andrews

Hi Jack, digging out the old concrete is just too much of a big and messy job. I'd rather work with what I've got.

Russell, the damp and cold will be dealt with. My main issue is the additional weight. I'm looking into using insulation with a screed layer. According to the FeRFA, a floating floor with light domestic traffic and a polymer modified sand/cement screed can have a thickness of 33/55mm of screed over high compressive strength insulation. I've worked out that should add about a ton and a half of extra weight to the extension. Do you think this would be an issue?

My property has a single extension that was built in the 1970's and the walls were constructed using 140mm light weight blocks with polystyrene insulation in between batons, covered with plasterboard and externally rendered. In an ideal world, I'd have the whole thing re-built to today's standards but for various reasons (cost being the main one), I can't do this. From an insulation point of view, the building is fine but I'd like to raise the concrete floor. At the moment, there is a wooden floor floating on wooden joists that were laid directly onto the concrete base. For years this has survived but as you can imagine, it's noisy to walk on and 'feels' cheap. I would like to remove the wooden joists (they are floating) and raise the concrete floor (about 70-80mm) so that I can lay some ceramic tiles. Would this be better done in concrete with a final top screed layer or is it better screeded that thick? A big concern of mine is the additional weight the aggregates will add to the base and the surrounding foundations. Should I be concerned about this? Having had a peek at the foundations around the extension by digging deep down, they do go down further than 800mm and appear to be constructed with concrete slabs at the base and block-work further up. The internal floor area is approximately 5.1 x 2.8m. Any advice would be welcome.