General Questions

What are Structural Insulated Panels?

Structural Insulated Panels, commonly known as SIPS consist of a layer of foam(Urethane, Expanded Polystyrene or Extruded Polystyrene) sandwiched between oriented strand board (OSB). SIPs make buildings stronger, more durable and more energy efficient than traditional stick-frame construction.


How long have SIPs been in use?

SIPS were invented in the 1930’s and throughout the years have been proven to be an effective building method in many applications. Frank Lloyd Wright was an early devotee of SIPs and used them in his USONIAN homes, designed and built from the 1930’s and 1940’s.


Why would I want to build a SIP structure versus a traditional “stick-frame” house?

Residential and commercial buildings constructed using SIPs are stronger and more energy efficient. They can be built in less time than traditional stick-frame construction with more sustainable materials and very little construction site waste.


Do the building codes allow SIP construction?

Yes they do. Starting in 2007, the International Residential Code has allowed SIP construction, devoting a whole section (613) to SIP construction. The NTA listing report VNT050211-16 will give your code official the information he needs to approve Green Mountain Panel SIPs for the project.


What are the advantages of panelized construction over conventionally framed buildings?

Panelized homes, made with Structurewall™ insulated panels, can be erected very quickly. They provide tremendous interior design flexibility. They also produce a stronger wall than conventional framing of equal thickness, and they are extremely energy efficient.


What holds the house up since standard framing lumber is not used?

Structural support is provided by the panel skins. Structural insulated panels use less wood than conventional framing, and it is optimally placed (as the panel skins), resulting in a wall assembly more than twice as strong as a conventional 2×4 wall. The 4-foot­wide panels, up to 24 feet long, are securely held together with plywood “splines” in both wall and roof systems.


What are the disadvantages to this type of panelized construction?

Many builders are not familiar with erection of the shell and techniques used for finishing. Fortunately, shell erection can be handled using standard carpentry techniques by a qualified local contractor or by an experienced crew recommended by Green Mountain Panel. Techniques required for construction are very easy to master, and are covered in The Complete Guide to Building with Green Mountain Panel.


Are SIPs compatible with other building systems?

Yes. SIPs serve as a great roof solution for concrete blocks or insulated concrete forms and they are seamlessly compatible with stick-framing. SIP builders can use SIP walls and a conventional truss roof or stick walls and a SIP roof.


If I am a builder and I decide to build with SIPs will I save money?

Yes, Builders can save a substantial amount of money in labor costs because of the speed of construction. Also, SIP construction does not require skilled stick framers and SIP homes have smaller HVAC requirements. Additionally, under the DOE Energy Star building program, SIP homes do not require a blower door test, they are that airtight!


How much money will homeowners save if they live in a SIPs home?

Homeowners can save as much as 50 percent on their energy bills and can qualify for energy efficient mortgages and reduced insurance rates. Energy efficient homes such as those constructed with SIPs have also been shown to have a higher market value.


Is there an advantage to the 6-1/2″ (R-38) wall panel thickness?

Yes. This construction system provides the highest level of energy efficiency for the given wall system available anywhere. You get more living space than in any other comparatively insulated house with the same outside dimensions. Using the 8 1/4” (R-50) panels for the roof provide a smaller profile and greater efficiency than a conventionally framed structure.


What is the interior layout like in a Green Mountain Panel Home?

Because the building shell provides most of the load-carrying strength of the house, there is tremendous flexibility of interior design. Use a Green Mountain Panel design, plan the layout yourself, or work with your architect, builder, or Green Mountain Panel’s designers to provide exactly what you need. Unlike many home designs, the structure itself does not constrain your design flexibility.



Structural Insulated Panels (SIPs)

How strong are SIPs?

Over twice as strong as conventional stick framed walls. Buildings made of SIPs offer exceptional structural strength — up to three times stronger than stick-frame construction — and can withstand up to 155 mph winds, the equivalent of a Category 5 hurricane. This structural strength prompted the Institute for Business and Home Safety to include SIPs in their FORTIFIED building standards.


Can I build faster using SIPs?

Yes. Building with SIPs allows the builder to get the building envelope to “dry-in” faster. Our designs allow builders to erect a SIP envelope all in one operation. This envelope includes framing, insulation, electrical chases and exterior sheathing and can be erected in the same amount of time that it would take to only frame the exterior of a traditional stick-frame structure.  By using factory pre-cut panels it is typical for SIP framing to take just a few days rather than weeks needed for stick-built construction.


What is the R-value and how do SIPs rank?

