Musings of an Energy Nerd

Hygrothermal Software Sometimes Yields False Results

Posted on August 28, 2015 by Martin Holladay, GBA Advisor

Building designers and researchers have begun to realize that computer modeling programs, including WUFI, sometimes falsely predict that certain common wall assemblies — wall assemblies that have been used successfully for years — should be failing. (WUFI is a so-called “hygrothermal” modeling program — that is, a program that calculates heat and moisture flows through building assemblies. For more information on WUFI, see “WUFI IS Driving Me Crazy.”)

Yet experienced builders know that these wall assemblies aren’t failing. So what’s going on?

Can Unvented Roof Assemblies Be Insulated With Fiberglass?

Posted on August 21, 2015 by Martin Holladay, GBA Advisor

Experts usually advise builders that you can’t install fiberglass insulation directly against the underside of 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. . If you want to install fiberglass between your rafters, you have two basic choices: either include a ventilation channel between the top of the fiberglass insulation and the underside of the roof sheathing, or install enough rigid foam above the roof sheathing to keep the roof sheathing above the dew point during the winter. These rules were developed to prevent damp roof sheathing.

Nuggets From the 2015 Westford Symposium

Posted on August 14, 2015 by Martin Holladay, GBA Advisor

Building science experts, architects, engineers, and builders from across the U.S., Canada, and Europe gathered in early August in Westford, Massachusetts, for the 19th annual Westford Building Science Symposium, a conference sometimes known as “Summer Camp.”

Over three lively days filled with education, networking, and drinking, experts gave ten presentations on a variety of building science topics.

Exterior Rigid Foam on Double-Stud Walls Is a No-No

Posted on August 7, 2015 by Martin Holladay, GBA Advisor

Many green builders like double-stud walls. Double-stud walls use affordable and environmentally appropriate materials to achieve a high R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. .

The classic double-stud wall is made up of two parallel 2x4 walls with a space between them. If the framers leave a 5-inch space between the two rows of studs, this type of wall provides room for 12 inches of insulation — for example, dense-packed cellulose, blown-in fiberglass, or mineral wool.

Liquid-Applied Flashing

Posted on July 31, 2015 by Martin Holladay, GBA Advisor

By now, most conscientious builders know that window rough openings need to be carefully flashed before a window is installed. For residential builders, the most common way, by far, to flash window rough openings is with peel-and-stick flashing.

However, an increasing number of builders are taking a closer look at something different: liquid-applied flashing.

Misconceptions About HRVs and ERVs

Posted on July 24, 2015 by Martin Holladay, GBA Advisor

Since refrigerators have been around for almost a hundred years, most Americans know what a refrigerator is used for. But heat-recovery ventilators (HRVs) and energy-recovery ventilators (ERVs) have only been around for about 30 years, and many Americans still don’t know much about these appliances.

GBAGreenBuildingAdvisor.com regularly receives questions that show that some homeowners are confused about the purpose of these appliances, so it’s worth examining and debunking common misconceptions about HRVs and ERVs.

Saving Energy With an Evaporative Cooler

Posted on July 17, 2015 by Martin Holladay, GBA Advisor

Evaporative coolers are appliances used to cool indoor air. Evaporative coolers use much less energy than air conditioners, but they can’t cool indoor air effectively in all weather conditions.

Installing Windows In a Foam-Sheathed Wall

Posted on July 10, 2015 by Martin Holladay, GBA Advisor

Every now and then, a GBAGreenBuildingAdvisor.com reader posts the question, “How do you install windows in a wall with exterior rigid foam?”

The answer to the question is surprisingly complicated. The best method will depend on several factors, including the answers to these questions:

  • Are the windows innies or outies?
  • What type of water-resistive barrierSometimes also called the weather-resistive barrier, this layer of any wall assembly is the material interior to the wall cladding that forms a secondary drainage plane for liquid water that makes it past the cladding. This layer can be building paper, housewrap, or even a fluid-applied material. (WRB) does the wall have: Zip 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. , housewrap, or rigid foam?
  • How thick is the rigid foam? (For more information on this question, see Calculating the Minimum Thickness of Rigid Foam Sheathing.)

GBA Prime Sneak Peek: Is Weatherization Cost-Effective?

Posted on July 7, 2015 by Martin Holladay, GBA Advisor

GBAGreenBuildingAdvisor.com Prime subscribers have access to many articles that aren't accessible to non-subscribers, including Martin Holladay's weekly blog series, “Musings of an Energy Nerd.” To whet the appetite of non-subscribers, we offer a “GBA Prime Sneak Peek.” This GBA Prime blog was originally published on July 3, 2015.

Is Weatherization Cost-Effective?

Posted on July 3, 2015 by Martin Holladay, GBA Advisor

A recent paper on the cost-effectiveness of weatherization work has received much more attention in the popular press than have similar studies in the past. The researchers concluded that weatherization measures performed at five nonprofit community action agencies in Michigan weren’t cost-effective. Newspaper headline writers have had a field day, trumpeting generalizations that aren’t supported by the limited data collected by researchers.

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