For Our Clients - Square Footage

*For Our Clients is a series of blog posts directed towards our current clients.  There are certain concepts we explain on each project and it's far more efficient to write it once and share than to write it again on every single project.  Writing about these topics as blog posts allows them to be a possible help to others as well.*

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Square footage and how it's calculated are a topic that come up on just about every project we do.  It's one of those things that everyone knows is really important (maybe too important), but very few people actually know the particulars of it.  In this post, I'll demystify square footage and how it's calculated.

First of all, when we're talking square footage we usually deal with two different numbers.  The "Heated & Cooled Area" and the "Total Construction Area".  The former refers to the "inside" areas of the home.  The spaces that will be conditioned.  The latter refers to that plus everything else.  So your Heated & Cooled Area PLUS your garage, porches, patios, and anything else drawn on the plans.

One of the biggest things that most people don't know, because most people don't ever think about it, is WHERE these areas are measured.  Walls have thicknesses to them.  You could measure to the center, to the exterior, to the interior . . .so where?

The exterior of the framing.

Almost all of our areas are calculated from the exterior of the framing.  Why?  It's what I like to call the "lock line". Nothing inside or outside of this line will change.  

If you change materials inside or outside of this wall, it will affect the thickness of the wall. Say you planned to use fiber cement siding on the exterior, but after getting your completed plans you decided to go with brick instead.  That greatly affects the thickness of your exterior walls.  But it won't affect your plan dimensions or your areas because those have been done to the exterior of the framing.  You could also change your interior finish material or even change from 2x6 stud walls to 2x4 or vice versa.  Anything that changes inside of that measured "lock line" will flex to the inside and anything that changes to the exterior of it will flex to the outside.  Simple right?  Sort of!

What does this mean for you?  It means if we say your heated & cooled area is 2400 SF, that doesn't mean you have 2400 SF of clear interior space.  A small amount of that is chewed up in framing.  Often 100 - 200 SF or more.

Let's look at this simple house for example.​  The overall dimensions go to the exterior of the framing, which is the industry standard.  (To the exterior of the framing on exterior walls and the center of the framing on interior walls . . .in case you were wondering.)  You can see this simple house is 40' x 28'.

When we measure that area it's simply 40 x 28 = 1120 SF.  Grade school math anyone??

See, simple and easy!  However, if we were to measure that same little house to the interior of the walls we would end up with an area of 1053 SF.  What's wrong with this?  Well, this house has 2x6 exterior stud walls and a 1/2" drywall interior finish.  If we were to change any of that, the number would change.  Change to 2x4 stud walls?  Change to 5/8" drywall or wood?  The number would change.  Same thing on the exterior.  Skewed numbers.

So why is that an issue?  Well, if you're basing your construction cost (and other things) off of a number, you don't want that number constantly changing.  You want it to stay the same as much as possible.  That's why we measure it to the place where it won't change.  The exterior of the framing.

And there we have not so basic square footage explained.  If you are a current client, potential client, or just have a question, feel free to ask below!  I can't explain what anyone else does, but I can sure try to explain how we do it here at Building 313.

As always . . .devoted to design,

​Megan  :)