R-value is defined as the resistance of a material to heat transfer. A material with a high R-value is a better insulator. The R-value value of a 4.5” SIP wall is R-25 using urethane foam compared to a traditional 2×4 wall panel with Batt insulation with an R-value of R-13.


What testing has been done on SIPs to prove their effectiveness?

Oak Ridge National Laboratory has conducted extensive testing that confirms SIP construction outperforms traditional stick-built construction in structural strength, energy efficiency and fire testing. For further information regarding our tests, please see our library (need to add ORNL study!)

What makes SIPs airtight and why is that important?

The connections between the panels are typically double splined together and the interior channel is foamed so there is very little chance for air infiltration. Adhesive is applied to all wood-to-wood connections before they are nailed off. Air infiltration is one of the biggest causes for increased energy use in buildings today. It is calculated that over 50% of a home’s energy loss is through air infiltration. SIP panel construction is up to 15 times tighter than stick-frame construction.


What skins are used on the panels?

Structurewall™ panels have an exterior grade of structural OSB on both the exterior and interior.


How are panels made?

Urethane panels are made in a continuous lamination process in which the foam is injected between the OSB skins and allowed to expand and bond to the OSB under carefully controlled conditions. EPS and XPS foam cores are bonded to the skins with an adhesive and cured under pressure in a vacuum process.


Why is OSB used instead of plywood?

For a number of reasons. First, OSB is more stable than plywood, particularly in high moisture conditions; delamination and linear expansion are much less likely to occur. Second, OSB is available in much longer lengths (up to 24′). Third, it is less expensive than plywood, producing a more affordable finished product. Lastly, the fast-growing trees used for OSB are grown in sustainably managed plantation forests.


Are there any problems with dimensional stability of panels?

Panels are quite stable, but will expand somewhat under high moisture and
temperature conditions. At 160°F and 100% relative humidity, panels will expand 5% over 24 hours. Lowering the temperature to -20°F will result in a .15% volume decrease over 24 hours.


What is the R-value of the panel?

R-value’s range from R-15 thru R-50 (this includes the R-value of the panel core and panel skins like OSB and drywall) and is dependent upon the foam core type and thickness. Urethane R-value/inch is R-6.8, XPS R-value/inch is R-5 and EPS R-value/inch is R-3.75.


Are these “aged” R-values?

Our Urethane R-values are conservative and are aged a minimum of twelve months.


Do I need to add a vapor barrier or use a vapor-retardant paint?

The panel itself serves as the vapor barrier. Most model building codes require a vapor barrier with a perm rating of 1 or less. The perm rating of our panels is less than 1. Because there are no voids in the panel where moisture could condense, moisture problems are not a concern. Panels will absorb and release some moisture on a seasonal basis, just as the wood in a log cabin does, but there are no harmful effects of this cycling. The only place where moisture migration could conceivably be a concern is at panel joints. Joints between panels are sealed during installation to prevent moisture migration.


Do I need to allow an air space for ventilation on the roof if I’m using panels?

Ventilation is usually only required on roof systems where moisture could condense in the roof system, or where high temperatures could damage the insulation. Neither of these is a concern with our panels. However, Green Mountain Panel does recommend the use of a “cold roof” when installing roofing. A cold roof creates an air space above the roof panel to ensure air-movement. This will ensure validity of the asphalt shingle warranty regarding installation on “hot” roofs. Details can be found in the Green Mountain Panel’s construction manual.

With a rigid shingle roof, such as wood shakes, tile or slate, horizontal strapping is generally recommended (follow roofing manufacturer’s recommendations).


Do Green Mountain Panel SIPs carry a warranty?

Absolutely. Green Mountain Panel SIPs carry a ten-year limited warranty covering the structural panels, provided the SIPs system is erected in accordance with company guidelines. For complete warranty information, contact the company.



Environmental and Health Concerns

Are SIPs environmentally responsible?

Yes. Homes built using SIPs provide exceptional indoor air quality while requiring smaller HVAC systems, often resulting in a reduction in fossil fuel consumption and greenhouse gas emissions. Compared to stick-frame construction, SIPs use approximately one third of the wood and reduce job site waste. The OSB used in the construction of SIPs is made from wood scraps and fast growth trees grown in sustainably managed forests. There is less formaldehyde in OSB than occurs naturally in wood.


Do I need an air-to-air heat exchanger?

Air-to-air heat exchangers or other types of mechanical ventilation are recommended in all tight houses including those enclosed by SIPs panels. Green Mountain Panel recommends that air-to-air heat exchangers be incorporated into all SIPs homes.


