Garage demolition and wooden workshop advice

8 May 2007
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United Kingdom
Afternoon all,

We've just bought a house with an old 60s brick garage with asbestos roof. Currently researching costs to get asbestos removed and dealt with.

The brick garage is knackered though, and too big. I want to demolish and put a wooden workshop in place (anyone got views on Tiger Sheds workshops?).

Main question though - can I just reuse the existing concrete slab sitting under the garage? It will be bigger than the shed (is this a problem for managing rain). Should I try to add an elevated slab for the shed to sit on? Or rest it on slabs/concrete beams?

Any suggestions or hard learnt lessons much appreciated.

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If the existing concrete slab is in good condition you can certainly use it as a base for a new shed. Raising the new shed on beams will prevent it sitting in water after rainfall.
I would suggest you stop the beams short of projecting out past the shed and to also lay a strip of DPC on the tops of the beams to prevent capillary action of the water.
I demolished our garage with asbestos roof in our 60’s bungalow just after we moved in and replaced it with a new concrete slab and brick base.
I have worked with asbestos before so taking appropriate precautions I removed it and had it disposed of by a licensed carrier.
Garage base is the same size as the building with no overhang, dpc between brickwork and timber.

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Taken me a few days to check back - thanks for the replies. The existing slab is pretty massive - the garage itself is around 13m x 3.5m and then there's some additional concrete/paving around the existing garage as well. I might - at some point - try and investigate the thickness of the slab, and might also try and remove some of the surrounding stuff. We're in the west of scotland - so plenty of rain going on - so the points on some beams and DPC is well made - I'll make sure this is done.

Can I just lay the DPC on the beams and have them loose? Or better to build a matrix/frame and pin the DPC to it around the edges (presumably not pinned from top or what's the point of the DPC?). Noted to make this smaller than footprint of the shed so there's an overhang for the rain to drip off. I might also fit guttering to the shed to feed a water butt.

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I used the composite beams as the base on the concrete, it never rots and allows the wood to stay dry
So - just coming back to this now the garage is down. We've managed to get rid of the old garage and now we've got a 9ft wide slab - unfortunately at slightly lower grade than the rest of the garden, and also completely flat - so it's not draining well. I want to get a 16x8 wooden workshop on there. I doubt it has a DMP under it.

I'm thinking of raising the shed off the concrete, and putting gravel down around it to cover the surrounding concrete, and to provide some reduction in splashing back onto the wooden shed (although I will fit guttering to take runoff away from the shed).

So - composite beams are an option - but these seem to be 50mm thick - this doesn't sound quite thick enough for what I'm wanting?
Or - do I build a plinth of concrete slabs at the right size to suit the shed footprint and give a bit more height - then use composite or wooden beams on top of this?
Composite beams for the size of shed I'm getting sound pretty pricey too - am going to end up spending a couple of hundred quid on these depending on spacing.

Any suggestions on the best approach much appreciated.

If you need to raise it more than 50mm then you could shutter to the size and position of the shed and make a concrete raft on top of the existing concrete that might be cheaper than huge composite beams, the ones I used were only 18-20mm high. and profiled to prevent water ingress, so would not stack well.

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