Breeze block shed base supports

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Torx

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Hi folks,

I’m designing a shed which will be 4.8 x 2.4m. I’m not planning to insulate the floor or anything, it’s mainly for storage although I might put a wood lathe in there at some point in the future.

I was planning to put 3 rows of 5 paving slabs down below the framed base, but have come across people using breeze blocks (like below) which are cheap and easy to handle. Thoughts? What base, MOT? Depth?

D6410311-7675-41DD-9736-71566A7BC1EB.jpeg


I’ve read some of the threads here about using 1m deep concrete piers etc. and it’s all made me a bit nervous about whether my approach will be enough, but I really need to make this just a shed and not over engineer it too much.

I’m planning on using treated 2x3 for the floor construction followed by 18mm ply, walls likely the same with OSB / gap / featheredge.

Tips appreciated!
 

Jameshow

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Hi folks,

I’m designing a shed which will be 4.8 x 2.4m. I’m not planning to insulate the floor or anything, it’s mainly for storage although I might put a wood lathe in there at some point in the future.

I was planning to put 3 rows of 5 paving slabs down below the framed base, but have come across people using breeze blocks (like below) which are cheap and easy to handle. Thoughts? What base, MOT? Depth?

View attachment 136059

I’ve read some of the threads here about using 1m deep concrete piers etc. and it’s all made me a bit nervous about whether my approach will be enough, but I really need to make this just a shed and not over engineer it too much.

I’m planning on using treated 2x3 for the floor construction followed by 18mm ply, walls likely the same with OSB / gap / featheredge.

Tips appreciated!
I'd go for 4x2 on blocks every 4ft apart.

I'd dig out a shallow hole and fill with a weak concrete mix and then the block on top of it.
 

eribaMotters

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I really would be thinking about insulating that floor as I'm sure you'll regret it at a later date. Look out for 2nd hand/damaged/offcuts of sheets on the likes of Gumtree, Facebook Marketplace, Preloved etc.

Colin
 

Jones

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I would consider concrete lintels, these are dense concrete which will be better than light weight blocks and will be easy to level , the 3x4 ones will be quite cheap. Your floor design has a lot of superfluous timber, if you space the joists out to 400 centres it will be stronger and less bouncy, the noggins are doing nothing .
 

Torx

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I doubt they are breeze blocks. More likely high density concrete.

You do seem to be able to buy some that are approved for use below a DPC, but you’re probably right

And I'm no expert, but my shed floor is 6 X 2. I very roughly followed Mike G's instructions. He doesn't post here anymore.

I read Mikes thread, but 6x2 seems a bit overkill for this, since your average bought shed is 1 x 1 or something like that?

I really would be thinking about insulating that floor as I'm sure you'll regret it at a later date. Look out for 2nd hand/damaged/offcuts of sheets on the likes of Gumtree, Facebook Marketplace, Preloved etc.

Colin

I don’t plan to be working in there in cold weather, it’s basically for storage, are there other benefits to insulation?

I would consider concrete lintels, these are dense concrete which will be better than light weight blocks and will be easy to level , the 3x4 ones will be quite cheap. Your floor design has a lot of superfluous timber, if you space the joists out to 400 centres it will be stronger and less bouncy, the noggins are doing nothing .

I’ll look into those, thanks. I designed it to be made in smaller parts which I can fix together but perhaps it’s not worthwhile if I’m not gaining anything from the doubled up timbers. How do I make the noggins do something? :unsure:
 

Jameshow

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I would just put one row of noggins in.

Also the extra timber around the perimeter isn't needed tbh. You have the floor and then the wall plate which will be strong enough.
 

morqthana

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You do know that Cheshire is full of animals as will love to take up residence under there? Foxes, rats...
 

Fitzroy

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I built a 6x3m shed a few years back, build thread here, using concrete blocks (not breeze blocks) for the frame to sit on. I dug a hole below each one slightly larger than the block and rammed hardcore into it, the block sits on top, mortar would likely be better but harder work. I would not have been happy stacking multiple blocks without mortar between them.

My base is 6x2 and I had a block roughly every meter. I don't know if it was insufficient support of poor workmanship but when I cam to lay the floor I found I had dips between the blocks and I had to addsome extra, see the post how. A 3x2 frame will just need more support points than a 4x2 or 6x2 frame. How many more I have no idea.

I placed DPM between the concrete blocks and the frame base as suggested.

