Extension roof - flat or pitched?

[RockytheBasket]

We are planning a 3m rear extension.
I know flat roofs are not really flat, there is a slight angle, about 5 degree, and I quite like the space we gain inside.

The pitched roof is obviously better for water drainage, but the kitchen doesn't look as nice as the flat roof.

What are the pros and cons of each?

Is flat roof a real risk?

We have an extension that pre-dates us, pitched roof, we are about to switch to a flat roof. Having a pitched roof doesn't let in as much light, and the extension feels like it's closing in on itself. I understand flat roofs get a bad rep, but from what I've read if you invest in good design and materials a lot of the risks can be mitigated.

Pitched with velux windows every time. It looks so much better and the velux let so much light in. Plus far less likely to leak ime

A slight pitch is better than flat - you don't want water pooling on it.
Personally I like pitched. It gives maximum ceiling height and I like the airiness - a flat ceiling, unless it's all at the height of the apex a pitched roof would be, can add to a boxy feel, especially if you are adding on to a room, rather than the extension being a room on its own.

Has anyone had any leak from a flat roof extension?

We have a pitched roof with a flat ceiling inside. Best of both worlds. Ours was too small for a window and it led from our old room so we continued the celining height. Looks great

I used to get leaks from a flat roof extension but only if the wind was blowing in a certain direction and if the rain was extremely heavy. No amount of redoing the lead flashing stopped it. Was glad to move and now have a pitched roof extension never had an issue.

I have been to two neighbours' extensions, one with a flat roof and one with a pitched roof, the extension with a flat roof looks much bigger because the ceiling is at same height as the rest of the house, while the pitched roof closes in and made the extension look smaller and separated from the rest of the house.

If there is no real risk/problems, I am leaning towards the flat roof option.

Would you be able to see the flat roof from any of your upstairs windows? Sounds daft, but if you can it means you can monitor the condition easily without getting ladders etc. out. We have a section of flat roof on the ground floor which we can see from the bedroom window. I see it every morning when I open the blinds and am confident I'd be able to spot any issues with it pretty soon after they arose.

We've had zero problems with ours and that side of the house is really exposed to the elements.

Yes, once it's built, we should be able to see it from the bedroom window. That's a good idea of checking.

A ceiling height can be adjusted within a pitched roof. It isn’t one height fits all. Look at open rafters with roof lights. I think you need to do more research and look at better examples of extensions.

We have a pitched roof with velux windows in our extension and it definitely makes it look more open and airy than a flat roof would have .

Pitched roof with 2 velux windows and a gabled end is what we had. Lets in so much light and looks beautiful too. A flat roof would have made it look coffin like but I am in a 90s house with low ceilings. It might not be bad if you’re in an older house

Definitely pitched the rain is designed to fall off it, flat roofs have more problems. In a hot country maybe flat roof but in the UK with all the rain we get, definitely pitched.

Pitched with floating ceiling? Out of interest, what doors are you going with?

We are thinking about bi-fold doors, however I wonder how many days in a year you get to open it fully, so also considering French doors. What's your opinion?

We have a large extension with a flat roof and it’s been nothing but hassle, constant leaks along where it joins the main house. Had to have the whole thing re roofed. I’d never have a flat roof again. (And it was done by a well thought of builder with good recommendations).

We're going for pitched with Velux windows. Fewer problems with leaks and can cost more in insurance, I'm always asked about Flat roof.

We went with large patio doors because of the cost, the fact it faced a fence and we have a patio that can pool water so wanted to keep a step to minimise flooding. They work great in our space - they are the same size as bifolds would have been so we didnt lose light.

Flat roofs need more maintenance than pitched ones in the longer term.

Ceiling height is a separate question from flat vs pitched roof. Whether the flat or the pitched roof gives the best ceiling height depends on the situation.

If the height of the roof where it abuts the existing house is constrained e.g. by existing first floor windows, then you're right that a flat roof will maximise the height away from the house.

On the other hand, the height of the roof might be constrained at the side away from the house, e.g. if you're trying to build near a boundary under permitted development.

We have a flat roof on our extension, we have a a roof lantern in it which let's loads of light in. The roof around it is slightly sloped to the drains and covered in a product called Sarnafil. I'd be wary of having felt on a flat roof, but some of the new products like Saranfil are very good.

We have two sets of large oak French windows which are in our kitchen and we like them. If you want to open up a big space, go for bifolds. If it’s 2m then it’s French windows. You could try sliding doors which don’t need parking space.

Sliding doors and bifold doors are both great in extensions! I have some bifolds in mine which make the whole place seem much brighter. I got mine on doubleglazingontheweb.co.uk/ if that helps you!

I’m opting for a flat roof and sliding doors. I like the thin frame, and not having to allow space to store the doors when open.