Hi
We're moving into a house that already has an established downstairs extension with a flat roof. We'd like to build on top of this to extend one of the bedrooms so you're looking at about a 10ft x 10ft (3m x 3m) extension with a roof and probably en suite. I'm told the existing extension has proper foundations to support the extra weight. We're being quoted between 20K and 30K for this work. Does this seem expensive? Going on the rough quide of 1K per m2 this should only be about 10K, maybe up to 15K as it's got a roof and en suite (this is above an existing bathroom so plumbing shouldn't be an issue)
Or do I have my sums wrong (entirely possible!) This is in Hertfordshire.