Build With SIPs

Is this the building technology of the future? Here’s why structural insulated panels are a great option for building sturdy, energy-efficient houses.
By David Wright
August/September 2011
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This home in Kansas was built with structural insulated panels, also known as SIPs.
PHOTO: MICHAEL MORLEY
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As an architect, I’ve been using structural insulated panels (SIPs) since 1992, when they were relatively new. Since then, I’ve designed several hundred residential and commercial projects using SIPs. In my opinion, they are superior to conventional framing systems in almost every way — SIPs are simply better insulated, stronger and faster to build with than standard stick-frame construction. SIPs also help conserve forest resources, because they produce almost no waste.

As worldwide timber quality and availability continue to decline and the costs of labor and energy increase, SIP construction should become more popular and cost-effective. I predict that in the next 10 years, the U.S. construction industry will adopt SIPs as the system of choice.

Advantages of SIPs

Structural insulated panels are typically composed of rigid foam insulation sandwiched between two skins of oriented strand board — kind of like a s’more. The exterior skins are attached to the foam core with a high-strength adhesive.

The foam core material is often expanded polystyrene — the same material used in ice chests and shipping “peanuts.” Some manufacturers use polyurethane or isocyanate foam cores. The skins can be plywood, metal or other rigid sheet materials, but oriented strand board is used by the majority of SIP manufacturers. The foam core serves as a spacer and insulator between the exterior skins. (Keep reading for more specifics about these materials, and their environmental impacts.)

Altogether, the structure acts as a monolithic whole — as opposed to stick-frame construction using 2-by-4s, where hundreds of individual nailed connections hold the studs and skins together. As a result, SIPs are twice as strong as a wood-framed house, which is a real advantage in locations that experience tornadoes or hurricane-force winds.

SIPs are also extremely energy efficient. Compared to a typical stick-frame house, a house built of SIPs will require about half the energy to heat and cool throughout the year in most climates. It’s not just the thickness of the polystyrene inside that makes SIPs more energy efficient — it’s that the whole panel is designed to function as one structural unit. The thermal “tightness” and resistance to heat flow work with the insulation value to achieve exceptional comfort and energy efficiency.

Cost and Savings

I have heard claims that SIPs are “cheaper than stick-frame or the same cost as conventional systems.” That may be true in some parts of the county where labor cost is high or skilled labor is unavailable. In my experience, using SIPs usually costs slightly more than stick framing, adding about 5 to 15 percent to the total cost of the home. (The framing, insulation and associated labor is usually only about 10 to 15 percent of the total cost of a new home.)

However, SIP construction is a better value than conventional wood-frame construction. When properly built, SIP buildings will be straighter, truer and smoother, which makes it easier to install the doors, windows, siding and sheet rock. The energy savings, structural stability, speed of construction and labor savings will pay for the extra cost of SIPs. In most cases, these savings will mean you’ll recover the extra costs in two to four years, depending on your location.

SIPs Construction

If you decide to build with SIPs, start by looking for qualified builders on the Structural Insulated Panel Association website. Or, do an online search with your state name, plus “SIPs.” If you plan to build your own home, consider looking for an experienced SIP installer to help you and your crew.

SIP building is actually easier than stick framing if you go about it carefully. I have introduced several professional contractors to SIP building who are now so enthusiastic about the quality and technology that they no longer want to build stick-frame houses.

Here are the basics of how a SIP home comes together. SIPs come in 48- or 96-inch wide panels that can be up to 24 feet long. The builder will use shop drawings, aka “panel drawings,” as a map to determine all construction details. These panel drawings delineate each roof and wall plane (yes, SIPs can also be used for roofs), giving each panel a discrete identification number. The architect and contractor each review and sign off on these drawings before the panels are ordered.

SIPs are manufactured in a large regional plant. They also need to be “fabricated,” which is the special cutting and additional preparation specific to a certain building. A manufacturer can provide panel drawings and fabrication, but fabrication is a secondary service. There are also contractors who provide panel drawings and fabrication in addition to panel construction.

A SIP building that has been fabricated in a shop before arrival at the construction site takes about a quarter of the time to frame as a SIP building fabricated on-site. Fabrication inside a shop allows continuous production unaffected by rain, snow, heat and windy site conditions. Plus, foam scraps from fabrication can readily be recycled.

The placement of SIPs is called panel erection or installation. Installing SIPs is not difficult. After the concrete floor slab or wood floor platform is completed, the process goes quickly through the finished structural shell stage. First, the builders attach a sill plate to a slab with anchor bolts.

