Spray foam math.

wpid1737-SMF6103.jpgOperation Insulation is moving along nicely.  Lots of light tan walls.  Tight is right.  A very noticeable change in the “feeling” within the house.  (Already much quieter.)

It’s also giving us yet another opportunity to appreciate how points of view around simple subjects can sometimes differ.

For example, let’s say — hypothetically — that a contract specifies : “Wood Framed Roof Assembly: 8” high-density closed-cell spray foam urethane insulation (R-49 minimum).”

One point of view might be 8″ equals 8″.  7″ + 1″.  Carl Yastrzemski’s jersey.  The number of maids-a-milking.  Trying from another perspective, there are 12″ rafters in the roof.  That’s an 11 1/2″ nominal width.  After spray foaming, you might expect to see 3 1/2″ of rafter sticking out.  And that conveniently equals the width of a 2×4.

The other point of view might be that 8″ is really equal to 6 3/4″.  Apparently when done correctly, 6 3/4″ of spray foam is equal to R-49.  Toss in that it seals the house much better and it’s far better than R-49 of fiberglass.

One definition.  Two very different points of view.

Math is funny that way.


The roof over the entry is also the floor of the upstairs bath.


Bulkhead entry.


Roof rafters on the 2nd floor.

3 Comments on “Spray foam math.

  1. Pingback: And now 3″ equals 4″ | A House In A Field

  2. “A very noticeable change in the “feeling” within the house. (Already much quieter.)”
    When I install Spray Foam Insulation I always notice a difference in the sound of the home throughout each room. Its a great way to get privacy within your home as well as reduce energy costs.

  3. Great stuff. Math definitely is funny sometimes. I myself think that houses get much quieter after installing spray foam installation.

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