Overview
The advances in structural framing provide alternatives to traditional stud-framed homes. The traditional, time-consuming to build, stud-framed homes are harder to air seal, more labor-intensive and more expensive to heat or cool over time due to large amounts of lumber that occupy space for insulation.
Is there a better alternative to old-fashioned stud framing? Structural insulated panels, also known as “SIPs,” are typically made by sandwiching a polyurethane layer of foam between two structural skins of oriented strand board, or “OSB.” Frames built with SIPs are stronger than conventional stud frames and a SIP framed home takes less time to erect, saving you money on labor. The airtight, draft-free nature of SIP frames also saves homeowners money on their energy bills.
There are several ways to analyze the different associated costs of construction in conventional stick-built dwellings vs. Structural Insulated Panels (SIP’s). In order to glean a better understanding we need to break down the different aspects. Only by a complete systems analysis can a contractor, developer, home or building owner understand the complete cost savings.
History of SIP’s
The US Forest Products Laboratory built the first Structural Insulated Panel structure in 1935; however, energy efficiency concerns didn’t exist until fuel prices increased. The first increase, in 1974, saw the cost of crude oil rise from $11.45 per barrel to $18.21, a jump of over $6.75 per barrel; in 2006 we have seen the cost of crude oil skyrocket to over $70.00 per barrel.
Product performance and affordability were impacted by the introduction of oriented strand board in 1981, which eliminated the use of plywood.
SIPs are high-performance building panels for floors, walls and roofs in residential and commercial buildings. Each panel is typically made using polyurethane foam insulation sandwiched between two structural skins of oriented strand board (OSB), but other surfaces are also available to meet your needs. The result is a building system that is very strong, predictable, energy efficient, and cost effective.
Benefits To The Builder
SIP builders establish a specialty market that separates their business from other builders because they provide the community with a final product that has superior energy efficiency and structural performance.
SIPs combine structural framing, insulation, and sheathing into one step, therefore providing the opportunity for more projects per year. SIPs are easier to work with during the cold winter months. After quickly installing the panels, the rest of the project can be spent completing the work on the interior
The pre-built nature of the SIP system requires fewer framers. In the United States, fewer people are choosing building as a career. Less than 30% of these construction positions are being filled. SIPs can help lessen this manpower shortage because it’s much easier to learn how to build with SIP panels than with traditional framing. In addition BORNHOFT Construction Services LLC can provide on-site technical training to contractors and builders.
SIPs reduce job site waste by reducing the cost of waste disposal. According to statistics, the average builder pays $511 per 2,000 sq. ft. home for waste disposal. Wood products account for 35% of this waste. The typical exterior framing waste of a SIP home can be hauled off in a 55 gal container. Also, every builder experiences job site material theft. It’s much more difficult for SIP panels to be stolen than it is with standard lumber.
BORNHOFT Companies LLC SIPs reduce the margin for framing errors. Each panel is numbered to correspond with a blueprint. Panels are built to specifications, taking the guesswork out of design and quality control on-site.
Maintaining a consistent profit margin becomes easier with SIPs, since the builder knows upfront exactly what the exterior framing cost will be. Stick framing relies on the integrity of a multitude of connection points between 2x’s and sheathing. With SIPs, loads are distributed across the entire panel due to the continuous bond between the sheathing and rigid insulation. A SIP panel can be compared to an I-beam, with the sheathing acting as flanges and the insulation as the web. Because of this, a SIP structure is many times stronger than a conventional structure.
Benefits To The Home or Building Owner
The biggest benefit of the SIP system is energy efficiency. The home is wrapped in polyurethane insulation without the thermal breaks experienced in 2x framing at each stud and around the electrical work. Also, polyurethane insulation maintains its integrity over time, whereas batt insulation settles and absorbs moisture.
The US Department Of Energy compared 5 different building systems for clear-wall R-value (measures the R-value of an uninterrupted insulation cavity section of a wall) vs. whole-wall R-value (takes into account the areas where most thermal performance is lost, such as corners, studs, wall to roof, window, and door areas). The test concluded that SIPs maintain 88% of their clear-wall performance after whole-wall R-value is measured. This is 58% better than 2 x 6 stick framing. SIP Panels provide a quieter and healthier living environment.
Polyurethane insulation is an excellent sound barrier, and the naturally tight construction of a SIP shell helps prevent dust and allergens from penetrating the home. The installation of air exchangers is recommended to promote healthier air quality and control humidity.
