SIP System Fabrication
SIP (Structural Insulated Panels) The Preferred Building
System by Quality Builders, Developers and Home Owners
GREEN SENSE BUILDER PROCESS FOR SIPS - DESIGN TO FABRICATION
a. Architectural design drawings and details.
b. Engineering-structural calculations and structural details
based on the design.
c. Title 24-energy compliance.
d. Fabrication drawings for SIP panel fabrication and assembly.
e. Ordering of “Stock” panel (known as blanks)
from panel manufacturer.
f. Fabrication of panels for specific house design.
g. Delivery of wall panels for owner or contractor installation.
h. Delivery of roof panels for owner or contractor installation.
i. Delivery of various other exterior finishes to complete
the weather-tight shell.
The typical “off-the-shelf” panel comes from
the factory (manufacturer) with the top and bottom relieved
for the plates (typically 11⁄2"). The factory
provides the detail to connect adjacent panels side by
side as part of their basic setup along with their spline
material. Panels usually come with two electrical chases
run horizontally at receptacle height and at switch height.
There will also be a vertical electrical chase in the middle
of the panel. (see previous illustration of “Stock” panel).
The fabrication shop takes these “stock” panels
and will begin the basic fabrication process for the specific
home being constructed. This fabrication process utilizes
the fabrication drawings completed by the design and engineering
team. These drawings are step-by-step procedures for both
the fabrication of the panels and assembly of these panels
in the field by the client or the client’s contractor.
Fabrication consists of additional cuts, such as windows,
doors, rakes, and roof-panel plumb cuts. For example, you
might want to order gable-wall panels with the rakes precut
and the foam relieved 11⁄2"or you might want
panel #22 to have a 3" relief on the right side for
a structural post to support a ridge beam or you might
specify the electrical chases at 16" and 46" instead
of at the standard height.
During planning and layout, it can be determined where
cutoffs from one panel can be utilized to serve as headers
or filler panels elsewhere, thus eliminating waste and
saving money. At this point, it may be that a slight
change in design can help your material and labor savings
efficiently utilizing the panels. This is accomplished
during the design phase as well as the production of
shop drawings. It also determines the dimensional lumber
headers that are required in each panel, all of which
are precut, labeled and installed in the panel. Accurate
drawings are the basic road map for ordering, fabrication,
CONSTRUCTING WITH SIP WALLS, ROOFS AND
The panel to panel connections are a very important part
of the SIP system. Besides being a structural joint critical
to the integrity of the building, there are more linear
feet of potential air leakage at the panel joints than
at any other part of the system. Splines are used at
panel joints to securely hold panels together and stop
air infiltration. An approved caulking material is applied
at all panel connections to maintain the integrity of
an airtight SIP assembly.
There are three common types of wall connections,
the thin OSB spline method has become the standard in
industry because it is inexpensive and has no thermal
bridge. Next most common are the single or double 2x
spline connection and the foam block spline. All panels
come from the manufacturer precut to fit their spline
system; the manufacturer supplies
the splines. There isn’t any
fabrication to be done with the factory splines. They
are glued and nailed in place during the site construction
The two end panels on any wall have a solid stud at the
outside corner for nailing and stiffness. These full
height studs in an 8’ wall actually measure 92
7/8" long, allowing them to fit between the top
and bottom plates. The corner stud is fabricated to fit
in the panel at the fabrication shop by scooping the
foam back 11⁄2", then applying a bead of glue
to both facings and to the center of the core, and positioning
the stud, then nailing the stud off through both facings
with 8d nails 6"oc. If this is the panel that runs
through to the corner, then there will be R-Control screw
holes marked off every 16"oc with a felt marker
and pre-drilled for the field crew to fasten the corner
panels together using a 8" long control screw. The
screws will fasten through the outside panel and into
the 2x end stud of the adjacent panel during erection.
This corner detail is suitable for exterior finishes
such as stucco, shingles, log siding, and stone and brick
veneers. When using wood sidings such as lap sidings,
cedar or pine log sidings, a cap corner detail will be
used to provide extra insurance for nailing the corners.
A cap corner adds another 2x at the corner to provide
additional nailing for siding or corner trim pieces.
HEADERS AND SILLS
The type of header required in a SIP structure depends
on the Engineered Header span of the opening
and the loads imposed on the header from above. This
is determined during design and structural engineering.
If the rough opening of the window is 4’ or less
and there is at least 12" of panel above the opening,
the header can be integrated with the panel or span two
panels. In this case, the window is cut out of the panel,
the foam relieved, and 2x material installed.
For walls with window and door openings
wider than 4’,
there will be a need to install a separate header. The
header is fabricated from panel off cuts. In most cases
a 4x timber is used at all openings over 4’. These
headers will come loose and be marked as to which panel
opening they are to be installed. Western Homes provides
Weyerhaeuser insulated headers with Insulspan panels.
