Second storey extension

[Birchgirl]

I'm looking to build ontop of an existing extension and was just wondering if anyone knew roughly how much it would cost. The extension it is being built on has strong foundations as its one we've previously had done ourselves.
The room measurements would be 4m x 4x. It would be a bedroom.

I understand that this is a 'how long is a piece of string' type question but I just want some rough figures / advice.

Thank you!

There are so many factors and variables but working on a rate of £2k per sq.m, you’d be looking at £32k. I’d be surprised if it was less.

Thank you for your reply!

Has anyone else got any past experiences?

I’d say it would be a bit cheaper as you don’t have to pay for any any foundations / drains .

That's what I thought. I read somewhere online that it's approximately half of the cost of the fist floor extension. But that would only be roughly 16k which sounds too little

There would be a cost to removing the current roof as well?

Yeah that's true. Has anyone had it done?

Are you sure the current extension has sufficient foundations to support two stories?

Yeah sure. We built the first story in mind that we plan to have a second ontop

The rates vary up and down the country. I used to use £1.5k per sq.m for single storey and £2.5k for two storey hence using an average rate of £2k per sq.m irrespective of the floor.

Will this Bedroom have an En-suite?

No, no bathroom. Just a window haha

Where are you based? That'll influence the cost.

I'm in the North West and I've just paid £44k for a double storey extension, 3.3m x 5.5m, so the guess of around £30k for a single storey without the need for digging foundations etc seems really steep to me.

Many builders don’t want to get involved in smaller projects. A £16k extension would qualify as a very small extension in London for instance, where many projects are 200k+. This means there is less competition on smaller jobs, hence prices being driven up.

I would speak to design and build companies, I think (but without any personal experience) they do this type of project often. They may be able to help if you don’t mind going on their waiting list.

You will need to have proof for structural engineer that foundations are sufficient.

You will need floor joists to replace your (smaller) ceiling joists.

If the foundations are ok, I can't see it costly less than about £35k

The new roof will have to fit into the existing roof of the house and the brickwork too. There’s demolition costs of the existing extension roof. The foundations may well be suitable but you also have to consider the joints with the existing house. I would think £1500 m2 would not be quite enough. Depends on quality of building and materials to be used though.

Thank you everyone got your responses!

We're in Wales so I'd imagine it would be a boy chesper than London?