Prefers Hot Roof to Cold
The article “Retrofitting an Insulated Cold
Roof” (11/08) does a good job of identifying the
problems of condensation, heat loss, thermal breaks, and ice
dams associated with this type of structure. I’ve used
the same technique successfully for a couple of decades.
However, times change, and I have discontinued this practice
because it’s too slow, too expensive, and —
most important — not the most effective method.
Today, I use a so-called “hot-roof”
approach, applying high-density spray urethane foam from the
inside. In addition to having a high R-value, this closed-cell
foam is a moisture barrier. It’s also quite strong and
adds rigidity to the roof structure. We haven’t had
any problems with this approach. If the client insists on a
“cold” roof, I install spacers over each
rafter, followed by an additional layer of sheathing, then the
roofing the client chooses. The standing-seam metal in the
article is a great roof, but it’s generally a hard
sell when the cost comes to light.
Cold-Roof Details Critical
The details shown in “Retrofitting an Insulated Cold
Roof” are wrong from an energy standpoint. Air leakage
is typically the No. 1 cause of ice damming, followed by lack
of insulation. If an attic is air-sealed, then insulated
correctly, attic ventilation is not necessary. In fact, adding
attic ventilation will increase air leakage into the attic and
can make ice damming worse, not to mention increase the
home’s energy bills. The ice problem can be treated
less expensively and more effectively by addressing air leakage
and lack of insulation from inside the attic.
The method the author describes can work, but the joints
between the foam panels need to be air-sealed and the sheets
need to be sealed to the roof. This should be done with caulk,
foam, or an appropriate tape (not duct tape) so that cold air
cannot move around, under, or between the sheets of foam. If
the foam board is not sealed in this manner, air will
definitely be moving through it. (Take it from someone who has
done blower door tests and infrared scans on 1,000 homes in
Vermont and has seen it many times.)
Also, the original soffit vents must be sealed off and the
soffits filled with dense-packed cellulose or a two-part foam.
If this is not done, cold air will come in under the new foam
insulation, negating its benefit.
The cold-roof method as shown may stop ice damming, but
it’s because of the standing-seam roofing: Snow easily
slides off and doesn’t stick around long enough to
make ice. But until that foam is air-sealed correctly and made
part of a seamless thermal envelope, the method isn’t
lowering the customer’s energy consumption.
Back to Basics
Overall, I really enjoy every issue, but I wish there were
more emphasis on time-honored techniques and materials rather
than so much coverage of the latest and greatest applications.
I feel our industry is losing touch with the tradition of
quality craftsmanship that comes from a good grounding in
fundamentals. As an example, there are many builders who think
they can stop any chance of future water damage on a new house
by plastering everything with a peel-and-stick membrane rather
than focusing on proper layering of all the parts of a good
Concrete Epoxy Anchor
In “Adding to an Existing Slab Foundation”
(12/08), the author mentions that he drills 1/2-inch-diameter
holes for #4 rebar pins installed with SET 22 High-Strength
Epoxy-Tie adhesive. The minimum drill-bit diameter that we
recommend for the proper installation of #4 rebar pins is 5/8
inch. While we certainly appreciate that the author cites the
use of our product for this application, we also want to make
sure the text is technically correct.
Bret Turley, P.E.