New Materials for Current Times: A Series of Articles on Green Building Materials
October 30, 2008, by David JoynerThis article was written because many I spoke with professed an interest about building and design with the newer "green" materials. We intend to discuss the merits of working with Structural Intergraded Panels.
Structural Intergraded Panels or SIPs as they are known are an environmentally safe building product with over 20 years in the building industry. Structural Intergraded Panels are typically used for exterior walls and roofs for residential and light commercial
buildings. Structures using Intergraded Panels can go up to four floors with the proper engineering. SIPs can also be used in multi-story structures in combination with concrete on the lower levels.
The panels are created by sandwiching ridged foam plastic insulation between structural skins. The two outside skins are typically oriented strand board (OSB) or plywood. Some manufacturers can go another step and install interior sheetrock, hardwoods, or other surfaces which will serve as the interior finished surface. I personally have experience as the roof of my own residence is made of SIPs. We had the manufacturers adhere green board on the bottom of the roof panels so that after installation minimal amount of labor was needed in order to finish out the sheetrock ceiling. Manufacturers in the Northeast even apply tongue & groove wood planks so the finish product has a "lodge" appeal.
The biggest benefit of SIPs panels is that the building envelope is much tighter with fewer leaks and penetrations through the wall1. This provides a superior thermal insulating effect. Since SIPs panels are sandwiched panels, structures constructed from SIPs panels for the walls and roof use up to 35% less timber than a traditional stick frame structure2. Since SIPs panels are manufactured in a controlled environment and prepared for the job site and shipped, this means that the insulation SIPs panels goes up faster than traditional stick buildings. This makes the use of the product ideal for apartments, some retail centers, garden offices, and home construction. It is likely that a doctor's office or retail center could go up faster with SIPs than with tilt wall or conventional construction techniques.
The excellent thermal qualities translate to a savings in the mechanical systems of the structure. Generally, HVAC systems can be downsized anywhere between 30 and 50 percent.3 Since heating and cooling represent one of the largest users of energy in your structure, using SIPs panels can reduce this portion of your energy consumption to as high as 50% depending on the location, geometry and size of the structure. SIPs use an insulation called EPS Foam (expanded polystyrene). EPS is composed of a ridged foam 98% air and requires only a small amount of petroleum to produce.4
The erection of intergraded panels generally goes up quite quickly, particularly if they are custom cut and fabricated in the factory and sent to the job. The cost of providing SIPs panels can look more expensive in the beginning but eventually when you take into account the construction time, labor costs, waste product, and energy savings of the structure; SIPs cost no more than 3% than typical stick built construction.5
Source: Structural Integrated Panel Association
SIPs can also take on the exterior just about any exterior covering typically used in residential or light frame commercial construction. There is a possibility, based on the city and state that you reside in, you might be able to receive tax credits for using SIPs construction6. If you are a home owner or residential home builder check and see if your mortgage company offers discounts for energy efficient homes with an energy efficient mortgage.
SIPs panels come in different sizes but typically they use ordinary sawed lumber as their cores. Three and a half inch cores have an R value of 14.5, while 2x6s are R Values of 22.5, eight inch interior cores have a depth of 7.5 inches and an R Value of 30.257. In conventional construction even when blown insulation or rolled insulation of R14 is installed the combined value of the total wall needs to take into account the studs, nails, electrical openings and others reduce the overall R Value of a stick frame construction. For information on how much a deduction in the insulation value this causes, go to Oak Ridge National Laboratory www.ornl.gov. For additional information on SIPs construction and their specifications also visit www.sipa.org .
As an engineer, we do a good bit of design in the windstorm areas along the Texas Coast. SIPs frame construction would be an excellent substitute for traditional stick frame construction in these areas. The structural characteristic of a SIP panel is similar to those of sandwich or an I-beam. As a wall panel, they can hold a tremendous amount of weight and the joints in the corners are very efficient at securing buildings and providing shear resistance. For fire protection purposes, SIPs need to be protected such as any other wood structure. One of the things we would advise is that the electrical design and installation needs to be coordinated with your SIPs manufacturer more closely to eliminate potential wiring headaches. Electrical chases are provided standard in some manufacturers of SIP panels (check with your manufacturer).
SIPs can be married to a lot of other standard building products, floor trusses work well, roof trusses can be used, SIPs can be used for the roof panels themselves, they can be the exterior skin for timber frame buildings (typical for homes and churches). SIPs panels can even be used for floors if a structural engineer will properly span the panels to meet floor loading criteria.
For structural performance of SIPs panels, we suggest becoming familiar with the loading for your particular design, the wall thicknesses that you intend to use and then check web sites www.SIPs.org and www.icbo.org for additional information on the vertical and horizontal loading SIPs panels can provide. Please check with your manufacturer to see if they have a loading chart. This will be instrumental to your project designer.
Whole Wall R-Value
*Study shows how typical installation imperfections such as batts with rounded shoulders, 2% cavity voids, no compression around wiring, and paper facer stapled to inside of studs, change the whole-wall R-value of fiberglass rated at R-19 to R-11 in a 2 x 6 wall with studs spaced 24" o.c.
SIPs Conserve Energy
The foam insulation used in SIPs is extremely effective because it is solid and consistant throughout the home. In addition, SIPs are made in large sections, up to 8' x 24', meaning there are fewer gaps and heat or cooling loss due to air infiltration.
SIP homes have repeatedly demonstrated annual energy savings of 50-60% when combined with other high performance systems. SIP test homes monitored by the Department of Energy's Oak Ridge National Laboratory had heating and cooling costs as low as 45 cents per day.
Home energy use has a suzable impact on the environment. Homes account for 15% of energy use nationwide, and release on average 22,000 lbs of CO2 into the atmosphere annually, roughly twice as much as the average car. Building a SIP home that uses half of the energy will be the same as removing one car from America's highways.
Source: Oak Ridge National Laboratory
What Are SIP Walls? A consumer brochure by SIPA (Structural Insulated Panel Association)