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What shed base for sloping concrete?

Hi, have been browsing through the posts and undecided (or overthinking) best shed base to use on sloping concrete…

Shed is 3650 wide, 900 deep and I want the back of it against the side wall of existing garage. It has a roller door 2700 wide.
Slope is falling 120mm over the 3650 width.
I’m unsure what is the best option for this situation:

Was originally thinking a timber frame with legs of different heights and formply on top but it’s a fairly wet area, concerned about how long treated timber legs will last,

Boxed up extra “mini slab” on top of existing concrete (concern is how this will look “built up” on top of current concrete)

Rip up all existing concrete and re-lay and have the new concrete falling towards the side fence instead of backyard 😅

(extreme)

Have also considered the use of adjustable footings similar to those used in decking projects, however I’d like to keep the height I have to raise the shed to a minimum. Site for shed and shed attached.

Any suggestions or tips? Thanks heaps!

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EricL

Hello @ceedub

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your shed base.

I propose building a concrete slab with a formwork that will blend in with your current retaining wall. The advantage of a concrete slab is that it will provide a long service life, it can be sloped in such a way that water will flow away from the shed and because it is concrete it will serve as a good anchor for your shed.

It is possible to build the base and remove the formwork, but I believe that the timber will provide a nice softening aspect to its overall look. I also suggest making the slab slightly bigger so that the shed will not have any issues with alignment.

I've placed a sample image below to give you an idea of what it could look like. Please let me know what you think.

Here is a handy step-by-step guide: How to pour a concrete slab by @tom_builds.

Let me call on our experienced members @Dave-1 and @Nailbag for their recommendation.

If you need further assistance, please let us know.

Eric

Dave-1

Afternoon @ceedub

Mmmm In your sketch/photo I dont see a slope that you are refering to? When I was going through your commenst I was thinking along the same lines as @EricL but instead of a solid concrete base I was thinking more along the lines of a timber edge box (larger then the shed by a little, think you called it "boxing up") and filled with a loose gravel base to allow water to drain freely and also so it would accomodate any slope that is existing.

Have you factored in that the rear of the new shed up against the existing shed may allow water to drain down and flow into the existing shed? I really like that style of shed that you have chosen as its unobtrusive but is large enough to store all sorts of things.

Dave

Nailbag

I agree 100% with @EricL on this @ceedub and go with the built up concrete slab, it's the most solid and practical solution. To cover the 120mm rise in the front, you could consider a sitting a rectangular self contained (plastic lined) garden be in front with the sides tapered to match the fall angle. This could be made of 50mm sleepers that were externally lined with 90mm deck boards to match the existing retaining wall.

Regards, Nailbag.

ceedub

@Dave-1 @EricL @Nailbag

thanks heaps for the replies, much appreciated. It seems the best option is to go for the concrete slab. So it’s better illustrated, I put the frame up and packed it to level to show how much slope there is.

Dave-1

Afternoon @ceedub

Thank you fo the pic 🙂

Idea 1 (tho I like idea 2)

I still like the idea of an oversized box (of the footprint) and then filled with gravel for free drainage. If you want a solid base to the floor then still with the box plus roadbase and then sand plus pavers. That way no ripping up of the concrete you already have.

Idea 2

It dosnt look like you will have to have too high a box to contain the gravel/concrete/pavers. Mmmm you have me thinking. Does the floor have to be level? You could build the shed level, having it sit on the almost the timber you have in play (make sure its treated tho). With the roller door you could add a long triangle wedge that corresponds to the level base of the roller door and the ground as it is now so when the roller door is down it all slots together. You would have to pave that bit of grass area to match but would look least intrusive.

Dave

Nailbag

Thanks for the photo @ceedub Albeit a decent rise, long term it will provide a smooth level surface within the shed, easy cleaning with no trip hazard and something solid to fix the shed frame to. It's still the option I would go with

Nailbag

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