Gribble

Thank you for your reply, it's very much appreciated. We can only lift it from beneath the walls, the nature of the build is that the wood is slotted together and uses gravity for stability, so (if I've understood you correctly) jacking up anything other than the planks of wood that are actually touching the concrete wouldn't work and would only pull the building apart. It's a reall conundrum!

What started out as just a summer house in the garden, has now become a bit complicated and we would appreciate some advice. It is 6m x 8m on a C25 concrete slab which has a damp proof course in it. We naively thought that was sufficient and started to build the cabin. We have the inner structure and first roof layer complete, but have now learned that we needed to put a waterproof membrane on top of the concrete beneath the wood. The only way to do this is to lever the building up a centimetre or so at a time in sections and slide oblongs of membrane in underneath the four walls, then lay a large piece over the concrete inside before screwing all the wood back down. A nightmare, I know... but it is what it is and we can't see any alternative. My question is, what dimensions do the sections of membrane need to be and how much overlap must they have to comply with building regs? We obviously don't want to be doing this again!