Musings of an Energy Nerd

Longtime readers of GBAGreenBuildingAdvisor.com know that I get frustrated by exaggerated energy savings claims. A glaring example is the statement that “a Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. building uses 90% less energy than a conventional building.” A variation on this claim: “A Passive House building uses 90% less energy than a code-minimum building.”

At the recent BuildingEnergy 17 conference in Boston, there were at least two presentations that touched on double-stud walls. John Straube, a professor of building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials. science at the University of Waterloo in Ontario, used his presentation to raise a warning flag, noting that “these walls will work if everything works — if there aren’t any defects — but they don’t work if there is something wrong.”

White cedar has an R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of about R-1.4 per inch, so it isn't too hard to calculate the R-value of white cedar siding. The trickiest part of the calculation is determining the siding thickness.

If we're talking about cedar shingles, there are usually a maximum of three layers of shingles at any one point in the wall. The shingles are tapered, so the total thickness of the siding includes layers with different thicknesses. (The butt of the shingle may measure 3/8 inch; the top of the shingle may measure 1/16 inch; and the middle of the shingle may measure 3/16 inch).

To design a residential heating or cooling system, the first step is to perform a load calculation. (A load calculation determines the size of a building’s heating loadRate at which heat must be added to a space to maintain a desired temperature. See cooling load. on one of the coldest nights of the year and the size of a building’s cooling load on one of the hottest afternoons of the year.) It’s important to know the size of these loads to determine the size of the required heating and cooling equipment.

Open-cell spray foam has an R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of about R-3.7 per inch, while closed-cell spray foam has an R-value that may be as high as R-6.5 per inch. If you want to install spray foam in a stud wall, and price is no object, then it would seem to make sense to specify closed-cell spray foam, right?

Not necessarily.

While I’ve designed a few single-family homes, I’m well aware that designing a high-rise office building is a whole ’nother kettle of fish. The challenge is far greater — at least an order-of-magnitude greater — requiring an experienced team that includes architects, structural engineers, mechanical engineers, and energy consultants.

Efficiency Vermont, a nonprofit agency that provides financial incentives for energy-efficiency improvements by homeowners, builders, and businesses in Vermont, has developed a certification program for new homes called the High Performance Certification.

California regulators have established an ambitious policy goal: Beginning in 2020, all new homes in the state must be designed for net-zero-energy operation. (GBAGreenBuildingAdvisor.com has published at least four news stories on California's net-zero target: here, here, here, and here.)

Two hundred years ago, a ship's carpenter had many duties. In addition to repairing the ship, a carpenter would be called on to perform emergency amputations. Why? He was the one who had the saws.

Modern surgeons still require saws, as well as drills, chisels, scrapers, and grinders. As a lighthearted exercise that has almost nothing to do with green building, I recently got the idea to compare surgical tools with carpentry tools.

Full disclosure: This blog is for fun. It is completely empty of any building science.

My fellow editors at Fine Homebuilding — Justin Fink, Rob Yagid, and Brian Pontolilo — have been hosting a weekly podcast for several months. They recently invited me to join them in a sound studio at the Fine Homebuilding office to record a conversation on a variety of building science topics.

This week, I'm taking a break from my usual blog-writing schedule, substituting a two-part podcast recording. Click on one of the green triangles to start listening.