The most recent blogs at Green Building Advisor

Like wind washing, thermal bridgingHeat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel. is something folks mention all the time during audits (meaning they never ask about it). But what is thermal bridging, and why do I keep bringing it up when my customers just want new windows?

To understand thermal bridging, you need to understand your home’s wall assembly and the various materials used in its construction.

There are lots of ways to insulate a low-slope roof, and most of them are wrong. In older buildings, the usual method is to install fiberglass batts or cellulose on top of the leaky ceiling, with a gap of a few inches (or sometimes a few feet) between the top of the insulation and the roof sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. . In some cases, but not all, there is an attempt to vent the air space above the insulation to the exterior.

My blog last week about Kansas and efforts to outlaw any mention or promotion of sustainability was so depressing (to write as well read) that I needed to find a more uplifting sequel. I needed to remind myself — and readers — that even if some politicians in Kansas don’t want to make the world a better place for their children and grandchildren, that’s not a universal attitude.

I just returned from Arizona, where I spoke at this year's conference of the Structural Insulated Panel Association. Since the conference was in Tucson, I also took the opportunity to visit with my friend David Butler of Optimal Building Systems.

Before I even get started, I want to point out that I am no expert on ventilation. I have learned a lot from (and rely on) many experts, including Paul Raymer, Gord Cooke, John Krigger, Joe Lstiburek, Armin Rudd, and Terry Brennan, among others. I depend on them to fuss about the details of how much ventilation a house needs.

A GBAGreenBuildingAdvisor.com reader who calls himself “Mr. Mike” is working on an 11-ft. by 14-ft. addition to his house in central New York that sits some 5 feet off the ground. The space beneath the addition is a great place to park a lawnmower, but it's also open to the cold.

My grandfather, William L. Holladay, was a refrigeration and cooling engineer. Decades ago, he wrote a pioneering, speculative article on ground-source heat pumps, “The Heat Pump: What it does, and what it may do someday.” The article appeared in the October 1948 issue of Engineering and Science Monthly. (For a basic explanation of how a heat pump works, and the difference between an air-source heat pumpHeat pump that relies on outside air as the heat source and heat sink; not as effective in cold climates as ground-source heat pumps. and a ground-source heat pump, see Heat Pumps.)

I love many things about Kansas — from the tall-grass prairies in the Flint Hills where I’ve hiked through rolling hills overlooking grazing bison to the dramatic waterfowl migrations in the Cheyenne Bottoms region in the western part of the state.

Really, the argument about whether you should vent a crawl space in a humid climate is over. Advanced Energy's research project from 2002 proved that closed crawl spaces outperform vented crawl spaces.

A quick look at the psychrometric chart below shows that the argument should never have existed in the first place. (Click the image to see an enlarged version.)

[Editor’s note: Liz Johndrow is a natural builder who specializes in the use of cob, strawbale, adobe, earthbag, and earthen plasters. During the winter months, she volunteers in Nicaragua, where she works with villagers, especially women, on construction projects in Sabana Grande, Totgalpa. What follows is a sample of Johndrow’s blog entries written from Nicaragua. You can learn more about her work at her website, Earthen Endeavors.]