We'd like to remind Forumites to please avoid political debate on the Forum... Read More »
📨 Have you signed up to the Forum's new Email Digest yet? Get a selection of trending threads sent straight to your inbox daily, weekly or monthly!
Cost of side extension?

GDB2222
Posts: 26,103 Forumite


We are looking at buying a house, and we would need to put in a long narrow side extension, around 2.1m x 8m. Can anyone give a rough idea of cost please?
It's for a utility room/storage, etc, so fairly basic finishes. We are in London. It would probably have a flat roof, with a skylight.
The house is 110 sqm, plus there's a double garage at the bottom of the garden. It was built 40 years ago, and there have been no alterations since. Would the extension come within permitted development?
It would need to come right up to the boundary. Is that a problem? Next door is a cemetery, so at least there's no danger of undermining the next door property!
Finally, how thick do the walls need to be to meet building regs? The 2.1m represents the external dimension, so the thickness of the wall is a significant reduction in the usable width.
It's for a utility room/storage, etc, so fairly basic finishes. We are in London. It would probably have a flat roof, with a skylight.
The house is 110 sqm, plus there's a double garage at the bottom of the garden. It was built 40 years ago, and there have been no alterations since. Would the extension come within permitted development?
It would need to come right up to the boundary. Is that a problem? Next door is a cemetery, so at least there's no danger of undermining the next door property!
Finally, how thick do the walls need to be to meet building regs? The 2.1m represents the external dimension, so the thickness of the wall is a significant reduction in the usable width.
No reliance should be placed on the above! Absolutely none, do you hear?
0
Comments
-
The thickness of the wall depends on the method used to achieve 0.18 U value.
0 -
External walls are 350mm now with a 150mm insulated cavity.
Can’t help with cost, labour and materials are still sky high, dread to think how much in LondonMaybe, just once, someone will call me 'Sir' without adding, 'You're making a scene.'0 -
Very rough ballpark figure - £3,000 per square metre. So something in the region of £50K plus the cost of fitting the space out. On top of that, you'll have architect fees, planning applications, and possibly Party Wall Agreement costs (depending on how close you are to neighbouring properties).
Her courage will change the world.
Treasure the moments that you have. Savour them for as long as you can for they will never come back again.0 -
Walk around, and knock on the doors who have had an extension - they might be able to give you the names of the builders and if they are nice enough, they might even give you an idea of how much they paid.0
-
Thanks everyone for your help. I was thinking £3k psm, so it sounds like I am in the right ballpark.
Would this be permitted development?No reliance should be placed on the above! Absolutely none, do you hear?0 -
You can use 100mm cavity with something like K106 cavity board if space is really tight.0
-
stuart45 said:You can use 100mm cavity with something like K106 cavity board if space is really tight.Maybe, just once, someone will call me 'Sir' without adding, 'You're making a scene.'0
-
The price might put them off.1
-
stuart45 said:The price might put them off.
It probably would’ve been a cheaper option.Maybe, just once, someone will call me 'Sir' without adding, 'You're making a scene.'0 -
Bad sign if she's changing her mind about the design before you've even got out of the ground.0
Confirm your email address to Create Threads and Reply

Categories
- All Categories
- 350.6K Banking & Borrowing
- 253K Reduce Debt & Boost Income
- 453.4K Spending & Discounts
- 243.6K Work, Benefits & Business
- 598.3K Mortgages, Homes & Bills
- 176.7K Life & Family
- 256.7K Travel & Transport
- 1.5M Hobbies & Leisure
- 16.1K Discuss & Feedback
- 37.6K Read-Only Boards