Structural Insulated Panels (SIPs) - for wall, floor and ceiling construction - vary in their thickness and type of core, as well as in their quality and type of boards; and prices vary accordingly.
SIPs are not all manufactured equal.
Fiber-cement SIP panels and common extruded polystyrene SIP OSB panels are rather different products, with different insulation quality.
»» Pay special attention to the thickness of their core. That's very important for insulation and low-energy homes.
»» There are poor constructed panels, with thin cores, poor adhesives and low-quality boards.
Typical SIP Insulation Value
Typical SIPs are made with an inner core of foam insulation - often XPS (extruded polystyrene) or EPS (expanded polystyrene) - between two skins of OSB boards.
SIPs are large engineered building panels for wall, floor and roof construction. SIPs provide framing, insulation and sheathing in a single panel. With SIPs, homes can be erected in a few days. Their insulation value (R-value) varies with their thickness, often R-4 to R-5 per inch (Metric U-value: 1.,41 to 1.13).
Aa 4 1/2 inch-thick panel has an insulation value between R-14 and R-20 (Metric U-value: 0.4 to 0.28), which is a reasonable or good value for walls in moderate and hot climates; it exceeds the recommended building code insulation requirements for most climate zones.
But you should require more. That's very important for energy efficiency, and SIPs provide the most inexpensive way of getting it (see data on table below).
Their skins (OSB) are a wood engineered product made from cross-oriented layers of thin wooden strips; you can imagine them as a special sort of plywood…
SIP core Alternatives
Though expanded polystyrene (EPS) is the most common material used in the SIPs manufacturing, there are other alternatives for their core: extruded polystyrene (XPS), polyisocyanurate, urethane, polyurethane, compressed straw, mineral wool... Adhesives are a key part of SIP construction (the adhesives bond the boards to the core). The strength and the quality of the glue determines the strength of the panel to resist to special forces, or even its moisture-resistance… Urethane glue is a good adhesive, very common in standard SIPs.
XPS SIPs are a bad option, from an environmental standpoint. And there are greener options made from recycled foams or from agricultural waste straw. The downside of these last panels is that they have a lower R-value per inch and are heavier (and costly to transport and more difficult to handle in the construction site).
Though foams are petroleum-based products, they are mostly made up from encapsulated air (98%) and, according to the SIPA, they can save in a single year up to 20 times the amount of the energy used in their manufacturing.
Most manufacturers use OSB boards with a tested and economical waterproof bond.
Fiber-cement SIP wall panels are a lot less common, costlier and more breakable, but do not rot and are mold-growth- and formaldehyde-free (they can provide the same air-tightness and R-value of OSB SIPs).
Prices vary with manufacturers.
Standard OBS SIPs (4'x8'-16' with 7/16" OSB/EPS foam) wil cost you between $3 and $4 per square feet, according to their thickness (4-7 inches). Improved cores (with graphite, for instance) and panels with alternative cores and facings will cost you significantly more.
SIPs are cost-competitive with wood-frame building. Material costs can be 5-10% higher, but labor costs are a lot lower.SIP sizes
Most SIPs panels (either OSB or fiber-cement) are 4 to 24 feet (1,2 - 7,3m) wide and 8 or 9 feet (2,4 or 2,7m) high. Typical SIP wall panels accept 2 x 4 bottom and top plates. Panel lengths can vary up to 24 ft (7,3m). Besides the rectangular-box designs, built with standard SIP panels, some manufacturers are producing customized panels for curved walls and special architectural features.
Standard OBS SIPs with average core-thickness and a good adhesive system are cost-competitive with other types of construction, particularly with conventional wood-frame construction.
But pay attention to the thickness of their core, and quality. There are poor constructed panels, with thin cores, poor adhesives and low-quality boards.
Take also into consideration alternative products: greener alternatives include polyisocyanurate SIPS (polyisocyanurate is a foam with high insulation level) and SIPS with compressed straw and mineral wool cores.
Fiber-cement SIP panels are also a greener alternative. They are mold and formaldehyde-free and have a higher moisture resistance; but they too are more expensive...