Cost to build a small flat above a double garage

Question

We have a detached double garage and want to build a studio flat on top of it for a family member to use. The garage itself is not going to be touched (thats the plan at least). What's a rough cost?

Ryan · Answer

Good evening,
Your probably looking Between £2000 and £2300 per square meter 👍

Rob · Answer

To remove the existing.
Needs to be checked to be whether it’s Asbestos or not so I won’t include that
To construct a new Roof Timber Joyce furring and 18mm OSB Layer on top.
You’ll be looking between £2,500 to £5000

Steven · Answer

It all depends on size but you work out the m2 24000

Thomas · Answer

It would depend on size and windows etc. It woukd also require plasterers, plumbers, electiricans and a roofer which would all need to be priced.

Garry · Answer

Possibly around £25,00/ £30,00
Depending on how far you are wanting to go with project, do you need water/ heating, is garage already installed electrics, hope this helps a little 
Regards Garry

Patrick · Answer

Its all about the existing foundations and the strength of the existing walls .
Exploratory excavation will need to be dug to access the foundations , in 90% of  cases the foundations are not addiquate.

Ashraf · Answer

Building a studio flat above an existing detached double garage can be an excellent way to create extra living space, but the first step is to establish whether the existing garage foundations and walls are capable of supporting an additional storey.

As a rough guide, you should budget £80,000–£150,000+, depending on the size, specification, and whether the existing structure requires strengthening. The cost typically includes structural alterations, steelwork, the new floor structure, roof modifications, insulation, windows, plumbing, electrics, heating, kitchen, bathroom and internal finishes.

You'll also need Planning Permission (in most cases) and Building Regulations approval, along with structural calculations from a structural engineer.

A site inspection is the best place to start, as it will determine whether the existing garage can support the new structure and provide an accurate quotation based on your property.

Herbert · Answer

Thanks for bringing this up but to my knowledge you can't build something on top of a garage for reasons below,
1) ground works done for a garage are not suitable for carrying a load on top other than the roof.
2) The foundation of a garage is weak to sustain the preasure  of carrying an RCJ  then a room on top inspectors will not allow or pass it unless you build without approval through cowboy builders who will simply take your money. 
3) We have seen such structures slanting  to the side others separating from the attached wall of the main house even the you would have used used wall brackets. 
Ground movement has more force that's why you need a proper foundation 50 cm to 100 cm or more if the place had a mine before. 

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John · Answer

Morning, it all depends on the strength of the foundations of the garage, you’d have to get it tested and see if it’s strong enough to add on top, with the extra weight, if it’s good enough you can build straight on but if not you’ll need to knock down and re do the foundations which is obviously a big difference in price

Mykhailo · Answer

Hi! Regarding your query about building a studio flat on top of your detached double garage, here is a rough estimate:
​For a full, self-contained living space (including structural work, insulation, electrics, plumbing/drainage for a bathroom/kitchen, and stairs), the average cost under current UK Building Regs usually ranges between £45,000 and £75,000+ turn-key.
​The main factor affecting the final price will be the existing garage walls and foundations. A structural engineer will need to confirm they can support the weight of a second floor without needing extra steel reinforcement.
​If you’d like, we can arrange an initial site visit to look at the structure and discuss some practical options. Let me know what you think!

Cost to build a small flat above a double garage

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