It's time to stop putting up "high cholesterol" buildings
As Steve Mouzon points out, before the thermostat age people really had to work to keep warm; they had to carry all the firewood or the coal, so they wanted to use as little as possible. The Urban Green Council picks up this theme in their new report, High Cholesterol Buildings. They write:
Centuries ago, when people had to gather their own wood and maintain a fire to keep warm, the relationship of quality walls and roofs to better protection from the elements was obvious. Today, a button on the thermostat or air conditioner takes care of that problem with no work whatsoever. Unfortunately we often forget that the cost of comfort in our subpar buildings can cause high energy bills, degraded air quality, and increased carbon pollution.
The result is that our buildings today perform marginally better (and often worse) than buildings built a century or two ago. We now build with floor to ceiling glass and rely on green gizmos to reduce our energy consumption and carbon footprint. We invent concepts like "net zero" to offset lots of glass with lots of solar panels.
© Urban Green Council
The Urban Green Council wants to reverse this trend, and build better envelopes. They note that a lot of glass is blocked by furniture and that it doesn't have to go to the floor. They also note that architects can increase the amount of spandrel glass (the glass that is usually just between floors and is backed with insulation) to reduce the amount of vision glass.
There are many reasons that developers and architects like all-glass buildings. The Council writes that "According to leading real estate owners, floor-to-ceiling windows have more impact on rent than just about any other building feature. The commercial reality is “the more windows, the better.”
© Standard measurement of office buildings
There are other, more subtle reasons. Under the usual office measurement standards, rentable space is measured to the inside of the dominant portion of the exterior wall, so developers insist that glass must be at least 50% of the wall between floor and ceiling. Otherwise they are losing revenue. So in an office with a 9' ceiling and a floor-to floor height of say, 13', you need at minimum a continuous strip of vision glass 4'-6" wide. It is usually wider, so that there is no question of where the rentable space ends.
To compound the problem, most municipalities that regulate floor area under the zoning bylaw measure to the outside of the building, So the developer wants the building's walls to be as thin as possible.
The Urban Green Council makes a number of great suggestions of what to do, including:
Better glass. (But not too much of it)
There is no question that glass can and will become a better insulator. But windows will never insulate as well as walls. The R-value of the typical New York City curtain wall assembly is R-2.5 to R-3.0; walls are R-30 or better. Even if we imagine windows improving two- or three-fold, there will still be an enormous gap between how well windows and walls insulate the building. More glass means a less efficient wall. It’s that simple. Ultimately, whole buildings of floor-to-ceiling glass need to go the way of high cholesterol.
2. Better design.
More glass does not necessarily mean better views. Glass near the floor is often blockedby furniture, and may only reveal a foreground of unattractive rooftop mechanical equipment. Selective use of glass can be used to enhance attractive vistas, creating “designed” views that conceal what’s not so pretty. In addition, spaces like bedrooms, where more privacy is required, don’t need so much glass.
3. Better training
Construction practices do not stress air sealing or preventing thermal breaks, and trades can do better.
4. Better Codes.
This is, I believe, the most important change. There is a requirement that walls have a certain R value and that windows have a certain U value (the reciprocal of the R value, I believe it's done that way to confuse people and hide the fact of how bad windows really are) but no overall R value for the entire wall/window package. Urban Green calls for "an overall building U-value (a measure of heat flow through a material) that would apply to buildings."
I would add a number 5 that I think would have a big impact on cladding choices:
5. Better Measurement Standards
Chrysler Buiding/ Wikipedia/CC BY 2.0
There is nothing shabby about the Chrysler Building, but the owners are taking a big hit on their rentable area by having smaller windows and a stone exterior. I would suggest that the rule should be measure to the glass, whether it is dominant or not, but then we will get totally flat facades as the glass gets pushed to the exterior. Perhaps it should be measure to the exterior, but then the emphasis will be on making the walls as thin as possible. I don't know what the right answer is, only that the current way it is done doesn't promote energy efficient wall design.