Sep 11, 2017
How do you quickly build a strong, thin, well-insulated wall without using stick framing? One approach is to use Structural Insulated Panels (SIPs). This increasingly popular building material combines structural support and insulation in one single panel. These are worth considering for your home construction and renovation projects. Here is how they work.
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.
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.
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.
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.
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.
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.
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.
There are many things to consider when designing and building a new home. Here we will give an overview of the pros and cons of this innovative building product.
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.
Look for SIPs with a high enough insulation value to meet high-performance building standards. For a Passive House in a cold climate like Canada, approximately R-40 walls are needed, about 10 to 12 inches thick for EPS insulation and 7 inches thick for closed-cell polyurethane.
To minimize the environmental impact of manufacturing the SIPs, ask your manufacturer if their foam is made with the lowest possible Global Warming Potential (GWP).
Want to use SIPs in your new home construction? Find a certified manufacturer here.
Located in Roanoke, Virginia, Maria Saxton holds a Ph.D. in Environmental Design and Planning from Virginia Tech. She works as an Environmental Planner and Housing Researcher for a local firm specializing in Community Planning, Architecture, Landscape Architecture, and Historic Preservation. Her dissertation explored the environmental impacts of small-scale homes. She serves as a volunteer board member for the Tiny Home Industry Association.