Arguments Against White Roofs in Northern Cities are Specious
Too small? Larger original in New York Times
Felicity Barringer writes about white roofs in the New York Times. She picks up on one of my favourite themes, that it is old-school and low-tech:
Unlike high-technology solutions to reducing energy use, like light-emitting diodes in lamp fixtures, white roofs have a long and humble history. Houses in hot climates have been whitewashed for centuries.
But then she picks up the canard about white roofs not being a good thing in the northern parts of the country, where some say that heat gain in the colder seasons is a good thing:White Roofs in Winnipeg
Still, the ardor of the cool-roof advocates has prompted a bit of a backlash.
Some roofing specialists and architects argue that supporters fail to account for climate differences or the complexities of roof construction. In cooler climates, they say, reflective roofs can mean higher heating bills.
Scientists acknowledge that the extra heating costs may outweigh the air-conditioning savings in cities like Detroit or Minneapolis.
The black membrane installers are all over this; an example is this long letter from the The EPDM Roofing Association entitled White roofs don't work in Winnipeg and more at the EPDM roofers trade site.
Barringer doesn't go into why these arguments are specious, even in Winnipeg:
1. A house in Minneapolis or Detroit probably doesn't need air conditioning in the summer if it has a white roof, it is that much cooler. It certainly will have a shorter air conditioning season. So just using degree day tables to figure out how many days require heating vs cooling doesn't work.
In most northern states you can almost eliminate air conditioning if you follow our 10 low tech tips.
2. Air conditioning is powered by electricity which for the most part comes from coal and is very inefficient; heating mostly comes from cleaner burning natural gas at far higher efficiency. The peak load of the electrical season is the hottest day of the year, so any air conditioning load taken off the top has a lot more impact than adding a bit of natural gas consumption in the shoulder seasons.
3. A properly insulated house in Detroit or Minneapolis has a white roof for most of the winter- it's called snow.
But otherwise, good reading in the New York TimesMore on white roofs:How To Help Prevent Global Warming On Your RoofLighter Roofs Could Save $1Billion USD AnnuallyWhite Roofs to Sweep the World, Fight Climate Change