Log Cabin DPC Help

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

  1. GordonK

    GordonK Member

    Slabs on ground. , brick on slab , dpc on top of brick , stud framework on top of Dpc ... job done ... tbh you could probably do away with the Dpc if you stick it on bricks..
  2. Knobby

    Knobby New Member

    If you've got time to waste knock yourself out.. lol..
  3. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Yep. Lifting it will be the problem. 40mm slabs cut or broken into 150mm sizes every 600mm or so. Slab on concrete, square of dpc on top of slab under bearer.

    Mr. HandyAndy - Really
  4. wiggy

    wiggy Screwfix Select

    You could use concrete gravel boards.
    Or engineering bricks.
    Or just slide some 4x2 under there.
    Opposite to the joist run.
    Couple inches in from the ends.
    4/5 bits should do it.
    If you do go down the 4x2 route it will rot over time so give it a good dose of creasote or similar.
  5. Knobby

    Knobby New Member

    This isn't how the manufacturer tells you to fit it though.. I appreciate your help but they wouldn't sell any if every customer had the same problems.
  6. Joe95

    Joe95 Screwfix Select

    Or use concrete lintels if the budget will reach. Run at the opposite direction of the joists.

    They'll last longer than timber and will allow the water to run under the cabin without causing any issues to the wood.
  7. wiggy

    wiggy Screwfix Select

    If you have followed the manufactures instructions word for word then they are advising wrongly.
    From what I can see you have built your slab too big. It should sit back from the edges of the exposed frame. How else is the water getting under there. You should have also put a dp membrane under the slab to stop rising damp.
    If you think you have done everything by the book then take it up with the supplier.
  8. GordonK

    GordonK Member

    If you look around the web you will see that most people have a gap for air. Look in the Tuin web site for lots of examples. They also sell some footing things which lift your cabin up , and help level it up ...

    Having slabs overlapping is fine IF you raise the floor.

    Maybe you could just get an angle grinder and cut the edges of the slabs round the shed to get your cabin overhanging it?
  9. sospan

    sospan Screwfix Select

    That isn't going to be an easy one to lift. If it goes out of square or you lift one end before the other even a few inches you will put a lot of load on the corner notches and door / window frames and it will never be the same.
  10. Dr Bodgit

    Dr Bodgit Super Member

    This thread has reinforced my thoughts about the best base to have, as will be building one this year. I thought long and hard about the best base, really only two options are available: concrete and timber
    - a concrete base is often touted as being the best, as its rock solid firm and level (if made properly). However you need to be sure it doesn't extent beyond the footprint of the cabin and as wiggy says, ideally a smidge smaller so the treated timbers protrude slightly. You really don't want any chance of water getting on the slab as it'll creep along the timbers and work its way up. And of course without any air gap there is zero chance of it drying out.
    - a timber base is what I'm going for, mainly due to there being a nice air gap underneath it and air can circulate. It does need to be built strong and level without the risk of any part of it sagging.

    I read somewhere that wood wont rot as long as its allowed to dry out. The timbers above are wet and won't dry and I'd say two courses of action are required:
    - figure out how the water is getting there in the first place - is it due to capillary action along and up from the concrete base and/or condensation from the warm moist air inside the cabin. If you leave that exposed part open you should see whether it dries and after rain, if its wet again.
    - you need some air movement around those floor timbers. I think the only way of doing that is to jack up the entire cabin, even slightly. Even a few mm may be enough to allow air to circulate, may be some slate pieces placed under all the timber would do the job. Not sure.

    Or another option - take the whole thing down and build it up again properly. The roof may get trashed but everything else are just pieces of a kit.
  11. sospan

    sospan Screwfix Select

    The main problems with these "log" :rolleyes: cabins. is that they a lot of the timber just sits on top of each other with no gaskets between each layer or seals at the corners or joints and can let water in. Some are obviously better quality than others but all the timber in terms of a single wall are relatively thin 100mm to 150mm so even with the best treatment will absorb water and pass it through to the inside.

    Traditional log homes were just "chinked" much like boats were caulked modern ones have gaskets on a roll and then chinked afterwards.

