Log Cabin DPC Help

Discussion in 'Carpenters' Talk' started by Knobby, Jan 29, 2017.

  1. Knobby

    Knobby New Member

    Nope. Concrete base is the same size as the bearers, we made sure of this.
  2. wiggy

    wiggy Screwfix Select

    Is there a dpc under the slab?
  3. wiggy

    wiggy Screwfix Select

    That slab protrudes past the bearers from what I can see in the pictures. It might only be a little bit but that's all it needs to catch water.
  4. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Here are the points most susceptible to water remaining, and the arrow points to what looks like concrete overlap.

    Mr. HandyAndy - Really
  5. wiggy

    wiggy Screwfix Select

    Spot on. And by the doors in one of the other pictures and plus two sides that can't be seen. It's almost definitely what's causing the problem. Easy to lift to place bearers
  6. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Yep, and the idea is that any cladding(logs in your case) should be outside the concrete base.

    Mr. HandyAndy - Really
  7. dwlondon

    dwlondon Active Member

    If the concrete was laid on the ground without a dpc it will get wet and be a constant source of damp.
  8. Knobby

    Knobby New Member

    See closer images below. The bearers are identical to the base. Agree think there is a very small lip on that edge. Think that's the problem.

    The second picture shows the logs over hang the lot so the water should drip to the floor.


  9. Knobby

    Knobby New Member

    No DPC went below the slab. I was told to go above the slab.
  10. GordonK

    GordonK Member

    Create a gap below your bearers , ensure none of the cabin touches concrete... it will fix the problem ...
  11. dwlondon

    dwlondon Active Member

    OK so the moist air is rising up at the corners and creating the mould.
    You can help by improving the ventilation. You need air in and out at base level.
  12. Paulie1412

    Paulie1412 Active Member

    And yet most chalets in Europe use the same design and have no problem with it being a rain-trap
  13. Dr Bodgit

    Dr Bodgit Super Member

    Ventilation will help but I would add the following:
    - it is common for there to be water ingress at the corner due to the design of the cabin. A treatment, of good quality and thickness, should seal the timber while allowing it to breath.
    - you also need to prevent splashback from the ground back up to the timber. Even though the base isn't protruding, any hard surface near the cabin will cause splashback. Best to use pea shingle or similar to prevent this.

    Its for this reason I'm going to build a timber sub-base for my man cave - will allow air to get under the entire cabin
  14. Dr Bodgit

    Dr Bodgit Super Member

    To aid ventilation, you might consider adding a couple of air vents on the side of the cabin - one lower down and another high up.
  15. 2shortplanks

    2shortplanks Active Member

    I wonder if the problem might be water running down the cladding, then back along the bottom edge of the cladding. The cladding comes out from the base, but there doesn't seem to be any drip groove etc? Perhaps a small bead tacked onto the bottom edge of the cladding would get the water to drip off. Might be a good idea to get out there and have a look at what's actually happening when it's raining.
  16. Dr Bodgit

    Dr Bodgit Super Member

    I suspect its a combination of things:
    - water penetrating the wood especially at the corners where there's a way in through the corner joint. Won't be as bad where the corners are sheltered. The paint/protection needs to be a suitable type and adequately thick to prevent this as well as the joints being well made. I've seen water stains on display cabins so its a common problem.
    - as 2SP says, water will also run down to the base and seep underneath. Ideally the bottom plank should sit proud of the tanalised timber so the water will run off rather than seep in. Adding some beading here as 2SP suggests might help but fitting it will depend if there's space to do so. I suspect not.
    - slash back from the ground back up to the timbers will back them sodden.
    - then any wet wood needs a chance to dry out, hence my suggestion of adding ventilation. The not-so-wet corners will struggle to dry out where they're sheltered so would be interested to learn which corners are worst - those that are more exposed or more sheltered. This should then point to whether the problem is more about water getting in, or inability to dry out.
  17. Knobby

    Knobby New Member

    Sorry for lack of reply.. Not been near the cabin.. After your comments I thought i was doomed and a load more work would be needed to rectify.

    So this evening I have pulled up part of the floor in the main area of the cabin. When I say floor, I just mean the floor boards. Under the floor boards is a vapour control layer, then Celotex, then small bits of baton to hold celotex off the concrete floor and then a vapour control layer again.

    Have a look at the following video.. Will explain things further. You will see where the moisture seems to be collecting on the vapour layer under the celetex and this is dumping straight on top of the DPC and the bearers are sucking it up from here.

    There are also some gaps between the cabin and bearers so there is some hope for slotting some DPC in between the bearers and the cabin.. Guess I will need to try and jack the building up somehow to get into the tight areas.

    Let me know your thoughts.. Thanks in advance..

  18. wiggy

    wiggy Screwfix Select

    The only way you are going to get over this is to create air flow under the building end of.
    You could do a proper cowboy job on it and flash band over where the shed sits on the base.
    Just lift it. You could get a scissor Jack under the walls at the corners. It's not a biggie
  19. Knobby

    Knobby New Member

    Lift it and what? Put blocks or something between the slab and bearers?
  20. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Knobby, do you realise you just gave access to your entire video collection?

    Mr. HandyAndy - Really

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