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Structural Insulated Panel Systems Make Timber Frame Homes More Energy Efficient

Timber framers -- and homeowners buying their frames -- have made structural insulated panel systems the preferred method of closing in timber frame homes. There are plenty of good reasons for their choice. Timber framers pour their hearts and souls into producing a frame that will be a work of craftsmanship and beauty. They and the new owners want to protect that frame as quickly as possible. With the use of insulated panels, the average-sized home can be enclosed in a couple of days with a protective envelope that will keep all the elements off the frame.

Structural Insulated Panels or SIPs offer superior energy efficiency

Insulated Panel Systems

Structural insulated panels are placed on the outside of the timber frame, so the entire frame is exposed to view in the interior of the home--unlike stick-framing, which is filled in between the timbers. And because the timbers are fully inside the insulated wall system, they are also protected from moisture damage. With stick-framed walls, on the other hand, moisture can penetrate into the wall cavities and cause rotting of both timbers and intermediate studs.

Another advantage over stick-framed in-fill is that panels are manufactured using OSB on the inside skin, which normally has sheetrock applied to it with screws and/or nails. As the panels are manufactured using engineered materials, they are very stable and will not shift. Because of this the owner will not have a nail-popping problem in the future.

As a result, homeowners can begin saving money immediately by buying smaller HVAC systems. And of course they continue to enjoy savings on energy costs, anywhere from 40%-60%, depending on the size and type of panels they select, for as long as they own the home.

We can't fail to mention the increased strength to be gained by the use of panels. Both timber framers and their frame owners aim to build homes that will stand the test of time. The use of panels provides significant additional strength to the home. But first, a clarification needs to be made: two types of panels are generally produced: structural insulated panels, which are used to build homes that do not have any other structural component; and insulated panels, which enclose the timber frames that provide the structure. The former are called SIP's (Structural Insulated Panels) while the latter are simply called insulated panels or stress skins, although sometimes they are all referred to (inaccurately) as SIP's.

True SIP's are structural, and since their loads are carried evenly throughout, they are stronger than stick-built walls in compressive strength and resistance to racking. In fact, according to a report from the US Department of Energy (November, 2001) "Testing has shown that a wall panel with two half-inch-thick OSB skins is nearly three times stronger than a conventional 4-inch stud wall." This can make a big difference, especially in parts of the country that experience severe weather. Houses built of SIP's have stood up to windstorms, tornadoes and earthquakes that have knocked neighboring stick frames flat.

Basic Panel Information

Now that we've described the basic advantages of insulated panel systems for use in building timber frame homes, let me list some of the aspects of polyurethane panels that make them better than all the others.

Most urethane panels are produced using a Computerized Drafting System to design the panel system to extremely close tolerances. The panels are produced and fabricated from the design in quality controlled plant conditions. This means they arrive at your building site already pre-fabricated and ready to go up without a hitch.

Urethane foam insulation generates the highest R rating for panels. We generally recommend our R-26 wall panels and R-40 roof panels for home construction. This will reduce your energy costs by a minimum of 50% over stick framing.

As the Urethane is injected into the panels, it seals itself to both OSB skins and completely fills the panel. This provides an automatic air and vapor barrier. And, as the panels are entirely filled, there are no air spaces for moisture to build up, thus greatly reducing any opportunity for mold to grow in your wall system.

In most urethane panels, your electrical plan is fabricated into the panels for you, some include chases lined with conduit and wiring boxes. You or your electrician need only fish the wires through once the panels are up.

In some panels, your electrical plan is fabricated into the panels for you, with chases lined with conduit and wiring boxes. You or your electrician need only fish the wires through once the panels are up. These wiring boxes are installed prior to the foaming operation, furthermore, effectively sealing them and eliminating any drafts through the boxes.

Polyurethane panels are manufactured using environmentally friendly products.

Insulated panels are relatively new in the centuries-old building industry. But while they have been in use only for the past 50 years or so, these "newcomers" are already tried and true. In fact, they have proven to be the strongest, most energy efficient and most durable method of high quality home construction. Polyurethane panels make the most of these advantages.

Panel Design

Panel design gives you the exact measurements for cutting and fitting the panels. Panel producers provide the design to the builder if the panels are going to be fabricated on site. Those companies that offer complete pre-fabrication generally design and engineer the panels to much closer tolerances. Many of the latter will also include your plans for electrical into the design and put in the chases and/or conduit and wiring boxes during pre-fabrication. The panel design generally does not include plans for plumbing or heating and cooling, since these are generally worked into interior space, as in conventional construction.


These are the various fasteners required to connect the panels. Some panel companies provide the accessories with the panels while others do not. The cost of the accessories is generally 10-15 % of the panel cost.

Panel Interior Treatments

If you are planning to use Tongue & Groove Decking on your ceiling, the proper procedure is to install it first and attach the panels over it.

