Green Building Topics

Green Building Materials Guide

STRUCTURAL INSULATING PANELS

Considerations:

Structural Insulating Panels (SIPs) reduce construction waste and provide superior insulation, in comparison to conventional stick or steel stud systems. Consider:

Design to minimize waste:
- Order SIP panels precut for your project, including apertures for windows and doors.
- Design to standardized panel dimensions.
Ask if your SIP supplier or manufacturer will take back any off cuts for recycling.
Consider the thermal performance of SIPs when sizing your heating system to save money up front and to save energy in perpetuity. Oversized heating and cooling systems are inefficient.
SIP roofs do not necessarily require ventilation. If your local jurisdiction mandates ventilated roofs, consider SIPs with integrated air channels under the exterior sheathing, or upgrading from composition roofing.
Some SIP manufacturers will provide SIP's with finish materials pre-attached, particularly for non-structural use.

Summary: Structural Insulating Panels

Structural Insulating Panels (SIPs) are premanufactured panels that consist of two sheets of rigid structural facing bonded to an insulating core that is 4 or more inches thick. Facings are generally OSB (oriented strand board) or plywood, and the core is most commonly polystyrene foam. SIPs offer excellent insulation, accelerated construction, airtight assembly, noise attenuation, and superior structural strength. Though SIP panels cost more per unit of wall, floor, or ceiling than conventional construction, total construction costs are often less than with conventional construction due to reduced labor and faster completion.

SIPs reduce construction waste; they can be delivered precut to the precise dimensions required, and each panel contains the structural, insulation, and moisture barrier of the wall system. OSB is the most common sheathing and facing material in SIPs, reducing wood use by as much as 35% and reducing pressure on mature forests by allowing the use of smaller farm-grown trees for structural applications. The exterior grade plywood used in some products requires more mature timber.

SIP wall assemblies tend to be well sealed, enhancing energy efficiency. As with any tight structure, moisture control and well designed ventilation are critical. SIP construction can contribute to very good indoor air quality; the plastic insulating foams (expanded polystyrene or polyurethane/polyisocyanurate) are very chemically stable, and OSB is a low-emitting material. In an SIP house, good ventilation and the use of non-toxic finish materials and cleaning products are more important for indoor air quality than emissions from SIPs.

SIP core materials have environmental tradeoffs:

Straw Core SIPs are made from waste agricultural straw. They are renewable and recyclable, and the pressed straw core does not require a binder. On the other hand, straw-core SIPs offer less insulation per inch of thickness and are considerably heavier than other options; energy use in shipping is a significant consideration.
Expanded Polystyrene (EPS): EPS is the most common SIP core material. It requires less energy manufacture than other options, and is more recyclable than polyurethane or polyisocyanurate. The potential for emissions from burning polystyrene in the event of a fire is a concern, albeit minor, because most polystyrene SIP products are more fire resistant than conventional stick frames. Many products offer a 1 hour fire rating when installed with 5/8" or thicker gypsum sheathing. EPS foam is expanded with pentane, which does not contribute to ozone depletion or global warming, and is often recaptured at the factory for reuse.
Polyurethane/Polyisocyanurate: Both of these materials offer greater insulation per inch of foam than EPS, are more resistant to thermal breakdown. However, polyurethane and polyisocyanurate are unlikely to be recycled. Polyurethane and polyisocyanurate use HCFC blowing agents, which contribute to global warming and ozone depletion (though to a lesser degree than CFCs.) New polyurethane/polyisocyanurate resins derived from soy are not available in SIPs yet.

For More Information:

Structural Insulated Panel Association

“Structural Insulated Panels - Strength and Energy Efficiency Through Structural Panel Construction”
Morley (2000) ISBN 1-56158-351-0, available via the Santa Cruz Public Library System

Oikos
A free website with information about a wide range of greener construction products

GreenSpec
A fee-based service that is searchable by the standard UniFormat, and is probably the most comprehensive source of green building product information

Center for Resourceful Building Technology
Information about environmentally preferable building materials

EPA Environmentally Preferable Purchasing

California Integrated Waste Management Board

Program Contact

Ecology Action

Phone: 831.426.5925
Fax: 831.425.1404
Email