Musings of an Energy Nerd

Fans in the Attic: Do They Help or Do They Hurt?

Posted on October 26, 2012 by Martin Holladay, GBA Advisor

There’s a lot of confusion surrounding attic fans. Here at GBAGreenBuildingAdvisor.com, we regularly receive e-mails from homeowners with questions about attic fans: What’s the purpose of the fan in my attic? How often should I run it? Do I need a bigger fan?

Before addressing these recurring questions, it’s important to define our terms. First, we need to distinguish between three different types of ventilation fans.

Rating Windows for Condensation Resistance

Posted on October 12, 2012 by Martin Holladay, GBA Advisor

Condensation forms on a surface when the temperature of the surface is below the dew point of the air. During the winter, when the coldest surface in a room is often the window, it’s fairly common to see water droplets or ice on window glass — especially in a room with elevated indoor humidity.

Condensation is more likely to form when indoor relative humidity is high. That’s why it’s more common to see condensation on a bathroom window than a bedroom window.

Air Leakage Degrades the Thermal Performance of Walls

Posted on September 28, 2012 by Martin Holladay, GBA Advisor

For the past five years, researchers at the Building Science Corporation (BSC) in Massachusetts have been testing the thermal performance of a variety of wall assemblies as part of an ambitious project to develop a new metric to replace R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. . (I last reported on the project in my August 2011 article, A Bold Attempt to Slay R-Value.)

Study Shows That Expensive Windows Yield Meager Energy Returns

Posted on September 14, 2012 by Martin Holladay, GBA Advisor

An architectural cliché from the 1970s — the passive solar home with large expanses of south-facing glass — is making a comeback. In recent years, we’ve seen North American designers of 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. buildings increase the area of south-facing glass to levels rarely seen since the Carter administration.

What’s the explanation for all this south-facing glass? We’re told that there’s no other way for designers to meet the energy limit for space heating required by the Passivhaus standard: namely, a maximum of 15 kWh per square meter per year.

Who Deserves the Prize for the Greenest Home in the U.S.?

Posted on August 31, 2012 by Martin Holladay, GBA Advisor

It’s not unusual for an architect to announce, with great fanfare, that he or she has just designed “the greenest home in America” — nor is it unusual for journalists to rush these stories to print. The phenomenon has been going on for years — so long, in fact, that I decided to do a small survey of the “greenest homes.”

On Shutters and Water Management

Posted on August 24, 2012 by Martin Holladay, GBA Advisor

I recently walked through a neighborhood in a Massachusetts town on the South Shore. As you might expect, the homes facing the ocean tended to be more luxurious, while the homes a few blocks in from the beach tended to be more humble.

It’s fun to look at houses from the sidewalk (or, in this case, the beach). During my stroll, I ruminated on house design and construction quality. In this blog, I’ll focus on two themes: the first concerns shutters, and the second concerns flashing and water-management details.

Just Two Minisplits Heat and Cool the Whole House

Posted on August 17, 2012 by Martin Holladay, GBA Advisor

Carter Scott was one of the first builders bold enough to build a cold-climate home heated by only two ductless minisplit units (one in the downstairs living room, and one in the upstairs hallway). Skeptics predicted that the unheated bedrooms would be cold and uncomfortable. Yet Scott was confident that the home’s excellent thermal envelope — with high-R walls, triple-glazed windows, and low levels of air leakage — would keep the homeowners comfortable even when the bedroom doors were closed.

Living Without Electricity Bills

Posted on August 10, 2012 by Martin Holladay, GBA Advisor

Chuck Reiss, a builder in northwest Vermont, had a bold plan in 2007: he wanted to build a cluster of six superinsulated homes on a 24-arce site in Hinesburg. Reiss planned to install a roof-mounted PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow. array on each house, with the goal of making the homes net-zero energyProducing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines., or close to it.

A New Passivhaus Standard for North America

Posted on August 3, 2012 by Martin Holladay, GBA Advisor

Katrin Klingenberg, the founder of the 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. Institute U.S. (PHIUS), caused a minor earthquake earlier this year when she suggested that the existing Passivhaus standard didn’t make sense in North America.

Do Foil-Faced Building Products Block Cell Phone Reception?

Posted on July 27, 2012 by Martin Holladay, GBA Advisor

It’s increasingly common for builders to install rigid foam on exterior walls and roofs. And among green builders, polyisocyanurate foam — a type of foam that often comes with foil facing — is generally perceived as the most environmentally friendly foam available.

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