This question is going to sound like "how long is a piece of string"...
During lockdown we have been thinking about doing a single storey extension (all within permitted development). Now, I've heard that basement extensions are v v expensive, but when we are doing the rear extension how feasible would it be to have a room under just the extension. Would be a useful place to put the boiler/utility room/bikes/garden stuff.
Is this completely loony? or has anyone done anything similar?
In SE london, so any guesstimates on price per sq m would be helpful!