Building Control will usually ask for confirmation from an SE as to the load-bearing capability of both the foundations and the superstructure.
The SE will look at the existing loadings to foundations, then the loads with the new structure applied. If the increase is more than, say, 10 to 15%, then strengthening works are likely to be required. This does not mean that all the foundations will require strengthening, just those where the loading increase is too high.
However, depending on the condition of the bungalow as a whole, he may well determine that it's too fragile in its current form to put any extra loading on, without causing problems and that remediation of the foundations is definitely required.
He will also give consideration to the condition of walls and lintels over openings that will be required to accept the new loading.
Sometimes it's not obvious which internal walls are load-bearing, in which case he will need to come and do some exploratory works beforehand; sometimes he will need to make what is currently a non-load bearing wall take load.
Having said all that, generally, if the bungalow is in an ok condition, then sticking a room or rooms upstairs will, for the majority of instances, not require any major works to be carried out to the foundations.