A SIP home provides flexibility and freedom of interior design. There is no need for a stud-finder. The entire inside is sheathed with oriented strand board. Finding a place to support a nail for pictures, curtains, or cabinets isn’t a problem. There is time and money to be saved when it comes to applying sheet rock! It should be noticeably faster since you don’t have to worry about hitting the studs.
BORNHOFT Companies LLC SIPS are typically composed of two materials- OSB and polyurethane or OSB and EPS, and are environmentally safe. The OSB is derived from short growth, or “Replaceable” tree crops. The polyurethane insulation does not contain any CFCs, (chlorofluorocarbons) or formaldehyde.
SIPs vs. Conventional Framing
The cost of SIPs is always compared to stick-frame construction, but is not an “Apples-to-apples” comparison, since 2x construction cannot compete with the thermal efficiency or strength of SIPs. To build a house out of conventional materials that would perform with the same thermal efficiency and strength as a SIP house would cost 40-50% higher than a SIP home. Although the material cost of SIPs is higher than 2x construction, you are actually paying for some of your framing labor when you purchase panels. The finished home cost difference is only 3%-5% more than a stick-framed home. The difference depends on labor and materials costs in your area. The minimum 50% energy savings quickly recoups any additional initial investment over the cost of conventional framing. The savings continue even when you sell your home. A study released by the EPA revealed that energy efficiency increases the resale value of homes by $20 for every $1 in annual energy cost savings.
The results of yet another construction process analysis was written in a 1998 report to the U.S. DOE, Department of Industrial Engineering and Management Systems, University of Central Florida, Orlando, FL. The study focuses on the construction of two similar single-family homes, one SIP and one stick-built, built by Habitat for Humanity during the fall of 1997. The data indicated that the SIP home saved 65% of the site labor when compared to the stick-built home. Cycle time savings are of similar magnitude. Volunteers were interviewed after framing the SIP house to gauge their perception of SIP construction. The results suggest that both construction professionals and other volunteers believed that SIPs reduced construction effort significantly, averaging about one-half the effort of conventional construction. The EPA has developed a program called Energy Star Homes to help homebuyers offset the up-front cost of building a better home. Some incentives include Energy Efficient Mortgages. The perks of Energy Efficient Mortgages include debt-to-income ratio loans, closing cost rebates, and lower interest rates. Also, congress is debating a tax credit of 1% of the purchase price with a maximum of $2,000 for newly built homes, which use at least 50% less energy than the Model Energy Code
Labor Savings
Labor today is the one single component of the construction costs that if properly controlled will benefit the contractor the most. SIP’s can help to manage and better control those costs in several ways.
Because of the superior structural strength of SIP’s over conventional stick-built construction, the erection of the building shell does not require the workforce to understand all aspects of construction. This is achieved by the manufacturer in their planning and design stage. For example, door and window openings of less than 48″ wide do not require the normal building components as in conventional construction. This allows for the journeyman carpenters to plan and construct other aspects of the job.
The erection of SIP panels on the job site is much faster than the stick-built construction of those same walls. Once again the design and layout is the responsibility of the manufacturer and builder long before construction begins. Once the panels arrive on the site, the job of the contractor is to set them in place according to a detailed drawing showing their placement.
Once the SIP panels are in place and secured, the construction of the shell is complete and ready for windows and doors to be installed. The openings for these items will have already been done in the manufacturer’s facility leaving any structural concerns to the manufacturer and their structural engineers and not to the contractor.
The last and most important time saving advantage of SIP construction is the insulating of the shell. With SIP’s this has already been done.
The Payback on Panels
Short installation time, reduced waste – builders reap the benefits of advanced panel systems. .By: Scott T. Shepherd, PATH Partners
A way to build better and faster — what’s not to like? Builders are finding there’s a lot to like when building with advanced panel systems. Panelized wall systems are prefabricated building panels that form a structural “envelope” for the home, eliminating the need for conventional wood framing. Panelized systems can be assembled on-site faster by less skilled laborers.
Despite these and other significant benefits, panelized wall systems capture only about 8% of the market, according to the Wood Promotion Council. Builders wary of panel systems point to the cost, noting that they have to pay at least as much, and usually slightly more, than they do for stick building their walls. They also express concerns about teaching crews new methods and meeting building codes with a less common product.
