Q&A Spotlight

Rob Graff is getting a new roof, and with it an opportunity to turn his vented attic into an insulated, conditioned spaceInsulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort. .

But he’s also got some concerns.

Christopher Solar had a simple plan for an addition to his Ottawa home. The one-room structure would have a shed-style roof with a cathedral ceiling and vertical board siding. Solar liked a wall assembly he'd read about at GreenBuildingAdvisor, which consists of exterior foam, batt or blown insulation in the stud cavities and airtight drywall on the interior. An interior polyethylene vapor retarder never entered the picture.

And that's where his story gets complicated.

As Steven Knapp and his wife plan a new house in Atlanta, indoor air quality (not energy efficiency) is at the top of their priority list. At least that's how a recent discussion on autoclaved aerated concrete began.

A GBAGreenBuildingAdvisor.com reader who calls himself “Mr. Mike” is working on an 11-ft. by 14-ft. addition to his house in central New York that sits some 5 feet off the ground. The space beneath the addition is a great place to park a lawnmower, but it's also open to the cold.

Kevin Dickson has come across an article about a high-performance house in Massachusetts that has got him wondering whether big photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. systems are overtaking 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. to become the next big trend in high-efficiency building.

The house is the work of R. Carter Scott and a design team that included Betsy Pettit and Joe Lstiburek of Building Science Corp., among a number of other experts. It was one of eight in Devens, Mass., that Scott’s company, Transformations Inc., was chosen to build for MassDevelopment, the state’s finance and development authority.

Ralph’s new home will be in Cleveland, Tennessee, not far from Chattanooga and solidly in termite country. And that’s the problem.

Michael Roland is designing a new house and trying to choose the right wall assembly. It’s down to a choice between a double-stud wallConstruction system in which two layers of studs are used to provide a thicker-than-normal wall system so that a lot of insulation can be installed; the two walls are often separated by several inches to reduce thermal bridging through the studs and to provide additional space for insulation. filled with fluffy insulation, or a single wall wrapped in a layer of rigid foam insulation.

Energy efficient houses are becoming more common in the U.S., even if progress sometimes seems halting. What about building practices in other parts of the world? Are builders elsewhere more progressive about using new materials and techniques, or sticking to the old ways?

We get one take on this question from Eric Matsuzawa of Connecticut, who's getting ready to build a house in a Climate Zone 4A region of Japan. Conditions would be similar to those of Virginia, not especially harsh. But what Matsuzawa is learning about local building practices is giving him pause for thought.

Sal Lombardo is planning a new home in the New York-New Jersey area (Climate Zone 5) and is looking at a long list of high-performance construction options: double-stud walls, structural insulated panels, insulating concrete forms, Larsen trusses, and walls built with light-gauge steel framing.

Wait a minute. Steel framing, as in the stuff that leaks heat 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. like a proverbial sieve? Maybe, Lombardo says, it deserves another look.

The tighter the house, the more it needs mechanical ventilation. That's become a rule of thumb for energy-efficient builders, and designers often turn to heat-recovery ventilators to get the job done. These relatively simple (but not necessarily cheap) devices use the temperature of outgoing air to moderate the temperature of incoming air, thus lowering the energy penalty for providing fresh air to the whole house.