After 30 years of remodeling, I figured I had done just about
everything there was to do — until I took on my first
structural insulated panel (SIP) renovation. The project
involved using SIPs to transform a modest cape into a country
French-style home, with a roof featuring numerous irregular
hips, turrets, steep pitches, and radius-top dormers.
Original estimates for stick framing the roof ran as much as
$80,000 higher than the SIPs plan presented to the owners by
project architect Bill Chaleff, of Water Mill, N.Y. Chaleff
designs exclusively with SIPs and takes advantage of their
structural characteristics — their ability to act as
diaphragms, for example, or large flat beams. This means that
roof loads are evenly distributed to the walls below, so that
the complexities associated with stick-framing —
structural ridges, hips, and valleys, and the point loads
created beneath them — can be avoided. A SIPs roof goes
together like a series of large planes (see Figure 1). For this
project, Chaleff used SIPs from Insulspan (517/486-4844,
Figure 1. The architect's plans provide a
key that shows each roof section (top, center) and detail
sheets that tell the builder how to assemble the multipanel
sections (bottom). Individual panels come from the factory cut
Rebuilding the Walls
The cape — which was built in the 1930s — had
already been remodeled three times. Because the first-floor
deck wasn't level, Chaleff sized the wall panels 3/4 inch
short. This gave us room to shim the top of each one, so that
the second-story subfloor would be level. Our benchmark was the
ledger for the second-floor framing, which was attached to the
first SIP wall section that we installed — the 14-foot
balloon wall at the front of the house. From there we
calculated the different top-plate heights, using various
combinations of 3/8-inch through 3/4-inch plywood to ensure
that the entire second floor came out level.
It took a three-man crew about three days to tack the
first-floor wall panels into position. While this crew moved on
to the roof, I brought in a few more crew members to secure the
wall panels, which involved screwing the panels to the bottom
plates on the deck and screwing the plywood splines at the
joints. To prevent air infiltration where the panels butt,
Insulspan SIPs have a small channel on the edge that must be
filled with spray foam; we drilled holes along the joints at 8
inches on-center, then injected a two-part polyurethane —
Dow's Froth-Pak 180 — into the channels.
Once all the first-floor wall panels were secured, a boom truck
delivered the steel beams that would support the second floor.
We framed the second-floor deck primarily with wood I-joists,
though we used some SIPs wherever there was exterior exposure
The second-story floor joists are attached to the SIPs walls
with top-mount joist hangers, hung from either a ledger
fastened to the walls or the blocking at the top of each panel.
We attached the ledger with four 2-inch-long #10 screws and
washers 12 inches on-center, plus construction adhesive, as
specified in the plans. The connection has to be strong enough
to not only carry the floor loads, but also allow the floor
diaphragm to resist lateral thrust from the roof.
Installing the Roof Panels
Stick framing can always be adjusted when sections of a
building don't align perfectly. SIPs are less forgiving,
however, and the complexity of this roof allowed practically no
room for error. If my layout was off by as much as 1/2 inch,
the hips wouldn't come together, the dormers wouldn't fit, and
the turrets would be a nightmare to install.
Layout. We had snapped lines on the first-floor deck
to help us lay out the wall plates. We wouldn't be able to
accurately locate the roof panels and turrets that spanned the
two floors unless these lines were perfectly aligned with new
lines on the second-floor deck. To do this, we projected points
along the lower lines to the underside of the second-floor
subfloor with a Stabila LaserBob, drove nails up through the
plywood to locate these points on the second-floor deck, and
then snapped new control lines to work from.
Assembling the panels. To assist in setting the roof
panels, we had a 42-foot extending-boom all-terrain forklift
delivered and ready to go when the two tractor-trailer loads of
The roof panels arrived with bevel cuts at the ridges and
plates. The foam cores were routed for blocking, which we
ripped from 1 1/4-inch-thick OSB rim-board stock and installed
with screws and adhesive. This was labor-intensive work; in
hindsight, having it done at the factory would have saved time
Working off a set of sawhorses made from 24-foot-long LVLs, we
assembled each roof plane on the ground. To keep the project as
dry as possible (and to avoid having to staple paper on a steep
18/12-pitch roof), we installed Tri-Flex synthetic roofing
underlayment before hoisting the sections (Figure 2).