Window, door and skylight openings can be cut into panels before installing them. The wall panels are usually joined with a proprietary system, unique to the manufacturer. Handling and installing the panels requires two people. The panel being placed slips into the previously set panel and over the sill plate. A caulking gun is used to place a bead of caulk/adhesive mastic on all joining surfaces. After the panel is set in place, it is common to place a few screws using a cordless screw gun, one at each joint to tack the panels in place. Exterior or interior wall braces help stabilize and align the panel wall until the top plate is installed and a corner connection completed.

SIPs are meant to be installed with an eighth-inch joint tolerance, and there should be a slight space between each panel for expansion and contraction. When the wall panels are up, the builder caulks and inserts the continuous top plate. This helps true-up and stabilize the wall. Later, when the walls are up, a nail gun is used to “nail-off” each joint on each side with 8-penny nails at 6 inches on center.

SIPs and Green Building

Many environmental experts consider SIPs to be a green product. SIP construction reduces wood waste, and the thermal properties of SIPs provide a long-term investment in energy savings and conservation. However, there is a healthy ongoing discussion about some of the chemicals used in SIPs.

One substance of concern is pentane gas, which is a low-level pollutant that is used in forming the expanded polystyrene. Manufacturers are required by law to take extra caution to contain the pentanes and other gases used in manufacturing, preventing them from releasing into the environment.

Another concern is that SIPs that use expanded polystyrene are treated with a flame retardant called HBCD (Hexabromocyclododecane) to prevent flammability. HBCD is toxic to aquatic organisms, and the potential health effects on humans are not yet clear. However, very little of this chemical will enter the environment, because it is enclosed in the insulation. (By definition, expanded polystyrene is closed-cell.) Outgassing is not a problem, as it is with some other foams.

Once the SIPs have been manufactured they are considered environmentally safe by the Environmental Protection Agency, and once they are enclosed in the walls and roof there is no danger to the environment. Personally, I think SIPs pose little risk to the consumer and are definitely a green product. However, I’m pleased by any dialogue between manufacturers of building products and the general public, because we all benefit when consumers pay attention to the environmental effects of the products they use.

I think that all materials used in construction should be sustainable and non-resource depleting. SIPs go a long way toward saving energy resources in a cost-effective way, and in my opinion they are an outstanding choice for green buildings. Someday soon I expect that rigid foam plastic will be made from soy or other organic agricultural products. There is also room for oriented strand board to become greener. For example, it can be manufactured from sustainably harvested wood chips and perhaps other natural products, such as rice hulls or hemp.

The Future of SIPs

The construction industry is sometimes slow to change and adopt new technologies. However, as interest in sustainability and energy efficiency continues to grow, I expect that not only will the use of SIPs continue to increase, but that the product will be manufactured with ever more environmentally friendly materials. I look forward to SIP systems becoming a major player in the search for more energy independence and the quest for zero energy buildings.


SIPs Resources

Building With Structural Insulated Panels by Michael Morley

Structural Insulated Panel Association 

American Foam Manufacturers 

Porter SIPs 

Premier SIPs 

Winter Panel Co. 

Fischer SIPs Co. 

Insulspan  


David Wright, architect with Solar Environmental Architecture Group, is the author of The Passive Solar Primer: Sustainable Architecture. Wright was first featured in MOTHER EARTH NEWS in a Plowboy Interview in 1977. 


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Post a comment below.

 

oldtimechevy
5/22/2013 12:34:55 PM

Excellent article with accurate information. I will be building a sips house in the near future. After much research I believe the benefits of sips construction are unmatched. Are sips the most green building method? No. Are they a drastic improvement over conventional bulding techniques, yes. While researching I came across an interesting case study where a builder built a sips building for a church and the exterior was not finished. The raw osb was left exposed. This building was built in the mid 80's and recently he went back to see if they ever finished the building. The exterior was never finished and surprisingly the sheathing had held up extremely well. Rot on the panel was very minimal after 25 years completely exposed. The explanation was that the osb used in sips is of much higher quality than the commercially available off the shelf product. I believe a properly constructed sips structure will have far less maintenance and issues than most other forms of construction. Compare the other benefits of sips construction like using up to 60 percent less energy every month and the speed of construction. Two houses locally began construction at about the same time and I watched each progress. One being built by a sips construction company called SIPS Solutions and the other being built by a local contractor. The sips house construction crew was only about 5 or 6 people but the house went up very quick compared to the other house. In less than a week the entire strucutre was up and the traditional house was still being framed with no sheathing or insulation done. I'm sure there were other factors as to the speed of construction but it just shows a well managed crew with a better building technology can out perform other methods. For my 2400 sq ft project the overall cost comparision for sips construction to stick construction will be about 3 to 5 percent more. This is negligible as cost overruns on traditional construction can easily offset this expense and the energy savings will quickly make up the difference and a lot more. My new house will be a sips house and I will have absolutely no concerns about it.


