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Drainage around shed

Discussion in 'In the Garden' started by ceres, 18 Mar 2013.

  1. ceres

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    House i recently moved into has a timber shed in the garden. It seemed to be in OK condition but a bit neglected and in need of maintenance - damp patches appearing in roof panels, rotten fascias, a couple of rotten planks along the back at the base. I want to keep it as it has power and light, is about the right size for me, has a built in workbench and I can't afford a new equivalent!

    Got a local shed and fence man in who agreed it's got a few years left in it - he re-felted the roof and replaced the rotten planks and fascias. It still needs a good paint which I can do if the rain, sleet and snow ever stops but a new problem has appeared and I could use some advice please.

    Since the re-felting, there is damp seeping across the floor from the back wall where new planks were put in. The problem appears to be that the new felt is stiff and where it's pinned onto the roof overhang, it angles in towards the wall of the shed so water is going down the back wall. I can sort that out with guttering which I intended doing anyway but.......

    I'm on a hill, the property behind me is slightly higher so I probably get run-off from them. The back wall of the shed is only a couple of feet from the boundary fence and the space between is gravelled. When I scraped back the gravel for a look I expected to find a weed membrane as that's what's everywhere else in the garden but this is thick stiff plastic that isn't letting water through. I can't actually see what the shed is sitting on at that side as the bottom two planks are sitting on the plastic and water is pooling there. On the opposite side of the shed, I can see a timber base.

    Should I do something like remove the plastic, dig a small trench along the back wall and backfill it with gravel/stones for better drainage and to try to keep water away from the wall?

    Thank you!


     
  2. big-all

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    do you have a gutter
     
  3. ceres

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    Hi Al,
    Not yet but:

    I have some guttering from a previous shed but need a few extra bits to extend it - waiting for these to be delivered. The guttering will take away a lot of the water that's currently landing at the back edge of the shed, but not all. It's the fact that it's landing on plastic and puddling around/under the wood that I'm worried about and wonder if I should do something to help it drain away from the wood.
     
  4. big-all

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    i would remove all plastic and try and get the ground at least 1" below any timber so it doesn't pool or sit in water
    you should have no water shedding to the side off the slopping roof
    water should only ever shed off a roof on 1 or 2 sides
     
  5. ceres

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    Thanks Al. I'm not sure how to best go about it. If I excavate to the depth you suggest, I'll have to do it over the whole area between the shed and the fence otherwise I'd be creating a slope towards the shed which is exactly what I want to avoid. Excavating that whole area will create a change in level at the front edge of the shed which isn't ideal and will also expose a gap under the decking at the back and the fence at the side.

    Is a deeper trench, maybe half the width of the gap betwen shed and fence, and backfilled to the existing ground level with gravel (like a mini soakaway) not a good idea?
     
  6. big-all

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    yes back fill with grave

    give it a good forking to loosen the soil before filling
     
  7. ceres

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    I could use a bit more help with this please! I've now got guttering up both long sides of the shed so there's no longer water dripping towards the base. But it looks like the damp inside is still getting worse, or at least not drying out any.

    So today, I decided to try to dig out the slope that runs towards the shed wall. I removed the gravel and underneath it's actually weed membrane, not plastic as I thought. I started digging the soil out and from approx the midway point to the back end, there was only around 2" of soil on top of a sheet of stiff black ridged stuff which looks impermeable (damp proof membrane maybe?) so there was a sandwich of weed membrane/very wet mud/black sheet. I removed th black sheet and dug a channel all the way along the shed and exposed the base. I think it's timber on top of a hard base - can't tell if it's slabs or somehting else. The timber was completely buried in mud and is wet but feels sound.

    The channel I've dug is about 6" deep and 6" wide. I've levelled and dug out a couple of inches over the rest of the area which is as much as I think I can safely do as the land behind the fence is higher.

    I've pinned the weed membrane up onto the shed wall to keep the base exposed to the air - my plan for the moment is to hope for dry weather to allow the base to dry out a bit and hopefully the inside of the shed too. After that, what should I do - fill the channel with gravel then weed membrane and more gravel on top? Is the depth and width of the channel enough? Or is there a better way of keeping water off the base?


    This image is the other way round to the others - shed wall is on the right, fence on the left.
     
  8. big-all

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    all timber must be off the ground and sat on say dpm[damp proof membrane] or felt so any dampness cannot get to the wood
    is it a wooden floor or concrete
     
  9. ceres

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    Hi Al, thanks! I've had a closer look at the other side of the shed where the ground level is lower. The side of the shed is sitting on what looks like a 4" deep timber - this side is dry as it's above ground level mostly. I can't tell if there are separate bearers or if it's part of a rectangular frame like a Portabase as the back of the shed has decking right up to it and the front has a deep half-moon shaped concrete step acroos it. The floor inside is wooden planks laid across the width.

    I can't see what's underneath the timber support and anyway, it's not something I could chabge. It's not a new shed but still serviceable if I can fix this damp area.
     
  10. big-all

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    are the damp areas around the edge??
    my betting is timbers every 2ft/600mm ish look for nails on the floor
     
  11. ceres

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    Yes, the worst damp area starts at the edge where I dug out the wet mud that was sandwiched between the top layer of weed mambrane and the bottom layer of DPM (i think). The damp patch tracks in a sort of pointed shape from the edge towards the centre of the shed floor.

    I've had a look at the floor. There is only a single line of nails at the midpoint of the width which is 77". Despite this the floor feels solid - it doesn't seem to bounce much. Something I hadn't noticed before is that the planks making up the floor are all the same timber (in appearance) but are completely different widths from around 4.5" up to about 9.5". I can just get a blade in one of the gaps between planks and have run it along - there are no other bearers apart from at the outside edges and the one in the centre and the floor isn't T&G. The man who lived here before was a carpenter so I think it's a custom job!
     
  12. big-all

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    there could be further support with the floor just resting on top a
    77" span would be like a trampoline without support
    do the sides sit on the floor ??
     
  13. ceres

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    Thanks Al!

    Yes, the sides seem to be sitting on the floor - I can get the blade horizontally under the batten at the lower edge of the wall but not vertically between the floor plank and batten. I've jumped up and down and it's definitely not trampolining - I'll have a look for more supports but I'll have to move things around to get access to every plank to check with the blade.

    Outside where I dug the mud away from the timber base, It looks to be drying out a little so that seems to be working. It's just what to do next that's the problem!
     
  14. big-all

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    do the sides cover the floor as in will the water running down the sides miss the floor
     
  15. ceres

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    Hi Al,
    Yes, the planks on the outside cover the edge of the floor, I can't see the floor from the outside, so water that runs down the shed side falls onto the ground. When I had the roof re-felted just recently, they also replaced the lowest two outside planks on the 'bad' side as they had some rot.

    Sorry it takes so long for me to answer questions. i can't see very well at the moment (waiting for surgery on my eyes to sort out problems caused by surgery last year!) so I need good light to look at things and even then it's tricky. Also accounts for spelling here - I can zoom the screen in but it's still a fuzzy blur!
     
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