. There is no bullet proof flat roof system. All have pros and cons. They are prone to drainage problems and ponding water. Ok for a small porch but can be problematic over larger areas and buyers are wary of them.

A friend had a flat roof put in and it's currently being used as a sun trap litter box by local cats.

Thanks for all the advice - I'm thinking we'll go for pitched if not hugely more expensive