Shed base

[AdamD]

Looking to install a solid base for 8ftx8ft shed - best approach dig down, hardcore (3inch?) then 3 inch of concrete on top?

 

Any other considerations?

[Temp]

Don't just put a shed on a concrete base that's bigger. Rain lands on the perimeter and runs under or rots out the bottom.

 

Either raise the shed on a coarse of engineering bricks or make the slab slightly smaller than the shed and raised above the surrounding ground. The idea is rain hitting the walls of the shed drips off onto the ground not the top of the slab. You can also put gravel filled trenches around to reduce splashing up onto the walls..

 

I'd probably go for 100 + 100mm.

 

 

 

Edited June 3, 2023 by Temp

[AdamD]

10 minutes ago, Temp said:

Don't just put a shed on a concrete base that's bigger. Rain lands on the perimeter and runs under or rots out the bottom.

 

Either raise the shed on a coarse of engineering bricks or make the slab slightly smaller than the shed and raised above the surrounding ground. The idea is rain hitting the walls of the shed drips off onto the ground not the top of the slab. You can also put gravel filled trenches around to reduce splashing up onto the walls..

 

I'd probably go for 100 + 100mm.

 

 

 

 

Thanks. Any other suggestions for a good base, or would that be the best bet what you said?

Starting with a clean slate of soil so want to get it right.

[Temp]

This is what I did on a bigger outbuilding with tiled roof. How much is necessary I don't know..

 

Install duct for electricity. I used rebar hammered into ground and cable ties to hold duct in position. 

Level ground and compact with wacker plate.

Add hardcore and compact in two layers.

Add 25mm sand blind and compact.

Add shuttering and plastic sheet to stop concrete losing water before it sets up.

Pour concrete and level with top of shuttering.

Push heads of long bolts into the concrete to later bolt building down. I used threaded rod and nuts.  Support while concrete sets if necessary. Put lengths of pipe over bolts to stop you being impaled if you trip over.

 

 

 

 

[Adsibob]

Other easier option is that it’s tear of pouring a concrete slab, you buy the plastic interlocking grids/trays. That will cost you about £120. Then you have the option of filling them with peashingle for extra stability/sturdiness, but it isn’t essential. You could just fill the grids at the perimeter or skip it altogether.

 

Edited June 3, 2023 by Adsibob

[Onoff]

You must have any "timber" at least 6" off of the ground.

[Adsibob]

15 minutes ago, Onoff said:

You must have any "timber" at least 6" off of the ground.

Says who? If the timber is treated regularly, it could be underwater. 

[Marvin]

Hi @Temp

 

I don't extend the concrete founds past the face of the stud walls to try and keep the concrete protected from the rain. 

[Onoff]

13 hours ago, Adsibob said:

Says who? If the timber is treated regularly, it could be underwater. 

 

You're funny 👍 Go for it and see how long it lasts. 

[AdamD]

On 03/06/2023 at 16:12, Adsibob said:

Other easier option is that it’s tear of pouring a concrete slab, you buy the plastic interlocking grids/trays. That will cost you about £120. Then you have the option of filling them with peashingle for extra stability/sturdiness, but it isn’t essential. You could just fill the grids at the perimeter or skip it altogether.

 

Yeah I’m going down this route i think, far easier than concreting.

Would I still need a hardcore base if I used this? If so, how deep? 3 inches of compressed hardcore then the plastic grid and then shed base?

[Iceverge]

On 04/06/2023 at 08:37, Onoff said:

 

You're funny 👍 Go for it and see how long it lasts. 

 

Plenty of electricity poles > 50 years old surviving just fine. 

 

Mind you the intensity of creasote treatment would give you sunburn. 

[Onoff]

1 hour ago, Iceverge said:

 

Plenty of electricity poles > 50 years old surviving just fine. 

 

Mind you the intensity of creasote treatment would give you sunburn. 

 

Traditional railway sleepers too.

 

He's talking I think though about "ordinary" pressure then subsequently DIY treated timber. It won't last underground. 

[Adsibob]

1 hour ago, AdamD said:

Would I still need a hardcore base if I used this?
 

