by Lloyd Alter, Toronto on 12.21.10
There is a strange debate going on at Green Building Advisor, where a writer thinks “home buyers have been “brainwashed” into thinking only about R-values, as energy codes give short shrift to the importance of airtightness.” The debate goes back and forth, but not once to they address the real point: How much energy is being consumed over all. They are preoccupied with relative efficiency when they should be concerned with absolute consumption.
Even as our building codes increase the R-values, absolute energy consumption goes up as the houses get bigger. So the rate of heat loss or infiltration is almost irrelevant.
I have made this point before in Big Steps in Building: Change our Building Codes from Relative to Absolute. Someone living in a 1950s- sized 983 square foot house doesn’t need the same insulation as the 2010 sized 2350 square foot house and the five thousand footer should have twice as much.
Even my beloved Passivhaus standard gets it wrong, setting a standard of maximum energy use in kilowatts per square meter, actually encouraging the building of bigger houses, since a given number of people will use about the same amount of hot water or electricity and have more square meters to spread it around in a bigger house.
If we want to really measure the right thing, we should forget about R-value of components in a wall and measure total consumption. Pick a number for a standard house and if you double the size you have to either insulate more, reduce windows or cover the roof with solar collectors. Cut it in half and you can cut the insulation and build at lower cost. Because what we are trying to do is cut our energy use rather than contemplate the perfect wall.
More at Green Building Advisor
More on absolute vs relative:
Big Steps in Building: Change our Building Codes from Relative to Absolute
How Should We Really Measure Green Building?
5 Building Code Changes That Absolutely Cannot Wait Until 2030
Stop With the Glass Façades Already
Save Energy, Move in With a Friend