State of Washington Energy Code for new homes—Efficient Building Envelope…
New Construction is based on a point system. A Small dwelling unit (<1500 square feet of conditioned air space and <300 square feet of fenestration area) needs .5 points, a Medium dwelling unit (>1500 and <5000) requires 1.5 points and a Large dwelling (>5000) unit 2.5 points.
You can earn points for an efficient building envelope; air leakage control and ventilation; high efficiency HVAC equipment; efficient water heating; and, renewable energy.
It is a builder’s and/or consumer’s choice of what to do to comply with the code.
I would like to define some words that will help understand the code regarding efficient building envelope:
Fenestration—the design of doors and windows
U-value—a measure of efficiency for doors and windows—the lower the number the better
R-value—a measure of efficiency of insulation—the higher the better
An efficient building envelope can earn between .5 points to 2 points. A prescriptive compliance is outlined as follows:
.5 points earned requires a Fenestration U valueof .28; Floor insulation of R-38; Wall insulation of R-21; and, Ceiling insulation of R-49. 1 point earned requires a Fenestration U value of .25; Floor insulation value of R-38; Wall insulation of R-25; Ceiling insulation of R-49. 2 points earned requires a Fenestration U value of .22; Floor insulation value of R-38; Wall insulation value of R-33; and, Ceiling insulation value of R-49.
If you wanted to meet the State of Washington Energy Requirements—it can be done just by improving the efficiency of the building envelope. What one has to think about is, what is the right approach? Doing the minimum is not always the best thing. Remember a point based code can easily be made stricter going forward. This means if you don’t build your home thinking long term it could cost you later.
Next week I will discuss air leakage and ventilation.
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