Q&A Spotlight

How to Insulate a Wall from the Outside

Posted on May 2, 2011 by Scott Gibson

Gregg is renovating his 50-year-old house in Wisconsin and trying to devise the best way of insulating exterior walls from the outside. The house was built conventionally, with 2x4 walls, fiberglass batt insulationInsulation, usually of fiberglass or mineral wool and often faced with paper, typically installed between studs in walls and between joists in ceiling cavities. Correct installation is crucial to performance. , fiberboard 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. , and hardboard siding.

He plans to tear off both siding and sheathing and remove the batt insulation, then apply 3 in. of spray polyurethane foam insulation into the stud bays. The existing kraft paper vapor barrier on the interior side of the wall will stay in place.

How Thick Can Foam Be Installed Beneath a Roof Deck?

Posted on April 25, 2011 by Scott Gibson

This week’s Q&A Spotlight begins with a confused architect. Like many other architects and builders, John Brooks had become accustomed to seeing spray-in polyurethane foam that completed encapsulated the rafters when sprayed on the underside of roof decks.

He’d seen Building America projects that included foam at this thickness, and points to numerous projects at GreenBuildingAdvisor where the same thing had been done.

Can Conditioned Attics Be Too Big?

Posted on April 18, 2011 by Scott Gibson

James Fincher is a builder in Oklahoma who’s leaning toward designs with conditioned attics insulated with spray polyurethane foam.

However, he’s not convinced that a conditioned attic is the best approach in a large home — something, say, in the 4,000 sq. ft. to 5,000 sq. ft. range.

The problem, as he puts it in his Q&A post, is the “sheer volume” of attics in a house this large, and whether the increase in volume will force him to use a bigger HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. system.

Using Sand to Store Solar Energy

Posted on April 11, 2011 by Scott Gibson

John Klingel's question was simple enough: what's the best way of heating up a thick bed of sand beneath a concrete slab with 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? But the underlying issue — whether a sand bed is a good idea in the first place — quickly takes center stage in this Q&A post at GreenBuildingAdvisor.

How to Keep Garage Fumes Out of the House

Posted on April 4, 2011 by Scott Gibson

Jack Woolfe wants to build a small, airtight house with an attached garage. The house will have an exhaust-only ventilationMechanical ventilation system in which one or more fans are used to exhaust air from a house and make-up air is supplied passively. Exhaust-only ventilation creates slight depressurization of the home; its impact on vented gas appliances should be considered. system, meaning the system will expel stale air from the house without providing a specific source for replacement air.

That's one of several options for whole-house ventilation, but Woolfe is weighing the possible risks.

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:

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