Shed foundations – how deep?

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  • Shed foundations – how deep?
  • Premier Icon siwhite
    Subscriber

    I’m relocating a small garden building at home – it’s about 6m x 3m. Current construction consists of two rows of concrete blocks on the foundations, then wooden stud walls and an asbestos roof. I’ll clearly ditch the roof and start again – most likely with clay tiles, after reinforcing the roof structure.

    What sort of size should I make the foundations which the blocks will sit on? I have a cement mixer but I need to guess-timate how much cement and aggregate I need to order. They will be strip foundations – floor will be paving slabs over sand and a DPC.

    Premier Icon matt_outandabout
    Subscriber

    Small? 😉

    iolo
    Member

    How long is a piece of string?
    How tall is the shed?
    What are the ground conditions like? ie is it solid granite or pure wet made up ground.
    Too many variables.
    Maybe sure building control will want this info too.

    Premier Icon stumpyjon
    Subscriber

    My footings for a brick built garage, same dimensions are 750mm deep with 500mm of concrete with one row of blocks bringing them back up to ground level. So an approx. 11m footing line (one wall already exists) took about 3 tonnes aggregate, 2 tonnes sharp sand and 750 Kg of cement.

    My biggest concern in your situation would be the weight of the roof on the timber walls.

    Edit – mine was into compacted builders rubble as well so good sub base, probably doesn’t need building regs as it’s not an occupied dwelling.

    Vern0n
    Member

    That’s no shed…. It’s a space station!

    Vern0n
    Member

    Concern for roof weight on timber +1

    Premier Icon wwaswas
    Subscriber

    just get corrugated metal roofing.

    you don;t need a concrete base I’d say, just level whatever the concrete blocks will sit on and put some weed control fabric down. (I am not a structural engineer)

    Premier Icon siwhite
    Subscriber

    Good thinking ref weight of roof – the Boss likes the look of tiles, so perhaps I’ll think again and have something lighter.

    Soil is quite clay-ey elsewhere in the garden but I’ve not checked in this particular bit.

    Stumpyjon – very useful info, thanks.

    Matt – comparitively small – I’m only moving this shed to make room for a 7m x 12m green oak framed garage…

    footflaps
    Member

    Our shed (not the workshop) is on paving slabs on the ground.

    The workshop is a slightly more robust affair:

    mk1fan
    Member

    As the vast majority of domestic roofs in the UK are timber then tiling the roof is not an issue.

    If it were me. I’d use C16 ‘2×4’s for the stud work and rafters. I’d include a collar contecting opposite rafters at their mid point. I’d then clad the inner face of the walls with 18mm wbp ply and the outer face of the roof with 12mm wbp ply. I would screw it together to.

    As for footings, I’d lay a reinforced raft raised 100mm out of the ground. I’d dig a 400mm deep, 400mm wide trench round the outside and then take 150mm deep out of the middle. whack down 100mm of MOT in the middle bit. Lay some reinforced mesh (held 50mm off the bottom) across the whole (with a 50mm gap around the edge). Then pour a slab.

    Good solid base that’ll move as one if needed and provide a options for the internal floor finish.

    Admittedly the most expensive route but it won’t distort or crack – a concern I would have on a ‘shed’ of this size.

    Premier Icon wwaswas
    Subscriber

    The workshop fallout shelter is a slightly more robust affair:

    ftfy

    [edit]
    As the vast majority of domestic roofs in the UK are timber then tiling the roof is not an issue

    although in this case a relatively lightweight roof is being replaced so the existing structure may not be designed to take the addtional load that a tile roof would give?

    iolo
    Member

    The cover to that top reinforcement is bloody awful on the edges footflaps.
    EDIT and bricks to the bottom mat – tut tut

    Premier Icon sam_underhill
    Subscriber

    If you like the look of tiles, take a look at felt shingles. I just put these on my new shed. They look pretty good and should last longer than felt. Many visitors have said “oh.. the tiles look nice, did you do that yourself?”.

    mk1fan
    Member

    although in this case a relatively lightweight roof is being replaced so the existing structure may not be designed to take the addtional load that a tile roof would give?

    Asbestos sheets aren’t that light so I would assume that the walls aren’t constructed of 11/2×2 frames with shiplap covering.

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