Building Science

Spray Foam Insulated Homes Need Ventilation

Posted on October 22, 2014 by Allison A. Bailes III, PhD, GBA Advisor

Most installations of spray foam insulation, when properly installed, act as 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.. When you use it instead of the fluffy stuff (fiberglass, cellulose, cotton), a house will be more airtight. That's good.

When a house is airtight, the nasties in the indoor air tend to stick around. Volatile organic compounds (VOCsVolatile organic compound. An organic compound that evaporates readily into the atmosphere; as defined by the U.S. Environmental Protection Agency, VOCs are organic compounds that volatize and then become involved in photochemical smog production.), water vapor, odors, radonColorless, odorless, short-lived radioactive gas that can seep into homes and result in lung cancer risk. Radon and its decay products emit cancer-causing alpha, beta, and gamma particles., and other stuff you don't want to immerse yourself in make the home's indoor air quality worse.

The Diminishing Returns of Adding Insulation

Posted on October 15, 2014 by Allison A. Bailes III, PhD, GBA Advisor

If you're building a house and want to have a really good building enclosure, you need it to be airtight, handle moisture properly, and have a good amount of insulation. Ideally, you'd also consider the effects of solar radiation on the home, but for now let's just focus on the insulation. What exactly is "a good amount" anyway?

Using Server Farms to Heat Buildings

Posted on October 8, 2014 by Allison A. Bailes III, PhD, GBA Advisor

Last week in my ASHRAE newsletter, I saw an interesting story about a cool thing that Amazon.com is planning to do with heat. Amazon, in case you didn't know, is a heavy user of computers. Not only do their run their online store but they also have a popular cloud computing service. Computers turn electricity into kitten videos, celebrity tweets, and waste heat.

The Difference Between Efficiency and Efficacy

Posted on October 1, 2014 by Allison A. Bailes III, PhD, GBA Advisor

When I was doing research for an article on ceiling fans a while back, I noticed that fans don't have energy efficiency ratings; they have efficacy ratings.

There's certainly confusion about the terminology among different sources, but since light bulbs are also described by their efficacy, I started wondering about the term. I'd just accepted it before, with a vague understanding that there was something different about how efficacy was defined. Now I know why.

Highlights from the North American Passive House Conference

Posted on September 24, 2014 by Allison A. Bailes III, PhD, GBA Advisor

The 9th annual North American 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. Conference happened two weeks ago in the San Francisco Bay Area of California. The Passive House Institute U.S. (PHIUS) has been holding this conference every year since 2006, and it just keeps getting better.

Study Finds Huge Variation in California HERS Rating Results

Posted on September 17, 2014 by Allison A. Bailes III, PhD, GBA Advisor

A home energy rating is supposed to tell you how energy-efficient your home is. A certified home energy rater goes to the home and collects all the data relevant to energy consumption in the home (well, all the data included in the rating anyway, which is almost everything).

How Your Thermostat Can Grow Mold and Make You Uncomfortable

Posted on September 10, 2014 by Allison A. Bailes III, PhD, GBA Advisor

I've been experimenting with my family lately. Or is it, experimenting on my family? In either case, I've got the data to confirm something I wrote in a 2011 article.

But before I tell you what I did, first let me show you what happened. In the graph at right, you can see Exhibit A: a moisture mystery. What do you think happened to cause the humidity (blue data) in the air in our condo to rise like that?

How to Tell If Your Air Conditioner Is Oversized

Posted on September 3, 2014 by Allison A. Bailes III, PhD, GBA Advisor

Back in 2009, I had a new air conditioner installed our condo. The previous one was an ancient 25 years old and barely limping along. It wasn't cooling much, and the summer electric bills had risen.

Is Oriented Strand Board as Impermeable as They Say?

Posted on August 27, 2014 by Allison A. Bailes III, PhD, GBA Advisor

Oriented strand board (OSB) gets blamed for a lot of problems that are really the fault of the designers and builders. Part of the problem, of course, is the perrenial confusion between correlation and causality. OSB hit the market as we really started getting serious about insulation and air sealing.

The Passive House Conference in California Is Where It’s At!

Posted on August 20, 2014 by Allison A. Bailes III, PhD, GBA Advisor

The 9th annual North American 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. Conference is less than a month away. You knew it's going to be in California, right?

It's unfortunate that the other Passivhaus group has chosen to use the same name that the Passive House Institute U.S. (PHIUS) has been using since 2006, but I've already discussed that confusion. (Full disclosure: I am on the board of directors of PHIUS.)

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