In the diverse housing stock in many older neighborhoods, such as the desirable Rockridge area in Oakland, Calif., three-bedroom homes range in size from about 1,300 square feet to more than 3,000 square feet. To say a house has three bedrooms tells a buyer little about the usable space.

When the number of livable square feet -- square feet excluding such things as decks, terraces, garages, basements and storage rooms -- is not provided in the listing information, buyers often search on their own for this information.

It's not that hard to come up with a figure. Simply go to Zillow.com and type in an address. The square-footage figure that pops up is presumably from the public record. Unfortunately, the "public record" often doesn't reflect reality. It may be accurate for new homes that haven't been modified since the original building permits were approved. The figure is far more subject to error for older homes that have been remodeled over the years.

Remodels are often done without building permits, which wouldn't be reflected in the public record. However, even when add-ons are done with permits, the public record is not always changed to reflect the increase in square feet.

HOUSE HUNTING TIP: It's a good idea for buyers to visit the local building or planning department to find out what documents are on record regarding a listing they're considering buying. This should be done during the inspection contingency time period. If possible, ask for copies of all the permits that were taken out on the property, starting with the original building permit.

If permits for obvious modifications to the property are missing, this could indicate the seller, or a previous owner, took shortcuts. Or, it could reflect a shortcoming in the planning department records. For example, fires in the City of Oakland Planning Department partially destroyed the permit archives.

Buyers often like to compare listings they're considering based on the price per square foot. This is a far-from-accurate way to figure out if you're paying a fair price for a property, unless you're looking at homes in a new housing development where there is little variability.

Also, if the figures you're using are from the public record, which is often wrong, the reliability is even more in question. The most accurate source of square footage is the information from the local permitting agency. If that information is not available, a licensed appraiser can measure the house to provide square-footage calculations.

THE CLOSING: Keep in mind that an appraiser might call a room a bedroom -- even though it wasn't permitted as such by the building department -- if the work was done by licensed professionals and complies with building-code requirements.

Dian Hymer is author of "House Hunting, The Take-Along Workbook for Home Buyers" and "Starting Out, The Complete Home Buyer's Guide," Chronicle Books.

Copyright 2007 Dian Hymer