I have just recieved plans for a single storey extension to the rear of my house. The drawings state the foundations are to be 600×150 at a depth of 900mm (dependant on the ground). I assume this is a minimum for strip foundations. If I use 900mm x 600mm trench fill foundations instead will this be ok with the building inspector? I believe this is the quicker and cheaper way to do it?

  • Mark Brinkley

    There is unlikely to be any issue with the building inspector if you want to switch to tench fill, though I would question whether it is necessarily cheaper (though it will be quicker). However what usually happens is that the final decision on foundations is made on site when the building inspector takes a look at the trench bottom. This is far more meaningful than sticking with a notional drawing of how the foundations might work, under ideal circumstances.

  • Geoff

    As already answered it is not usually any problem to use trench fill. It is often preferred simply to avoid awkward construction in a trench and to save time. I would however suggest you keep the top level at least a couple of brick courses below finished ground level on a level site as this will give greater flexibility in external finishes. For sloping sites, steps may be required in the top level.

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