Change is never easy, but there are real benefits to builders willing to make the leap, says Kirk Grundahl, executive director of the Wood Truss Council of America, an international trade association representing structural wood component manufacturers. “A lot of the hesitancy about panelized walls is traditional mind set,” says Grundahl. “Builders who use them can build homes better and faster.”
Curtis Stendel of Panelworks Plus in St. Francis, MN, wholeheartedly agrees. Stendel, who teaches other builders about advanced panelized construction, says that he and other panel builders find that they not only have less need for skilled labor, but they also shorten their installation time, reduce waste and have less risk of theft on-site than their stick-building counterparts.
Different Panels for Different Builders
Advanced panel systems take many different forms. The usefulness of each one depends on the builder and the client. The most common systems are structural insulated panels (SIPs), which are closed walls made from polyurethane foam core adhered inside and outside to oriented strand board (OSB) or plywood skins. The foam has some strength, but when bonded to OSB or plywood, it acts as a bridge to augment the panel’s structural capacity.
A variety of materials can be incorporated into other open- and closed-wall panel systems, including wood studs or light gauge steel with foam insulation, structural concrete, concrete with foam core insulation, aluminum, steel and fiberglass skins. SIP panels usually come in modules of 4 feet by 8 feet or greater with a thickness of 4 to 6 inches, depending on the type of panel and the insulation required in that region. SIP panels are assembled to form exterior walls or roofs with minimal additional framing. Installation techniques vary by type and manufacturer. Typically, connections along the top and bottom of the panel and at panel abutment edges are required.
The Pluses of Panels
Of course, the builders who use SIP panels didn’t switch simply out of curiosity. They were seeking — and are finding — bottom line benefits. Through the ease and speed of assembly, SIP panel wall and roof systems can be built in days rather than weeks. The faster construction time also greatly reduces the chance of theft and of bad weather creating construction delays. Because most of the cutting is done in a remote factory, the builder has to deal with much less waste on-site. Only basic carpentry skills are required for laborers which mean assemblers don’t need the skill of conventional framing crews. For some builders, reducing the need for skilled labor is extremely beneficial.
To ease construction costs even more, manufacturers offer prefabricated home packages that compare with the cost of conventionally framed structures. This is helpful for standard builders, but is less advantageous for custom builders since the cost of producing and engineering panel layouts may drive up the cost of custom designs.
Stevens points out that SIP panels also offer greater durability than stick-built walls. Panels can be produced in an automated factory environment using computer-controlled equipment that transfers panel-cutting instructions directly from digital computer aided design (CAD) drawings. The resulting components are precisely engineered and easy to inspect for quality control.
Beyond the greater durability, SIP panels have other attractive selling points. With better overall air tightness and thermal performance of the walls and insulation — common traits of SIP panel systems — customers will be warmer in winter, cooler in summer and they’ll enjoy energy savings to boot. SIPs, in particular, can improve energy efficiency by replacing lumber or other structural thermal bridges with insulation material. In addition, the thicker walls will also add some soundproofing as well.
Making the Switch
Before switching to advanced panel construction, Stevens suggests builders consider the availability of skilled labor, time for design and the time to learn a new technology. The time a builder is able to commit to design issues figures prominently because the factory relies on receiving accurate measurements and data from the builder in a timely fashion. How far in advance the builder needs to do this depends greatly on the type of panel and the manufacturer. “If measurements are inaccurate or incomplete — as is often the case — then the designers have to make assumptions and there is a chance for problems on site,” Stevens says. Taking the time to get those measurements right the first time will save some headaches down the road.
Several big builders — including Pulte Homes, NVR Homes and Toll Brothers — are willing to commit that time because of the time they save in the end. Big builders can easily use panel systems because they have specific and repeatable designs. “You want it to be repeatable because of the time investment necessary to properly develop the factory’s software to cut the panels,” Stevens says.
Small builders may also benefit from using panels if their building designs are fairly reproducible. Because of the difficulties managing wood use and costs, panels provide a way for builders of any size to develop more predictable fixed costs for the project. “Builders can get a better handle on fixed costs, and managing the quantity of material is always a big issue with wood,” Stevens says. “When using panels, it’s much easier to estimate those numbers.”
The Cost of Quality
While it may be easier to etimate fixed costs with advanced panels, do they cost less? With improved quality and speedier on-site construction time often comes greater material cost, because now the builder pays for partially fabricated walls.
