Musings of an Energy Nerd

How To Buy a Ductless Minisplit

Posted on June 19, 2015 by Martin Holladay, GBA Advisor

Green builders usually specify high-performance windows and above-code levels of insulation, while striving to reduce air leaks in their homes. As a result of these efforts, most green homes have relatively low heating and cooling loads.

All About Vapor Diffusion

Posted on June 12, 2015 by Martin Holladay, GBA Advisor

Building scientists talk about several different moisture transport mechanisms. Most of these mechanisms — for example, water entry due to a roof leak — are easy to understand. Other transport mechanisms, like vapor diffusionMovement of water vapor through a material; water vapor can diffuse through even solid materials if the permeability is high enough. , aren't quite as intuitive.

First, some basic definitions. Water vapor is water in a gaseous state — that is, water that has evaporated. It is invisible.

Water vapor diffusion is the movement of water vapor through vapor-permeable materials. Vapor diffusion happens through a solid material even when the material has no holes.

Cost of Passivhaus Compliance Is Sometimes Hard to Justify

Posted on June 5, 2015 by Martin Holladay, GBA Advisor

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.

Net-Zero Homes Show Signs of Convergent Evolution

Posted on May 29, 2015 by Martin Holladay, GBA Advisor

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.

Sub-Slab Mineral Wool

Posted on May 22, 2015 by Martin Holladay, GBA Advisor

UPDATED on April 5, 2016

The Return of the Vapor Diffusion Bogeyman

Posted on May 15, 2015 by Martin Holladay, GBA Advisor

Fully aware that I am engaging in gross oversimplification, I’m going to offer a cartoon version of the History of Vapor Barriers. (I’m not a cartoonist, though, so someone else will have to make the drawings.) Here goes:

Panel 1: In the late 1940s, residential building codes in the U.S. began requiring the installation of vapor barriers on the interior side of walls and ceilings. These requirements had complicated historical origins but were not based on credible building science.

Books for Homeowners Interested in Saving Energy

Posted on May 8, 2015 by Martin Holladay, GBA Advisor

Two books that do a good job of explaining residential energy use issues to homeowners are Consumer Guide To Home Energy Savings and No-Regrets Remodeling. Both books have been around for years. Recently the publishers of these two books issued new editions, so I decided to give them a careful read.

Consumer Guide To Home Energy Savings

Using a Tankless Water Heater for Space Heat

Posted on May 1, 2015 by Martin Holladay, GBA Advisor

You can buy a gas-fired tankless water heater for $600 — or even $300, if you want a bare-bones model. These appliances are remarkable: they are compact enough to hang on a wall and can begin producing an “endless” flow of hot water almost instantly. Many people look at these small appliances and think, “Why can’t I use one to heat my house?”

The answer is, you can. However, just because you can, doesn’t mean you should.

Site-Built Ventilation Baffles for Roofs

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

Roofs often require ventilation channels directly under 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. — either for a short section of the roof (for example, near the eaves) or for the entire roof, from soffit to ridge. When the wind is blowing, these ventilation channels allow air to move from the soffit vents to the ridge vents.

Fixing Attics With Vermiculite Insulation

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

If you're under the impression that natural insulation materials are the safest ones to use, it might be time to think again. Vermiculite is a natural insulation material — but it’s one that you definitely don’t want to have in your attic.

Vermiculite is a mineral mined from the earth, composed of shiny flakes that look like mica. When this mineral is put in an oven, it expands like popcorn. Expanded vermiculite is lightweight, fire-resistant, and odorless; since it 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-2 per inch, it was used for decades as an insulation material.

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