Concrete base for shed (ed.)

Hi all,

I am planning on building myself a new 4.8m by 2.4m Shed/workshop. I want to build a decent shed that will last. I know that to make it last I have to build it well, with the right materials and cant take short cuts. I cant afford to spend unnecessarily and making mistakes is an easy way to waste money. Base, floor, frame, roof… as I am not a builder nor carpenter, I am going not going to rush. So I might be posting many more updates and questions.

I will have loads of questions of the “how do I” and “is this right” kind and will really appreciate wealth of experience on this site.

So here we go.

I am not planning a heavy industrial workshop with serious metal work lathes etc. A simple bottom of the garden workshop/shed. Framing is going to be 2by4 on 600cm centres and rafters 2by6 supporting OSB and EDPM roofing. So, a reasonably robust construction with a bit of weight.

In terms of the foundations, I am thinking of digging down 15cm. Laying down 7Cm of rubble, 3cm of sand, a DPM topped with 5 cm of concrete.

So that gets me a nice flat concrete base to build on.

I will put a DPC down before any wood.

Most sheds I see being build have floor joists with OSB board. Because of the 2.5 height restriction, I am trying to leave myself enough headroom and could do without loosing the joist and OSB depth.


If I put underlay and linoleum down on the concrete, with all the wood protected by a DPC – would that be OK?

I am not building this like one of those posh outdoor living spaces which are all about insulation etc.

I might put a heater in there but it is mainly a workshop and I can always put on an extra jumper when I am working in it.

Is a concrete floor OK or a no-no?

Thanks all.

Just a few things I've learned over the years, many through mistakes!

That concrete base sounds too thin, and best to be the exact size of the shed and raised a bit leaving the base plate timber above the ground, so the rain water can run off better down the sides at the bottom.
Would also use MOT. And DPC on top of the base/under the frame in addition to the DPM.

I'm assuming the height restriction is because it's less than 2m from a boundary?
If not you can get greater height. 3m for pent and 4m (2.5m eaves) for apex.
The taller the better especially if moving longer pieces of wood around.

Personally unless it's a fully insulated/heated outbuilding and for light use, I'd leave it a concrete floor.
The number of times you'll probably end up dragging heavy items means you won't have to worry about ripping lino or damaging an OSB floor.
Although you say you won't be using 'serious metal work lathes etc ', it's amazing what you might end up doing!
And it gives greater stability than a wooden/OSB floor for work benches, whether fixed or portable.

I'd be wary about any heating, especially portable gas due to condensation or the cost of electric.
So a woolly jumper and a Beanie is the way to go!

You haven't mentioned what you are going to do to the inside walls.
One of the best bits of advice I got was to clad a shed internally in OSB.
Because it means you can put up any small shelves, hooks, tool hangers etc wherever you like, instead of just on the frame . Avoiding any cabling of course!

amatureleccy said:

a DPM topped with 5 cm of concrete.

Click to expand...

Much too thin, double that is still pushing it a little, without reinforcing rebar.

OK - I hear you. I will have a rethink on the base and rework the depth with MOT.

So a concrete base sounds OK in itself - I can work with that.

As regards heating, I am thinking of phasing this project - heating will come much later and will be either a stove or solar powered. I am a bit of a green and will always try and recycle something first - so I will intend to make everything based on green energy - I wont run any heating off mains power - but like I say that is a later stage in the project.

In terms of insulation - I will probably come back to this group with more questions. Like I say - I am not expecting a pristine fully insulated unit - but I will have to think about what goes between the outside cladding, the frame and the insde sheets.

Thanks for responding.

How about this -

Concrete - 10cm
DPM
Sand - 7cm
Rubbble - MOT - 15cm

Sorry about the rudimentary drawing.

what are you going to use for shuttering?

By shuttering, do you mean cladding? If so, the exposed walls will be cladd with treated Shiplap with Tanalin. The walls at the vary back will be clad in outdoor plywood board.

amatureleccy said:

By shuttering, do you mean cladding? If so, the exposed walls will be cladd with treated Shiplap with Tanalin. The walls at the vary back will be clad in outdoor plywood board.

Click to expand...

I would think they meant how will you hold the concrete in position when you pour the floor. Most folks use timber boards pegged into the ground to shutter the shape.

Ah, I see, thanks you. Yes, I will peg some boards down to hold the poured concrete.