Q&A Spotlight

Wall assemblies that incorporate rigid foam insulation over exterior 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. , followed by furring strips and siding, are becoming common. The extra layer of insulation helps 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. through wood framing, and the furring strips create a ventilation space behind the siding that promotes drying.

Does it pay to turn down the heat at night when you have a radiant-floor heating system? David Meiland and a heating contractor are having trouble seeing eye to eye on that question.

Meiland says the house they're discussing is a slab-on-grade with R-10 insulation below and PEXCross-linked polyethylene. Specialized type of polyethylene plastic that is strengthened by chemical bonds formed in addition to the usual bonds in the polymerization process. PEX is used primarily as tubing for hot- and cold-water distribution and radiant-floor heating. tubing cast into the slab. In another part of the house, the floor is framed, with PEX installed below in tandem with aluminum plates that help distribute the heat. The boiler is a 30-kW electric model with an outdoor reset.

Aaron Vander Meulen is building a house whose exterior walls will consist of 2x4 framing with cellulose insulationThermal insulation made from recycled newspaper or other wastepaper; often treated with borates for fire and insect protection., bracing, 2 in. 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.) foam, furring strips and, finally, Extira siding, an exterior grade wood composite.

Meulen is leaning toward horizontal rather than vertical furring strips because they’ll make it easier to install the 2-ft. by 4 ft. panels.

Scott Jacobs’ 1,100-sq. ft. Cape is a perfect candidate for an energy upgrade. The 90-year-old house is gutted, and Jacobs wants to insulate it well even if his budget is not unlimited.

The house, located in Climate Zone 6, now has a 1/2-in. thick layer of rigid foam on the exterior walls. Jacobs’ plan is to insulate the house from the inside with spray polyurethane foam.

Wood stoves used to be pretty uncomplicated devices. Even though they weren’t airtight and they weren’t especially efficient, these cast-iron stoves warmed plenty of New England farmhouses in the dead of winter.

Our forebears never considered the source of makeup air to replace all the heated combustion gases that were going up the flue. They didn’t need to, because back then, houses were leaky. As the stove burned its load of oak or maple, makeup air had no trouble finding its way into the house.

Tile can contribute thermal massHeavy, high-heat-capacity material that can absorb and store a significant amount of heat; used in passive solar heating to keep the house warm at night. to a passive solar house, and to Christa Campbell it would make a more appealing finish floor than concrete.

Although tile can be placed directly over a concrete slab, products such as Schluter’s Ditra are designed to separate, or “uncouple,” the tile from any potential movement in the substrate and protect the tile and grout from cracking.

The question for Campbell is whether using Ditra offsets some of the thermal mass gains in a passive-solar design.

Windows are often a dominant architectural feature in old houses. A six-over-six sash with wavy, bubbled glass has a charm that modern windows can only aspire to, more than offsetting their less-than-stellar energy performance.

Or so many local historical preservation committees would argue. And, as Mike Keesee has discovered, that’s a frustrating problem for builders and homeowners who want to make energy-efficient windows part of a renovation.

What began as an attempt to track down the source of air leaks in his one-year-old home has led Kevin Hilton to a deeper mystery — a natural gas odor that is apparent only when energy auditors are running 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..

As Hilton explains in a Q&A post at GreenBuildingAdvisor, the source of the gas leak has been impossible to track down so far.

A range hood that whisks away cooking odors, moisture, and grease is almost always recommended as a way of keeping indoor air healthy. But what happens to the equation when the range hood is a behemoth, capable of sucking up 900 cubic feet of air per minute?

That’s the dilemma that Sean McLoughlin is facing as he designs a 3,500-sq. ft. house in southern California. The kitchen will be outfitted with a professional-size range and barbecue grill.

Leaky ducts in a forced-air heating and cooling system are an all-too-common problem contributing to significant energy losses and lower indoor air quality.

Mark Renfrow knows that. Duct tests at his 3,400-sq. ft. home revealed “huge leakage.” A contractor addressed the problem by applying mastic to any accessible ductwork. But the key word is “accessible.” Many parts of the system apparently are not so easy to reach.