Q&A Spotlight

How to Make a SIP Roof Better

Posted on November 9, 2011 by Scott Gibson

Roger Lin’s Washington, D.C., house will have a roof of 12-inch-thick structural insulated panels (SIPs). By most standards, that’s a well-insulated roof. But Lin wants to add 2 inches of rigid foam on top of the panels to reduce thermal bridgingHeat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel. .

He’s uncertain about the details. He has already installed roofing underlayment over the panels. Can he put expanded polystyrene foam on top of the underlayment and cap it with metal roofing? Or does he need a layer of plywood or furring strips over the foam before the metal roofing is installed?

Can Cellulose be Used in an Unvented Roof?

Posted on October 31, 2011 by Scott Gibson

Dean Manoogian has a Cape Cod style house in Portland, Maine, and is puzzling over the best way to retrofit the roof with rigid foam insulation.

Working with both an insulation company and a roofing contractor, Manoogian has come up with a plan: apply 2-in. rigid foam on the interior of the dormered roof and then fill the rafter bays with dense-packed cellulose.

Can Polyethylene Be Used as an Air Barrier?

Posted on October 24, 2011 by Scott Gibson

Polyethylene sheeting has had its ups and downs as a preferred building material over the last 20 years.

At one time, it was routinely used in wall assemblies as a vapor barrier. As building scientists learned more about air and moisture movement through walls and ceilings, however, they began to advise builders that an interior vapor retarder is better than an interior vapor barrier, and the perceived usefulness of poly plummeted.

Is There Such a Thing as a Perfect Building Envelope?

Posted on October 17, 2011 by Scott Gibson

Is there such a thing as a perfect 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.? One that could be mass-produced from readily available materials, and be appropriate for 90% of all new homes?

Andrew Homoly thinks he’s found one, as he explains in this Q&A post at GreenBuildingAdvisor.

Are Blower-Door Regulations Too Big a Burden?

Posted on October 10, 2011 by Scott Gibson

Building tight houses is a fundamental step toward energy efficiency, and figuring out how well you’ve done is actually pretty simple.

Air leakage is calculated with a blower-door testTest used to determine a home’s airtightness: a powerful fan is mounted in an exterior door opening and used to pressurize or depressurize the house. By measuring the force needed to maintain a certain pressure difference, a measure of the home’s airtightness can be determined. Operating the blower door also exaggerates air leakage and permits a weatherization contractor to find and seal those leakage areas.. A technician depressurizes the house with a blower sealed into a doorway and measures how much air can pass through 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..

Does R-Value Trump Thermal Mass?

Posted on October 3, 2011 by Scott Gibson

Jesse Lizer’s plans for a new house in Climate Zone 6 call for a 60-foot long walkout basement wall on the north side. The three below-grade foundation walls will be built with insulated concrete forms (ICFs) with an R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of roughly R-25.

How to Build Efficiently in Massachusetts

Posted on September 26, 2011 by Scott Gibson

Noah Kaput and his wife seem to be off to a good start in planning their 2,100-sq. ft. house in Massachusetts.

Is the Green Movement Just Spinning Its Wheels?

Posted on September 19, 2011 by Scott Gibson

For GBAGreenBuildingAdvisor.com senior editor Martin Holladay, it all started with a column in The New York Times provocatively titled “Going Green But Getting Nowhere.”

The author, Gernot Wagner, contends that individuals can make no meaningful impact on reducing carbon emissions and staving off global climate change.

Even if each of the 1 billion Catholics on Earth decreased their emissions to zero overnight, Wagner writes, “the planet would surely notice but pollution would still be rising.”

Is Green Building for Everyone?

Posted on September 12, 2011 by Scott Gibson

Is green building too narrow in focus, suitable only for people who keep the windows closed and let mechanical systems regulate temperature and humidity? What about people who like fresh air, even in winter, and are looking for minimal intervention from mechanical heating and cooling equipment?

That seems to be at the heart of a question from Maria Hars, a GBAGreenBuildingAdvisor.com reader who lives in a passive solar house built 30 years ago in northern Massachusetts.

The Pros and Cons of Running a Dehumidifier

Posted on September 6, 2011 by Scott Gibson

Superinsulation is the most effective weapon we have against wintertime heat losses. R-values of 60 or more in the roof and 40 in exterior walls can slow the movement of heat to a crawl, keeping energy costs far below what they’d be in a conventionally built house.

Yet Harry Seidel puts his finger on a potential problem. During the summer, any heat generated inside the house will have just as much trouble getting out of the house.

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