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Groundwork & Foundations

Filling trench foundations with just concrete or hardcore and concrete

Anonymous user 09/03/2024 - 2.34 PM

Hi, I am building a 7x5m shed in my garden. I have dug trenches of 350mm width x 500mm depth for the perimeter, and also a central trench for floor joists support. I will be filling the trench with Concrete 1:5 ratio (Ballast/Cement) and will also use Formwork to ensure the concrete form is 100mm off the ground. So, in total my filling space is 600mm deep. Question: Can I chuck loose concrete blocks/broken bricks/hardcore in the bottom 400mm of the trench, leaving concrete only for the top 200mm or must I fill the entire 600mm depth with concrete? It seems quite overkill to fill all the space with concrete for an all-timber structure on top, used as a playroom. Thank you for your help.

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4 Answers

D C Mcguire Interiors

Rating: 5 out of 5

Bournemouth

you could have only dug down half of that for a timber structure and this would have lasted longer than any timber sheds life span 10/15 yrs

Answered29 September 2015

Anonymous user

yes, you can fill the bottom of the foundation with rumble and them concrete on the top of that. Is this standard size shed? if yes then 60cm foundation is quite overkill.

Answered19 May 2016

Highgate Handyman

Rating: 5 out of 5

Muswell Hill, London

Yes.. That's a very solid footing indeed.

Answered29 May 2017

A1 Building & Groundwork

Rating: 4.5 out of 5

Gloucester

For a shed base a 150mm thick slab is fine. 100mm hardcore base ( type 1 ) compacted. Broken slabs and bricks not recommended , it creates a habitat for vermin as it can leave voids etc.

Answered12 November 2022