Expert: Richard Taylor, AIA - 12/22/2005

Question
When houses are listed for sale either new or resale, they list a square footage for the size. Is the square footage figured using the outside wall dimensions or the inside wall dimensions?

Answer
Gerald - thanks for your question!

You've hit on an issue that's been a thorn in the sides of architects, builders, bankers, realtors, appraisers, and confused owners for years!

The problem is that there's no adopted standard - everyone measures it differently.  There has been a move in the last few years to create a universal standard like the one architects use, but it isn't mandatory.  The one thing that is always true is that area is never measured from the inside of the walls - the area of a house always includes all wall thicknesses interior and exterior.

More often than not, builders and realtors want to show the largest number they can - so they measure the entire perimeter of the house on both floors.  They may or may not include porches, stairs, and two story spaces.  Since you don't know their basis, it's very hard to compare one house to another.  That's not accidental.

A relatively impartial source is your county auditor - they calculate the size of the house for tax purposes, and therefore measure all houses the same way.  And although their measurements aren't always a true reflection of the size of the house, they use the same protocol - so it's easier to compare one house to another.  Auditor information is public record so you can get access to it.  More and more auditors are online now, which makes the finding of real estate information - including areas - very easy.

Here's the way we calculate areas at our office.  We measure the perimeter of the house at the exterior wall sheathing - not the siding or brick, just the wood-framing - on both floors.  Next we subtract the upper part of any two-story spaces and deduct the area of stairs on the second floor (since they've already been counted on the first floor).  Spaces that are less than 6' high aren't counted in the "main" number (areas with sloped ceilings).  Instead, we list those areas separately.  In fact, we show a listing of square foot areas that lets you know where the areas are being counted from, something like this:

First floor: 2,000 sf
Second floor: 1,500 sf
Subtotal heated areas: 3,500 sf
Finished basement: 1,000 sf
Total heated areas: 4,500

Screened porch: 200 sf
Open porches: 200 sf
Garage: 600 sf
Total unheated areas: 1,000 sf

To simply say that this house is 5,500 sf or 4,900 square feet, or (if you included upper volumes and stairs) 6,000 square feet, would be misleading.  It's more informative to say it's a 3,500 sf house with a screened porch, garage, and finished basement.

The best you can do right now (other than measuring it yourself) is to ask the realtor their basis for measurement.  What's included in the number?  It's a good guess that many won't know.  If they want to sell you the house however, they'll find out for you!

Hope this helps!

Richard Taylor, AIA
Richard Taylor Architects, LLC
www.rtastudio.com
www.betterhomedesign.blogspot.com