Construction question to anyone with handyman skills

[al78]

On the local community allotment there was recently a problem with water butts next to the shed which, over time, became lopsided because the ground has shifted over time (we've had extreme wet and extreme dry over the last few years). This resulted in one water butt overflowing onto the shed wall and seeping through. I have volunteered to come up with a way to make a stable platform to hold these butts so they stay in place and upright when full.

There are four water butts capable of holding somewhere between 200-250 litres of water which means four of them together will weigh close to a tonne when full. I have an idea of materials to source and how to construct a strong platform capable of supporting that weight, but am not sure how best to construct foundations which will hold the frame. One issue is the soil in that location is compacted heavy clay with clay subsoil so I could manually dig down no more than a foot or so. The foundations need to be sturdy enough that they will hold the structure in place even if the site gets waterlogged or if we have a drought and the soil becomes bone dry. Any ideas? I'm currently considering either a fence post spike or dig a hole, fill partly with aggregate, put a treated post into the hole then pour concrete.

 

[Cowley]

On the local community allotment there was recently a problem with water butts next to the shed which, over time, became lopsided because the ground has shifted over time (we've had extreme wet and extreme dry over the last few years). This resulted in one water butt overflowing onto the shed wall and seeping through. I have volunteered to come up with a way to make a stable platform to hold these butts so they stay in place and upright when full.

There are four water butts capable of holding somewhere between 200-250 litres of water which means four of them together will weigh close to a tonne when full. I have an idea of materials to source and how to construct a strong platform capable of supporting that weight, but am not sure how best to construct foundations which will hold the frame. One issue is the soil in that location is compacted heavy clay with clay subsoil so I could manually dig down no more than a foot or so. The foundations need to be sturdy enough that they will hold the structure in place even if the site gets waterlogged or if we have a drought and the soil becomes bone dry. Any ideas? I'm currently considering either a fence post spike or dig a hole, fill partly with aggregate, put a treated post into the hole then pour concrete.

Could you put concrete slabs on sand and build off them? That’s what I did with the cabin in our garden and it’s heavy. Touch wood it’s never shifted or sunk.

 

[al78]

Could you put concrete slabs on sand and build off them? That’s what I did with the cabin in our garden and it’s heavy. Touch wood it’s never shifted or sunk.

That sounds like a possibility, I'll look into that, thanks.

 

[Magdalia]

I'm definitely not a handy person, but when I had a house I had a water butt. Its installation was supervised by my father, who could have bodged for England.

The most important things are to spread the weight of water over a wide area and to keep everything absolutely level. The water butt also needs to be sufficiently high off the ground so that it is possible to get a watering can under the tap.

I built a little lego style square tower with some housebricks, I'd guess 24 bricks in a 2 by 2 square with 3 layers of 8 bricks. I then plonked a big square concrete slab on top, and stood the butt on that, all the time using a spirit level to ensure that everything was level. If everything is kept level, and the butt is in the centre of the slab, then the weight of water will hold the butt upright.

Always draw the water from the tap at the bottom not by dunking the can in the top. It is difficult to get water out of the top without tilting the butt and destabilising it, especially for people who aren't very tall. As soon as the butt is "off centre" the weight of the water will cause it to list. If a butt becomes lopsided then empty it out and rebuild from the bottom.

And where does the water go if there is more rain after the butts are full?

 

[al78]

And where does the water go if there is more rain after the butts are full?

It flows from a small pipe directed onto the ground. Unfortunately there is nowhere to divert excess rainwater so that is the only option (theoretically it could be diverted into the nearby pond but that would require uplifting a section of brick path to run a pipe underneath). It is very rare (I'm not sure it has ever happened) to have all four butts full, the collection is from an 8'-6' shed roof of which half the roof diverts the water into those four butts and a large tree overhangs the shed, so it takes a long time to fill all the butts.

If the butts can hold 0.9m^3 of water in total, the area of roof which can catch rain for those butts is 0.5 x 2.4m x 1.8 m = 1.44 m^2 and the average annual rainfall for Horsham is 871mm, that equates to a maximum possible collection of 1.25m^3 of rainwater over the year. The big overhanging oak tree will prevent a lot of this rain falling on the roof so the actual amount collected will be less than this which may end up being lower than the capacity of the butts even during the autumn and winter when the harvested rainwater is not used.

