How best to support base for log cabin

Discussion in 'Builders' Talk' started by Dr Bodgit, Nov 2, 2016.

  1. Dr Bodgit

    Dr Bodgit Super Member

    I'm planning a 5.5m x 3.5m log cabin as the man cave, have pondered the various options for a base e.g. concrete, paving slabs, timber etc and have decided on a timber base. It will allow air flow underneath, is less costly than concrete and not have to lug all the heavy materials down the garden. But what's the best way to support it? I'm thinking of creating the base like in this photo, using 95mm x 45mm treated timbers (4"x2") and doubled up around the perimeter which is where all the weight is (unlike a shed construction)

    [​IMG]

    Was thinking of digging down at various points around the perimeter and internally, a layer of hardcore in each hole then a cheap concrete slab on top sitting on a mortar bed. Then using 5"x5" wooden "legs" sitting on the slab on a dpc with the above structure on top to make it level. The legs would be very short - practically nill at the highest point, perhaps a foot long at the lower point. I find this preferable to sinking the 5"x5" legs into the ground as that might cause the wood to rot.

    Wondered if the folks here have other ideas on how to support this timber structure on uneven ground?
     
  2. KIAB

    KIAB Super Member

    Sit it on recycled plastic fence posts,either a complete length or a post cut up into short sections, they don't rot, or soak up moisture..
     
  3. Dr Bodgit

    Dr Bodgit Super Member

    Good idea, however I'm not sure where I could source them locally.
     
  4. 2shortplanks

    2shortplanks Active Member

    I think the solution in the pic would be ok, provided the gravel bed is above ground level and you treat all the cut ends. When I built my shed though, there was a thick layer of topsoil and I didn't like the idea of putting the shed onto it, so I dug trenches ~1m apart, down to subsoil, filled with compacted hardcore and laid rows of concrete blocks. Put the shed base onto the blocks with plastic dpc. I put down weed control mat + gravel, with the concrete blocks ( laid on their sides ) finishing 50mm above the level of the gravel. If you are working to permitted development, then you need to be careful about having the base too high if you want decent headroom in the shed.
     
    norma and Dr Bodgit like this.
  5. Dr Bodgit

    Dr Bodgit Super Member

    Thanks 2sp...concrete blocks are a good idea instead of paving slabs. I too have topsoil and intend to dig trenches.

    I am very aware of the need to keep the structure within the 2.5m height limit so the entire base will need to be no higher than the highest point of the surrounding ground, so likely most of it will be below ground level.
     
  6. koolpc

    koolpc Super Member

    What about, concrete fencing posts, cut up to sections of say 24". Each section cemented into the ground leaving say 12" above ground and then bolting on the frame as in your pic? Solid base, above ground and rot proof! Cheap to do too!
     
  7. sospan

    sospan Screwfix Select

    Or just get some traditional railway sleepers and rest the shed on those. If you get the old ones, they will be covered in layers of old tar and oil and will probably outlast all of us on this board
     
    norma likes this.
  8. koolpc

    koolpc Super Member

  9. sospan

    sospan Screwfix Select

    There are quite a few solutions like this around. However, the only advantage over using building blocks is that you can fix the structure to the post - but then with the weight of a shed it is unlikely to shift. There is a problem with these in that you have to prop the structure up off the ground at the desired height and then fit them one by one digging or packing underneath as you go. And you can see the problem in the top right where a post is resting on a block. It is a neat idea but I wouldn't want to have to fit them :D
    upload_2016-11-3_9-29-48.png
     
  10. koolpc

    koolpc Super Member

    Take time and i am sure it would be a good solution. I would measure and cement each post into the ground. Getting all the levels right and then build the base to fit the concreted posts!
     
  11. Dr Bodgit

    Dr Bodgit Super Member

    Thanks for the ideas. Railway sleepers won't work as this is a log cabin not a shed - different construction completely. The walls are erected first, then the base inside, so the perimeter needs to be solid and level as it takes all the weight.

    I'm also not a fan of supporting the wood base by the method shown in the photo i.e. where the legs are bolted to the frame. The bolts are taking all the strain, I want to have the legs sitting underneath the frame so will probably use 150mm x 150mm treated timbers for this.

    I thought about concrete blocks, would be easier to lay than paving slabs, but thicker. So still thinking the layers would look like:
    compacted hardcore - mortar bed - paving slab - DPC - 150x150 leg of appropriate length - subframe on top
     
  12. sospan

    sospan Screwfix Select

    By a log cabin do you mean log lap, real logs or this sort of thing?
    upload_2016-11-3_12-2-54.png

    In Kool's solution the weight is supported by the shoulder not the bolts. The bolts only stop movement. The sleepers would be used either as pads or use them to form a ring. Quite a common way to do it for all types of timber buildings and retaining walls

    http://haddyma.blogspot.co.uk/2014/04/look-how-to-build-shed-base-with.html
     
  13. Dr Bodgit

    Dr Bodgit Super Member

    Its "that sort of thing", and didn't notice the shoulder on the post, so that may be an option. Still not sure sleepers would work that well as the ground is quite uneven and forming a ring would mean quite of a bit of digging down in some places and hardcore to build up in others.

    So either slabs to form pads, or use dekposts to support the base.
     
  14. koolpc

    koolpc Super Member

    I would go with the concrete posts. Should be easy to get them all level. I would concrete then in too.
     

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