Trench block - How shallow can i go

[Mick Leek]

Hi all...

Firstly i would like to say well done to tony for providing such a valuble source of information...

Ok creeping over, now to business. I am in the process of doing a small DIY project, namely building a single storey extension at the side of my house. i have dug the footings, laid 12" of concrete and am now at the stage of building to DPC. I have read up on Trench blocks and feel these would be easier to start with than concrete blocks.

My question is, after reading within this site about frost protection of the footings, does this also apply to the trench block ? i notice these are areated and will hold quite a lot of water in them. If i were to use 2 courses, this would leave me only 1 face brick below the final finished patio level and a further 2 courses above the patio to the DPC.

Will this be ok ??? or shouldnt the blocks be left so shallow...

Thanks gang in advance.

Regards,

Mick.

[farmerboy]

what you have described is to current NHBC guidelines. so you should be ok. Forgive me if its not word perfect with the guidelines but i'm doing footings all the time to that spec under nhbc supervision and they dont have a problem.

[Mick Leek]

So the fact that the blocks will be a matter of only 3 to 4" under the top of the block paving is ok ?

I was told that frost could and probably would freeze the blocks with being so shallow causing damage.....

But if you do this without any problems on hundreds of new houses then that will do me..

Thanks Farmerboy..

[Tony McC]

AFAIK, Trench blocks are completely frost resistant, so there shouldn't be a problem.