Building Science

How Much Air Leakage in Your Home Is Too Much?

Posted on April 10, 2012 by Allison A. Bailes III, PhD

Whether you want to build a new home or fix an old one, the way to ensure that you get the best performance is to do the building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials. right. That means installing the right amount of insulation and installing it well, and it means having an 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. with minimal leakage. But how do you know when you've done enough air sealing? How tight is tight enough?

A Net-Zero-Energy Home in Rural Tennessee

Posted on March 27, 2012 by Allison A. Bailes III, PhD

On my thousand-mile quality assurance road trip last week, I visited a house that was designed to produce more energy than it uses, making it a net zeroProducing 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. Calculating net-zero energy can be difficult, particularly in grid-tied renewable energy systems, because of transmission losses in power lines and other considerations. energy home. You can take any house all the way to net zero just by giving it enough on-site power production (photovoltaics, wind, hydropower...), but that's not the most effective way to achieve the goal of net zero energy use. First, you want to make the house really efficient, and that's what these folks did.

Is the Pretty Good House the Next Big Thing?

Posted on March 7, 2012 by Allison A. Bailes III, PhD

I love the Pretty Good House concept! The folks up in Maine who've been developing this idea in their monthly green building discussion group (Steve's Garage) have struck a chord with a lot of us who design, build, or verify green homes. The growing complexity and expense of green building and energy programs has ledLight-emitting diode. Illumination technology that produces light by running electrical current through a semiconductor diode. LED lamps are much longer lasting and much more energy efficient than incandescent lamps; unlike fluorescent lamps, LED lamps do not contain mercury and can be readily dimmed. to growing frustration.

Who Knew the Stack Effect Could Be So Controversial?

Posted on February 15, 2012 by Allison A. Bailes III, PhD

Recently, I wrote a little article about the stack effect to explain that the flow of air and heat is upward in winter but downward in summer. Turns out, the stack effect is a hot topic. That article has gotten 25 comments so far. When I posted it to the RESNET BPI group on LinkedIn, it got another 22 comments.

Using Hot Water to Heat Air with a Hydronic Furnace

Posted on December 15, 2011 by Allison A. Bailes III, PhD

I'm embarrassed to admit it, but yes, that photo shows the gas furnace and water heater in my condo. (I used to live in a very green SIP home that I built, but that's another story.) It's an 80 AFUEAnnual Fuel Utilization Efficiency. Widely-used measure of the fuel efficiency of a heating system that accounts for start-up, cool-down, and other operating losses that occur during real-life operation. AFUE is always lower than combustion efficiency. Furnaces sold in the United States must have a minimum AFUE of 78%. High ratings indicate more efficient equipment. (80% efficient) furnace and natural draft water heater.

Are You a Green Building Geek, Nerd, Dork, or Dweeb?

Posted on November 8, 2011 by Allison A. Bailes III, PhD

I hear a lot of people call themselves building science geeks, energy nerds, green building dorks, HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. dweebs, weatherization wonks, and policy poindexters. (It's true! Some of them are imaginary people in my mind and some are aliens, but they really do say that.) What I see, though, is that most such people seem to throw these words around without understanding which is which and how dorks and nerds and geeks and dweebs differ.

Blower Door Testers Wanted — Scientists and Engineers Preferred

Posted on October 5, 2011 by Allison A. Bailes III, PhD

OK, the title here may be a little extreme, but if you've taken a look at the new chapter on performance testing and scope of work in the HERS Standards, you know what I'm talking about. RESNET just adopted this as the new chapter 8 in August of this year, and it goes into effect on 3 January 2012.

An AC Sizing Benchmark for High-Performance Homes

Posted on September 21, 2011 by Allison A. Bailes III, PhD

One of the most frustrating parts of my job as a Home Energy Rating (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.) provider is dealing with the size of air conditioners installed in Energy Star homesA U.S. Environmental Protection Agency (EPA) program to promote the construction of new homes that are at least 15% more energy-efficient than homes that minimally comply with the 2004 International Residential Code. Energy Star Home requirements vary by climate..

Lstiburek’s Rules for Venting Roofs

Posted on July 24, 2011 by Joe Lstiburek

Building Science Fundamentals: Roof, Part 1: Ventilation

By Dr. Joseph Lstiburek

Dr. Joseph Lstiburek talks about the not-so-controversial ways to maximize the efficiency and airflow of your roof and attic.

Video Transcript:
There’s been so much stuff said about roofs that you sometimes lose perspective. I’m going to start off by saying what might seem controversial but really shouldn’t be.

Is There a Downside to Lumpy Attic Insulation?

Posted on January 6, 2011 by Allison A. Bailes III, PhD

If your attic is going to have 50 bags of insulation blown into it, does it make much of a difference if it goes in flat or lumpy?

One reason that I'm interested in the question is that my dissertation in grad school was called “Flat or Lumpy.” (Of course, it had the requisite incomprehensibility in the subtitle, with words like “heteroepitaxy.”) Those two words in the title, which cut to the heart of what my surface physics research was all about, also describe a property of insulation that's important in building science.

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