Open-Cell Foams Can Work in Unvented
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
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
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.
GreenSeal Spray Foam
North Kingstown, R.I.
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.
Bees in Brick? Not to
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
A simple screen (smaller than 1/4 inch) inserted into the weep
holes would deter similar swarm infestations in the
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
Smith Design Studio
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
Alaska Housing Finance Corp.