Do the major “Green” Building standards recognize SIPs?

Yes, SIPS are considered very environmentally responsible by the USGBC, which awards SIPS 72 LEED points, while the National Green Building Standard awards SIPs 242 points.


What kind of foam is used in the panel?

Urethane, developed for high R-value, structural strength and fire safety. Expanded or Extruded polystyrene can be substituted as less expensive but lower R-value options.


Is there any out-gassing from the foam?
What kind of gas is it, and do I need to worry about it?

245fa is used as the blowing agent for the foam. A very small amount will outgas from the foam over time, but the gas is considered completely harmless.


Is there any formaldehyde in the foam?



What about formaldehyde out-gassing from the Oriented Strand Board?

Exterior grade OSB such as that used in Structurewall™ panels is made with phenol-based resins that do not release significant amounts of formaldehyde gas. Urea formaldehyde resins, on the other hand, which are used in interior grade particle board products, release far more formaldehyde gas, and it is these products — not OSB — that have heightened concerns over formaldehyde in houses. The Federal Government requires that warnings be put on products that may release formaldehyde; our products do not require that warning.


How do SIPs perform in fires?

All Green Mountain Panel SIPs comply with the flame spread requirements set forth by UL, Class C(III) and building codes.  Additionally, due to the air tight nature of SIPs, fire tests conducted inside a SIP envelope have resulted in fires becoming extinguished because of lack of new oxygen infiltrating the SIP envelope.


What happens when the panels burn?

When the panels burn, a number of gasses are given off. Some of these are dangerous, including carbon monoxide and certain hydrocarbons. The exact composition of combustion products depends on the fire conditions (how much oxygen is available, etc.). You should assume that the gasses given off by all SIPs are dangerous. The toxicity of gasses given off from our panels during combustion is about the same as that from white oak or Douglas fir. A key advantage of urethane foam is that the foam does not melt. Urethane is a “thermo-set” plastic and will retain its structural integrity until consumed by fire (like wood). Other types of foam (EPS) melt with temperatures as low as 170ºF, and can contribute tremendous quantities of fuel to a fire very rapidly. Additional information on fire safety of panels is available from Green Mountain Panels.


What is the wall finish fire rating of Structurewall™ panels?

ASTM testing by an independent laboratory showed the wall finish rating of Structurewall™ panels to be greater than 15 minutes with ½ inch drywall attached. Complete information on wall and roof finish ratings is available from Green Mountain Panel.


What are the building code requirements for panels relative to fire?

Building and fire codes vary from place to place. Usually, a 15-minute finish rating is required for light construction. Structurewall™ panels, with an interior layer of 1/2″ drywall, exceed this requirement substantially.



Erection of the Shell

Who takes care of erecting a Green Mountain Panel SIPs shell?

General contractors or SIPs installation crews are responsible for shell erection. Green Mountain Panel can recommend experienced SIPs installers in many regions.


What are the foundation requirements?

The buyer is responsible for having the foundation installed to the specifications provided by Green Mountain Panel. A Green Mountain Panel home can be built on a slab-on-grade foundation or on frost walls over a full basement or crawl space. It is extremely important, however, that the foundation is built to close tolerances. Because of the accuracy of the supplied components (factory pre-cut panels), even slight inaccuracies in foundation level or being out of square can result in problems with shell erection.


How long does it take to erect a Green Mountain Panel shell?

The complete shell, including walls, sub-floors and roof, can usually be erected in one week or less by a skilled crew on a standard house. With larger houses, or more involved custom designs, erection can take longer.


What happens if it rains while the shell is being erected?

Structurewall™  panels are not damaged by rain. However, long-term exposure to water will cause the OSB at the cut panel edges to swell. After erection of the shell, these swollen edges should be sanded down with a belt or disk sander.


How far along will the shell be when the SIPs contractor or installation crew leaves the site?

The shell will be fully erected and ready for window and door installation, roofing, siding and interior partition walls and finishes.



Finishing a Green Mountain Panel Home

What skills are required for finishing a Green Mountain Panel home?

General carpentry skills are all that you will need to finish a Green Mountain Panel home. Skilled homeowners can do most of the work themselves, subcontracting out work requiring specialized skills, such as electrical and plumbing work.


How is the roof finished?

With asphalt and fiberglass shingles and metal roofing, a cold roof system is recommended. With some types of roofing, such as wood shakes and slate shingles, horizontal strapping is required.


What kind of roof trim can I use with Green Mountain Panel SIPs?