WINDOWS & DOORS
CUT INTO SIPS
Rough window and door openings are cut and foam is scooped
out and 2x headers, trimmers and sills are installed.
The foam for the trimmers and sills is relieved back
11⁄2". The headers are relieved back 11⁄4",
glued and nailed starting with the sill first using 8d
nails at 6" oc, then followed by gluing and tacking
the header followed by the side trimmers. A complete
window is fabricated in a few minutes.
STRUCTURAL CONNECTIONS AND HOLD DOWNS
In California, Oregon and Nevada, as well as other states,
there are specific seismic connections required. It
will be necessary to install hold-downs to lock the
SIP into the foundation or to the wall below. The typical
hold down is a Simpson STHD8RJ, which is cast in place
during the concrete pouring of the foundation and nailed
off on the outer side of the panel (see illustration).
RAISED FOUNDATION WITH SINGLE TIMBERSTRAND
SIP PANEL CONNECTOR TYPICAL DETAIL USED IN NON-SNOWLOAD
The floor and foundation plans will have
the locations of their respective wall connections shown.
The shop fabrication drawings will also note what panels
are to be connected. Because a SIP wall behaves more
like a structural unit than a stick-built wall, fewer
hold-downs are typically needed to ensure the connection
to the foundation.
It is rare that a special chase has to be placed in an
exterior wall panel if the design of the home has been
thoroughly thought out. Many times vent piping and water
piping can be placed in the interior walls, and with
under cabinet “loop vents” there is rarely
a need to install plumbing in the SIP wall. If for some
reason it is necessary, the plumbing chase can be cut
out using a two handled, hot-resistance wire tool during
fabrication. The simplest and most effective way to route
plumbing supplies and vents is to build a chase, the
same approach used in masonry and log home construction.
Roof panels excel beyond the stick-system by doing most
of the fabrication on the ground rather than up in
the air. A significant advantage of SIP roofs is that
they do not have the same ventilation requirements
as a stick-built roof. A critical and expensive step
in the planning of a stick-built roof is how to ventilate
it, and these details can be expensive, time-consuming
to build, and questionable in their performance. But
because of the consistent density of the foam core
of a SIP and its low moisture permeability, ventilation
issues become simpler, whether or not a cathedral ceiling
The SIP roof comes with fasteners (panel
screws), adhesive, and each panel will include 2x sub-fascia
installed in the panel. Depending on the type of roof
cut, the ridge blocking may come already installed in
the panel or pre-cut and marked where it should be installed.
The connection splines can come in one of three ways:
OSB spline material for no load roofs, double 2x spline
connection, or “I”-joist connection using
TJIs, Micro-lams, or Para-lam material where higher snow
loads dictate. A typical SW roof system that provides
an insulation value of R-33 will be 81⁄4" thick
up to R-52 for a 121⁄8" panel. The very best
application for SIPs is on the roof, where all of a buildings
heat tries to exit and where the most amount of time
is spent going from the ground to the carpentry task
at hand. With some planning and basic roof math, there
isn’t a roof designed that would not be cost-effective
and energy-efficient to fabricate first on the ground,
out of SIPs. Although the materials for a SIP roof are
somewhat more expensive than a conventional framed roof
or a pre-fabricated truss roof, the over all savings
is realized in the time savings (labor) to build the
roof, as well as the long term energy efficiency.
The subcontractor who will have to adjust his approach
the most, when working with SIP buildings, will be the
electrical contractor. Basically, installing wiring in
a SIP home is a lot like running wire in a commercial
job, except that the electrician doesn’t have to
install the conduit because the panels come with factory-cut
chases. When the builder erects the shell correctly,
he has already drilled most of the required holes in
the exterior walls. On raised foundations, the sill plate
must be pre-drilled for the vertical electrical chases
in the panels by the contractor. If requested, the top
plates will be marked for their specific location in
each panel and will come pre-drilled to line up with
the vertical electrical chases in the panels.
for installing wire in the exterior walls comprises only
part of the overall scope of the job,
the rest of the tasks are the same. Having the electrician
involved in the planning prior to installation of the
wiring will save time and money. For instance, if a receptacle
outlet is located 14" up from the floor, a switch
is located 44" up from the floor, and an exterior
light fixture is pulled from the same vertical chase,
the electrician’s life is made easier.
A typical 4’ wide panel has a 11⁄2" diameter
horizontal chase cut into the foam core about 14" up
from the bottom of the panel and another horizontal chase
about 44" up from the bottom. These locations will
accommodate most receptacle circuits and switch locations.
In addition, a 11⁄2" diameter vertical chase
is in the center of a 4’ panel. This basic grid
allows the electrician to run almost all of the wiring
for an electrical plan without significant drilling or
cutting of panels.
Besides the standard configuration, factory-installed
custom chases can be ordered to virtually any specification
to accommodate the most elaborate wiring plan. In addition
Western Homes offers a third horizontal chase located
about 3" above the plug height chase to accommodate
residential cabling systems (cat 5 wiring) to create
a “smart” house layout.
