SIPs - A Quick Overview!

Although SIPs are an important part of energy coservation, they have a "life of their own."  Because of the structural properties, SIPs can, and do, take the place of exterior walls and roof  systems.  When we discuss hybrid or minimum structural timber concepts, SIPs still create the balance of the exterior envelope.

What are SIPs?

Structural Insulated Panels, or SIPs as they are called, create the outside shell, or exterior envelope of a building - even floors when the floor system is exposed to ambient conditions.

A SIP is a building product made of two outside layers, or skins, that are laminated to a solid interior core of rigid insulation. The outside skins are usually OSB and the best inside core product is modified Expanded Polystyrene, or EPS. Better EPS cores also include borate as in insect deterrent, and we use nothing else.

Structurally, a SIP performs in the same fundamental way as a steel or wood I-beam. The outside skins act as flanges while the insulating core is the web member. SIPs are therefore incredibly strong. Typically they test between 2 to 10 times stronger than conventional framing materials.

SIPs create a superior insulation system.  To understand why, we need to analyze a conventionally framed and insulated wall. We all tend to think of a 2x6 conventionally framed wall with R-19 fiberglass insulation as having an insulating value of the fiberglass value, or R-19. When the actual analysis of the stud constructed wall is made, we find about 30% of the total wall area is actually wood, not insulation. All the wood plates, studs, headers and jacks that make up the stud wall can only product an R-1 insulation value per inch of wood depth. Averaging together the wood and fiberglass areas product an actual stud wall insulation value of about an R-13. Further, fiberglass insulation can loose some of its insulating properties when subjected to even small amounts humidity. Improper installation can also account for additional losses. The result - even the lower net R-13 stud-wall insulation value is diminished even more.

SIPs, however, contain only about 2% to 4% wood members, so it’s initial R-value remains virtually in tact. Further, the insulating value of the EPS core in a SIP panel is not affected by moisture.

A 6-1/2" SIP panel measures an insulation value of R-24.3. A 2x6 Stud Wall with fiberglass actually nets to at or below an R-13. The SIP is the clear winner with virtually double the installation value for a 6" wall system.

More SIP information is widely available in books and many other sourses.

We want to make it clear - SIPs are a great product, but there are many other factors that go into designing the best energy efficient structure possible. Our Energy Analysis process helps to pinpoint the best overall options.