The outer roof edge, both along eaves and gable ends, will require two-by blocking to be installed. You can add any trim to this you wish to meet your design preferences. At the eaves, some people choose full-return horizontal soffits with ornate fascia trim, while others choose simple sloped soffits, nailed directly to the panel overhang.


Is exterior siding applied directly to the panel skin?

Green Mountain Panel recommends that all siding is vented with either furring or a rain screen material which keeps the siding at least 3/8 inch away from the panel to provide a vented capillary break. Felt paper or other drainage material should be used between the panels and siding. An air barrier such as Tyvek™ or Typar™ may be used, but it is not required. In most situations, especially such as with wide board-and-batten siding, wood strapping should be attached to the wall first, then the siding secured to the strapping.


How should siding be applied?

Horizontal siding is nailed directly to the panel wall passing through the air and moisture drainage systems. Keep nails at least 6″ from splines to avoid rippling of the siding. With shingles, you may nail into strapping without worry. With vertical board-and-batten siding, horizontal strapping is recommended. Use 6d galvanized or stainless steel nails for clapboards and 8d galvanized or stainless steel nails for board-and-batten.


Are windows and doors difficult to install?

No. Windows and doors are very easy to install in a Green Mountain Panel home. Units are set into the rough openings (which were built into the shell) and shimmed to level, as per instructions provided by the window and door manufacturers. Then the perimeters are sealed with low-expanding foam sealant, resulting in an extremely energy-efficient installation. Care must be used when foaming around windows and doors so as not to swell the casings.


How are interior walls installed?

Interior partition walls are generally constructed of 2x4s and sheathed with drywall as in conventional frame construction. Where an interior partition wall meets an exterior wall, the edge stud is nailed or screwed into the OSB skin of the panel.

How do you run wiring in panels?

There are a number of options for running electrical wiring in a Green Mountain Panel home. Horizontal wiring runs are usually carried in the basement, with short upward extensions for outlets made in the Structurewall™ panels. Some electricians push the wire through the foam core of the panel, while others make a vertical rout through the inner OSB skin from the outlet down to the floor level and push the wire in before drywall is installed. Other options include surface-mounted wiring and wiring concealed in a baseboard raceway. Green Mountain Panel has a technical sheet available on wiring details and it is included in the construction manual.


How are electrical boxes attached to panels?

The boxes are cut into the wall and either nailed to splines or secured to the OSB or drywall with “Madison” straps.


How do you run plumbing in a Green Mountain Panel Home?

There will be almost no differences between plumbing a Green Mountain Panel home and plumbing a conventionally framed house. Plumbing runs should be kept in interior (conventionally framed) partition walls or in specially constructed plumbing chases.


How are walls finished in a Green Mountain Panel Home?

Walls are usually finished with drywall on the interior face. On SIPs walls, drywall is installed directly over the OSB surface of panels, applied either vertically or horizontally. Some builders use construction adhesive in applying drywall to the panels, enabling them to use fewer fasteners. Be sure not to end the drywall edge on a panel joint. On interior partition walls (which are framed conventionally), drywall is installed in a standard manner, nailing or screwing drywall to the studs. With cathedral ceilings, some builders prefer to substitute Green Mountain Panel Pineclad™ panels, which have an interior facing of T&G pine.


How are kitchen cabinets installed?

Kitchen cabinets are very easy to install in Green Mountain Panel homes. Along exterior walls, cabinets are screwed directly into the OSB skin of the panels. Because a single layer of OSB is not as thick as a stud, you should use a few more fasteners. Screws are recommended for cabinet attachment. For the strongest attachment, cabinets should be secured directly to the OSB before drywall is installed but it is possible to mount the cabinets to walls after drywall has been installed. On interior (non-SIPs) walls cabinets are installed conventionally by screwing or bolting them into studs.


What is the best type of heating system for a Green Mountain Panel SIPs home?

Any type of heating system can be used. Talk to your heating contractor or general contractor for recommendations.


Can I heat with wood?

Absolutely. Many people living in Green Mountain Panel SIPs homes are able to provide all their heat with just one to two cords of firewood per year! With wood heat, a source of outside combustion air is recommended.


Do I need to worry about insects with Green Mountain Panel SIPs?

On occasion, carpenter ants will take up residence in the Structurewall™ panels of a Green Mountain Panel Home. To protect your house from possible ant infestations, Green Mountain Panel recommends that you have your house protected by a certified pest control professional both during construction and periodically thereafter.



For additional information on Green Mountain Panel’s prepackaged or custom house designs and details on shell erection and finishing contact the company or visit us on the web at greenmountainpanel.com.