The most recent blogs at Green Building Advisor

The Science of Air Flow in Flex Duct

Posted on September 16, 2015 by Allison A. Bailes III, PhD, GBA Advisor in Building Science

Sagging flex duct is bad for air flow. We all know it. We all talk about it. It turns out there's research data to prove it, too. Texas A&M did a study a few years ago to look at the pressure drop that occurs for different levels of compression. If you're not familiar with this study, the results may astound you.

Building a Small House in the White Mountains

Posted on September 15, 2015 by Brian Post in Guest Blogs

Editor's note: This is the first in a series of blogs chronicling the design and construction of a house owned by Brian Post and Kyra Salancy.

Should I Skip the Radiant Floor Heat?

Posted on September 14, 2015 by Scott Gibson in Q&A Spotlight

With an R-90 roof and R-60 walls, Jenz Yoder's new off-grid house will be well insulated. Yoder's quandary, outlined at Green Building Advisor's Q&A forum, is whether radiant-floor heat is a good idea.

"I had two consultants tell me that I will not need radiant floor heat, [that] it will be too much," Yoder writes. "We will have a whole-house air circulation system and a gas fireplace. I am worried about not putting in the pipes in the floor and then being wrong."

Flash-and-Batt Insulation

Posted on September 11, 2015 by Martin Holladay, GBA Advisor in Musings of an Energy Nerd

Closed-cell spray polyurethane foam insulation has several desirable characteristics. It’s an excellent 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., an excellent vapor retarder, and it has a high insulating value per inch (about R-6 to R-6.5). Unfortunately, it’s also expensive.

Carbon Fees Are Not the Best Solution to Climate Pollution

Posted on September 10, 2015 by David Goldstein in Guest Blogs

Several prominent articles this year that have taken a position against energy efficiency have attracted enough press attention to require formal refutations. But these articles all have something in common: an ideological belief that markets work best unconditionally and therefore that a carbon pollution fee is the "first-best" best economic solution to climate change.

A Few Pressure Testing Tips and Tricks

Posted on September 9, 2015 by Allison A. Bailes III, PhD, GBA Advisor in Building Science

A typical BPI Building Analyst spends four to five days in a class learning how to do blower door testing, along with all the other stuff they need to know. 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. raters get all that, too, but also have to learn how to do duct leakage testing. Then there’s that whole big bunch of people who have gone through one or two day intensive blower door and duct leakage training for energy code compliance. When they’re done with the training, how do they figure out how to do pressure testing in the real world?

Rethinking Ventilated Attics

Posted on September 8, 2015 by Marcus Dell in Guest Blogs

Sloped roofs over ventilated attics are one of the most common, if not the most common, roof configuration in Canada. This type of roof assembly is typically associated with single family houses but they are also commonly used on townhouse complexes and large architecturally complex multi-unit residential buildings.

I work for RDH Building Engineering in British Columbia, Canada. RDH has investigated hundreds of attics throughout the Lower Mainland of B.C., and mold growth on the underside of the sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. is a common condition.

U.S. Clean Power Plan Is a Game-Changer

Posted on September 7, 2015 by Susan Casey-Lefkowitz in Guest Blogs

On August 3, President Obama announced the first national limits on carbon pollution from power plants under the Clean Air Act. Laid out in the Clean Power Plan, the new limits are a game-changer that will give a big boost to state efforts to tackle climate change through clean energy solutions. In a video announcing the Clean Power Plan, President Obama said, "We can't condemn our kids and grandkids to a planet that's beyond fixing. Climate change is not a problem for another generation. Not anymore."

Cold-Weather Performance of Polyisocyanurate

Posted on September 4, 2015 by Martin Holladay, GBA Advisor in Musings of an Energy Nerd

The ability of insulation products to resist the flow of heat changes with temperature. Most insulation products — including fiberglass batts, 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.), and 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.) — perform better at low temperatures than high temperatures. At lower temperatures, there is less conductionMovement of heat through a material as kinetic energy is transferred from molecule to molecule; the handle of an iron skillet on the stove gets hot due to heat conduction. R-value is a measure of resistance to conductive heat flow., less convection, and less radiation — so insulation materials usually work better than they do at warmer temperatures.

Retrofits versus Reductions

Posted on September 3, 2015 by Marc Rosenbaum in Green Building Blog

Anyone who is contemplating a deep energy retrofit has to consider multiple approaches and techniques for taking the diverse building stock we have and transforming it — from the standpoint not just of energy use, but also comfort, health and safety, and durability — because so much of our building stock is plagued with deficiencies. Retrofits fix the issues with the building — and saving energy almost ends up as a desirable byproduct.

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