    If someone asked me to build them a garden room, I would suggest a frame build structure with shiplap, vapour barrier etc. which can be insulated and boarded to whatever standard your budget or taste dictates.
  12. wiggy

    wiggy Screwfix Select

    There is no need to over complicate this.
    Get a spade and stick under the short wall at mid point.
    Lift it enough to get some sort of Jimmy bar under there.
    Lift it again. Enough to get a couple of bricks under each corner.
    Do the same at the other end.
    You will need to take the fence down to get to that side.
    And then just work round the building lifting it enough to get some bricks under the rest of the joists.
    If you find the doors or window stick after. Just give the cabin a nudge one way or the other.
    Joe95 likes this.
  13. Dr Bodgit

    Dr Bodgit Super Member

    I would hesitate to lift any part of the cabin more than around an inch more than any other part, but I agree with wiggy that the whole cabin could be lifted up...just do it bit by bit.
    mr moose likes this.
  14. GordonK

    GordonK Member

    ive got an existing concrete/slab base which has an old Marley garage on it (nice asbestos roof too :( ) but I will likely put some additional slabs under key points to support it and hence get that airflow working ... I will be installing the cabin in about 2 months..
  15. Knobby

    Knobby New Member

    Sorry for late reply.

    Decided I'm going to lift as suggested. I want to raise it 10-15mm and am thinking about using a concrete tile or similar.

    Sound like a plan?
    wiggy likes this.
  16. wiggy

    wiggy Screwfix Select

    I would go a bit more than that. Wickes do a 34mm concrete slab.

    Did you speak with the supplier?
  17. Hendy

    Hendy New Member

    Hi all
    I'm so glad i found this thread. i would of gone wrong even further if it hadn't

    I had a 6x4m concrete base (raised) put down and I missed the trick to put dpc down first but read later that it could be used on top.
    The main reason i opted for a raised slab is that i live at the bottom of a slope with a fairly large garden and during the Autumn/winter when it really rains a lot, i get the run off from driveways and road from a small housing cul de sac which my garden backs on to. Thus leaving a fair section of that part of the garden sodden. And guess where the only place the cabin can go?
    The cabin is 5x3.5m and much like Knobby's ( sorry mate for hijacking your thread) but a slightly different design , so i've already started on the wrong foot with the slab being bigger than the cabin, but i had planned to put the small bike size shed ( holds the garden tools ) which will be at the side and will take up the excess 1m when looking at it from the front.
    Don't know what i'm going to do about the excess 0.5m of slab which will run the the length of the cabin ( front or back). Probably be at the front as the pipe inserted for electrical/data cabling is sticking out at the back and I thought i could put a couple of chairs or something, Any or all ideas are welcome if this not desirable

    Ventilation (cabin on bricks) - Not something i wanted as it will make the cabin even higher but after reading this thread thought it best to put the cabin on bricks to allow air flow as there be no other way of it getting any. Damproofing and airflow was a concern and the video for the log cabin ( Billy Oh) makes no reference to it. So spent a bit of time researching it as well as floor insulation.

    I have some engineering bricks courtesy of the previous owners but not enough as this will be required for all bearers and not just corners. Am i correct in think that? Also stops floor bowing
    However, I do have enough old patio slabs that i got for free. I think the thickness is around 25mm. Can these be used?

    DPC - How thick should that be?
    DPM - I plan to have the DPM below the insulation. Do i need to get 1 big uncut sheet or can it be done in strips ?
    Would this be correct for the damproofing and floor insulation: SLAB - DPC - BEARERS - DPM - INSULATION - FLOORNG?
    Floor insulation - i have 2 sheets of 40x2400x1200mm celotex insulation that i plan to use. How much of a gap should i leave between that and the flooring? And should the gap be between the flooring and celotex or celotex and slab.
  18. snappyfish

    snappyfish Active Member

    Knobby, have exactly the same problem, what did you do in the end? And how is now a few months later? Thanks
  19. Knobby

    Knobby New Member

    All fix...

    I lift the shed.. used some of those pump up bags. They lift 150 kgs each.. I had some left of porcelain tiles which i cut up and used to left it up.

    Had no problems since lifting it.

    Attached Files:

  20. snappyfish

    snappyfish Active Member

    Thanks for the reply, Looks like this is a very good solution. Notice the jack there too, the log ends support that well enough? What size is your cabin?

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