mark.hutchins.125
5/3/2013 3:32:40 PM

My experience with SIP construction has been good. My brother built his first in 1975 and it is still in excellent shape. For strength and efficiency it is hard to beat. Fiberglass insulation is obsolete. Fiberglass allows convection air currents within the walls - therefore not as good as closed cell insulation. Another choice would be Insulated Concrete Forms. When I think of "green products", I think of saving energy and these 2 methods work well. The Kobe earthquake in Japan proved the strength of SIP construction. Stick frame houses around the epicenter were flattened and SIP houses were not. SIP construction has been around well over 20 years. Willful ignorance about these products will probably never go away, unfortunately. Just about everything outgasses. Should use fresh air ventilation on all tightly built homes.


Charles Giltner
3/3/2012 4:15:50 PM
I volunteered on a Habitat for Humanity project in S. Sarasota County Florida that was begun with a SIP duplex, but when the housing bust came the local manufacturer went bankrupt. These SIPs were not made with OSB but green board exterior and drywall interior. I believe these were created to withstand the new hurricane building codes/prevent water intrusion issues. I agree with other comments that this product is far from green, but it is an advanced building technique that could have its place in certain built environments where quick and uncomplicated building methods would benefit. If space and conditions allow, I find that earthbag or rammed earth methods are very green and are unmatched for energy efficiencies although labor intensive. The OSB SIPs are not recommended simply for the fact that no matter how well one seals the exterior, water will get in and WHEN it does it WILL totally damage the OSB and the integrity of the structure eventually. SIP technology relies heavily on the three/quarter inch overlap at the framing ties between SIP panels. If poorly aligned, incorrectly fastened or damaged during installation the integrity is compromised, more so on the roof connections. I believe the technology is sound and good for use generally but with properly trained installation crews. The H4H project was a complete delay due to lack of or poor understanding of the SIP methods by the "experienced" construction crew foremen. Their rigid understanding of conventional building methods was a barrier to learning the SIP methods because it changes how nearly all aspects, foundation to finish are treated. Resulting in repeated consultations with the manufacturer and the building inspector that was uninformed as anyone there, resulting in educating the govt officials as well, creating more delays. Well, after the first of the nine buildings was completed the project reverted back to block and stick framing methods (even if the manufacturer hadn't bellied-up, I believe they would have abandoned the SIPS due to delays and engineering issues that couldn't be resolved between the newer hurricane codes and officials not being flexible and lack of knowledge concerning SIP effectiveness under hurricane loads. (read as: can't cover their a$$, liability-wise if something goes wrong.)) Overall the SIP experience was positive but not green. Other than being energy efficient and using less building materials overall. As a CAD designer, the SIP method would be great for quick construction projects in remote areas where the panels could easily be delivered or for additions and remodels where quick turnaround is required. Possibly in heavily built areas where conventional methods might be cumbersome or create too much trade traffic.

Robert Riversong
12/29/2011 9:32:00 PM
Michener says "Off Gassing and OSB getting wet are both easily solvable." This is the engineer's answer to every problem, and it follows the law of Unintended Consequences. Using highly-processed wood materials, like OSB, encourages mold and rot (not to mention irreversible swelling), but that can be solved by a "perfect" envelope that will never leak, and a lifetime of :perfect" maintenance. Using highly-manufactured materials (like petrochemical plastics and OSB) that may contain toxic additives or break-down products can be compensated for by permanently sealing in those toxins with other materials or methods. A real solution to a problem is to avoid the problem, not try to engineer yet another "solution" to a problem created by the last "solution". SIPS are recognized as the most expensive thermal envelope system on a otherwise-framed structure - expensive both to the customer and to the environment. The only method that makes SIPS cost-effective is using them as the structural frame, which relies on plastic and glue to keep the house standing for 100 years and makes it extremely vulnerable to fire, as well as insect damage.

