Guide to Structural Insulated Panels (SIPs)

What Are SIPs?

A Structural Insulated Panel is a large, flat, panel-like sandwich, with two pieces of plywood or oriented strand board (OSB) and a layer of insulation bonded in between. Many SIPs are available, from standard 4-foot by 8-foot pieces to panels as long as 24 feet. These are manufactured in factories and then delivered to the job site. They can be sized for almost any building design.

What Insulation Is Used in SIPs?

The most popular type of insulation used in SIPs is expanded polystyrene rigid foam insulation (EPS), with an R-value of about 3.6 per inch. A lesser-used but more efficient insulation type is polyurethane (PUR), with an R-value of about 6.8 per inch. Other options to consider are polyisocyanurate, graphite, magnesium oxide, OSB, and plywood, and straw bale insulation, although these are not as common.

If you can choose between EPS and PUR insulation types for your home, we recommend going with the PUR option. Given the substantially higher R-value, you will likely experience a shorter payback on your investment. In addition, you'll likely require a smaller HVAC system since your home will be more efficient.

How Are SIP Panels Joined Together?

A wall is constructed with Structural Insulated Panels by joining them with splines (smaller SIP pieces that lock between the panels) or other joining systems. Window and door openings are cut out with a saw. The finished product is a strong, secure wall that will withstand the roof's weight, snow, and the pushing force of the wind. Even roofs can be made with SIP panels.

Are SIP Panels Popular for Home Construction?

In recent years, SIPs have become more prevalent in residential construction. However, it may surprise you that SIPs date back to the 1930s. It is interesting to note that famous architect Frank Lloyd Wright used SIPs in his Usonian houses.

What Types of Rigid Board Are SIPs Panels Made From?

OSB is by far the most common type of rigid board used to make SIPs. This board is often referred to as the insulated panel skin.' Other types of materials used to create the 'skins' for SIPs include cement board, metal, fiberglass, and plywood, although these are less commonly used.

SIPs can be very large using rigid boards, which allows them to cover a large surface area and reduce gaps where air can escape. This approach helps to create a very tight building envelope.

How Much Do SIPs Panels Cost?

Panels are purchased by the square foot in sizes ranging from 4x8 to 8x24. The cost per square foot can vary between $5 to $7 and depends on the thickness of the panel, leading to a higher R-value. Purchasing larger panels at a higher quantity can reduce the price for manufacturers and suppliers that sell SIPs in bulk pricing tiers.

While the price of SIPs themselves is often more than traditional building materials, they reduce the labor and waste usually required during the building process. To frame a house using SIPs generally takes about eight days, compared to 12 for conventional stick framing. This reduced construction time is primarily because SIPs are made in factories, reducing the time needed to frame and insulate a home. The less labor required, the less you will spend on labor costs. And the less waste produced on the construction site, the less you will spend on waste removal and disposal. In addition, smaller heating and cooling units are required for SIPs construction. Smaller units can save you money on both the units themselves and the energy needed to heat and cool your home. 

Cost savings can largely depend on the size, location, and design of a home. According to one case study by Fine Homebuilding, a 1,000 square foot home in West Virginia built with SIPs saved the homeowners over $14,000 after ten years. These savings were due to the smaller (and less expensive) HVAC system required, tax incentives for building with SIPs, and reduced utility costs.

Are SIPs Panels Sustainable?

SIPs provide a sustainable alternative to traditional wood framing for your home because of the substantial energy they will save on heating and cooling your home. Operational energy use accounts for approximately 90% of a home's environmental impact throughout its lifetime. In a traditionally constructed home, about 40% of the energy loss is from air leakage alone. To compare a SIPs home with a traditional stick-framed home, we dove into some research studies.

An independent study conducted by the Oak Ridge National Laboratory found that a home built with SIPs significantly outperforms a home with traditional stick-framed walls. A later study by the same laboratory found that a room built with SIPs was 15 times more airtight.

A life cycle assessment (LCA) is the best way to evaluate a product's impact on the environment. An LCA of SIPs would analyze the building materials' embodied energy, construction process requirements, general maintenance, operational energy, and disposal of the building materials.

One study by BASF conducted an LCA of a home built with SIPs compared to a home built with conventional stick construction. They considered three climates in the U.S.: Minneapolis, Minnesota, Las Vegas, Nevada, and Tampa, Florida. They found that the energy savings with SIPs construction greatly outweighed the higher installation costs for all scenarios.

SIPs require less forest acreage to produce than conventional wood framing since it requires less wood (about 30%) to make. Water pollution is a byproduct of wood harvesting and production, so with less wood required, SIPs lessen water pollution.

What Are The Pros of SIPs Panels?

• SIPs go together quickly on the construction site, reducing construction labor required.
• SIPs are structurally strong.
• They can be made to a high insulation value to combat colder climates if you get the thicker versions.
• SIPs construction has minimal thermal bridging (heat loss) associated with studs in a traditionally framed wall.
• SIPs have relatively few joints, so they are simpler to seal for a tight building envelope.
• Interior and exterior finishes attach easily to SIPs.
• SIPs can help you to achieve many points toward LEED for Homes certification.
• They are suitable for any climate. SIPs have been tested in both extreme cold and heat. 
• Construction using SIPs will require less energy to heat and cool your home's interior space.
• It allows you to better control your home's air quality by creating a tight thermal envelope that will limit the air coming in and out of your home. 
• Construction materials for SIPs require little to no volatile organic compounds (VOCs) that can negatively harm your health. 
• SIPs should last about 60 years. If kept dry, it should last much longer. 
• By using SIPs, your house can be constructed on-site very quickly. In some cases, it may only take a quarter of the time used for traditional construction.

What Are The Cons of SIPs Panels?

• The most common SIPs are too thin (R-15) for high-performance Passive House insulation standards (R-40). You may have to custom order thicker panels, thereby increasing the cost of construction. 
• Wiring and plumbing take more work. You need vertical slots cut into the board and foam to run the wires and pipes. Any long horizontal slots for wiring or plumbing in the SIPs will damage their strength.
• SIPs use large quantities of plastic foam insulation from a sustainability and cost perspective, which has high embodied energy and initial cost that counters some benefits. However, the same high insulation values can be reached with high-performance framing and more sustainable insulation types like blown-in cellulose.
• The bonding of the foam to the OSB or plywood is essential to the structural strength. Therefore, you must be doubly sure to prevent it from getting repeatedly wet, especially around windows and doors and where the wall meets the foundation, so it doesn't weaken. If consistently moist, the life span of this material likely will not exceed 60 years. 
• There are no wall studs to use to attach any heavy accessories to the wall, like shelf brackets, bicycle hooks, etc.

SIP walls are an innovation that can make your walls quick to assemble and provide high insulation value and airtightness in a narrow profile. On the other hand, typical SIPs made with EPS or polyurethane insulation need a large foam quantity. In general, the foam has high embodied energy. When used, it is challenging to meet the highest energy standards like Passive House.