Structural insulated panels (SIPs), also known as foam core, stress-skin or sandwich panels, are a highly energy efficient alternative to stud-frame construction. These wall and roof sections, that are custom fabricated for every Sunlight home design, are factory-built under controlled conditions which increases the quality and precision of the finished product. Door and window openings are precut using state-of-the-art CNC (Computer Numerical Control) computerized cutting equipment which ensures square and level openings. The structural insulated panels (SIPs) are shipped flat on a truck to the building site where they are assembled like a big jig saw puzzle, resulting in a highly insulated, tight, precise, finish-ready structure. Because SIPs have the insulation and sheathing built in, there is less on-site assembly, which means a more predictable, higher quality result. In comparison, a site-built, frame structure has many site-related variables such as weather and the skill level of the building crew. There are many more pieces to assemble, opening the project up to more variation. It's worth considering structural insulated panel construction if you're interested in a well built, energy efficient, comfortable, green home.
SIP R-Values + Energy Star
R values measure the capacity of a material, such as insulation, to resist heat flow. The higher the number, the better the resistance. We use Murus polyurethane SIPs that have an impressive aged R-value of 6.76 per inch. We use 5-1/2", R-33 wall panels and 6-1/2", R-40 roof panels in our homes. When the finish materials are added, the composite R-values are R-37 (walls) and R-42 (roof). Murus's SIPs are Energy Star rated and are listed in the Greenspec Directory; an independent agency that qualifies green and sustainable construction products.
Less Wood!Structural insulated panel construction contains much less wood than conventional construction because using polyurethane panels means
that there are no studs! The only lumber used in the panels is oriented strand board (OSB), a structurally-rated sheathing material made from fast-growing, renewable, self-regenerating forests or plantation-grown trees. Even with less wood, polyurethane structural insulated panels are much stronger than conventional frame construction because the walls are, structurally, like an I-beam. The load is carried in the skins (the OSB), hence the name stress skin panels. Murus's OSB manufacturer is a member of the Sustainable Forestry Initiative.
Polyurethane Foam SIPs
Polyurethane foam has been used extensively for decades in projects small and large. It is safe to humans and the environment. It does not contain formaldehyde or CFCs. Once cured, urethane is an inert, thermo-set material that does not support combustion. It has a Class 1 fire rating, the best available. Several of our past clients with chemical sensitivities have tested samples of urethane panels. Not one has ever had a reaction. We like polyurethane because with its high R-value. It does its job better in a smaller amount of space.
Structural insulated panel construction is considered an alternative building system. SIPs are made from either polyurethane or polystyrene. Murus makes both. There are significant differences between the two types of foam. Polystyrene (the white "coffee cup" material) has an R value of 3.85 per inch, compared to 6.76 per inch in polyurethane panels. Polystyrene is a thermoplastic. When heated to high temperatures, as in a fire, thermoplastic materials melt. Polystyrene panels are much more common and are manufactured in many locations across the country because the manufacturing is more simple. Sheets of styrene are glued to skins, usually OSB. As a result, polystyrene panels are less expensive than polyurethane panels, and more readily available.
Manufacturing Polyurethane SIPs
During manufacture, polyurethane (a two-part, epoxy-like foam) is injected between two OSB skins. The OSB skins are held in a press as the foam expands to fill the cavity. As the urethane cures, it forms a mechanical bond with the skins, creating an incredibly strong, monolithic structure. The resulting SIP panel is like an I-beam with foam instead of webbing. Polyurethane panels are much stronger than frame construction or polystyrene structural insulated panels because of the mechanical bond between the skins and the foam.
The machinery used to manufacture polyurethane SIP panels is more sophisticated and costly than the process used to make polystyrene panels. For that reason there are only a few polyurethane SIP manufacturers in the US.
We are not affiliated with any manufacturing system. This allows us the flexibility to choose whatever system best fits our needs. We could purchase styrene panels more conveniently and for less, but we prefer to use Murus's polyurethane SIPs because of the quality of their product, their integrity and their customer service, which has impressed us for over 25 years. Having a long-term working relationship with one panel company allows us a higher level of consistency, predictability and quality in our end product.
Polyurethane structural insulated panel residential construction has been around for decades. At Sunlight Homes we have used polyurethane panels as our primary building method with great success for over 30 years. Ask an engineer about structural insulated panel (SIP) construction and you're sure to hear great things!