The most recent blogs at Green Building Advisor

How to Insulate a Foundation

Posted on June 8, 2015 by Scott Gibson in Q&A Spotlight

About to start a new house in Climate Zone 5, Nicholas C is working out the details of how to insulate the basement slab and foundation walls. There is more than one type of rigid foam insulation he could use, and it could be applied on either the inside or outside of the foundation.

For a couple of reasons, he's planning on 2 inches of extruded polystyrene (XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation.) beneath the slab rather than expanded polystyrene (EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest.). The XPS would perform better in a wet environment, Nicholas says, and Owens-Corning, one insulation manufacturer, claims it no longer uses a "bad" blowing agent.

How to Provide Makeup Air for Range Hoods

Posted on June 8, 2015 by Martin Holladay, GBA Advisor in Green Building Blog

When Cheryl Morris moved into her new home, she realized that the kitchen exhaust fan was probably too powerful. Whenever she turned on the 1,200-cfm fan, strange things happened. “It pulled the ashes out of the fireplace, halfway across the room, right up to my husband’s chair,” she says. Those dancing ashes demonstrate an important principle: Large exhaust fans need makeup air.

Cost of Passivhaus Compliance Is Sometimes Hard to Justify

Posted on June 5, 2015 by Martin Holladay, GBA Advisor in Musings of an Energy Nerd

In most climate zones, achieving the PassivhausA 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. standard requires more expensive windows, higher insulation levels, and greater attention to air-sealing details than less stringent construction practices. It should come as no surprise that homes with these features cost more to build than homes complying with easier-to-meet standards.

Canned Lighting Conundrum

Posted on June 4, 2015 by Stu Turner in Guest Blogs

In the fall of 2014, I was approaching the rough electrical stage of construction on a (hopefully) net-zero-energy “pretty good house” in the mountains northeast of Los Angeles. My goal for lighting was to specify fixtures to create attractive, properly lit spaces, with minimal impact to my air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both..

Fundamentals of Psychrometrics, Part 2

Posted on June 3, 2015 by Allison A. Bailes III, PhD, GBA Advisor in Building Science

Psychrometrics, you may recall, is the science that involves the properties of moist air and the processes in which the temperature or the water vapor content or both are changed. To understand how all that works, we need quantities and we need them to be well defined. Some are easy to understand (e.g., dry bulb temperatureAir temperature as measured by an ordinary thermometer. and barometric pressure); others are a bit more abstract (e.g., enthalpy). Here we'll take a look at the main psychrometric quanitites, define them carefully, and tell which commonly used term you should avoid.

Friendlier Foam Insulation On the Way, Eventually

Posted on June 2, 2015 by Scott Gibson in Green Building Blog

Builders who have been waiting for a new generation of extruded polystyrene insulation with a lower global warming potential (GWP) than what’s currently available may have to wait a little longer.

Dispatch from the AIA Convention

Posted on June 1, 2015 by Carl Seville, GBA Advisor in Green Building Curmudgeon

Last week I had the opportunity to attend the 2015 convention of the American Institute of Architects (AIA) — a simple matter for me, as it took place in Atlanta. I find that it is often challenging to attend local conferences because we let our daily work take over in a way that we don’t when we travel out of town for events. This time, however, I was able to block out two full days for the event, and was interrupted only occasionally by calls and emails.

Net-Zero Homes Show Signs of Convergent Evolution

Posted on May 29, 2015 by Martin Holladay, GBA Advisor in Musings of an Energy Nerd

A few weeks ago, my wife and I went on a short hike with our college-age son. As the three of us drove to the trailhead in Norwich, Vermont, we passed a construction site. “Looks like a zero-energy house,” I observed. The sign out front read, “Prudent Living Homes.” I decided to get more information on the house and return later to try to talk with the builder.

I called up Prudent Living Homes, and the owner of the company, Paul Biebel, agreed to meet me at the site. When I showed up a few days later, two carpenters, Gary Castellini and Maynard White, were working on exterior details.

Fundamentals of Psychrometrics, Part 1

Posted on May 27, 2015 by Allison A. Bailes III, PhD, GBA Advisor in Building Science

I have a confession to make: I've fallen in love with psychrometrics! After water itself, moist air has got to be the most interesting substance in building science. And the psychrometric chart, in all its many manifestations and with its multitudinous quantities, is a thing of beauty. Well, at least it is to me, and maybe it will be to you, too, after you get to know it a bit better.

Get Ready for a New Energy Code

Posted on May 26, 2015 by Stuart Kaplow in Guest Blogs

The 2015 version of the International Energy Conservation Code is soon to be upon you.

Modern building codes are most often adopted by local government legislative bodies and as such vary from place to place. The IECC International Energy Conservation Code. is in use or adopted in 47 states, the District of Columbia, the U.S. Virgin Islands, New York City, and Puerto Rico.

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