Building Science

How to Install Flex Duct Properly

Posted on March 13, 2013 by Allison A. Bailes III, PhD, GBA Advisor

I've written a lot about duct problems (especially those in flex duct) because they're so abundant. A couple of years ago, I even wrote an article in the Energy Vanguard Blog about whether or not flex duct should be banned. My answer was no — but that we need better quality control.

The Science of Global Warming Is Older Than Quantum Mechanics

Posted on March 6, 2013 by Allison A. Bailes III, PhD, GBA Advisor

I'm new to global warming. I didn't hear about it until 1983. Even thirty years ago, the science behind the greenhouse effect and global warming was well known. French Physicist and mathematician Joseph Fourier is generally credited with being the first to hypothesize that the earth is warmed by its atmosphere and even that we humans can change the climate. That goes all the way back to 1827.

Should the Paper Facing of Batt Insulation Face the Inside or Outside?

Posted on February 27, 2013 by Allison A. Bailes III, PhD, GBA Advisor

If you install fiberglass batt insulationInsulation, usually of fiberglass or mineral wool and often faced with paper, typically installed between studs in walls and between joists in ceiling cavities. Correct installation is crucial to performance. * with a kraft paper vapor retarder in a home, which way do you face the vapor retarder? To the inside of the home or the outside of the home? For many building science questions, the answer is, “It depends.” For this one, however, the answer is clear.

SPOILER ALERT: The answer is in the next paragraph — so if you'd rather wait and find out when you see the movie in the theater, don't read any further.

Air Leakage at Electrical Switches and Outlets

Posted on February 20, 2013 by Allison A. Bailes III, PhD, GBA Advisor

One thing that invariably surprises people when I walk them through a house during their first blower-door testTest used to determine a home’s airtightness: a powerful fan is mounted in an exterior door opening and used to pressurize or depressurize the house. By measuring the force needed to maintain a certain pressure difference, a measure of the home’s airtightness can be determined. Operating the blower door also exaggerates air leakage and permits a weatherization contractor to find and seal those leakage areas. is how much air leaks in through the electrical switches and receptacles. On a recent Friday, we went out to do the last home energy rating in our latest HERSIndex or scoring system for energy efficiency established by the Residential Energy Services Network (RESNET) that compares a given home to a Home Energy Rating System (HERS) Reference Home based on the 2006 International Energy Conservation Code. A home matching the reference home has a HERS Index of 100. The lower a home’s HERS Index, the more energy efficient it is. A typical existing home has a HERS Index of 130; a net zero energy home has a HERS Index of 0. Older versions of the HERS index were based on a scale that was largely just the opposite in structure--a HERS rating of 100 represented a net zero energy home, while the reference home had a score of 80. There are issues that complicate converting old to new or new to old scores, but the basic formula is: New HERS index = (100 - Old HERS score) * 5. rater class, and we got to see something even better. But first, let's talk about that air leakage. We have a number of surprises waiting.

The Thermal Bridge to Nowhere

Posted on February 13, 2013 by Allison A. Bailes III, PhD, GBA Advisor

Let's play a little game today. Take a look at that photo at right. See anything that bothers you?* Well, pretend that you're the heat in the house once everything is finished and people are living in it. Does that help? If your answer is still no, let me give you a little help. Here are the approximate R-values of wood and the standard insulation you might find in a wall (fiberglass, cellulose, open-cell spray foam):

Insulation: R-3.7 per inch

Wood: R-1.1 per inch

The 7 Biggest Opportunities for HVAC Contractors

Posted on February 6, 2013 by Allison A. Bailes III, PhD, GBA Advisor

Heating and air conditioning contractors have a lot of opportunities to make homes better and to be profitable. The surprising thing is just how few HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. companies take advantage of all the opportunities that are available to them.

Ventilation Requirements for Weatherized Homes

Posted on January 30, 2013 by Allison A. Bailes III, PhD, GBA Advisor

I went to school with Cajuns in south Louisiana, and fights were a big deal. They happened frequently, and when they did, a small crowd would gather. The noise would grow quickly and soon everyone in the schoolyard would run over to where the fight was happening. One day in sixth grade, we exploited this tendency and staged a fight between two shoes at recess. Sure enough — our tight circle of boys banging two shoes on the ground and making a lot of noise brought the whole school to us.

A Ventless Gas Fireplace Doesn’t Belong in Your Home

Posted on January 23, 2013 by Allison A. Bailes III, PhD, GBA Advisor

First of all, let's call it what it really is. The industry likes the term “vent-free” when talking about gas fireplaces that keep all the exhaust gases in your home. I prefer the term “ventless” or, even better, “unvented.” Some people suggest “room-vented” or “lung-vented.”

Not a huge deal, but the ventless gas industry wants you to feel that you're being liberated of a burden by not having an exhaust vent. I think it's important for people to know that they're actually missing something important when they go with a ventless gas appliance.

How to Install a Branched-Drain Graywater System

Posted on January 16, 2013 by Allison A. Bailes III, PhD, GBA Advisor

Back in the summer of 2003, I was finishing up the green home I'd started building in 2001. One of the last pieces we had to complete was the graywaterWastewater from a building that does not include flush-water from toilets and (as most commonly defined) water from kitchen sinks or dishwashers. In some places, graywater can be collected and used for subsurface irrigation. system, and we'd already put a lot of work into it before we ever moved a spadeful of dirt.

An Innovative Net-Zero Solar Decathlon House

Posted on January 9, 2013 by Allison A. Bailes III, PhD, GBA Advisor

Twelve years ago, I discovered the Solar Decathlon. I was a new physics professor at a small university in Georgia, and I'd received a packet from the US Department of Energy describing the competition. It was set to have its first run in 2002, so I tried to figure out how to get involved and put together an entry. We didn't have design or construction programs, however, and the physics department that I was in was one of the most dysfunctional groups of people the world has ever seen.

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