Base for log cabin

[FrankWebby]

Hello all - first time poster (and semi-competent DIY-er), please be gentle...

I'm replacing a 6 x 4 garden shed with a 13 x 8 log cabin. The shed site on a concrete slab which isn't big enough for the log cabin, which will be built on a timber perimeter base.

This will go in the back of my garden, which slopes upward to the back fence. The concrete slab has been built above ground level, meaning that where it stops, the drop to ground level is 8 inches. I've attached a diagram showing the site.

So the options are as follows:

1. Remove and relay concrete slab to the correct size. This is not the preferred plan, for a whole bunch of reasons (including that everything coming out/in has to go through the terraced house, which makes big work pretty unpopular with the family);

2. Extend size of slab by pouring new border - but change in elevation, and slightly ropey nature of existing slab may make this difficult - I also don't particularly want huge amounts of new concrete in the garden for environmental reasons;

3. New foundation footings laid to match footprint of cabin, with cement blocks used to level (or perhaps cement blocks + plastic pads (yellow on attached plan) on top to hold the wood and slab to fully level and provide joist support).

Questions:

Does option 3 make sense?

If so, what kind of footings do I need to lay for the blocks? How deep/what materials?

How do I insulate the floor of the cabin? How would I support Kingspan (or whatever) in the section which effectively floats?

All help very gratefully received!

[FrankWebby]

Red Leader said:

Nothing to add technically I am afraid but I am looking for a log cabin of that size. Do you mind me asking where you have bought form (unless you are self building of course)

Thanks
RL

Still not 100% confirmed, but like the look of the offerings from Tuin.

[FrankWebby]

@uluru - that looks great, nice build. What did you put (if anything) underneath the paving slabs?

What slope do the paving slabs and timber supports deal with - my drop is 8" from front to back, and I'm not sure your solution looks like it would sufficiently fill the height.

Do you think stacking paving slabs would be ok to get to an appropriate height?

[FrankWebby]

@uluru

I've noticed that you trimmed the overlap of the roof (it looks like it basically just fits a tiny bit wider than the footprint of the corner locking section). Any thoughts on that?

I'm going to have to do the same to, likely take 15cms off each side so that it fits my width (I'll have no side or rear access once it's up, so will be treating extensively as I build - but also it will be sheltered from weather by fencing).

[FrankWebby]

No, but useful to see that - did you use any kind of additional moisture barrier/breathable membrane before finishing the roof?

My question was re the sides of the building - the overlap there looks to me like you've reduced it a little - I have a very restricted site, so will need to trim back pretty much to the overlapping corner width, so was wondering if you had any views.

[FrankWebby]

Kingdom35 said:

Hi
I'm going to be in a similar situation. I'm going for the Aiste Log Cabin from tuin a 5m by 3m and ive spoken to a builder who will be making a Concrete base for me at 100mm in height with a sleeper edge which will be 100mm thick (ie sleepeers on their side running the perimeter of the base).
I will ring up Tuin beforehand to see if this is suffice but as far as I'm aware the base needs to be level as a must. I'm very wary too of over complicating the base.

Watching developments with interest here.

I've discussed with them, and also spent a lot of time on their (excellent) site - I've come to the conclusion that I'm going to use compressed paving slabs on top of a base of MOT, then sand/cement mix. Spacing these out every metre (or whatever makes most sense to provide support for perimetre and joists) leaves good air circulation under the cabin.

So my plan overall for the base/floor:

- DPM on top of existing slab
- Trench (depth?) around slab to footprint of cabin, filled with MOT, and topped with concrete pavers on base of sand/cement (maybe postcrete would do the job) to height 50mm above slab (slab level raised to level with pavers, using tanalised timber/additional thinner pavers)
- damp course on pavers
- Foundation beams built
- joists run at suitable intervals (say every 350mm), on joist hangers, with 20mm expansion gap at each end
- 50m Celotex or similar (does anyone recommend a particular product?) inserted between joists, with support from below as necessary

- - - WALLS BUILT - - -

- some kind of membrane/vapour barrier - (anyone know what I should be using)?
- 18mm? OSB sheet pinned to joists
- Underlay
- Carpet/laminated floor

Edited by FrankWebby on Tuesday 15th January 11:59

[FrankWebby]

There's no way I can pour a new concrete slab - no access to the garden, other than via the house, and so just too painful.

Have just got a quote for groundscrews from Stop Digging - which look like a relatively cost-effective (and reusable/environmentally friendly) option. They will install and laser-level, for £60 per screw.

Anyone got any experience with these?

[FrankWebby]

trickywoo said:

I'm sat in my office / shed set on these now. Been up for 18 months and I'm happy I made the right decision. I went for 20 to sit a 14ft x 11ft shed on. Could have got away with 16 though. The guys who built the shed for me really liked the screws and said they actually preferred it to a slab.

They had to do a little shimming as the U shape of the top of the screws obviously have to face the same way so potentially you will have some a 1/4 to 1/2 turn out of true. It wasn't really an issue though.

One guy put my 20 in in half a day for £800 - £40 a screw. I'm near Clacket Lane on the M25.

Awesome, that's really great to hear. Suspect I'm paying a central London premium, but they said 14 would be enough for me. Given I've just laid 2m deep foundations (ruddy neighbour's trees) for my rear extension/side return, I'm loathe to add more concrete to the garden.

[FrankWebby]

magooagain said:

Is the celotex exposed from underneath? If so,what is there to stop vermin eating into it and nesting underneath?

Good question - what do other people do? I was concerned about having the insulation open to the air (even though it's foil on both sides, and then solid foam).

[FrankWebby]

rustyuk said:

I've used these for my Tuin Cabin

https://www.shedbase.com/quickjackpro/

I saw these, and thought they looked good (and also half the price of the Stop Digging screws). But I did worry about installing them on a London clay soil - I'm not sure they'll go deep enough into the ground for my purposes.