Damp proofing Log cabin Concrete Base

6 Mar 2007
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United Kingdom
I've had a 4 x 5 M concrete base laid for a Log Cabin (Lugarde kit), but no DPM underneath, it sits on 5 piles.

I've built a berlin wall to retain soil on the high side (see pic) and dug a 4" drainage channel around the perimeter of the base. The base is slightly oversize (about 100/150mm all round) so there will be a lip. The roof overhang is 300mm so rain should drip outside the wall and drain shuttering.

The cabin walls will sit on 70 x 70mm tanalised bearers, and the internal floor the same. My intention is to use celotex and either T&G chipboard or ply for the floor.

My question is; How should I best damp proof the building? What would be the best arrangement of DPM and DPC?

As mentioned in a previous post (thanks for the replies) the base has a slight dip in the middle (20mm) so if water gets underneath it'll probably just sit there.

I'd be grateful for any suggestions as to the best solution.

Thanks, Neil. View media item 12714
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If you can bin the timber bearers and replace with standard concrete blocks spaced accordingly (every 600m in every direction, that would be a good start. At the end of the day it doesn't matter what you sit it on as long as it's isolated from the concrete base using damp proof course, heavy guage polythene or bitumen felt between bearer and structure.

Also be aware that any part of the structure within 6" of the concrete base may get wet due to rain splashing up. This can be alleviated by laying pea shingle around the perimeter, which will help to reduce the rain splash.

You can probably 'fill in' your dip. Using a weak mortar mix. Alternatively you can cut a channel to the edge, using an angle grinder. Do a few passes spaced ever so slightly apart and chisel out the excess afterwards.
Thanks, I don't think I can ditch the wooden bearers - they're grooved to accept the first log/plank. I am considering cutting out the channel though.

If I put a DPM on top of the slab, should I run it under the bearers or in between the bearer and the first log/plank?

I've been considering putting a 300mm DPC under the bearer so it protrudes inside and then laying a DPM inside the cabin and taping it onto the DPC. Would that work?

Thanks for the help, Neil.
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i have a similar setup for my new shed when it arrives concrete base gravel around the edges. The bearers are wooden and im not sure if i need to put some 150mm wide DPC around the bottom of each bearer and then stape it to the sides or not? there will be insulation between the 70mm bearers then a t&G floor on top of them. Is this the best method or should i lay a breather membrane on top of the bearers also before the floor?

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