Q&A Spotlight

Are Seven Heads Better Than Three?

Posted on August 20, 2012 by Scott Gibson

John Bell, building a 3300-sq. ft. house in eastern Pennsylvania, is weighing his options for heating and cooling, and it comes down to a conventionally ducted air-source heat pumpHeat pump that relies on outside air as the heat source and heat sink; not as effective in cold climates as ground-source heat pumps. or a multi-head ductless minisplit system made by Fujitsu.

Air-Source or Ground-Source Heat Pump?

Posted on July 9, 2012 by Scott Gibson

Dana is building a tight, well-insulated house in climate zone 6 and now faces a choice between a ground-source heat pumpHome heating and cooling system that relies on the mass of the earth as the heat source and heat sink. Temperatures underground are relatively constant. Using a ground-source heat pump, heat from fluid circulated through an underground loop is transferred to and/or from the home through a heat exchanger. The energy performance of ground-source heat pumps is usually better than that of air-source heat pumps; ground-source heat pumps also perform better over a wider range of above-ground temperatures. and an air-source heat pumpHeat pump that relies on outside air as the heat source and heat sink; not as effective in cold climates as ground-source heat pumps. for heating and cooling.

“After the 30% tax incentive, there is not much increase in cost for the geo system,” Dana writes in a Q&A post at GreenBuildingAdvisor. “I am being told different stories in regard to system performance and longevity of equipment (depending on what side of the fence you’re on).”

Choosing a Cost-Effective Wall System

Posted on June 18, 2012 by Scott Gibson

Erik Olofsson is planning a small house in the Rocky Mountains of British Columbia. Ideally, he’d like to get the walls close to R-40. The question is how.

“Seeing that the received opinion around GBAGreenBuildingAdvisor.com is the tandem of polyethylene sheeting and exterior rigid foam is not ideal, what do the builders on this site recommend?” he asks in a post at the GBA Q&A forum. “Larsen trusses seem fairly labor-intensive and rigid foam is expensive ... Is 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. the answer?”

Staying Cool with a Metal Roof

Posted on May 21, 2012 by Scott Gibson

David Martin is intrigued with the idea of replacing his existing roof with a standing-seam metal roof. It should last longer than the alternatives, he says, and it would be compatible with 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. panels should he decide to add them in the future.

So what’s the issue?

David Martin is troubled by some of the advertising claims he’s seen about metal roofing, specifically a statement from the Metal Roofing Alliance that a “cool metal roof can save 25% in energy costs compared to a dark grey asphalt shingle.”

Can Vinyl Siding be Applied Over Furring Strips?

Posted on April 18, 2012 by Scott Gibson

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.

Should I Turn Down Radiant-Floor Heat at Night?

Posted on March 26, 2012 by Scott Gibson

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.

What’s the Best Approach for a Rainscreen?

Posted on February 27, 2012 by Scott Gibson

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.

Weighing the Merits of Spray Foam Insulation

Posted on January 23, 2012 by Scott Gibson

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.

How to Provide Makeup Air for a Wood Stove

Posted on December 19, 2011 by Scott Gibson

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.

How to Install Tile Over Concrete

Posted on December 12, 2011 by Scott Gibson

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.

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