Going to slab shed base today

[Croolis]

I have advice from friend (and lots of online research) but he doesn't express himself terribly well so I'm going to ask here, why not.

Have bought a cheap metal shed. It's for midgets, roof very low, and I want to use it as a small workshop for some mid-life crisis carpentry hobby, so I'm needing to raise the whole thing a bit by spending oodles of cash on wooden floor (it's still going to work out a damn sight cheaper than a full on wooden clad shed).

So it's standard shed wooden floor with 18mm OSB on joists with span joists underneath them, then a dwarf stud wall on top of the floor, metal shed then just sits on stud wall. This means a big bastard doorstep to get into the shed as the doorstep will get raised as well but I might be able to do something with that later (these cheap metal sheds can be iffy so I'll get the door working as designed before I start modifying it).

I'll use feather boards to cover the dward stud and I'll hang some plastic trim from between the metal shed base and the top of the stud wall so it covers the top of the feather boards. Breathable membrane behind all cladding

I have the timber already delivered so I'm committed to this route now, but I've yet to buy the feather boards, trim or membrane.

I've CADed the floor in Sketchup, attached. The yellow is 18mm OSB that I've extruded just a bit just to show what's going on.

Today, I shall be digging holes something like 100mm deep or less, for 9 pavers and/or concrete blocks to fill with crushed stone, in three rows of three, so there's a block bang in the middle of the floor. The span joists will sit on these. There will be membrane between slab and span joist. The ground slopes away towards the back of shed, but the front right corner is higher than everywhere else, so front left will have a concrete block instead of a paver, with blocks likely at the back. Gotta get my spirit level out.

There will be no concrete base or anything like that. It's going to be the nine block/pavers and that's that.

Any thoughts, anything I may have missed? Thx for replies.

[Fenlander]

Could you not gap the stud plinth wall at the door and extend the door down? A big step will prove very annoying.

[chipko]

Perhaps worth adding a weed control membrane/dpm over the full footprint area. Under the slabs if feasible.

[Croolis]

Originally Posted by Fenlander

Could you not gap the stud plinth wall at the door and extend the door down? A big step will prove very annoying.

Yeah, it will. But it's sliding doors , so the rail guide at the bottom must remain somehow if extending the doors.

Three options:

• The ground at where the door will be is sloping so I may be able to just have a little bridge/ramp thing going more or less horizontally to the doorstep, and then steep little ramp inside the shed. I won't be able to gauge feasibility on this until I have the floor down. On the ramp inside the shed, if it goes 400mm out and it'll be 170mm down, that's 23 degrees slope. I'm crap at gradients, dunno if that's prohibitive for wheeling things in on a sack truck.
  
• Replace the stud wall with a hinged board that will fill the gap, and either swings open like a door (doubt that will work 'cos space) or hinges down. The sliding door rail guide at the bottom of the door would need to be cut out and then positioned on the top of the hinged board so it's perfectly flush with everything when board is in closed position so the sliding door works.
  
• Or, cut out the stud wall and guide rail, relocate rail at the bottom on the OSB and then make the doors deeper by addding some metal sheeting to the bottom of the door. This would require metal sheeting that will match the door and being able to attach any sliding rail things to the bottom of modified door. Until I unpack the doors (can't do that yet) I don't know about that for sure. Might be easy, might not.

The stock imagery on the shed vendor website is unreliable I expect and unpacking the whole shed just to find a few bits before I'm ready to build, following the instructions, is a bad idea. I do have the metal plate rim joist things that form the shed perimeter and what the metal walls will sit on out though, so I can lay them out for slabbing and cutting timber to size.

I'm going to just build the stud wall as if I was going to keep it complete and then cut out as required when I make a decision. This low roof/stud wall thing is all a bit challenging and awkward, but I've saved something like £600 I reckon by going this metal shed route rather than a wooden build one. And I have more time than money.

Originally Posted by chipko

Perhaps worth adding a weed control membrane/dpm over the full footprint area. Under the slabs if feasible.

The ground I have cleared (which in itself has taken weeks of here and there, between work and fishing trips), actually is covered in old weed control membrane already. Originally, bark had been laid over it, but not enough, and over last 5 years it's mulched down and stuff has grown on top of it. Took a lot of effort to get rid of all that, but now it's clear and the ground basically now consists of old membrane. I've got a roll of some new stuff standing by if I need it.

[Steve509926]

Hi Croolis, now you are committed with a stud plinth, the only thing I would add to what Fenlander and chipko have said is, a 100mm of aggregate for your pavers/concrete blocks to sit on isn't enough. Depending on your ground conditions a minimum of 200, preferably 300 is required otherwise you will find some of your concrete piers will start to sink when you use it as a workshop.

