Portland Area Real Estate Appraisal Discussion

How to Calculate Square Footage of a House
June 2nd, 2016 12:25 AM

How to Calculate Square Footage of a House
One small part of what real estate appraisers do is
measure homes to calculate the living area or “square footage.”  The standard that is typically used by most home appraisers to measure and calculate living area is provided by ANSI (American National Standard Institute).  However, in this post I’m focusing on the geometry and simple math of determining the total area.

Normally, appraisers draw homes using software that automatically calculates the area.  Our company recently measured a home of an engineer by using just such software.  After examining the computer generated home sketch, the engineer said that the upper level of his home (shown in the illustration above) had been incorrectly calculated.  He then provided his handwritten calculations as support. 

When I heard this, my stomach knotted up and I thought, “Did this engineer find a bug in our software?”  A Quality Appraisal associates measure many homes each year all around the Portland area.  I thought, “Is this an isolated bug or something that could have caused errors in hundreds of appraisals or measurements?”  We don’t manually check the calculations of the software on all of our measurements before they are delivered to a client.  Maybe we should.

I could not wait to get back to my office and check for myself.  Once in the office, I deconstructed the drawing into five smaller shapes (a composite figure and some appraiser software will do this automatically) and then I was able to easily calculate the area as shown in the figure above.  To my relief, I came up with exactly the same number as the software total for the upper level.  After this experience, I concluded it is good practice for appraisers to occasionally check the calculations totaled by our sketching software.  For more information on how to deconstruct a composite figure and add up the individual areas, here is a short helpful video from Mathtrain.TV.

Did I leave anything out or do you want to join in the conversation?  Let me know in the comments below.

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Thanks for reading,

Gary F. Kristensen, SRA, IFA, AGA

Wow, my stomach was in knots as I read that the software calculations may be off. Good to see they were not but that is a great idea to double check the calculations from time to time. Thank you for the helpful video you've included showing how to find the area of a figure. I'm curious what you told the engineer about his calculations?

Posted by Tim Packard on June 2nd, 2016 12:36 AM
Thank you Tim for following. I presented the measurement calculations to the engineer exactly the same way that I presented the information here and he never responded to me directly. He did tell his real estate agent that he was ok with the floor plan measurements now.

Posted by Gary Kristensen on June 2nd, 2016 12:43 AM
Nice job, Gary. I'll admit it's been a while since I've heard the word "isosceles" as you said in the video. Nice throwback to Geometry class. I honestly did not like Geometry when I took it. I don't think my mind was ready for it when I was 14 or 15. Yet here I am today using it all the time. :)

Posted by Ryan Lundquist on June 2nd, 2016 6:38 AM
Thank you Ryan for following and watching the video, but this is not my video. This is just a video that I shared.

Posted by Gary Kristensen on June 2nd, 2016 9:29 AM
Ryan, I just added a comment in the blog as to where the video is from. You're not the only one who thought that video was me.

Posted by Gary Kristensen on June 2nd, 2016 9:34 AM
Gary, Nice post. Just like Tim, I was curious about the engineer's response. Fortunately the error was with his calculations.

Posted by Casey Lyon on June 2nd, 2016 11:05 AM
Thank you for following Casey. Yes, what a relief to not call into question all of the Portland home measurements we have done in the past.

Posted by Gary Kristensen on June 2nd, 2016 11:40 PM
Great post Gary. Thanks for breaking it down to something easy to understand. I think this can help agents who rely on county records because it can show them that measuring a house is not that difficult, especially smaller homes with more basic shapes that they can do themselves. If they have a larger home with more difficult angles that they are not comfortable they can then hire someone with more experience.

Posted by Tom Horn on June 4th, 2016 6:51 AM
Looking at the above sketch, it looks like you included the stairwell in the total GLA. So I would think that the Architect was correct in that the upper floor calculation was wrong.

Posted by Robert on June 5th, 2016 11:53 AM
Thank you Tom and Robert for your comments. Tom, you're correct, the more complicated homes probably do need an expert to measure the home. Robert, I'm glad you pointed that out. The example home was measured using ANSI standards (Click on the ANIS link in the article and read the caption for Figure 6 on page 11). There are other home measurement standards used in other parts of the country that do not include stairways. In Portland, we measure using ANSI standards and include stairways. Also, the engineer that thought the area of the second floor was incorrect, thought we were too low in our square footage measurement estimate, not too high. I really do not know how the engineer came up with something larger using the same measurements.

Posted by Gary Kristensen on June 5th, 2016 2:28 PM
Gary, you are so right about doing a double check every once and a while. It helps keep us on our toes! Hope you have continued success providing accurate measurements in the Portland area!

Posted by Conrad Meertins on June 11th, 2016 3:30 PM
Thank you Conrad for following. You're correct, double checking is so important in home measurement. That is absolutely the name of the game.

Posted by Gary Kristensen on June 13th, 2016 1:17 AM
Very well written that my stomach dropped reading it. I as well will tell the homeowner the calculations. I typically find that if it's within the ball park of what they were told they when they were buying it they don't care all that much; however, I don't recall any of them being an engineers.

Posted by John Tsiaousis on June 23rd, 2016 6:35 PM


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