The most recent blogs at Green Building Advisor

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.

Does This Roof Need a Vapor Retarder?

Posted on May 25, 2015 by Scott Gibson in Q&A Spotlight

David Amenhauser is buying a home near Boston, Massachusetts, that's apparently still under construction, but far enough along to have the roof framed and insulated.

How to Hang Airtight Drywall

Posted on May 25, 2015 by Myron Ferguson in Green Building Blog

Stopping air leaks is the single most important part of making a house more energy efficient. You can stop air on the outside with plywood, housewrap, and tape, but the best 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. is a system that incorporates the whole wall or roof assembly.

Sub-Slab Mineral Wool

Posted on May 22, 2015 by Martin Holladay, GBA Advisor in Musings of an Energy Nerd

Most green builders who need a layer of horizontal insulation under a concrete slab specify 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.), an affordable product that performs well in this application. If a builder specifies high-density EPS rated for below-grade use, the product is very durable.

That said, many green builders don’t like EPS. Some object to the fact that polystyrene is made from petroleum, while others worry about possible health problems associated with the brominated flame retardants that polystyrene manufacturers add to EPS.

Prepping for Spray Foam

Posted on May 21, 2015 by Michael Chandler, GBA Advisor in Green Building Blog

Spray-foam insulation is gaining popularity these days, and for good reason. Not only does it offer lots of R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. per inch, but it also air-seals the house. I’ve been building custom homes in North Carolina for more than 20 years, and I’ve been using spray-foam insulation for the past four. These days, all my projects get 8 in. to 12 in. of foam under the roof deck, and I often use foam to insulate walls and crawlspaces as well.

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