INTRODUCTION TO SIPs

SIPs, a historical perspective

The first residential development that extensively used structural insulated panels took place in 1952 in Midland, Michigan. Interest and development in insulated panels began to grow as SIP technology improved. As the thermal efficiency of SIPs became more well known, the cost of building with SIPs was still viewed as being too high for general residential use. However, as the cost of lumber and construction labor has risen, SIP construction has become increasingly competitive with traditional building techniques. SIP building systems are now one of the fastest growing segments in the residential building industry.

Bill Porter was one of the pioneers in the development of structural insulated panels, and a founding member of SIPA (the Structural Insulated Panel Association). He was quick to see the enormous potential for panels in residential and light commercial construction. In 1964, W. H. Porter, Inc. (now called PorterCorp) began producing panel systems for a variety of applications under the product name PorterSIPS. Over the following years, as new products and technologies were developed, PorterSIPS integrated these advances into new panel systems, becoming a key industry innovator.

The PorterSIPS type "A" Structural Insulated Panel

The PorterSIPS "Type A" panel is a basic building component with a very broad range of applications. It is made by pressure bonding modified expanded polystyrene (EPS) between oriented strand board (OSB) outer sheeting. The EPS core serves as a rigid glue base material and an economical, high performance insulation. The OSB acts as the "stressed skin" of the panel, and also provides a sturdy nail base to which interior and exterior finish material can be attached. The SIPs is, in effect, a omni-directional "beam", with the EPS acting as the web and the OSB the load bearing flanges.

OSB basics

Oriented strand board (OSB) is an engineered wood product developed in the 1980’s. Made by processing first growth trees, OSB is produced by orienting the wood chips of the exterior layers length-wise and random or cross-aligning the inner layers. Using waterproof glue, the alternating layers are then bonded in the presence of both heat and pressure. The resulting product is dimensionally stable, strong, durable, and in many ways shares the same properties as plywood. OSB is made in large 8’ x 24’ sheets, making the production of large size panels possible.

EPS basics

Expanded polystyrene (EPS) is the most cost-effective structural core insulation material available. Compared to other foam insulation products, EPS has the highest R-value per dollar invested. It has a much higher R-value per inch of thickness than fiberglass or cellulose insulations. Unlike most insulation products, the R-value of EPS actually increases as the temperature drops. In addition, EPS is physically stable, unlike fiberglass or cellulose, which tend to settle, creating voids and reducing their effectiveness. EPS is an inert, organic, recyclable material containing no chlorofluorocarbons (CFCs). It provides no food value to plants, animals (including rodents) or micro-organisms, so it will not rot and is highly resistant to mildew.

R Value basics

As insulation, EPS provides an "R" value of 3.85 per inch of thickness at 75º F (and 4.13 per inch at 40º F). By including the "R" value for the OSB skin and surface air, the total "R" value for complete panels is as shown in the table below:

In comparison, the R-value of a 4 ½" SIPs panel is 15.2, while the R-value for a stick built house with fiberglass insulated wall is 13.8. However, because of the numerous thermal breaks resulting from studding, voids, settled and compacted insulation, etc. the thermal efficiency of the fiberglass-insulated wall is effectively downgraded 15 – 18%.

SIPs Panel Testing and Sustaining Loads

PorterSIPs have been thoroughly tested and evaluated by third party agencies. The results of this testing and evaluation have been examined and approved by a number of code agencies.

Manufacturing is done under a quality control system, which is monitored by a third party agency, PFS-TECO. Look for the stamp that shows panels meet exacting quality control standards.

PorterSIPs "Type A" panels have been recognized by the major building codes in the National Evaluation Service report  # NER-467 & ICBO Report # ER-5737.

SIPs (Structural insulated panels) represent a greatly improved means of building homes and other structures more quickly, simply and cost effectively. SIP building also yields greatly improved energy efficiency. Because of these benefits SIP construction will be the building method of choice in coming years.

PORTER SIPs are capable of sustaining loads typically imposed on walls, floors, roofs, and other load-bearing elements. The most surprising characteristic of SIPs is their ability to span long distances. For example, cathedral style ceilings are an excellent application for SIPs.

SIPs are easy to work with. Standard carpenters tools, with a few exceptions, are sufficient to erect a SIP home. Lower level wall and floor installations can be done by hand when using 4' X 8' panels. Larger panels or upper levels require the use of lifting apparatus such as a crane or boom.

It’s easy to recognize the qualitative superiority of SIP construction. Builders have consistently noted that building with SIPs dramatically improves on-site construction quality and workmanship because the structural “frame” and the thermal envelope are one and the same, thereby simplifying construction.