Figure 2. Roof sections are assembled and
prepped on the ground; sealing the panel joints with asphalt
cement helps prevent the OSB skins from absorbing moisture and
swelling, while extra strips of underlayment laid over the
patch keeps the tar under control (top). Placing the panels on
30-inch-tall LVL sawhorses allows crew members to work
underneath (middle). After assembly, each section is rigged
with lifting straps and hoisted into place with an all-terrain
Fitting the roof sections. Assembled SIPs are incredibly
strong; Chaleff estimates that more than 90 percent of the load
transfers across the joints, turning each panel assembly into a
huge box beam. We didn't have to use any bracing when lifting
the sections with the forklift. Locating the lifting point in
the upper third of each one made it easier to drop the lower
end onto the beveled top plates. We used tag lines to control
the lift, and chain to prevent the lifting straps from slipping
off the forks. The straps had a 5,000-pound rating; two of them
provided plenty of capacity for lifting the panels.
The first roof section was the trickiest (Figure 3). We
fastened it to the top wall plate with adhesive sealant and
10-inch-long structural screws 6 inches on-center — a
connection strong enough that it requires no additional straps
or hurricane clips.
Figure 3. To set the first roof section,
the author projects the centerline of the ridge connection
(marked on the deck) with a vertical laser line, then props the
section into position with the forklift (top). After the roof
pitch is verified with a digital level (above), the section is
temporarily braced until the opposing roof section can be
rigged and set into place.
After driving in the screws at the base, we braced the panel
and also strapped it down to the deck to prevent wind from
lifting it. We then rigged and set the opposing section,
applying adhesive to the ridge blocking and fastening the ridge
together with 3-inch-long #10 screws 6 inches on-center.
Once the main roof sections were fastened together, it was
easier to install the adjoining large and small hips (Figure
Figure 4. With the main roof sections
fastened together, the adjoining hips are installed (above
left). To save time, the author's crew preinstalls the
connecting screws on the ground before lifting the panels into
position (bottom), and preassembles small hip sections before
placement (above right).
Because the panels were so accurately cut, we had to modify
only one roof section — by cutting 1 inch off the edge of
a panel connecting two hip sections (Figure 5).
Figure 5. When a panel has been trimmed in
the field, foam must be removed with a hot iron to make room
for new blocking.
After the roof sections were assembled, we foamed all of the
spline connections (like the walls), working from the inside.
Then we applied an adhesive vapor-barrier sealing tape supplied
by the manufacturer to all the seams and the underside of the
ridge to prevent warm, moist air from migrating into these
critical joints and condensing.
Turrets and Dormers
We preassembled the turrets on the ground before placing them
with the forklift (Figure 6). Like the flat roof sections, all
of the connections were made using adhesives and an assortment
of 6- to 14-inch-long special SIP screws and washers.
Figure 6. Small and large turrets are
assembled on the ground out of precut SIPs (top) and then
hoisted into place with the forklift (middle). The
radius-roofed dormers — which were preassembled at the
factory — are lifted straight from the delivery truck to
the roof (bottom).
The radius-roofed dormers came assembled from the factory; we
simply lifted them off the back of the flatbed and dropped them
Even with all the extensive planning, we overlooked one thing:
I was admiring a newly assembled SIP turret sitting in the
driveway when I realized it wouldn't fit under the power line
running across the front of the property. Rather than wait for
the line to be lowered, we drove the turret around the property
via the street, where the lines were higher. It was quite a
sight for the neighbors to watch a roof drive by.
Roof assembly (not counting the time spent building the curved
rafter tails) took about three weeks. I estimate that, for the
same price, we could have framed a similar roof — but I
would have needed more skilled carpenters (only two were
available for this job), the project would have taken a little
longer to finish, and we still would have had to insulate the
roof.Mike Sloggatt is a remodeling contractor in