fill foundation trench to what level below ground level?

30 Apr 2008
Reaction score
United Kingdom
Hi, was hoping to get some advise re: a small outbuilding I'm building at the end of my garden.

my footings are going to be 2 m deep since i live in a clay soil area and there is a small tree 1m away.

question is how far below ground level should i start building. SHould i fill the trench to ground level and start building my blockwork from there? if not how far below ground level should my footings stop and my blockwork start (i presume that any building below ground level will be frostproof bricks?)

Thanks for your help.
Sponsored Links
Sort out the floor level, which will be the DPC level and guage down from this to work bricks or blocks - bearing in mind you need a minimum 225mm frost cover (ie frost rated bricks or blocks) if the wall is going below ground level.

Your concrete can finish anywhere below ground level but remember the paving or whatever so finish it at a suitable height so that it wont be seen
if ground conditions do not deviate too wildly, then an ideal concrete height is 7 courses of bricks below dpc.

this translates to 525-530mm or about 21 inches (below dpc).

what this means is you will have two courses of blocks plus one course of bricks on the inner leaf.

having a top course of bricks on the inner leaf means that when it comes to screeding, you can remove the top course of bricks, within any external door opening and allow the screed to meet the door sill.

it is easier than trying to hammer off the top three inches of a 7n block, anyhow. ;)

this situation also allows plenty of room for drain gullies.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links