2 story or single story for a 557sqm block

hi there

i am in the final sstages of making a decision on a renovation of my house. a 1950's red brick 3 bdrm on a 557sqm house set back 7.5 from the front

i have had several quotes and am stuck on deciding between 2 that i am happy with with regard to price and design

one is single story. rear extension (@ 66sq) with an open plan living / alresco. the end result will be a 3 bedroom / 2 bathroom but twice the curent size. 

the second is a double story, adding 60sqm to the top and opening the bottom (removing most walls).  the end result is a 4 bedroom 2 bathroom

both cost close to the same amount.  the single story is 145 + 50 to finish and the second story is 155 and about 50.

the big advantage i see of the second story is a save the back yard

from a re-sale perspective is there a clear winner?  if it was going to cost me similar amount to do a double story extension of 60sqm vs a single story rear extension of abit bigger, would i necessarily go with the double story?

i like the idea of the extra bedroom and having 2 living areas of the double story, but i the downside is i dont have the undercover outdoor area (as i cant afford to do this as well at the moment).

one of the big advantages of the double is i dont have to move the sewerage / storm water lines – whereas if i do the single this has to be moved as the house extension will build over the boundary trap

one thing i am worried about wth the second story though is having to meet the energy rating requirements (the wall of the down stairs area is not insulated it is brick veneer).  i am replacing the windows and i realise these may need to be double glazed but can council force you to install wall insulation (this would be a big unforeseen cost i think)

thanks for your opinions