re-level wonky cabin

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Dominic Coleman

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24 Jun 2023
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We had a 14’ x 8’ cabin installed on a newly laid concrete slab. The builder assured us the slab was level. To allow drainage his men inadvertently made it with a slight slope.
We built the cabin and now it is settling it is leaning. From left to right the slab is approx 20/25mm height difference. Is it possible to jack up, the cabin and ‘underpin’ by adding shims to the tantalised floor base supports? Or other than totally rebuilding, can you suggest a way to resolve this?

Would installers be prepared to attempt this?


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normally for a timber structure, if on a concrete slab, the slab should be slightly less in size then the framework of the structure so the timber cladding overhangs the slab, ensuring water doesn’t run under the structure.

Im not sure how this is dealt with on a log cabin style, but if it’s put on a larger slab, the bottom of the cabin will sit in water all the time, slope or not.

I managed to raise a corner of my large shed with a hydraulic trolley Jack
hello and welcome- yes it is possible to do but not straightforward as your shims will decrease as you move further back . You would need to raise the cabin a significant amount as you would need to get the shims evenly spaced and of course your arms are only so long . Also is the base fixed to the base or is it freestanding ( with the cabin built on top . Not an easy job and if you built it yourself then it’s probably a bit late to get the builder back . I quoted to build one similar but the base wasn’t level and instructions said the base must be completely level . Customer didn’t want to redo base so I never accepted the job. It’s a tough call but I think I’d take it down and start again. Get the floor perfectly level and supported at regular intervals then seal any remaining gaps with a frame sealant, then rebuild cabin . There was a similar post on this issue a couple of weeks ago but i forget the thread title. Edit ( is the floor fixed to the base or is it freestanding )
Not very professional, but you could lift the lower side with a lever and put boards underneath.

I just done the same thing to fix a 1 inch gap a the top left corner of my shed door.

I used a 4x4 block of wood and a length of decking board as a lever to lift my shed.
...not straightforward as your shims will decrease as you move further back

He says it is leaning left to right so front to 'further back', the shim will be constant.

If, instead of shimming from zero to 25mm across the width, you shim from 15mm to 40mm, thus raising the entire shed 15mm, the process becomes easier.

Not suitable for this case, but having a non-zero shim means that you can use something that looks like a furring strip for a flat roof, which makes it easier to install.

In the pictures, it looks like the only access is from the front (the sides look to be trapped in). Consider removing the floor (either entirely only in the four corners) to give access for jacking* and then slide long shims in from the front. Floor removal and reinstallation will be less aggravation than a complete rebuild.

* Assess how strong it is - with four holes cut in the floor, you could use acrow props (hired, cheap) between the underside of the roof and the concrete base to lift it, akin to the jack legs on a portacabin. If the four corner posts are strong but the roof is weak, screw a cleat to them and use trench props (hired) or bottle jacks to raise it.
If you can raise the shed then do so. Shim with quarry tiles and slate along the full length of each joist so the whole thing is up of the slab.


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