Building Science

Choosing a Base Temperature for Degree Days

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

Degree days are a combination of time and temperature. We looked at their uses and where they come from in Part 1 of this series, and now it's time to go a little deeper.

The temperature enters as a temperature difference, ΔT (delta T), but it's not the ΔT between inside and outside of the building. It's the difference between the outdoor temperature and the base temperature. But what is this thing called base temperature?

Energy Efficiency Is Narrowing the Stupid/Hurt Gap

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

The gap is narrowing. What gap, you ask? Why, the gap between stupid and hurt, of course. So says Dr. Joe Lstiburek. Allow me to explain.

Sometimes when you do something stupid, it hurts immediately. A toddler touches a hot kettle, for example, and instantly starts crying in pain. That's a learning experience.

If that pain didn't happen until an hour or a day had passed, however, the child would have a tough time learning not to touch hot kettles. Building or remodeling homes is a lot like that.

The Importance of Defining the Building Enclosure

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

The photo at right shows a common problem in new homes. It's also one that can make it difficult to pass the blower door test required by many building codes these days. If I tell you that the wall pictured here separates two rooms in a basement and one of them is not conditioned, can you see the problem? If so, how many mistakes do you see here?

The Principles, Uses, and Limitations of WUFI

Posted on November 26, 2014 by Allison A. Bailes III, PhD, GBA Advisor

Dr. Joseph Lstiburek started it in 2012 when, in his keynote address at the Passive House conference, he said igloos were the first passive houses and you don't need WUFI,1 the hygrothermalA term used to characterize the temperature (thermal) and moisture (hygro) conditions particularly with respect to climate, both indoors and out. modeling tool, to design and build a good house.

How NOT to Install Windows in a New Home

Posted on November 19, 2014 by Allison A. Bailes III, PhD, GBA Advisor

I see a lot of interesting stuff at construction sites and in people's homes. I also see stuff I never got to see because people send me photos. I like photos! Remember that
ice chest someone had incorporated into a duct system? That was sent to me. So are the first two photos in this article.

Calculating Heating Degree Days

Posted on November 12, 2014 by Allison A. Bailes III, PhD, GBA Advisor

Let's say you did some work on your home to make it more energy-efficient: air sealing, more attic insulation, and a duct system retrofit. You've got your energy bills for 12 months before and 12 months after you did the work, and now you want to see how much energy you saved. So you sit down with all 24 months worth of utility bills, convert everything to a common unit if you use more than one type of fuel, and take a look at the numbers.

A Best Practices Manual That Can Help You with the Details

Posted on November 5, 2014 by Allison A. Bailes III, PhD, GBA Advisor

When I was building a home in 2001, I came up against a gazillion little things that I needed guidance on. I'd never built anything larger than a bookcase, so new home construction was quite a big step.

How Worried Should You Be About Asbestos in Older Homes?

Posted on October 29, 2014 by Allison A. Bailes III, PhD, GBA Advisor

AsbestosMineral fiber once commonly used in many building materials, including insulation, fireproof siding, and resilient flooring. Inhalation of invisible asbestos fibers can lead to chest and abdominal cancers as well as scarring of the lungs. The use of asbestos in some products has been banned by the EPA and the U.S. Consumer Products Safety Commission; manufacturers also have adopted voluntary limitations on its use. When found in older buildings (most commonly in floor tiles, pipe and furnace insulation, or asbestos shingles), the product's friability is a major determinant in how it must be handled during renovations. More information: http://www.epa.gov/iaq/asbestos.html was a popular material for most of the twentieth century, mainly because of its ability to insulate and act as a fire retardant. In fact, it's still used heavily in some parts of the world, such as India and China. We know enough about the risks now, though, that it's banned outright in more than 50 countries and banned for some uses in the U.S.

But how worried should you be if you find it in your home?

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?

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