Robert Riversong
12/29/2011 9:21:13 PM
Neither the author nor commentor George Michener understand the difference between truly green and greenwashing, the hygrothermal dynamics of a building or the purpose of a house. I have been building superinsulated homes (R-45/R60+) for 30 years without petrochemical insulations (except sub-grade, where little else will suffice). For the past 20 years, I've insulated with nothing but cellulose - 100% recycled, environmentally benign, fire-resistant, insect-resistant, rodent-resistant and mold-resistant. I also teach Hygro-Thermal Engineering and Building Science. Michener can't imagine how a hermetically-sealed picnic cooler house with OSB (junk wood) sheathing can get wet. No house gets built perfectly, and no house remains perfect. Every house gets wet during its lifetime - either from exterior environmental sources or from moisture migration. Dozens of SIPS-roofed homes in Anchorage Alaska had major sheathing rot from very minor imperfections in sealing the SIPS joints (which is a common problem). The answer to inevitable leakage and moisture migration is NOT to build a plastic picnic cooler, but to use hygroscopic materials which can safely buffer (absorb and release) excess humidity with no loss of insulating value (contrary to Michener's misperception). SIPS are expensive and result in a container unfit for human habitation. All natural membranes are semi-permeable. We did not evolve to live in a spaceship, but rather as part of a breathing earth environment.

GEORGE MICHENER
11/23/2011 3:23:22 PM
Why oh why would the OSB in a SIPs get wet?- if it does, someone has done something wrong and in that case-what happens when any other building material gets wet?Polyiso, Fiberglass,cellulose and even ground up blue jean and straw insulation all lose their insulating properties when they get wet-and they also allow for and trap condensation because of temp differentials which in turn causes mold on the more conventional building materials-by which I mean both the support and sheathing elements.I believe I saw a comment on "unproven" come on people.Off Gassing and "OSB getting wet" are both easily solvable-and are part of the finish work-not an extra expense. Any type of interior finish prevents offgassing (personally I prefer clay based plaster on the interior).Any exterior finish prevents the OSB from "getting wet and ending up in a landfill" and in the off chance that someone decides to build their SIPs house without a roof and exterior finish(the only way the OSB is getting wet)-the polystyrene can be removed from the OSB with a hotwire cutter and be reused-either in sheet or granular form-try that with conventional framing and insulations mentioned above.These uninformed criticisms-especially when unaccompanied by any useful suggestions,solutions or alternatives are what makes the green movement easy fodder for opponents and undefendable/indefensible by main-streamers.Are SIPs the end-all be-all for construction?-no-but they are a step forward from stick framing and the common insulations used for the last century and anyone who has ever built or torn down such a structure can see that they too are ecological disasters-AND they leak energy like sieves the whole time theyre standing! .I have done both-for many years-and have NO affiliation with ANY SIPS business/manufacturer. Solutions people-solutions that work in the real world. Believe me -anyone trying to alter the status quo in the building world for the better has an uphill climb already....been there- done that.

sydney watson
11/23/2011 10:21:30 AM
I too think the polystyrene is not "green" as some of the other commenters put it, however i am hopeful for a different type of SIP, one built without polystyrene, but straw instead. Heres a link to a video building a leed certified 'habitat for humanity' house built by students of Sir Sanford Fleming College in Ontario. Its not exactly the same but similar enough. http://www.youtube.com/watch?v=q61og2ydZKc

LENNARD FEDDERSEN
11/22/2011 9:29:40 PM
Disappointed to see this in Mother Earth News. Polystyrene sandwhiched between OSB is not green. Furthermore, what happens when that OSB gets wet over time and starts to deteriorate - a house that goes down in value and eventually gets knocked over and thrown into a landfill. No thanks.

DARNELL ASHURST-THOMAS
9/7/2011 2:14:32 PM
I like the idea of using SIP, but is it expensive?

SteveR
9/2/2011 1:45:19 PM
When I think of 'green' products, I think of materials which are natural and renewable and have a natural beauty and longevity to it. I can't think of anything less green than SIP panels. Designed entirely for ease for construction, not for the occupants health, aesthetics, longevity or charm. Caters entirely to the building industry, but not to people! Polystyrene sandwiched between OSB.Green? Both offgas, neither is natural and each one is unproven over a long period of time. And to marry SIPs with timber frames - ugh - what an insult to the craft! I predict that in 20 years time, we'll be wondering what we were thinking when we went to SIP panels.

Newell Pledger-Shinn
8/23/2011 2:34:15 PM
Thanks David for this straightforward and insightful discussion of SIPs! While this article contrasts SIPs with conventional construction, we've been successfully integrating SIPs with our traditional mortise and tenon timber frame buildings for decades. For a SIP/timber frame structure we also see a 5-10% premium in price, which is quickly offset by energy savings due to the efficiency. Wrapping around the outside of the post and beam structure in a complete insulated envelope SIPs provide incredible thermal efficiency while also displaying the natural beauty of the wood. We've also completed projects that are hybrids, incorporating both SIPs and timber structure in the same project. I want to reiterate David's advice about contacting a qualified instational crew or supervisor and having the rough openings fabricated by the panel supplier. This is generally crucial to the success of your project. - Newell Pledger-Shinn, www.hardwickpostandbeam.com








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