Q&A Spotlight

Reviving an Old Debate on Vapor Barriers

Posted on March 21, 2011 by Scott Gibson

The post was simply labeled “Martin Holladay” — for the GreenBuildingAdvisor senior editor — but the question from architect Stephen Thompson went to the heart of one of the most contentious building questions in recent history: is a polyethylene vapor barrier a good idea?

Thompson tells Holladay he's read much of what Holladay has had to say about vapor barriers, but he still is puzzled by several comments.

Are High-Performance Windows Worth Their High Cost?

Posted on March 14, 2011 by Scott Gibson

Randy George is in the final planning stages for a new house he will be building this summer in Vermont, and from the sound of it he won't have much trouble staying warm through those long winters.

In addition to R-45 walls, an R-65 roof and R-20 slab, the house will have air infiltration rates lower than one air change per hour at 50 pascals of depressurizationSituation that occurs within a house when the indoor air pressure is lower than that outdoors. Exhaust fans, including bath and kitchen fans, or a clothes dryer can cause depressurization, and it may in turn cause back drafting as well as increased levels of radon within the home.. Although not quite meeting the 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. standard, that's extremely tight construction.

How to Calculate the Value of Energy Improvements

Posted on March 7, 2011 by Scott Gibson

Adding more insulation, replacing an inefficient furnace, or performing air-sealing measures are oft-recommended strategies for lowering energy consumption and saving money.

Aaron Vander Meulen puts his finger on a key issue, however, when he wonders whether there is a way of determining exactly how much money improvements such as these will save.

How to Insulate a Cathedral Ceiling with Mineral Wool

Posted on February 28, 2011 by Scott Gibson

John Roy is building a house in southeastern Massachusetts, and at least part of it will have a cathedral ceiling. He's thinking of insulating the ceiling with dense-packed rock wool.

The president of a local insulation company tells him there's no need to install air chutes in the rafter bays before the insulation is blown in because the insulation does not absorb water. The local building inspector is prepared to go along with the recommendation providing soffit vents are installed.

Should It Be a Passivhaus or a Passive House?

Posted on February 21, 2011 by Scott Gibson

Jason Kibbe is in the enviable position of planning the construction of a new house that will be financed entirely by the sale of his current home, leaving him in new digs without a mortgage.

Kibbe plans to swap his 4-bedroom, 2 1/2-bath house in south-central Pennsylvania for a 3-bedroom, 2-bath house of between 1,500 and 1,700 sq. ft, and he's upfront about his motives:

Right Idea, Wrong Result: A Cellulose Insulation Job Goes Off Track

Posted on February 14, 2011 by Scott Gibson

Jason Shapiro took the plunge and invested in more insulation for his house: blown cellulose for his attic and dense-packed cellulose in the exterior walls. No doubt he'd like to be enjoying a warmer house and lower energy bills. Instead, he's dealing with a mess.

How to Insulate a Slab Foundation—With Straw-Bales?

Posted on February 7, 2011 by Scott Gibson

Superinsulated houses need insulation under the slab as well as in the walls and roof, and the most common choice for sub-slab insulation is rigid foam.

Is Radiant Floor Heat Really the Best Option?

Posted on January 31, 2011 by Scott Gibson

Lukas Smith, a framer by trade, is building a 3,100-sq. ft. house in southern Ontario and plans to install a radiant-floor system in the basement slab as well as the first and second floors. The house will be built with structural insulated panels (SIPs) and have R-values of 33 in the walls and 50 in the roof.

Are Masonry Heaters a Good Match for Superinsulated Houses?

Posted on January 24, 2011 by Scott Gibson

In New York City, it's been considered a real coup to land an apartment with a fireplace. Now, according to The New York Times, those once lucky urban dwellers are having second thoughts. New concerns about the environmental and health hazards of wood smoke, an article this week said, are outweighing the charm of those cheery winter fires.

Can Open-Cell Foam Waste be Used as Attic Insulation?

Posted on January 17, 2011 by Scott Gibson

UPDATED 1/19/11 with comments from Peter Yost

Open-cell polyurethane foam expands dramatically as soon as it hits its target, rapidly filling wall cavities and typically mushrooming beyond the stud line. After it's firmed up, installers trim away the excess so drywall or other wall finishes can be put up.

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