Workshop foundations

[Henrik]

I've got a space behind the log cabin and in front of the garage, where I want to build a little workshop.

The space is 4.5m x 3.6m, so not massive, and I realistically can only build it as 3.0x4.5m, as I need space for maintenance of the log cabin.

Anyway, access to the site is terrible. Basically any materials will have to be taken over decking etc etc, so a digger is out of the question (Even if a mini could fit, I'm not sure the decking is strong enough to take one, and the mrs would kill me if I damaged the decking).


All the above means that I'll have to do digging by hand for foundations, and as I don't like digging much, I'm thinking of building a "raft" foundation, however I cannot really find anything on the actual design online... Every page I seem to find says "consult a structural engineer".

The walls will be double skinned, as I want to insulate, and in block (which will be rendered on the outside to match the house).



Basically, I think my question is how deep and wide I have to dig the wall foundations? Would 50 x 50cm be enough, if there was enough rebar inside? The main floor slab I'm hoping to get away with 15cm, as I can then have 10cm or thereabouts hardcore underneath the main slab.

Does the above sound sensible? I would rather spend a bit of extra money on concrete than dig

 

[Mr Fro]

15cm really isn't much, especially if you're going to have reasonable point loads as it'll crumble like a wafer.

I'm doing my workshop now (31m2) which has an existing 11" slab and I still have to excavate and underpin to provide sufficient footings for the load required and that's just single skin.

A structural engineer will be able to calculate the appropriate slab stuff for a few hundred and it you don't like digging then just pay a couple of blokes a couple of days to do it for you. It's a pain now but at least you won't be ****** off a couple of years down the line when your slab cracks and your walls sink.

 

[Henrik]

How deep are you going with your underpinning?

 

[Arc Tourist]

Not sure what your situation is, but you mentioned poor access for getting a micro digger in. I had the same dilemma for getting one in to dig deep & wide retaining wall footings. The company I spoke to sent a guy out to look, and he said "no problem". Just to show you what's possible..... The digger was delivered and craned in from the street, over my neighbour's yard, and 12' down into my back yard; about 35' away. Brilliant!

.

 

[gaz1]

to give you a good idea this failed



the original house foundation slab is at rear of pic about 6-8" thick

the garage was built on 4-5" and it failed due to a pipe leak the wholewall has dropped 1, 1/2" too 2"

the new hole is 18" deep for the foundations due to the council being involved

my advice dig your foundation walls right in the first place the floor can be 3" thick but heavy machines 3" is not the best choice 4-5" is better then you want insulation under your floor so then your going deeper

 

[Henrik]

gaz, ouch - that looks painful!

Hmm, starting to look like a big and painful job, even though I like Arc Tourists idea The closest access point is about 8m away, so it might be possible to drop a digger in that way.

 

[addjunkie]

What are you going to do in your workshop.....will a simple shed not suffice, be easier, cheaper and a lot less hassel. Perhaps one thats a log design to match your log cabin.

 

[Henrik]

What are you going to do in your workshop.....will a simple shed not suffice, be easier, cheaper and a lot less hassel. Perhaps one thats a log design to match your log cabin.

Well I was hoping to do metal work in there, and have ano outside toilet etc, however my main concern is fire safety... the log cabin is already a large wooden structure, and I don't want to accidentally create an enormous bbq.

I wouldn't mind a wooden building otherwise, and if there was something else non combustible, I'd be all ears tbh.


Perhaps the sensible option would be a nice insulated metal shed.

 

[gaz1]

weather concrete or steel you need supports going in them

for the metal shed id go down the route of insulated roof panels or fridge panels but your still going to need supports built within the structure

theres the free garage option but that still needs a base to rest upon

thats the way i choose to do and then lay 2" concrete flags inside of it at that i have a shed 10' x 8'

 

[Wendelspanswick]

You could put piers in to support a steel ring beam and build off that with timber framing, line the inside with plaster board.
On the outside of the timber framing you would put vertical battens on, then cement board and then render to match the house.
You end up with a well insulated and fireproof workshop but it would have a suspended floor. If you used big enough steels you could have a block and beam floor.

 

[Mr Fro]

How deep are you going with your underpinning?

The wife has hidden the plans and I can't remember exactly - think it was 1m down and 0.6 lip under the slab.

You could go wooden if you clad the inside with fire resistant plasterboard maybe. Still got the problem of point loads on the floor though.

Another option could be to pile and use steel and concrete beams. No idea how much that would cost though.

Edit: Wendel beat me to it!

 

[gaz1]

has been discussed before by spencer

http://www.mig-welding.co.uk/forum/threads/metal-workshop-shed.58440/#post-713392

and other examples

http://www.mig-welding.co.uk/forum/threads/alternative-to-crap-shed.58097/page-2