DIY Doctor

Building External Room Help

Postby emphasis303 » Fri Jun 01, 2007 12:42 am

Im new here and hopefully looking for a little advice

I wish to build just a simple single storey shed like or garage like room just for storage.

Im still deciding on which bricks to use but the main concern for me is the foundation. When i moved in I had a builder concrete over the outside area which is where i want to build.

The question is, do i need to now dig into this and build foundations underneeth or can i just build on top of the concrete since i wont be placing anything heavy on top of the roof.

For the roof i will just place joist like wooden beams and cover it with chipboard and waterproof covering.

I would really only build under this concrete if theres no other choice so if any one has any ideas or advice please please please dont be shy I could really do with it.

Thanks alot and i cant wait to hear back

P.S Do i need planning permission, the room will be about 80inches high and 80inches long.


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Simply Build It

Postby thedoctor » Mon Jun 04, 2007 7:40 am

It depends on how thick the cocrete is. Any thinner than 4 inches (100mm) and we would not build on it and even then it needs to show no signes of cracks or flaws and show no movement when walked on.

See our project on planning permission.
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Postby simplysimon » Mon Jun 04, 2007 11:58 am

you need planning permission which may involve visits from a building control officer to start with.
And yes you should excavate to the correct foundation depth which is determined by ground conditons irrespective of being a single storey building. Dont cut corners. It may bite you when or if you sell up later
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Postby shiv123 » Tue Jul 03, 2007 10:17 pm

You should not need planning permission as long as the area of the proposed building does not cover more than 50% of the original house area (which includes the garden). Furthermore if it is less than 3m high (4m for a pitched roof) you do not require planning permission.

With regards to building on the concrete base, please do not take short cuts !!. You do need proper foundations with trenches filled with concrete upto to at least 18 inches depth. I was advised by my bricklayer to dig upto 24 icnhes and to pin the concrete with steel rods at intervals. The soil can be very pliable and whilst you think there may not be much weight, you have to remember that the bricks/blocks also put a load on the foundation. A liitle bit of extra work now will hopefully prevent problems of subsidence or walls collapsing in the future.

Good Luck
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