[Steve509926]

Just thought of a couple of things. I'd advise you to screw the metal shed to the wooden base, they are light and move easily in a strong wind.
Not only will that step be annoying as Fenlander has said, I think it will be dangerous. A possible solution would be to build the shed as you have said leaving off the sliding doors. Once it's completely secured to the wooden base, cut off the bottom sliding door guide and that part of the wooden base (you'll need to reconfigure your concrete piers supports. Then build a simple wooden door frame, attach the shed doorway to it and make some full length wooden shed doors. Step gone, easy access and no need for a ramp.for

[Croolis]

Originally Posted by Steve509926

Hi Croolis, now you are committed with a stud plinth, the only thing I would add to what Fenlander and chipko have said is, a 100mm of aggregate for your pavers/concrete blocks to sit on isn't enough. Depending on your ground conditions a minimum of 200, preferably 300 is required otherwise you will find some of your concrete piers will start to sink when you use it as a workshop.

Right oh. It's worth pointing out that I'll be storing stuff roughly using load limits on span tables such as this one:

https://www.timberbeamcalculator.co....b/span-tables/

My floor joists are 2x4, not 2x6, so I'm gapping them according to the values on that table, around 360mm from centre, which is overkill. So I can have quite a bit of weight despite them being 2x4. So I dunno if I need crazy foundations. But I bow to your wisdom.

Originally Posted by Steve509926

Not only will that step be annoying as Fenlander has said, I think it will be dangerous.

What's that?

I'll be screwing the metal shed to the stud wall, yes. What else is dangerous, beyond it possibly getting moved by wind?

Originally Posted by Steve509926

Then build a simple wooden door frame, attach the shed doorway to it and make some full length wooden shed doors.

If you think the door frame and doors hanging on it would be supported adequately by only being secured near the bottom into the stud wall and into the OSB it will sit on? The shed is very flimsy, you see. I'd have to see what the metal framing parts there are around the door frame when it's up. It's entirely iffy that the door frame and any wooden doors hanging off it can be supported by the metal shed.

[Steve509926]

Originally Posted by Croolis

My floor joists are 2x4, not 2x6, so I'm gapping them according to the values on that table, around 360mm from centre, which is overkill. So I can have quite a bit of weight despite them being 2x4. So I dunno if I need crazy foundations.

The foundations are there to support everything above them including the floor joists, so the heavier the floor joists and what's above them, the greater the foundations need to be.

Originally Posted by Croolis

What else is dangerous, beyond it possibly getting moved by wind?

The step could be dangerous,carrying stuff in and out.

Originally Posted by Croolis

I'd have to see what the metal framing parts there are around the door frame when it's up. It's entirely iffy that the door frame and any wooden doors hanging off it can be supported by the metal shed.

If the shed won't support the door frame and doors, it's easy to make an internal light weight wooden frame to support everything.

[Brinormeg]

Difficult to imagine without actually seeing it, but I have a small metal shed that has a runner top and bottom with sliding double doors.
I did consider a similar idea to yours before to gain height, but ended up just screwing a few fencing boards to some horizontal fence posts laid down…..then screwed the built shed to that. 15 years on…..still fine but is bloody low to go into to get stuff.
But in your scenario….if only one door…can you not just stop the door rails short, make a small wooden frame as suggested, then use the metal door itself as the door, hinged to your new doorway frame with a couple of boards to extend it.
Ild advise insulting it, as the tin is a bugger for condensation…..just a couple of tins of spray contact adhesive and the cheapest of foam boards would do the trick..

[Croolis]

Originally Posted by Brinormeg

Ild advise insulting it, as the tin is a bugger for condensation…..just a couple of tins of spray contact adhesive and the cheapest of foam boards would do the trick..

Two sliding doors, it has.

I'm going to line the inside with the cheap as chips silver tin foil type insulation, believe that'll do it.

I'm going to build it as in the drawing and just live with the step in the short term. My front room looks like a cross between a chandlery, a tackle shop and a furniture warehouse, my garden looks like a lumber yard and I'm sick of it. The door issue will get addressed another time.

Dug one hole for concrete pad to 200mm today, that's as deep as I'm going and hang the consequences. Eight to go lmao.

[Oldman2]

About 12yrs ago I bought one of those metal sheds with sliding doors, its 8 x 10ft and I remember it being a bit of a pig to put up, a million self tappers and holes that didnt match the drawings so some improvisation was required. But it was cheap and was only going to be up for 12 months.
My garden slopes some so I levelled an area of soil and put ex council 2inch pavers down to make an area just bigger than the shed footprint. Mine didnt come with a floor, just the frame at the base of all the walls.
I didnt want to go drilling all the slabs to anchor the shed so used 3x2inch sawn to make a frame for the shed to screw down to. Once built its pretty heavy so I didnt worry about it blowing away.
12yrs later the 12month shed is still in place, the roof started to rust on the outside just as the metalwork warranty expired but apart from that and the grief assembling it (needs 2 persons but I did it on my own) Its been well worth the £299 I paid for it.
Very little trouble from condensation, the roof has good vents, the council slabs laid on levelled earth have given no trouble and very few weeds have ever dared to try and access the shed.
Its been such a good trouble free storage shed with no problems having to creocoat it yearly I have bought some new roof sheets for mine.