Garage or "Cooled" space?

Looking at a home with a converted garage or other recently added space(maybe porch)? Have you converted your garage? Central Austin has a ton of converted garages into living rooms and bedrooms. Increasing the size of small cottages built in the 30's and 40's for better closets and storage has been popular. Depending on the market here are some considerations in pricing if you are a seller or a buyer. Scope of the conversion is instrumental in market value.
Seperate the original square footage from the converted garage space (this can also work for converted porches and other spaces incorporated into the heating / cooling of the house that is noticeable). Typically a 2 car garage is around 400 square feet. If the "original" house was 1600 square feet, with the converted garage we now have a 2000 square feet home. The original 1600 sqft tends to have a higher valuation per foot than the converted space of 400 sqft. Too often, a home is listed at the peak of the market for the area using all 2000sqft.
This can work when having trouble selling your own home or wanting to establish a method of pricing to make an offer. Of course market conditions apply. If you are selling in a buyers market the pricing of the converted space could be lower than higher. Buying in a seller market could mean inventory is low and you don't have many options.