DIY Pier and Beam foundations

RobAMerc

I am planning a sizable wooden shed in my back garden on fairly uneven ground.

I think given the ground level and my being a lazy git, I will therefore try to avoid digging it all level and build a pier and beam foundation.

My plan is to dig 18" round holes in strategic spots cut the end of some 18" ish black bins as forms, level out by using the tops of the forms, and pouring the postcrete mix ( maybe ) into these.

The shed will be about 5m*4m ( although not square )

What do folks think?

listermint

There is a thread on this by Lumen very recently

I suggest looking it up.

Posts done like that will rot relatively easily / quickly in Ireland.

RobAMerc

thanks listermint - I had a look. I think the referred to post was regarding posts buried into the soil with postcrete to secure.

I am talking about making concrete pads and laying the beams of the floor substructure on top of them ( on a damp proof course to protect the wood )

Have I got the wrong thread ?

Thanks Again

Lumen

Honestly, if you want to be a lazy git, pour a reinforced slab with readymix out of a truck.

But I like your idea too.

When you say "uneven" do you mean "sloped"? Because that's the only thing that makes slabs harder. I did one of those for my oil tank project this spring.

RobAMerc

its a long old hike from where the truck would do the pouring to where the slab would be. thats no shortcut !

The ground is uneven as in a big mound in the middle with ditches at one end near a wall and its a bloody tough dig as its chock full of roots and vegetation.

Lumen

OK. Have you done the maths on how much concrete you need to fill your 18" bins. And what's under them? Subsoil? 804/SR?

As I understand it (not well), foundations work either by having a large thin layer resting down on the earth (slab), or by having a series of tall thin pillars resting sideways on the earth (pile). It maybe that your proposed bins are neither one thing nor another.

Maybe consider getting someone in to put in proper pile foundations. Or you could attempt a diy by driving steel pipe into the ground with a post basher and filling with concrete, but I don't know how far you'd get without a hydraulic post basher on a digger/tractor.

RobAMerc

I've not really done any calculations yet, I am at early conceptual stage! :pac:

Really what I was thinking was a diy version of these with the concrete forms used to allow me get an accurate level.



My intention is to use dig 18" square holes with a relatively horizontal base. fill with 804 as a base and then pour my piles on top to get the frame off the ground and level.

My Dad said - "Why are you not just using using building blocks" - he has a point but I imagine it would be move difficult to level them.

Glass fused light

RobAMerc wrote: »

The shed will be about 5m*4m ( although not square )

What shape do you intend to have?
Anything other than a square or a rectangle would be quite complecated to roof.

What are you intending to use the shed for?

RobAMerc wrote: »

My plan is to dig 18" round holes in strategic spots cut the end of some 18" ish black bins as forms, level out by using the tops of the forms, and pouring the postcrete mix ( maybe ) into these.

the weight of the building (gravity) flows down into the foundations, so you need to figure out the building and it's eventual contents to figure out the number of pads needed. And make sure all the foundation pads are level. rather than bins I would suggest PVC groundworks piping (wavin etc) as it would be better to accurately cut to lenght and could be cut and adjusted in the ground. Consider how to go about embedding the bracket's fixings into the pad too.

Have a read of this
https://www.boards.ie/vbulletin/showthread.php?t=2057890777

If the site is a mess of different levels and plantlife I would think about spending time spraying and using a (mini) digger to ger the best out of the site before starting the shed.

RobAMerc

Glass fused light wrote: »

What shape do you intend to have?
Anything other than a square or a rectangle would be quite complecated to roof.

Really it needs to be more pentagonal - but with 3 right angles ( rough sketch attached )
My intention was to shim rafters up on the back upright frame ( longest ) with a slight pitch to the front and then basically deck with OSB and get it ( or attempt myself to ) fiberglassed.

Glass fused light wrote: »

What are you intending to use the shed for?

Its a shed initially but my wife thinks it could become a garden room.

Glass fused light wrote: »

the weight of the building (gravity) flows down into the foundations, so you need to figure out the building and it's eventual contents to figure out the number of pads needed. And make sure all the foundation pads are level. rather than bins I would suggest PVC groundworks piping (wavin etc) as it would be better to accurately cut to lenght and could be cut and adjusted in the ground. Consider how to go about embedding the bracket's fixings into the pad too.

Have a read of this
https://www.boards.ie/vbulletin/showthread.php?t=2057890777

Yes, I had thought of that, hadn't thought about how much easier they would be to cut, thanks its a great insight!
Will read the post tonight, thanks

Glass fused light wrote: »

If the site is a mess of different levels and plantlife I would think about spending time spraying and using a (mini) digger to ger the best out of the site before starting the shed.

The site is already sprayed and its very shaded so little growth there anyway.
When you dig there is a serious amount of roots etc, it seems to be very compacted too, making manual digging difficult.

Borzoi

RobAMerc wrote: »

My intention is to use dig 18" square holes with a relatively horizontal base. fill with 804 as a base and then pour my piles on top to get the frame off the ground and level.

My Dad said - "Why are you not just using using building blocks" - he has a point but I imagine it would be move difficult to level them.

I did a similar job for a shed, actually an old site office container so steel, 3 X 6mtr. Again similar uneven ground. And I wanted air underneath the container to slow down rusting.

I did four corner pads. Each approx 18" square. I dug down about 12", half filled with hardcore, then a concrete pad about 6" thick made with s homemade former. On top and to raise levels I used 9" solids, 2 or 4 per pad, and topped those with a 16" paver about 40mm thick. Job done.

Getting the container craned in was another issue ☹️

my3cents

I'm about to extend our 20 x 12 foot shed (another 8ft) and I'm going to use exactly the same foundations as I did before.

We are in a location that can flood so the shed is about a foot off the ground.

All I do is take off the surface soil down to the subsoil for each foundation pad and fill with a dry sand and cement mix (3-1) and then level up a block on its side in the hole. Its not too hard to level the blocks up as its easy to take out or add the dry sand and cement mix (wear gloves). I then put 3-4 blocks flat on there sides on top of the first bedded in block to get the required height. Tolerances for me would be to the nearest 1/4 inch (blocks are 30 inch centers down the length of the shed and four pads of blocks across the width) because the tolerances of the shed base would be poor so some wooden packing blocks are always needed anyway. Even though the blocks are just layed on top of each other I have never had any of them crack as one might expect. The dry sand cement mix goes solid in a couple of days.

GreeBo

RobAMerc wrote: »

Yes, I had thought of that, hadn't thought about how much easier they would be to cut, thanks its a great insight!
Will read the post tonight, thanks

You should be able to get similar to sonotube from any builders provider, just ask them for concrete formers, then you can get a nice pad raised above the ground, cut them so the tops are all level and pour away.