Cables cannot be surface-run and are required to be run
in conduit on the outside of the building. If the main
panel is in a basement, the approach is standard practice.
But for a slab building or if the main panel is scheduled
upstairs, the installation is different and the main
panel will have to be located in a mechanical room. There
are specific code requirements for clearances from the
panel to other objects, as well as in which rooms a panel
can be located and will be determined by local building
OUTLETS AND SWITCHES
Before the wiring is run, devices need to be located
and openings made for the wire runs. To prepare for switch
boxes, receptacle boxes, and fixture outlet boxes, the
electrician will need to make openings in the facings
of the panels. These can be cut either with a jigsaw
or with a hole saw. The boxes most commonly used in SIP
walls are plastic boxes with side mounting brackets that
can be screwed to the OSB. Steel boxes with adjustable
mounting ears are handy for offsetting the face of the
box to accommodate different interior finishes.
There is not much of a concern when a building has
a basement or raised foundation because most circuits
looped from below into the vertical chases provided in
the panels. But this method cannot be used with slab
construction. When the SIP structure is built on a slab,
wiring has to be pulled horizontally to feed receptacles
and switches, and some way must be found to go around
One common solution is to pull wire up
the vertical chase and along the top plate, then drop
in the next chase
around the corner, but only certain top-plate details
allow for this. Another approach involves drilling the
corner studs at the same height as the bottom chase of
the panels, where the power feeds are run. The end stud
of the panel that butts into a full-length panel needs
to have a hole drilled in it at an angle so that the
wire will sweep through it and into a connecting hole
in the adjacent panel. Upon request these holes should
be drilled during the fabrication stage. If not, they
will have to be drilled in the field prior to installation
of the corner system.
A typical well-built SIP house (designed by Green Sense
with 51⁄2" EPS core walls (a 61⁄2" panel),
a 71⁄4" EPS core roof (an 81⁄4" panel),
a passive solar design, an ICF basement, and argon-filled
low-E dual glazed windows, would allow as few as 1.0
air changes per hour (ACH) compared with the average
ACH for stick-built houses. As a measure of air leakage
through the exterior envelope of a building, ACH is the
best indicator of a building’s air-tightness and
energy efficiency as it gains or loses heat to the outside
environment. The fact that SIP buildings are typically
many times as tight as conventional stick-built homes
adds up to significantly lower heating and cooling requirements,
lower initial installation cost, and much lower operating
costs over the lifetime of the home.
In climates where temperature can fluctuate
60 degrees or more in a single day, systems such as radiant
heating are thought to be marginally effective because
their slow, even heat delivery cannot keep up with drastic
meteorological changes. But a well-insulated, airtight
building can retain a given temperature for an extended
period of time, regardless of outside air temperature,
thus placing a smaller demand on the heating and cooling
systems. As the required size of these systems decreases,
the options for the type and configuration of the system
The most common energy source for heating
and cooling systems is natural gas, propane, or electrical
heat units. To a lesser extent is air-source or ground-source
electric heat pumps, or various types of pellet fuel,
geothermal sources, or solar-powered systems. Heating
and cooling strategies can be divided into general
of active or passive and subdivided into ducted systems
and radiant approaches.
The most common approach relies
on ducting for the supply and return of forced air.
This system consists of some
type of furnace to produce hot air, a compressor or
chiller to produce cool air, and an air handler to distribute
the conditioned air. The return side of the system
also be easily tied into heat-recovery ventilators
(HRV) to maintain fresh air quality.
Vaulted spaces add
to the feeling of volume in a room, and the dramatic
spaces created can be a big selling
point for new homes. The tight qualities of a SIP
house will mean that warm air will tend to be trapped
the high side of the vaults. To gain maximum efficiency
the cold-air returns with a damper grill high up
on a wall of a vaulted room. A more flexible approach
have one grill high and one low in the same chase
have them both dampers. This way, hot air can be
returned to the cooling unit from the top grill and re-circulated
in the summer, while in the winter the hot air can
be left to condition the room and the cooler, lower
can be returned to the HYAC system to be warmed from
the lower grill.
When sizing the HVAC system the contractor
must take into account the ACH factor of SIP construction
higher R values of the walls and roof. Most residential
HVAC contractors use a basic rule of thumb formula
calculated per square foot of living space and cubic
feet per minute
per square foot to airflow. Indoor air quality unlike
some engineered wood products. SIPs are relatively
benign as far as off-gassing of harmful chemicals. However,
because of the airtight nature of a SIP building, there
will be a need to deal with interior pollutants from
such items as carpets, furniture, and paints, as well,
as appliance fumes, radon, and excess humidity. Most
of these air pollutants can be controlled by mechanical
ventilation. The goal is to exhaust the stale indoor
air and replace it with fresh outside air while controlling
The money and effort spent installing a
well-designed, efficient whole-house ventilation system
in an airtight
SIP house is well worth it, in terms of indoor air