Homeowners > FAQs - MURUS POLYURETHANE (PUR) SIPs
What is the difference between a “stress skin” panel, a “foam core sandwich” panel, and a “structural insulating” panel?
The terms “stress skin”, “foam core sandwich”, and “structural Insulating” panels (SIPs) all refer to the same product and are interchangeable. The industry terminology has standardized and the term “SIPs” is most often used among panel manufacturers. However, “stress skin panels” and “foam core sandwich” panels are still popular terms among timber frame professionals.
How does Murus Polyurethane differ from other manufacturers’ foam?
The properties and characteristics of Murus Polyurethane are superior to Isocyanurate and Polyisocyanurate foams typically produced by the lamination method. Murus’ proprietary manufacturing method, Uniform Dispersion Molding (UDM) is key to creating our SIPs’ superior characteristics. Liquid foam is dispersed uniformly throughout the mold; the foam expands, bonds, and cures under 12 to 14 psi. UDM's polymerization process produces uniform foam density throughout the panel, with spherical cells that give the foam superior and uniform strength as compared to elongated rice-shaped cells produced by Isocyanurate and Polyisocyanurate lamination foams.
Is there any danger of the foam off-gassing?
No. There is a trace quantity of off-gassing which is emitted by the blowing agent during the manufacturing process. Once the manufacturing and curing processes are complete, the foam is stable and inert.
How is wiring accomplished in Murus SIPs?
If ordered, Murus can mold horizontal electrical chase(s) through the panels during the manufacturing process. The chases are centered in the foam and are typically at standard horizontal heights for outlets, depending on how the panels are ordered. In some cases, you may have to do some pre-wiring before the panels are installed and during the installation process, but often the majority of the wiring can be accomplished after the panels are installed.
How is plumbing accomplished in Murus SIPs?
Good building practices will keep plumbing out of exterior walls.
Most SIP home designs incorporate plumbing into interior partition walls.
What can be done to insure the indoor air quality of my Murus SIP home?
Indoor air quality has become a major health concern in homes and buildings that are built to meet or exceed today’s energy conservation codes. A structure that is properly built with SIPs can be very airtight, so many manufacturers, including Murus, require the inclusion of a mechanical ventilation system into your heating and/or cooling system. Typically this is done through a Heat Recovery Ventilator (HRV) or an Energy Recovery Ventilator (ERV). Most of the major HVAC system manufacturers now offer these units, as do many smaller companies, so consult with your mechanical contractor. Read more: Mechanical Ventilation
How strong is the Oriented Strand Board (OSB) used in SIPs?
OSB has come a long way since it was first introduced. The OSB used in the manufacture of SIPs is quite different from a lot of the material used for wall and/or roof sheathing because the wood fibers are oriented in a way that gives the board more than adequate strength for satisfactory performance . The strength and integrity of the OSB is fully tested and documented by the manufacturer and other agencies.
How are kitchen cabinets and other wall elements mounted?
The standard installation procedure of screwing cabinets to the walls is usually acceptable, although you may want to use a few more screws. Excessively heavy items may require readily available specialty fasteners. Consult with the cabinet manufacturer for recommendations.
How are Murus SIPs installed?
In structural applications, SIPs are typically installed over a 2x plate that is attached to the sill or subfloor. The foam is removed from between the skins so the panel sits over the 2x and nails are driven through the skins into the 2x. Usually a double 2x top plate is installed in the same manner. There are many variations on these procedures.
Murus recommends a cold roof. What is that?
If you use SIPs for the roof, Murus has always felt that a “cold” roof, or vented roof on top of the panels, is the best application. Typically this is accomplished by first installing 15-pound roofing felt on the roof panels, then installing 1x or 2x lumber vertically from the eaves to the ridge. These “straps” are put on 16” or 24” centers and sheathing (OSB or plywood) is attached over it before the roofing material is applied. The eave is left open or vented through the soffit, and the ridge is vented with a vent cap.
Does the PUR foam contain formaldehyde?
No. Our foam system is, and always has been, an MDI base and does not contain urea-formaldehyde. Urea formaldehyde-based foams were used in the 1970’s as a field-applied, spray-in-place insulation system. These foams are no longer used. However, the adhesive used in the OSB is manufactured with some Phenol resins. Most OSB manufacturers are now using a combination of Phenol and MDI resins. Some of the newer mills are producing board with 100% MDI resins. Phenol resins used in OSB do off-gas. The amount of off-gassing is listed as TL (trace levels) and is well below any set threshold. As a TL, it is considered more than safe and does not pose any health problems.
How do I protect my Murus SIPs from insects?
No matter what type of home you are building, whether a SIP home or a conventional stick construction home, it is recommended that a regular preventive program of insect treatment be initiated and maintained when building in a known insect risk area. Most pest control companies offer maintenance plans, renewable periodically or annually, and will automatically treat your grounds and structure at pre-determined intervals. With such a program and proper maintenance of the property, you should be able to comfortably minimize the risk of insect infestation.
What does a “Class 1 Fire Resistance Rating” mean?
Murus Polyurethane SIPs conform to test standards set by the American Society for Testing and Materials (ASTM E-84) for acceptable flame spread and smoke development for combustible construction materials. ASTM E-84 is a similar test to UL-723, NFPA 2255, or UBC 8-1. Testing is accomplished by suspending a sample of material in the tunnel of a horizontal test chamber. The material is exposed to gas flame on one end of the tunnel for 10 minutes. The flame progression on the material is compared to selected standards and calculations designed to produce a flame spread rating. Smoke from the fire in the tunnel is measured in the exhaust stack via a light beam to establish smoke developed ratings. There are three classes of acceptability for rigid foam used in construction: Class 3 is unacceptable, Class 2 is the minimum standard required for residential construction, and Class 1 is the best classification available. The Polyurethane cores of Murus Sips have a Class 1 Fire Resistance Rating.
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