wet shed base

DogsBody

DogsBody

DogsBody

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Ashbourne, Derbyshire
Have recently had a new shed installed at bottom of my garden.
the edges of the floor inside are all starting to get wet up to about 3 inches into the shed.
The shed has been built on a base of paving slabs and the base of the shed has 3" tanalised timber bearers.

I believe the water is soaking upwards into the shed but not sure why it is only around the edges.

What can I do to stop this happening ?
 
As nightglow says you need a dpm to stop the water being sucked up into the structure - 1000 grade polythene would have done the job nicely but its a bit late for that now...

Your bearers are pressure treated, so rotting will not take too easily, unfortunately your shed structure is probably not.

Short of striking the shed and placing a poly membrane I doubt much can be done. Others may know differently though.

[edit] You could try improving the drainage around the base by digging a small trench around the slabs and filling it with shingle. If rainwater is collecting on the slab base and then soaking into the bearers you could wait for the bearers to dry out completely (next summer now probably) then paint them with a pva solution or better still a bituminous paint (the kind used to seal flat roofs). You could even run a thick mastic line between the bottom of the bearers and the slabs after you have painted them, but you'll have to replace the mastic every year or so and even then all the above is a major bodge and ultimately probably won't completely fix rising damp. [/edit]
 
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I have in the past use a scissor jack & trolley jack to raise a shed around 100mm to slide in fence posts & dpm, to solve a similar problem a neighbour had.

You would only need to raise by about 25mm, giving you enough room to pull through some dpm, so the existing floor bearers are protected.
 
Thanks for the replies guys.

Raising the shed up will be difficult as it has a fence around it on 3 sides.
The whole shed has been pressure treated, the only thing I am not sure about is the floor, they have used rough sawn floorboard for the floor, everything else is definitely pressure treated however.

The moisture is only soaking up around the edges of the shed, the middle of the shed floor is dry.
pea gravel has been put around the slabs, probably only an inch deep though.
 
You need guttering - the rain is dripping off the roof, hitting the floor and then splashing up into the bottom of the walls/sides of the base.
 
Quink said:
You need guttering - the rain is dripping off the roof, hitting the floor and then splashing up into the bottom of the walls/sides of the base.
Click to expand...

When I first got the shed the rain was only light and it was only soaking
up into the front edge of the shed (on the door side) I installed guttering on this side and the issue went away, now the rain is a bit heavier the issue is back, it isn’t as bad, BUT it is soaking up on all 4 sides (not all the way along I might add)
 
What size is this shed, mine is 14' long & the slimline/ mini 76mm gutter had a too small capacity for the amount of water coming off the roof, & would cascade over the edge with heavy rain.:(

Had to upgrade to 112mm half round gutter.:mad:
 
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You'd be surprised how much water you get from the gutter as well so if you go that route (which I'd recommend) then make sure you have either a good place for it to drain or some water butts (plural). We have an 8x6 pent with a gutter. We filled a 320 litre drum in a week so going to have to buy another one as we don't have anywhere (for now) to drain so I'm going to have to build a soakaway eventually.

As has been said, polythene is the only real way to stop that problem.

When I built mine recently I went overboard but knowing the hassle to move the thing wasn't worth thinking about. Mine has two lots of 1000 grade polythene, one on top of the medium sized hardcore with patio slabs on top, then more polythene on top. Haven't had a problem yet.
 
shed is a 11' x 8' apex, gutter is smaller one (no room for larger due to crap shed design) down pipe is pointing at the pea gravel down one side of the shed, as there is no drain so to speak of that I can direct it towards, the shed is no more damp on that side than it is on the other side.

Jacking it up will be a pain as the 2 8' sides and the back 11' side are the ones up against a fence, and the bearers run along the length of the shed. Although this does sound like the only solution.

If I can find a way to put a polythene sheet under it do you just cut it along the edge of the shed so that it doesn't show or do you staple it to the bottom and hide it with a seperate piece of trim ?

Think I need a visit from a shed expert :p
 
You could get rainwater gulley head, bend & a 6mtr length of soil pipe & create a soakaway, cost about £30 for the bits..
This setup would take the water away from area surrounding the downpipe.

As to jacking, you just need enough height to get the bearer out, so you can attach some dpm to it.

If you had vehicular access, & knew someone with hiab to lift the shed, it would be a easy job.
 
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DogsBody said:
If I can find a way to put a polythene sheet under it do you just cut it along the edge of the shed so that it doesn't show or do you staple it to the bottom and hide it with a seperate piece of trim ?
Click to expand...

I'd just let the weight of the shed hold it down, any loose bits then you could peg down but if you cut it to shape once in situ then at least you know you've covered the entire underneath.

I think the hi-ab idea is best if it's accessible from one of the sides. Might cost a few ££ but be a much easier/less hassle process.
 
Unfortunately no vehicle access.
Having had a think about it though I can perhaps get access to one of the ends of the shed and jack it up from there, as has been suggested though perhaps going to have to wait for better weather now.

I have been in it again tonight and it looks like about 4 inches pretty much all the way around the edge is damp/wet.
nothing in the middle.

so you guys defo think a DPF will resolve this issue ?
 
DogsBody said:
I believe the water is soaking upwards into the shed but not sure why it is only around the edges.
Click to expand...

Probably all that water soaking in to the pea gravel along the edge of the shed, it soaks in & spreads far enough in the ground to reach the first bearer,which is most likely saturated.

That's why I suggested installing a soak away some distance from the shed.

By using pea gravel for drainage, you have created basically a 'French Drain', which is too close to the building.
 
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No Pea gravel along the front edge though and that is still wet, however in the middle where the double doors meet seems to be fairly dry.

I don't mind digging up all the pea gravel and sticking some cement down.
How/where would I install a soakaway ?
I have about a foot between the fence and the shed, and on the other side and at the back about 6 inches, so not a huge amount of room.
the fence is sat on gravel boards, behind the shed the gravel boards have soil/waste behind up to the level of the gravel boards.
 
So, you guttering on both sides of the apex, & the gutter downpipe(s) just let the water soak in the ground?

Ideally you need to get this water far enough away, so it can soak away in the ground without affecting the shed.
 
maccapacca said:
Take a picture and show us.

Is the last shiplap passing by the base?
Is there any grass growing up the sides?
Click to expand...

This would be what i'd check.

I'd have thought you'd get patches of damp where the bearers are, rather than a continuous strip of damp, if it was soaking up through the bearers?
 
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