 

[Magdalia]

It flows from a small pipe directed onto the ground.

This won't help to keep the butts stable, and possibly isn't good for the foundations of the shed either. Draining any overflow into the pond would definitely be preferable. A labour intensive way of doing that is to monitor the contents of the butts, and carry a few bucket loads of water to the pond if they get near to full. But there's a risk of destabilising the butts when just checking to see how full they are.

Ideally the butts should be near to full in the spring to give maximum amount of water in case of a dry summer.

 

[al78]

This won't help to keep the butts stable, and possibly isn't good for the foundations of the shed either. Draining any overflow into the pond would definitely be preferable. A labour intensive way of doing that is to monitor the contents of the butts, and carry a few bucket loads of water to the pond if they get near to full. But there's a risk of destabilising the butts when just checking to see how full they are.

Ideally the butts should be near to full in the spring to give maximum amount of water in case of a dry summer.

It is not ideal but it is very rare the butts get full to overflowing. I think the last time it happened was February 2020 which was the wettest February on record for the UK. Any overflow from the butts was inconsequential as the pond had burst its banks and much of the area around the shed and compost bins was underwater (the allotment is on one of the lowest parts of the site).

To get the butts full over a typical winter would require some hard pruning of the overhanging oak tree. I keep wishing for another October 1987 storm to do the same job but nothing yet. That is one of the other problems, the tree significantly lowers the amount of rain falling on the shed roof which limits how much can be stored over winter. We've had some dry periods in recent years and we cannot store enough to get us through something like last summer or the very dry May - July period in 2018.

It might be possible to run an overflow pipe across the brick path and build a small ramp either side of the pipe to prevent anyone tripping over it.

 

[32475]

After a very dry summer and hose pipe bans, I got hold of a few of these 1000 litre tanks. I made a sturdy timber base with a concrete base to each post and was able to stack one on top of the other. In my case I pump the water from standard water butts up to this high point location so that I get a good natural water pressure to water the garden.
However the simple standard solution is to have a tank adjacent to a rainwater down pipe; put the tank on a base of two or three old timber pallets so that you can fit a watering can under the bottom outlet; connect your down pipe into the top a Bob’s your Uncle.

 

[Bald Rick]

What I would do is dig 300mm deep strips, each strip 250mm wide by 650 long (assuming the butts are around 550mm diameter). The strips need to be perpendicular to the line of the butts, and I’d do 5, along a length of 2400mm, ie roughly 600mm apart.

Fill each strip 120mm deep with concrete. When that’s gone off, lay two courses of dense blocks (440 x 215 x 100) lengthways along the strips but ’lying down’ if you see what I mean (the largest face lying on the concrete) - you’ll need 3 blocks per strip (ie 2 x 1.5 block courses) and mortar them both to the concrete and between the courses. No need to be fussy about the pointing! With that done, the top of each ‘pier’ will stand about 50mm above ground level. Then you have two options:

1) Bridge the piers with cheapo slabs 600x600x38, ie one slab per butt
2) Bridge the piers with concrete lintels 1200x100x65, you’d need 4 or 5 per per pair of butts (Which would leave some gaps)

Both options would need mortaring in.

Building the piers will cost about £75 in materials, the slabs another £50, or the lintels, ahem, about £150. Would prob take half a day for two people (and try not to be the one mixing the mortar / concrete by hand).

Blocks: https://www.wickes.co.uk/Tarmac-Standard-Dense-Block---7-3N-100mm/p/166859#
Slabs: https://www.wickes.co.uk/Marshalls-Richmond-Smooth-Natural-Paving-Slab-600-x-600-x-38-mm/p/144651
Lintels: https://www.wickes.co.uk/Wickes-L03-Steel-Reinforced-Concrete-Lintel---100-x-65-x-1200mm/p/220307


Alternatively dig the whole lot out to at least 200mm and fill with concrete. But for that you’d need a mixer as it would be 700kg of the stuff - about 6-8 mixes. About £100.