If you are going to use sheet rock on ceilings or walls, a furring strip should be nailed on the exterior of the frame members before installation of the insulated panels. This leaves spacing that will simplify installation of sheet rock. The dry wall installers simply slip the sheet rock behind the timber frame braces and posts in the space provided by the furring strip. The same method can be used to make it easier to install wood paneling on the walls. Be sure to tell your designer what material you plan to use, and which dimension (both sheet rock and wood paneling come in different thicknesses) so the proper size furring strip will be indicated in the drawings.

Exterior Finishes

Panels allow for the whole range of exterior finishes on roof and walls. This versatility is just one more of the advantages of enclosure with panels, as it allows you to build a home that fits into any setting. Neither EPS nor polyurethane foam contains formaldehyde or CFC's. On Roofs: You can use metal, shingle or shake roofs over the panels. Shingles come in a wide range of quality. If you are using shingles, therefore, it is best to choose a company that will warranty their product over panels. It is also wise to avoid a dark-colored shingle in a hot climate. At this point no studies have been completed to indicate that a cold roof will increase the life span of composition shingles over panels. The typical panel roof is simply covered with felt and shingles. Although this is theoretically a hot roof, in fact, because of the extremely high R-Value of panel roofs, it is more accurately defined as neutral. The insulation prevents heat from building up in the interior and over-heating the roofing material. On Walls: The panel walls can be covered with any kind of wood, vinyl, stucco, stone or brick. Your siding manufacturer will provide specifications for attaching the siding to the wall panels.


Enclosing a frame with insulated panels is faster than stick-framing, but of course the type of panel used will make a big difference as well. The pre-fabricated panels can be installed very quickly and offer almost immediate protection for the timber frame. Once the panels are installed, you have only to get the roof covering over the panels and your home is dried-in and safe from the elements. At this point, you have much more leeway in scheduling the work to complete your home.

Finishing Your Home

In general, finishing a timber frame enclosed with insulated panels is not significantly different from finishing a stick-framed home. However if the contractor is not familiar with panel construction, he can consult with the timber frame company on questions concerning finishing the house.

Again, the more sophisticated pre-fabricated panels make finishing your home easier. Since they are pre-fabricated, you will not have the time-consuming and messy process of cutting the panels on site. The best panels have chases lined with conduit and wiring boxes installed in the panels for your electrical. The rough openings for windows, skylights and doors are cut and framed in with wood. The subfacia is already installed on the roof edge. All of these features provide significant time savings and make the contractor's job easier.


While panels protect the timber frame from moisture, they themselves require protection from moisture. There are three key preventative measures. The most important is that the panels must be properly sealed with foam during installation. As a second measure, you should wrap the home in a vapor barrier. This step is not required by all panel manufacturers, but is good building practice. The third measure-one the homeowner can take-is to install an air exchange system to exhaust the moisture-laden air that builds up in any tightly sealed structure. Some state energy codes require air exchange systems in all new construction, now. More will adopt that requirement in the future.

Indoor Air Quality

An air exchange system will also bring fresh air into your home and exhaust the stale air. This is recommended in all tight houses, including those enclosed with insulated panels, because there are no drafts or leaks to allow air exchange with the outdoors. Many products found in the home, such as furniture, curtains, carpet, and cleaning products, emit gasses that can built up and pollute the air inside the home unless there is a mechanical air exchange system. You can get an air exchange system with a whole house air purifier, if you want to take that next step.


Insulated panels do not contribute to the pollution of air with formaldehyde or other gasses. Neither EPS nor polyurethane foam contains formaldehyde or CFC's. While trace amounts of formaldehyde are found in fresh OSB, it is well below the limits established by the U. S. Department of Housing and Urban Development. In addition, they diminish to undetectable levels within the first few months. (HUD's limit is 0.2ppm for plywood and 0.3ppm for particle board. Fresh OSB is below 0.1ppm and for this reason has been exempted from testing and certification.)


SIP's pass all the standard fire tests required of wood-based construction. They contain no air within their foam core, so the crucial element required for a fire to burn, oxygen, is absent. This means that the fire will not run up the wall cavity. The sheetrock usually used as the interior wall finish adds another 15 minute thermal barrier to protect the SIP's and any other underlying structure. Urethane panels typically have a Class 1 fire rating. Urethane does not burn.


Insulated panel systems have no insect problems that are unique to them. The same insects that can infiltrate a stick framed home may get into a panel enclosed house. It is advisable to take the same precautions that one would take in building any home.

Keeping out carpenter ants and/or other insect pests such as termites, may require a multi-pronged approach, which includes treating the soil, putting in the metal shields between the foundation and sub-floor, keeping flower beds away from the foundation and removing overhanging limbs. It is advisable to talk with your local pest control professional and your builder about which steps are most effective in your area.


The panel materials cost more than stick framing with fiber glass batting, but less waste, cheaper labor costs and the savings on heating and cooling systems often allow SIP's to stay competitive in the long run. Prices vary region by region, so the best procedure is to get competitive bids locally, figuring in the long term factors as well as short term.

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