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Extension over existing patio


I'm planning to build full width rear extension 8m x 4m. There is currently a patio that covers the areas we are planning to extend over. The slabs are around 28mm with a sub base around 100mm. Could a lay sand then a DPM following by concrete slab, insulation and screed over the patio? I guess a lot depends on how low below floor level the current patio. I think it's around 20mm. If it's not enough could I remove the slabs and use the existing sub-base? I'd rather not dig it all up only to have to lay another base for the slab.

1 Answer from a MyBuilder Extension Builder

Best Answer

You need to work out your levels and then dig it all up, get your hardcore down, your dpm, insulation and slab over (or insulate over the slab - whichever you prefer). You have no idea what the ground is like under the patio and laying a floor slab is a lot different to laying a patio....If still unsure, get a good builder in to do the ground works for you - its the most important part of the build....if the foundations are bad, then you are heading for failure...


Answered 14th Mar 2015

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