Working On a SIPs Roof - VELUX

Working On a Sips Roof
Removing the EPS — the stuff disposable coffee cups are
made of — is not as simple as it might seem. The material
resists being cut with sharp-bladed tools, and sawing, slicing,
or chopping it produces a blizzard of foam particles that
are a pain to clean up. A “hot knife” — an electric resistance
wand that resembles a plug-in charcoal lighter — is the
right tool for this job. The wand’s element heats up quickly
and cuts through the foam like a hot knife through butter; it
quickly carved away the thick foam in repeated passes.
A rough opening in a SIP requires the support of solid
wood framing around all edges. After we finished cutting the
opening, the crew used the hot knife to recess the foam along
all four sides to receive the framing members (Figure 2, page
3). The tool shown here is sized to remove foam from the edge
of a nominal 6-inch-thick SIP so that 2x6 framing can be let
in. The adjustable depth gauge rides on the OSB and sets the
depth of the cut according to the thickness of the framing to
be installed. For this job, we set it at 1 1 /2 inches, and made two
passes to accommodate the 2x10 framing we would need for
the 10-inch-thick panel. As we inserted the framing, we used
canned spray foam to fill gaps and adhere the framing, then
nailed it off through the interior and exterior OSB skins.
The rest of the skylight installation was straightforward.
As usual, we flashed the Velux units with the manufacturersupplied
metal flashings.
Figure 1. After laying out the skylights from the interior
and removing the drywall (top), the installer transfers
the location to the roof (center). The bulk of the foam
is removed with a recip saw (above).
Prepping the Roof for the Collectors
Because the Velux solar thermal system we were using was
still new to the U.S. market, I first contacted the manufacturer
to make sure we would receive on-site technical support.
I also called the manufacturer of the SIPs to discuss the
installation.
The collectors mount directly to the roof deck without
any additional mounting hardware like stand-off brackets
or racks. Because the SIPs were attached to timber-frame
rafters spaced several feet apart, I was concerned about
not having solid anchoring points for the collectors. There
was another issue as well: In the two decades since the home
was built, some structural settling had taken place, resulting
in an uneven roof deck (Figure 3, page 3). Although
settling is normal in any wood structure as the framing
dries and gravity sets in, timber frames are somewhat
more prone to it because the heavy beams may be green
when they’re installed and can have a higher moisture content
than dry framing lumber. So even though the SIPs were
dry and stable when installed, over time they settled as the
MAY 2010 l JLC l 2