Build a new extension and join existing uninsulated extension to the house

pikachuLondon

Hi,

I have an existing half-width back extension (extension is 3m wide and my house is 6m wide) which is quite old (I guess it existed since beginning as all the neighbouring house has similar structure) and I think it is made up of single-wall as it feels quite cold there which means there is no insulation.

I want to build a full-width extension (6m wide) - 3m wide new extension and refurbish the existing 3m wide extension (with proper insulation).

I don't want to demolish the existing extension (cost-effective). I am also not sure how deep is the existing foundation. Will the planning department or building control object if I insulate and do all the necessary things to make that place habitable. I don't want to do anything which can create a hassle for me in future.

Can people advise how I should proceed for this?

PS: I have a picture of the plan but as a new user, I am not allowed to post the links
If someone helps me with this, then I'll be able to share the picture.

Bossypants

I don't know the answers to your questions, but this is one of those cases where I would sit down and work out exactly how much you're really going to save by not just knocking it all down ans starting again, and then weigh that against ending up with a hodgepodge which is never going go look/feel completely 'right', and may count against you during future sales. Once you're going to the trouble and expense of doing an extension, it's almost always worth saving for that little bit longer to get it all done properly.

Slithery

pikachuLondon wrote: »

Hi, I have an existing half-width back extension (extension is 3m wide and my house is 6m wide) which is quite old (I guess it existed since beginning as all the neighbouring house has similar structure)

In which case it is, by definition, not an extension.

FreeBear

pikachuLondon wrote: »

I don't want to demolish the existing extension (cost-effective). I am also not sure how deep is the existing foundation. Will the planning department or building control object if I insulate and do all the necessary things to make that place habitable. I don't want to do anything which can create a hassle for me in future.

You can "refurbish" and insulate - Building regs require a µ value of 0.30 W/m²K for walls. That equates to around 65mm of Kingspan/Celotex type PUR insulation. With a solid brick wall, you will need an air gap of around 25mm between the insulation & brickwork and some way to ventilate it. Attention also needs to be paid to the detailing around window/door reveals so that you don't end up with cold spot. The ceiling & floor will also need insulating. In all, not a simple job. Also bear in mind future uses for the space - With insulated walls covered in plasterboard, they will never be strong enough to take the weight of wall units unless substantial battens are put in place from the outset. These will compromise the thermal efficiency of the walls and could cause cold bridging.

Discuss the options with your architect & building contractors - You may well find the long term advantages outweigh the short term cost savings in demolishing & rebuilding.

lincroft1710

Bossypants wrote: »

I don't know the answers to your questions, but this is one of those cases where I would sit down and work out exactly how much you're really going to save by not just knocking it all down ans starting again, and then weigh that against ending up with a hodgepodge which is never going go look/feel completely 'right', and may count against you during future sales. Once you're going to the trouble and expense of doing an extension, it's almost always worth saving for that little bit longer to get it all done properly.

I agree, a 6m completely new extension will look better than 2 x 3m extensions.

HIC1

You can send plans to building control and get them to advise on what will be acceptable in writing so that nothing further can be imposed on you later. I recommend a private building control rather than your local council.

pikachuLondon

Thanks all for the advice. I am going to speak to a few architects and structural engineers.