Strong Raised Timber Floor

by David
(Hertfordshire)

Because my plot slopes, it is rather impractical to build a concrete base for my shed, which would be the best option.

I want to use my shed as a workshop to carry out some DIY woodworking, which means the use of some machines such as table saws, router, woodworkers bench and a lathe.

Some of this equipment weighs up to 50kgs and isn’t just a dead load (like a bench) but will effectively be a live load when used.

So - Jon, can you advise on the structure of the shed base (possibly sub base) which will be on pillars / posts up to 1m long out of the ground?

shed likely to be 24-30ft long x 12ft wide and 8ft to eaves with a shallow gable roof.

Thanks in advance

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Strong Raised Timber Floor

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Timber Size
by: GreenBoy

Thanks John

Glad to see the competition was such a success - clearly the world loves shed too :)

Thanks for the advice on the foundations - this is a great help.

The timbers i was planning to use were 50mm x 200mm on the main grid with some intermediate 50x100 inbetween - i dont think even 18mm ply can span 1.8m without aditional support - i was therefore planning on placing these at approx 400 centres - does this sound ok?

Thanks again for the support - and such a great we site.

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Pad foundations for a shed
by: John - Admin

Hi Greenboy,
Not sure if it is the floor design or the foundation design that you are after here. A few figures that you might find useful:

The self weight of the shed can be roughly assessed as 22.5kg/m² for the walls, roof and floor.

The load for equipment and people in your shed would be typically around 150 kg/m². This is a typical domestic floor loading, the equipment you describe is relatively light. If you were to have a big lathe or industrial saw bench you would need to increase this quite a bit further.

A roof load of 75 kg/m² should be allowed for small buildings such as this to allow for snow and access for maintenance etc.

One you have assessed these you come up with a self weight of the shed of approx 2500kg. With an imposed load of 5850kg.

A poor soil for foundation purposes has an allowable bearing capacity of 5000kg/m² so my mental maths reckons that you need about 15 pads on a grid of approx 1.8m with each pad at about 400mm square.

Is this the sort of info that you were after or was the timbers for the floor?

Good to hear from you.

All the best

John

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