Building a concrete floored shed, dealing with moisture?

GiraffePencils

GiraffePencils

GiraffePencils

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Joined
15 Feb 2013
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Edinburgh
Hey all,

I'm looking to put up a shed in my garden, due to dimensions I'm planning on just building it myself.
I'm just wondering about how you prevent moisture build up when having a concrete floor?

Usually you'll raise the shed up on batons to let air flow underneath, but I was wanting to have the floor concrete, rather than wooden.

Any advice would be helpful.

Cheers
 
I live in South Wales so high humidity all year I built a workshop on a concrete base, with half height block walls then windows then a near flat felt roof. It's unheated and uninsulated. I don't get much in the way of condensation although the humidity is relatively high. In order to keep the wood dry for wood working stability I often put a dehumidifier in there. If it were a shed without my woodworking machines and wood I probably wouldn't bother. Although is block wall with wooden cladding so it doesn't get any direct rain against the block walls which I think helps a lot.
 
GiraffePencils said:
You do yes, but if you stick the framework down to the concrete, then you could get water laying against the timber etc.
Click to expand...

Why not put plastic sheeting under the frame then, all I remember is putting 6 or 8 large concrete slabs as foundation then I assume the frame just sat directly on top, no need for fixings or the like, can't remember about moisture but I'm meeting him in half an hour so will ask.
 
Putting a full blown (plastic or proper dpm) down is ok as long as your sure its not going to trap moisture as opposed to helping it drain away

Or use a treated angled piece of timber to drain and act as the sacrificial part, for example our cabin has pressure treated foundation beams, most/all cabins have these, designed to be the bit that rots (if you go wood)
I bought timber, but if I was doing a cabin again I would use composite

https://www.tuin.co.uk/foundation-bases.html

You could just use some composite "wood" they basically make a plastic wood effect product into planks just like wood, googling
 
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So I'm wondering if I wrap the DPM up the side of the frame, then put the cladding over it, will that be a reasonable solution?

I'll have a look at those angled base boards too
 
So just put a sheet of plastic(the heavy duty black stuff) between the foundation and frame, maybe raise the foundation by a few inches if your that bothered but it shouldn't be a problem also treat the wood with creosote or the like.
 
Yes you can use a sheet like your plan. The dpm only needs to protect the wood in contact with the concrete base. So you could happily just use damp-proof course at the contact point. You can buy 30m x 100mm for £4. That's more than enough for the largest shed. Either way is fine.
 
If you use dpm then I would buy it 200mm and turn the overlap up the outside of the wood batton on floor - that will stop splash back getting to timber below outer finish.

Also if you can run to it wrap roof felt horizontal around frame before you cover the outside - stops drafts.
 
You could even go as far as running one course of bricks around the perimeter of the slab then putting a dpm ontop of it, then screwing your wall down onto the bricks.
 
I did this with my shed, I used some plastic batons I got off facebook to make a ring around where I was going to put the frame, this was screwed to the concrete base. Put the frame down on to the plastic ring and filleted up to the plastic ring with mortar. From the frame I ran round with 2 inch flashing tape to allow the rain to run off and away from the frame. Works for me.
 
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