Q&A Spotlight

Ted Storm is in the midst of a construction project and at a point where he needs to make a decision about attic insulation. The unvented roof consists of standing-seam metal over synthetic felt and oriented strand board (OSB) 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. . Both HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. equipment and air ducts will be located in the attic of this house in Climate Zone 4.

Three insulation contractors are unanimous in their recommendation to spray a 6-in. layer of open-cell foam on the bottom of the roof deck.

While the advice is consistent, Storm is having second thoughts about his decision not to vent the roof.

In Dallas, Texas, Marc Kleinmann is working on plans for a house which the owner wants to look like the the iconic designs by California developer Joseph Eichler: lots of glass, a low-sloped roof, and roof beams that penetrate the exterior walls to support a broad roof overhang.

That style was all well and good back in the 1950s and ‘60s, but with our keener interest in energy efficiency, Kleinmann wonders in this Q&A post at GreenBuildingAdvisor whether it really makes much sense.

Most houses with solar electric panels remain grid-tied, meaning the house is still connected to the utility’s grid even as it has the means to produce its own power. Off-grid houses, which once accounted for the lion’s share of installations, are now in the minority.

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.

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.

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.

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.

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.

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.

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.