I am looking to self build a large shed this year, but lack of access will make laying a solid concrete plinth quite difficult and probably expensive.

My alternative solution is to dig suitable holes at the corners/middle, pour concrete, then use either concrete lintels or sleepers to span the pads and support the floor joists of the shed.

The shed is going to be more substantial than the usual bought variety. Using 3x2 stud walls, 6x2 floor joists and 4x2 roof joists. Clad in feather edge board, insulated throughout.

Any recommendations on the foundations? Depth and cross section? Should I reinforce?

If you are in a position to mix the concrete for the corner pads, can't you just mix more next to the base using a small mixer, it doesn't take that long ?
It would surely be the best solution.
However, if you are fixed on the pad method, 6"- 8" deep should be ok if you use a good mix and with the 6 x 2 Floor joists I don't envisage any movement.
6 x 2 joists spanning support pads is the same method as many use for deck bases.

We built a large deck last year in my daughter's garden and used concrete strips about 12" wide to support the Joists along their length.

This should be ok for your shed and will reduce the amount of concrete you need to mix.

The advantage of a full base however is that you get no weed growth.

I hadn't thought about joining up the pads, the only negative to that is the shed will be 5x3mtrs...so quite a bit of extra digging!

The other point I forgot to say, there is very little scope to put the spoils as I dig out. That was the other reason for not making a full slab.

I was thinking of membrane and a couple of inches of gravel for weed control.

Yes, we used that method for weed control between the pads.

If there's little scope for removing the spoil and you don't want to go to the expense of a skip, why not just raise it slightly, so there is no or very little digging.

You could always hide the pads with some decking board ?

Thanks, it may have to be like that on one long side, the ground slopes a bit.

It's mainly access making the project tricky to start. Any skip would have to be out in the road, across the garden and down a narrow path. Just not my idea of fun!

Think I'll stick with the pads and raise them a few inches. That would help to keep moisture off the timber as well.

just laid concrete blocks on the ground, works ok very large shed bigger than the house and lots of heavy machines inside

before you decide the exact size remember sheet material still comes in feet so might be more economical to make it say 4880mm x 3047mm[10 ft x16 ft]then the floor would be exactly 5 sheets off ply

or if you are using planking it needs to be planed to avoid waste remembering it comes in 300mm increments starting at 1.7/2.1/2.4/2.7/3.0 ect up to around 5.4 dependant on where you get it from
my shed is a mere 10x12ft
http://s21.photobucket.com/albums/b270/bigall2005/

iff you haven't seen my very messy shed before it may give you some ideas

Good point about sheet material, although I was making plans based around Travis Perkins treated timber sizes, ie 4.8mtrs and 3.0mtrs.

I guess I will have to sit down with the chippie who is helping me and decide on the best strategy.

Maybe I could invite comments on the general structure....

Floor is 6x2, with 100mm Kingspan and shuttering ply on top.

Walls are 3x2, with 75mm Kingspan and either plasterboard or ply.

Roof is simple sloping roof, 4x2 with shutter ply on that, some waterproofing membrane and finally the Coroline stuff.

I want to use cedar feather boards on the outside, with another waterproof and bugproof membrane underneath.

Windows and door will come off ebay.

The idea is to create a) more storage b) play area and c) computer area. So it will need to have a snug feel to it.

all the timbers on my shed are 3x2" at 2ft centers[floor/walls] with the roof at anywhere between 2and 4ft spacings

the floor and roof is 25mm ply 9 sheets in total
walls 5" txg shiplap

floor on slab/brick set on sand topped with felt at 2ft centres in a grid pattern [to be pedantic its nearer an 1ft11" as they are set back 1 inch from the edge]

Hi Robbox

I built a 6m x 3.6 m shed recently.
Alot of people seem to think laying a concrete base is the best way to go but it can quite a bit to the cost
so here's what i did !
For the foundation i built up 9 pads using blocks and paving slabs
1 in each corner then 1 in between them and finally 1 dead centre
I then used 150 x 50 to span these and nailed 2 x 1 between each to which i laid rigid celotex type insulation.Finished it off with 18 mm far eastern ply.
Very solid it is too !

if you'd like to see some pics pm me and ill forward them.

PS I see you are in somerset next door to me....if you need a contact for the cedar feather edge again let me know

sure, I'd like to see the pics.

If you have any like construction pics that would be great.

I am thinking of doing something very similar, 150x50 floor joists with a ply floor, insulation in-between.

Did you have to take some care in levelling up the pads? My spot is on a slight incline.

I think I will go for poured concrete pads, probably no more than 300mm deep.

I did find a cedar board mills, Milverton Saw Mills in Somerset. Dunno about price....

Hi

Levelling the pads wasnt too hard, did it with cheap laser level and a long piece of wood. dont worry if you are a litttle out the joists can easily be lifted with bit of slate.

Milverton Is the place i was gonna recommend. funnily enough I built a little office for the sawmill bosses wife a few years ago and used ex 175 x 38 cladding
Their prices are quite competative too.

pm'd pics