How to improve existing extension?

[Buffty]

We've just moved into a house which the previous owners extended. The extension consists of two rooms at the back of the house (which are in total about 23m2 in area) and has a flat roof. The ceiling height of these rooms is quite low, a couple of inches above the top of the door frame. The extension is quite poorly insulated and there is an obvious temperature difference between these rooms and the rest of the house. In one of the rooms there are two roof windows and one of these leaks slightly whenever it rains very heavily. Also the ceilings and walls are covered in artex.

Ideally we'd like to raise the height of the roof so the ceilings are not so low, get it properly insulated and get rid of the artex. However I'm not sure how to go about this. Do we need an architect or will a decent builder be able to sort this all out? Will we need to get planning permission?

Also I've no idea how much this would realistically cost and as we won't have a massive budget I'm wondering whether it will be a case of being able to get it all sorted now or just fixing the leak and sorting the rest at a later date.

Check the planning situation with the planners - it may be the roof height was part of the original planning consent (if consent was needed). Then get 3 different builders in to talk through the rest of it: there are loads of options from knock it down and start again to just patch it up and improve it. It sounds like it was a bit of a cowboy job to be honest, or maybe just built back in the days when building standards were much lower. I don't think you will need an architect unless you want to completely redesign the extension and how it connects to the house.

If you were knocking down and building from scratch, assuming the foundations are OK and you aren't going for a Grand Design, you would be looking at £1,000 - £1,500 per square meter, very very roughly, depending on where you live and how much diy you want to do. Just replacing the seal on a rooflight would cost hardly anything.

Oh dear, I've just realise I'm broody for a Project.

You could look to get a pitched roof which would look more attractive and could go for a vaulted ceiling look. You could get someone to draw up plans as it's likely to need building regs and maybe planning.

I would ask a builder first so that you get an idea on costs. Building regs for insulation have increased so extns are now built with loads of insulation - the windows (glass) could also be a factor - are they double glazed?