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Concrete slab vs trench foundation for SIP outbuilding

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I am planning to have a SIP outbuilding built at the rear of my garden. It will come as a kit from the fabricators and will measure 6m x 4m. I will also having decking installed around the structure which will be 2m wide and will need to put a concrete slab down for it. I am thinking about the following 2 options for the foundations:


Opt 1: dig a trench and fill with concrete and install sole plate (and sips) on 7N concrete block frame - as I am limited to a 2.5M height this will allow me to install 100mm insulation and screed.


Opt 2: install a 200mm concrete slab (100mm hardcore + 100mm concrete) measuring 10m x 8m upon which I fix the SIP structure and will give me the necessary 2m around it for the decking and leave the insulation out, as height would be reduced


Option 2 would be cheaper but am wondering how much impact not have insulation would be?


Thoughts/advise would be greatly appreciated





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This really depends on what the outbuilding is to be used for? I assume a nice living space given you want decking, hence insulation might be better. But again all relates to what you want to use the space for. 

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