SIPs Panels for Roof Use

SIPs are not only energy efficient, they can span long distances. For example, our 8 ¼" SIP has an "R" factor of 33. Our Uniform transverse load chart shows at 13'-6" span (14' with 3" bearing on each end) a load of 46 pounds per square foot (PSF) is allowable.

To put this to practical application, suppose a home or portion of a home has a width of 24'. The roof pitch is 6:12. This design would allow the panels to span from a ridge beam to the exterior wall without intermediate support.

PorterSIPs precut roof panels come with the foam recessed for blocking lumber on the eave and rake ends. The ridge is cut at the appropriate angle for suggested fit. The eave ends can be cut to be parallel to the wall (plumb cut).

PorterSIPs roof panels can be made to cantilever with a 48" overhang. A separate transverse load chart should be referenced for this design.

Roof panels are available in 6 ½", 8 ¼", 10 ¼", and 12 ⅛" thickness. Sizes as large as 8' x 24' are available.

Nailbase Panels for Roofing

In situations where a roof deck is being re-roofed or a new roof is being placed over rafters or trusses, PorterSIPs Nailbase panels may be used. A deck of sheathing is applied over the rafters or trusses and the nailbase panels are installed prior to applying the roofing felt.

PorterSIPs nailbase panels are EPS insulation with 7/16" OSB on one side. The OSB face is installed face up and serves as a nail receptor for the felt and shingle system.

Nailbase panels are available in thickness to 12". The panels are 4' wide and lengths to 12' are available.

Caution about Roof Panels

SIP roof panels require a 15-minute thermal barrier be applied to the interior surface. A 15-minute thermal barrier is defined by the code issuing authorities as ½" gypsum wall board or equivalent rated material.

When installing SIPs, care should be taken to fill all voids in the EPS by using spray foam and securing panel connection splines using an approved styrene friendly sealant. Rake and eave blocking is to be sealed with approved sealant to prevent air flow.

Panels are to be installed with a minimum spacing of ⅛" between the OSB faces of the adjoining panel. This spacing is to allow for expansion of the OSB without buckling.

Porter SIPs are attached using pancake head SIP screws with a 3" washer. Our normal recommendation is to in to install a screw and washer every 12", for the perimeter of the walls, into the top plate of the wall. In addition, a screw and washer shall be installed each LF of truss or rafter.

The panel warranty will be voided if installation connection details are not followed.

SIPs Panels for Walls Use

SIPs can be used for any wall height. For 8' height walls, panels are available to 24' length. For wall higher than 8', panels will have a maximum length of 8'. SIP wall panels are normally 4½", 6 ½" and occasionally 8 ¼". The "R" factors are: 15.2, 24.7 and 33, respectively.

SIP walls have the advantage of 100% nailing surface on the interior wall. Unlike stick construction, there is no need to look for a stud to hold nails. This speeds interior finishing.

PorterSIPs precut wall panels are delivered to the jobsite ready for installation. Installation drawings and details are included with each project. Panels, screws for comer connection, splines for panel connection, spray foam, sealant and 5/4" top spacer plate are normally quoted in each proposal.

For post and beam, timber frame or steel frame construction, wall panels are available in sizes to 8' x 24'. The panels can be used like tilt up construction.

Type A SIPs are faced with 7/16" OSB on both sides. A type C panel is also available with 7/16" OSB on one side and 19/32 grooved plywood on the other. Type C panels have ship lap edges on the long sides.

Caution about Wall Panels

SIP wall panels require a 15-minute thermal barrier be applied on the interior surface when used for residential use. A 15-minute thermal barrier is defined by the code issuing authorities as ½" gypsum wallboard or equivalent rated material.

SIP wall panels require a protective exterior cover of house wrap or felt paper. This should be installed immediately after the panels have been installed.

Wall panels are required to have a minimum ⅛" space between adjoining panel OSB faces. Splines of either SIP splines or dimensional lumber are to be used.

Spray foam is used to fill EPS voids and styrene friendly sealant is supplied for sealing the plate connections, panel joining and blocking lumber.

The panel warranty will be voided if installation connection details are not followed.

Interior Surface of a SIPs panel

All major building codes require that the interior surface be covered with ½" drywall or equivalent to act as a thermal barrier.

Exterior Surface of a SIPs panel

OSB exposed to the weather must be protected. House wrap or felt paper are both acceptable protection.

For walls, house wrap or felt paper should be applied in such manner as to create a drain plane. This includes window openings and other penetrations. Cladding would then be applied over protective wrap.

For roof, felt paper should be applied in an overlap method to provide a drain plane. The final step would be to apply to roof material.

Type C panels are faced on one side with 19/32" reverse board and batten fir plywood. As in the case with all panel installations, the  use of a recommended sealant is important to seal the wall system. A protective finish should be applied.

Copyright: 07/26/2006