Need is a strong word, but yes it’s recommended to do that.

 

 

1 hour ago, AdamD said:

 

If so, how deep? 3 inches of compressed hardcore then the plastic grid and then shed base?

That’s pretty much what I did, though slightly less. Maybe only 5cm or 6cm.

Edited June 5, 2023 by Adsibob

[Chanmenie]

I used the gravel grids 

https://www.ibran.com/products/plastic-shed-base

i think they are great, timbers stay nice and dry.

 

Edited June 5, 2023 by Chanmenie

[AdamD]

5 minutes ago, Chanmenie said:

I used the gravel grids 

https://www.ibran.com/products/plastic-shed-base

i think they are great, timbers stay nice and dry.

 

Nice. Sub base as well?

 

Cut the grid to the size of the shed or a slight over/under hang?

[Adsibob]

1 minute ago, AdamD said:

Nice. Sub base as well?

 

Cut the grid to the size of the shed or a slight over/under hang?

Definitely over, at least by 12cm extra, so if your shed is 300 by 400 go for 324 by 424 base. I also ordered the shed to have a roof overhang. On the front elevation the overhang is about 50cm. I made the shed base about 40cm buffet on that elevation, and this enabled me to put a doormat outside the shed and keep it dry. Wish I’d done the same on my actual house!

[Chanmenie]

The ground was just sandy gravel, after I’d removed the topsoil so compacted that, put down a weed membrane then levelled the grids and filled with 10mm crushed gravel.

Crushed is much better than shingle as it compacts so much better.

no didn’t cut the grids I left overhang 

[AdamD]

How much sub base and what type? 50-60mm depth for the aggregate do the job?

[Chanmenie]

I didn’t need to add sub base, I compacted what was already there as it was sand and gravel. My whole plot is sand and gravel.

So depends on your ground, but the grids spread the load so 60 -70 mm of compacted crushed concrete should be fine,

Assuming you won’t be parking cars in the shed 😀

[AdamD]

7 hours ago, Chanmenie said:

I didn’t need to add sub base, I compacted what was already there as it was sand and gravel. My whole plot is sand and gravel.

So depends on your ground, but the grids spread the load so 60 -70 mm of compacted crushed concrete should be fine,

Assuming you won’t be parking cars in the shed 😀

Ahh yes, fair enough. Fairly soft soil here so guess I need hardcore first.

I am thinking 60mm hardcore then the grid filled with pea gravel.

[AdamD]

Are most of the plastic grids much of a muchness in terms of quality? B&q etc ok?

[saveasteading]

1 hour ago, AdamD said:

Are most of the plastic grids much of a muchness in terms of quality? B

No. The thickness and strengths vary dramatically. 

But for a shed base.? No they should all be ok.

Note that smaller grids usually result in less waste.

 

60mm hardcore is stingy. You wont fall through, but it might move after construction.

 

Have you decided how to hold the shed in place?

Edited June 6, 2023 by saveasteading

[AdamD]

4 minutes ago, saveasteading said:

No. The thickness and strengths vary dramatically. 

But for a shed base.? No they should all be ok.

Note that smaller grids usually result in less waste.

 

60mm hardcore is stingy. You wont fall through, but it might move after construction.

 

Have you decided how to hold the shed in place?

How much sub base would you suggest?

 

the shed itself is screwed into the base. How would you suggest securing the base itself?

[saveasteading]

For my greenhouse I used first a geomembrane, then 100mm hardcore and blinding which has to be exactly level.

Then another layer of membrane, then the grids.*

 

For fixings I replaced the grids with paving slabs at the corners and half the long length and screwed into them.

 

* actually I used a vapour control layer to allow water to escape downwards (greenhouse spills) but keep dampness below.  A bit "off the wall" but seems to work.

 

It has been 5 years now. The grids have moved a bit, perhaps 5mm here and there.

Winter storms haven't budged it, but I put the hanging baskets in there for winter as hanging dead weight.

 

I would recommend gutters to limit the water splashing down the sides.

[AdamD]

Thoughts on this one?

 

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