The most recent blogs at Green Building Advisor

Fundamentals of Psychrometrics, Part 3

Posted on June 17, 2015 by Allison A. Bailes III, PhD, GBA Advisor in Building Science

In Part 1 and Part 2 of this series of articles, we’ve taken a look at what exactly psychrometrics is and defined the top nine psychrometric quantities. Now we’re going to delve into how we can combine those quantities and create the psychrometric chart.

As you might expect, taking nine variables and putting them into one chart puts a lot of information at your fingertips. It also can take a while to figure it all out. On top of all that, having nine different variables means you’ve got a lot of options for how to show them in a chart.

The Case for Nuclear Power — Despite the Risks

Posted on June 16, 2015 by Gary Was in Green Building Blog

Nuclear power is likely the least well understood energy source in the United States. Just 99 nuclear power plants spread over 30 states provide one-fifth of America’s electricity. These plants have provided reliable, affordable, and clean energy for decades. They also carry risk — to the public, to the environment, and to the financial solvency of utilities.

Pretty Good, Not So Big Maine House

Posted on June 15, 2015 by stephen sheehy in Guest Blogs

After adding a big addition to our already too big house in 2006 (what were we thinking?), we have decided to downsize and build a new, much smaller, highly efficient single-floor house for the two of us.

We live on 43 acres in rural Maine, in a town called Alna about an hour northeast of Portland. We love the land and love our house as well. But at almost 4,000 square feet for the two of us, keeping our house cleaned and maintained and heated and so on has become a bigger burden that we need at this point in our lives.

All About Vapor Diffusion

Posted on June 12, 2015 by Martin Holladay, GBA Advisor in Musings of an Energy Nerd

Building scientists talk about several different moisture transport mechanisms. Most of these mechanisms — for example, water entry due to a roof leak — are easy to understand. Other transport mechanisms, like vapor diffusionMovement of water vapor through a material; water vapor can diffuse through even solid materials if the permeability is high enough. , aren't quite as intuitive.

First, some basic definitions. Water vapor is water in a gaseous state — that is, water that has evaporated. It is invisible.

Water vapor diffusion is the movement of water vapor through vapor-permeable materials. Vapor diffusion happens through a solid material even when the material has no holes.

The Difficulty of Stopping Air Leakage Between the House and Garage

Posted on June 10, 2015 by Allison A. Bailes III, PhD, GBA Advisor in Building Science

A home with an attached garage is usually a home in which people breathe more carbon monoxide (CO). Of course, having an open carport or detached garage is better for air quality (and a feature that usually gets points for you in green building programs like LEED for HomesLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. and EarthCraft House), but what if you don't want to give up that attached garage?

A Straw-Bale Home in Vermont

Posted on June 10, 2015 by GBA Team in Green Building Blog

The owner of Vermont Natural Homes, Chad Mathrani, is building his own home near Brattleboro, Vermont. The walls of the house are built using several different construction methods, including timber frame, straw-bale, and double-stud framing insulated with cellulose.

This video of Mathrani's project was produced by a distributor of building products, 475 High Performance Building Products in Brooklyn, New York.

The Sun Also Rises in the Southeast

Posted on June 9, 2015 by Luis Martinez in Guest Blogs

Anyone who's ever sat out on a Georgia afternoon or wandered outdoors in the bright Florida sunshine knows that the solar power potential in these two Southeastern states is enormous. Now, after a slow start, so is the headway that the clean power technology is making in the Southeast's two most populous states. "In 2011, if you told me we'd be where we are today with solar," says one Georgia solar advocate, "I would have laughed."

How to Insulate a Foundation

Posted on June 8, 2015 by Scott Gibson in Q&A Spotlight

About to start a new house in Climate Zone 5, Nicholas C is working out the details of how to insulate the basement slab and foundation walls. There is more than one type of rigid foam insulation he could use, and it could be applied on either the inside or outside of the foundation.

For a couple of reasons, he's planning on 2 inches of extruded polystyrene (XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation.) beneath the slab rather than expanded polystyrene (EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest.). The XPS would perform better in a wet environment, Nicholas says, and Owens-Corning, one insulation manufacturer, claims it no longer uses a "bad" blowing agent.

How to Provide Makeup Air for Range Hoods

Posted on June 8, 2015 by Martin Holladay, GBA Advisor in Green Building Blog

When Cheryl Morris moved into her new home, she realized that the kitchen exhaust fan was probably too powerful. Whenever she turned on the 1,200-cfm fan, strange things happened. “It pulled the ashes out of the fireplace, halfway across the room, right up to my husband’s chair,” she says. Those dancing ashes demonstrate an important principle: Large exhaust fans need makeup air.

Cost of Passivhaus Compliance Is Sometimes Hard to Justify

Posted on June 5, 2015 by Martin Holladay, GBA Advisor in Musings of an Energy Nerd

In most climate zones, achieving the 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. standard requires more expensive windows, higher insulation levels, and greater attention to air-sealing details than less stringent construction practices. It should come as no surprise that homes with these features cost more to build than homes complying with easier-to-meet standards.

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