How SIPs Work

And the multiple uses of pre-insulated panels…

STRUCTURAL INSULATED PANELS: SIPs are a composite building material. They consist of an insulating layer of rigid EPS (Expanded Polystyrene) foam sandwiched between two layers of OSB (Oriented Strand Board). . SIPs are a unique building product because they combine structure and insulation in one large rigid panel – up to 8’ x 24’.

How they work:

SIPs share the same structural concept as an I-beam or I-column. The rigid EPS core of the SIP acts as the web, while the OSB sheathing exhibits the same function as the flanges. SIPs combine several components of conventional building, such as studs, rafters or joists, insulation, vapor barrier and air barrier. They can be used for many different applications, such as exterior walls, roofs, and floor systems. The key to this structure’s performance is that the EPS foam core keeps the OSB skins from buckling by keeping them “in plane”.

One material with two benefits:

The rigid plastic foam core of expanded polystyrene (EPS) is the insulation and the web of the “I” beam. The thicker the panel, the more load the panel will carry and the greater the insulation value.

CNC cutting for ease of assembly:
Factory manufacturing does not just stop at the bonding of the OSB to the EPS, it continues on with precision cutting of the panels to match the specified building envelope. PorterSIPs uses 3D parametric modeling techniques to define all the panels which will be used to construct the client’s home or building. This method ensures an accurate accounting for all panels and their connections. The modeling techniques ensure rapid design, easy modifications and thorough downstream manufacturing instructions. The manufacturing instructions include shop drawings, field drawings, bills of materials, and CNC data which drives PorterSIP’s CNC machines. Final SIP cutting is done on our state-of-the-art Hundegger PBA.  This machine has a 29 horsepower, 36″ diameter, 5-axis circular saw; a 5-axis chain saw, and two different end-mill tools used for radius cutting. The accuracy of this machine, and the fact that we do a perimeter cut on all panels, means that field cutting is typically not necessary. All these features enable rapid, accurate and reliable delivery of our SIPs.

SIPs are an evolution of stick construction:
SIPs have evolved as a hybrid of stick-built construction and use dimensional lumber for corner connections, plates and window/door framing point loads, and sub-fascia. SIPs are sized to work with standard dimensional lumber; 2 x 4, 2 x 6, 2 x 8, 2 x 10 and 2 x 12.  Compared with stick framing, construction with SIPs eliminates many steps and time is saved.  SIPs contain the “framing”, sheathing, and insulation in a product that is assembled in one step.

Jumbo SIPs vs small sandwich panels:

Jumbo SIPs use large sheets of OSB; usually 8’ x 24’. Keeping the panels large is a real advantage to the contractor and structural designer. The contractor can more rapidly assemble a structure with large panels and fewer parts. With a minimum of joints the building is stronger. Jumbo SIPs can span greater distances than smaller sandwich panels.

Jumbo panels allow long spans:
Although the EPS foam core may have butt joints, the facing OSB sheets are continuous for structural reasons. Higher walls and longer roof spans are another great reason for building with PorterSIPs.

SIP erection is very similar to stick construction:

Switching from stick-built to SIP is a rather easy process that requires only a few changes. Many standard carpentry tools are still used when building with SIPs. However, power lifting equipment is required as a SIP can weigh up to 800 pounds. SIP screws are required for attaching SIPs together at corners or interior walls and fastening the roof down. The SIP screws are special fasteners which are typically 1-1/2″ longer than the thickness of the panel. These high strength screws utilize a 3” diameter washer to pull the SIP tightly to the adjoining wall, beam or corner connection. Also, these fasteners are available in three configurations: course threads for wood connections, a small drill point for light gauge metal, and heavy duty drill point for heavier gauge steel.  Using screws for the major SIP connections ensures the panel will not pull off like nailed connections are known to do. By looking at the connection details, you can see how these fasteners are used in various configurations.

Important installation differences:
Installing a base plate for rough framing and installing a base plate for SIPs vary only slightly but in two important ways. With SIPs, the OSB faces carry the axial load and with stick-construction the studs carry the axial load. Since the faces or skins are load bearing, they must bear a structural member – usually a treated plate or a structural wood deck.  Also, when using SIP walls on a concrete slab, a treated sill plate cut to the width of the panel thickness is required to separate the OSB face of the panel from the concrete slab.  This is required to keep water from wicking through the concrete into the OSB and causing moisture damage. On top of that treated sill plate is a 2nd untreated bottom plate sized to fit between the OSB faces. The panel’s OSB faces are then fastened with nails. Learn more by viewing our details.

SIPs and fire codes:
The panel’s OSB skin is typically clad in the field, both inside and out. According to building codes, interior cladding must meet a 15 minute thermal barrier requirement for most applications. To meet this requirement, ½” thick drywall or equivalent qualifies.

No-Burn® is a product we offer in conjunction with our SIPs. It offers “Class A” fire rating, and a 15 minute thermal barrier over 7/16” OSB when tested according to UL 1715.  No-Burn can replace primer at virtually the same cost as conventional paints and can even be tinted.  Additionally, it is mold resistant. Only PorterSIPs can provide this factory applied, code approved, gypsum board alternative that meets thermal barrier requirements over foam plastic insulation.  Read more on No-Burn® MIH Plus.

SIPs can also be part of a 1 hour UL rated assembly.  Follow this link to learn more.

The exterior surface requires an approved exterior siding applied over an approved building wrap or secondary weather barrier.