I insulated the floor with glassroll and was told I'd made a rat heaven. Had no issue in 6years but my garden has 4' high solid granite walls and lots of cats with neighbours. Your milage may vary!

The method means the shed is not anchored down, but mine has not yet blownaway, again our garden is quite sheltered.

Fitz.
 

Jones

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Concrete blocks will be ok but I suggested lintels or fence posts as they're denser so will be less prone to rising damp and will be easier to level up. Noggins or strutting in floors are needed to stop joists capsizing if the joist is tall relative to its width and the span is over 2.5 m which yours is not so no noggins required. A glance at the span tables shows a 2x5 can do a 2.4 m span either c16 or c24 grade which would mean you can miss out the centre block support, might be worth considering the cost/ effort difference. I would use class 3 treated or better class 4 for the base and put a small piece of dpc or slate under the joists where they sit on the support.
 

Torx

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I'd go for 4x2 on blocks every 4ft apart.

I'd dig out a shallow hole and fill with a weak concrete mix and then the block on top of it.

Concrete blocks are cheap, or at least they were and so just bed these on mortar at regular intervals and don't overthink it which will lead to over engineering and increased cost.

Like these?


You do know that Cheshire is full of animals as will love to take up residence under there? Foxes, rats...

Can’t see what I can do about that, same as all sheds? I like foxes and I’ve got a cat…

I built a 6x3m shed a few years back, build thread here, using concrete blocks (not breeze blocks) for the frame to sit on. I dug a hole below each one slightly larger than the block and rammed hardcore into it, the block sits on top, mortar would likely be better but harder work. I would not have been happy stacking multiple blocks without mortar between them.

My base is 6x2 and I had a block roughly every meter. I don't know if it was insufficient support of poor workmanship but when I cam to lay the floor I found I had dips between the blocks and I had to addsome extra, see the post how. A 3x2 frame will just need more support points than a 4x2 or 6x2 frame. How many more I have no idea.

I placed DPM between the concrete blocks and the frame base as suggested.

I insulated the floor with glassroll and was told I'd made a rat heaven. Had no issue in 6years but my garden has 4' high solid granite walls and lots of cats with neighbours. Your milage may vary!

The method means the shed is not anchored down, but mine has not yet blownaway, again our garden is quite sheltered.

Fitz.

Thanks, that’s an amazing build I’m working my way through the thread. I think the price of cladding like that at the moment is out of my budget but it looks lovely. This is a bit of a practise run for a second building which Id like to think would be a similar style.

Concrete blocks will be ok but I suggested lintels or fence posts as they're denser so will be less prone to rising damp and will be easier to level up. Noggins or strutting in floors are needed to stop joists capsizing if the joist is tall relative to its width and the span is over 2.5 m which yours is not so no noggins required. A glance at the span tables shows a 2x5 can do a 2.4 m span either c16 or c24 grade which would mean you can miss out the centre block support, might be worth considering the cost/ effort difference. I would use class 3 treated or better class 4 for the base and put a small piece of dpc or slate under the joists where they sit on the support.

Good tips, thanks. I think I’ll go back to the drawing board this weekend!
 

morqthana

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Can’t see what I can do about that, same as all sheds? I like foxes and I’ve got a cat…
Do you like the smell of foxes?

Pressure treated timber, or composite decking boards, at ground level, screwed into the blocks, fill in the gap between those and the frame with perforated aluminium sheet, galvalnised expanded metal etc. Basically anything that will keep ventilation but won't be chewed through by vermin.
 

JimMc

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There is an old method ( rule of thumb) for sizing floor and roof timbers. It’s take the span ( in feet ) and half it, add 2 and thats the depth in inches. For roof rafters take the span in feet and that’s the depth of timber you need.
For example, If your floor timbers are spanning 6 feet then you need a joist to be (1/2 of 6 = 3 plus 2 ) ie 5 inches by 2 inches.
if you are sizing timbers for your flat or pitched roof then for an 12 feet span you will need (1/2 of 12=6) a 6 by 2 inch timber.

Put in insulation, it’s easy to do at this stage, is not expensive and worth it for storage. Think condensation. You can drape rolled insulation ver the timbers and just nail the flooring on top. This future proofs the shed, if not for you then for a future owner.
Hope this helps.
 

Torx

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I’m being persuaded on the insulation, even if I just do floor. With a 50mm air gap below the floor joists using 4x2 is there any reason not to insulate the full depth of the joist?
 

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