While cost varies greatly with the different types of advanced panels and the size of the structure, most panels are somewhat more expensive per square foot than a stick-built home of comparable size.
During the transition period, inexperienced crews or poorly coordinated panel dimensions can make the process more costly. However, panel builders say these issues are easily overcome with experience. “For a typical builder, the proficiency comes after maybe three to five projects,” Stendel says. “But for some projects, you get it right the first time and they are off and running. It’s not really difficult.”
Weighed against the additional cost is the prospect of greater savings — from reduced time for construction, reduced chance of theft and weather delays, less waste and less need for skilled labor. The equation will differ for every builder, but advanced panels may be most cost-effective in those areas where labor is difficult to obtain.
Learning Curve
While it may not be difficult, there is a learning curve, as with any change in building methods. That was certainly the case for Scott Bergford, founder and president of Scott Homes in Olympia, Wash. Eleven years ago, Bergford was using the conventional stick building method when a customer asked him to use SIPs. “We had never even heard about them,” says Bergford. He was intrigued by what he learned. To experiment, he built his business partner’s home with SIPs. “We had to redo things and we made mistakes, but we worked them out,” says Bergford. This decision led to a long-term commitment to panel building.
For Bergford, the biggest difference was learning how to manage utilities while installing wall panels, particularly SIPs that have foam attached to the panels. Bergford learned he needed more chases in the kitchen walls. The panel provider was happy to oblige. Bergford and his crews also started using a flexible drill bit to make their own chases to snake wiring through the walls. “Every once in a while we get a new subcontractor and he doesn’t follow the directions and he will have sliced the panel in half,” Bergford says. “So now we have learned how to fix a SIP panel once the plumber has destroyed it.” “At this point, I really don’t know what we could run up against that we wouldn’t know how to fix.”
SIPs Outperform Stick & Batt:
Oak Ridge National Laboratory – R-Value Test
When someone says “R-value”, what they’re really talking about is resistance to heat flow in a given medium, such as fiberglass insulation. The higher the number the greater the resistance. So when a builder is asked “What’s the R-value of this wall?”, the natural inclination is to think of the material that most commonly specifies its rating. More often than not, it’s the insulation, and the response is something along the lines of “Oh, that wall has an R-value of 24″ – fairly impressive, but also strikingly inaccurate.
It’s not that the builder is intentionally misleading his client or associate, but that he’s just following common practice. In reality, this reasoning doesn’t take into account all the other components that go into making a wall: wood or steel studs every 16″ or 24″, bracing, nails or screws, wiring and switch boxes – any number of things that are not insulation, and in all likelihood, have R-values that fall well short of the stated R-24.
A new study by the Oak Ridge National Labs (ORNL) proves that a 4-inch SIP wall outperforms 2″x4″ stick and batt construction, and even edges out 2″x6″ construction in terms of thermal performance. Because SIPs are the structural elements, there are no studs or braces to cause breaks in the insulative action. The end result is a more comfortable, energy efficient structure that performs up to spec in real-world conditions. Unlike stick and batt construction, which can be subject to poorly installed – even missing – insulation, the nature of SIPs is such that the structural and insulative elements are joined as one. There are no hidden gaps, because a solid layer of foam insulation is integral to panel construction.
By contrast, state-of-the-art technical analysis of whole wall performance indicates that the losses in a stud wall are much greater than you might think: on average, the other standard components in stick and batt construction can reduce R-values in as much as 30% of the wall area. Fortunately, that’s not the case with structural insulated panels. The ORNL study found that SIPs perform at approximately 97% of their stated R-value overall, losing only 3% to nail holes, seams, splines, and the like. Wiring chases are precut or preformed into the foam core, providing a continuous layer of insulation keeping the elements at bay and the interior free of drafts and cold spots.
A SIP wall also outperforms stick and batt when it comes to maintaining consistent interior temperatures, and that translates to improved occupant comfort. The interior surface temperature of frame construction drops precipitously at every stud, while the SIP wall remains consistent across its entire surface. No temperature dips mean improved occupant comfort, regardless of where you are in the room. That’s a big part of what people are talking about when they say they can immediately “feel the difference” in a SIP-built residential or commercial space. With SIPs, thermal efficiency and comfort are built in at the factory, and now the lab results prove it.
