Open-Cell Foams Can Work in Unvented Attics
As custom home builders and remodelers, and owners of a spray-foam insulation business, we would like to commend Mr. Morshead on his article "Insulating Unvented Attics With Spray Foam" (3/07). He addressed several misconceptions that we deal with frequently in our work with architects, homeowners, and other builders.
There is one point, though, that needs clarification. Mr. Morshead discusses the fact that spray-foam insulation (both closed-cell and open-cell) is an extremely effective insulation and air barrier all in one. He writes that in his climate zone, "it's important to avoid excessive vapor diffusion," and he thinks "the best way to do this is to use closed-cell foam." Mr. Morshead later states that "some companies that make both open-cell and closed-cell foam advise insulation contractors not to use the open-cell material in unvented assemblies — or to do it only in certain climates where vapor diffusion will not be a problem."
We feel that this statement projects a misconception that open-cell foam should very rarely if ever be used in unvented attic assemblies.
As an authorized installer for Demilec, USA, we spray both closed-cell and open-cell foam. While Demilec does note specific circumstances and climate conditions for which it would recommend closed-cell foam over open-cell foam, for the most part the company voices no concerns about installing open-cell foam in unvented attic assemblies. We install foam in southeastern New England, where there are four distinct seasons, and we have not experienced any moisture or mold problems after having installed open-cell foam in numerous unvented attic assemblies over the past five years.
The important issue to stress is that if the indoor moisture level of a building is not controlled, and moisture levels are above the acceptable standard of 25 percent to 50 percent, the building is going to experience moisture problems regardless of the type of insulation installed in the attic assembly.
Paul Forsell
Shawn Ward
GreenSeal Spray Foam
North Kingstown, R.I.
Code Clarification
I would like to clarify an issue regarding the sizing of birdsmouths (Q&A, 5/07). According to the IRC (exception R802.7.1), if the birdsmouth occurs at the end of a rafter with a 24-inch overhang or less, the notch can be deeper than the D/4 limit, provided that at least 4 inches of material is left to carry the cantilevered overhang. For overhangs greater than 24 inches, the D/4 notching rule would apply.
Michael Stayman
Stayco Construction
Chambersburg, Pa.
Bees in Brick? Not to Worry
I'd like to address Mr. Newman's concerns about honeybees behind brick veneer (Letters, 6/07). Unlike some wasps, honey and honeybees (Apis mellifera) pose absolutely no threat to a building. If the hive is healthy, either the honey will be capped in airtight and watertight cells in the comb or it will be dried by the bees. The conditions in the hive are clean and nearly sterile, thanks to the hygiene habits of honeybees. Unless there are existing structural or weather-sealing issues, the bees simply won't affect the building.
If, however, the hive were to die (from the misuse of insecticide, for example) any dead bees and the honey would eventually be cleaned out by other bees or other insects. The tragedy is that the insecticide could be transported with the honey to otherwise healthy hives nearby.
Probably the largest concern around honeybees behind a brick veneer would be the stinging risk to the human occupants as the bees defend against perceived threats near the hive entrance. For the most part, though, honeybees are docile, beneficial insects.
A simple screen (smaller than 1/4 inch) inserted into the weep holes would deter similar swarm infestations in the future.
As a beekeeper who also happens to be a residential designer, I encourage anyone with a similar problem to consult with a local beekeeper. A beekeeper will be able to clarify whether the insects are bees or wasps, and might even remove them free of charge.
Gregory Smith
Smith Design Studio
Olympia, Wash.
Correction
The article "A Builder's Guide to Energy Codes" (6/07) lists Alaska as utilizing IECC 2003, which is incorrect. As of April 1, 2007, a new residential energy code has gone into effect; it consists of the IECC 2006, second printing, and the ASHRAE Standard 62.2-2004 for ventilation, both with Alaska Amendments. For more information, go to www.ahfc.state.ak.us/reference/bees_standard.cfm.
Cary Bolling
Alaska Housing Finance Corp.
Anchorage, Alaska
