Tech Spec: The Hole TruthBoise Cascade system accommodates HVAC ducting in joists between first and second floors.

  • By William F. Gloede
  • Source: BIG BUILDER Magazine
  • Publication date: 2011-05-01

Up here in the deep Northeast, we have a word for homes in which HVAC lines and other utilities are run through uninsulated crawl spaces and attics: Seasonal. Even down in New Jersey, where Tech Spec was formerly located, such lines were run through basements where, aside from the occasional condensation problem on uninsulated ductwork in the basement in A/C mode, all worked well.

This, of course, is not true in many other areas of the country, where most production home builders build amid an environment in which water tables, milder climates, and construction efficiencies make basements impractical, if not impossible. Problem is, HVAC systems that run through crawl spaces and attics, with the air handler often tucked into a garage or an attic, can waste 20 percent to 35 percent of their output to the surrounding air, according to myriad academic, government, and building industry studies. Sealing, pressure testing, and insulating ductwork can help, but it's expensive.

Boise, Idaho-based Boise Cascade has come up with a solution to this dilemma. It's a system called Conditioned Airspace HVAC framing that was introduced at IBS in January. It uses Boise Cascade's BCI and ALLJOIST engineered wood floor joists, ostensibly wooden I-beams meant to take the place of traditional 2x10s and 2x12s. Those are combined with Boise Cascade's automated SawTek systems in markets where they are located and a manual Matrix Xtreme Saw where they are not.

Basically, what it does is cut holes in the joists between the first and second floors that are big enough to accommodate HVAC ducting, even in close proximity to load-bearing walls. This is not possible with traditional lumber without compromising structural integrity.

Moving the ducts inside allows the air handler to be installed in an interior closet or an equipment room and allows shorter runs and easy takeoffs into individual rooms, where the second-floor registers are in the floor and those on the first floor in the ceiling. Less run, less energy wasted, not to mention that the space is conditioned.

A true HVAC maven will note that ceiling registers are considered fine for A/C but not for heat and vice versa for floor registers. But Mike Carver, area manager for Boise Cascade's Engineered Wood Products in the Northwest, says testing at various heights in both upstairs and downstairs rooms has shown very little temperature variation, largely because houses are much better sealed and insulated than they were when those opinions were formed.

SOLVING THE DUCT DILEMMA: When installing Boise Cascade's BCI joists, the holes can be cut manually with a Matrix XTreme Saw after the second floor is framed, or ahead of time, automatically, if the dealer or distributor owns Boise Cascade SawTek processing equipment.

Photo: Courtesy Boise Cascade

Mark Wickman, president of Vision Homes, a small home builder in Medford, Ore., has built three homes using the Boise Cascade Conditioned Airspace system (using the manual saw as he is in a rural market without access to a Saw-Tek site). “It's a real easy thing to do,” he reports. “You just need to plan ahead for it. The execution has really been pretty simple out in the field.”

Now, just for the record, this builder is not some enviro-nut. “I'm not a big greeny. I don't believe you can save the planet by building a house.” However, he is conscious of costs. Of each installation he's done, he says, “It probably cost us about a thousand dollars to do it.”

Carver allows that, on a lineal foot basis, the engineered joists are more expensive than traditional lumber. But since they are structurally stronger and thus allow for more space between joists, the cost differential can disappear rapidly.

Plus there's the marketing advantage of achieving greater energy efficiency and the necessity of complying with ever-stricter energy standards in building codes (recall those in Rep. Henry Waxman's failed energy bill in 2009, which are likely to resurface at some point elsewhere). And the simplicity. “One of the biggest challenges is that people don't understand how large a hole you can cut into an I-joist,” says Carver. “It's probably the easiest thing to do to grab 20 percent to 30 percent [in energy savings], right now.”