Message Board Thread - "Dow STYROFOAM SIS™ Brand Structural Insulated Sheathing "

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Dow STYROFOAM SIS™ Brand Structural Insulated Sheathing bwrooster 2/11/2009
Has anyone out there in the magic world of Building Science used this product or heard the pros and most importantly any "cons" of it? i work for a builder in Portland OR. and they are considering using it. I have some concerns of its ability to breathe aswellas being the primary WRB especially in the Pacific NW. It as a new product therefore i can find reports of field results on it. Thanks!
 
Re:Dow STYROFOAM SIS™ Brand Structural Insulated Sheathing Scott Wood Associates 2/16/2009
Seems like a nice system. We are using the outboard foams, much more especially in the colder climates such as Portland. Way worry in regard when exterior mounting the system if it is installed correctly? We use OSB and it has similar perm considerations. Even though it conforms to ICC-ES AC269 I’d run the product specification through the engineers first regarding sear racking, just to understand the differences between it and the commonly used OSB. Remember it is the spacing of the fasteners that provide the sear value. Speaking of fasteners, Dow suggests nails or staples. Metal is a conductor as well as potential penetrations for water and air, though probably not of great significance.
Exterior foam panels are a great way to prevent moisture problems, stop the 20-25% thermal bridging through the studs as well as provide part of an air barrier system.
Two cautionary notes: First, even though the installation describes using their 2 7/8” weathermate™ tape to seal the joints, I’d be very careful to provide design detail (and contractor “training”) in regard to connections (ESPECIALLY roof and foundation) and penetrations to insure they are air tight as well as moisture tight. I cannot stress the importance of a “system” to provide an acceptable air barrier include the roof and foundation details. Failures of foam panels such as SIPs has been found even without air movement through the material. Convective loops can occur within the material at the gaps within the joint system driven by natural convection and heat differences.
Second, outboard insulation is the best approach to a thermal barrier, but with our inherited practices for the need to stuff the walls with pink stuff, we tend to fill the stud bays even though it may not be necessary. Yes, this provides more R-value, but also pulls the condensation plane into the interior of the building, sometimes within the stud bay itself causing condensation problems. A building will always leak some air causing potential condensation. Fluffy stuff will not prevent air movement and therefore not block convention. Filling the stud bay with insulation and including exterior insulation such STYROFOAM SIS™ will slow energy transfer from the interior (in cold climates) thus pulling the condensation plane inward, possibly causing condensation within the fluffy stuff. The designer must look at hygrothermal modeling to ensure this will not happen in the climate where constructed and the contractor keep from filling the stud bays when specified otherwise by the designs.
 
Re:Dow STYROFOAM SIS™ Brand Structural Insulated Sheathing bwrooster 2/18/2009
Scott Wood Associates wrote:
ike a nice system. We are using the outboard foams, much more especially in the colder climates such as Portland. Way worry in regard when exterior mounting the system if it is installed correctly? We use OSB and it has similar perm considerations. Even though it conforms to ICC-ES AC269 I’d run the product specification through the engineers first regarding sear racking, just to understand the differences between it and the commonly used OSB. Remember it is the spacing of the fasteners that provide the sear value. Speaking of fasteners, Dow suggests nails or staples. Metal is a conductor as well as potential penetrations for water and air, though probably not of great significance.
Exterior foam panels are a great way to prevent moisture problems, stop the 20-25% thermal bridging through the studs as well as provide part of an air barrier system.
Two cautionary notes: First, even though the installation describes using their 2 7/8” weathermate™ tape to seal the joints, I’d be very careful to provide design detail (and contractor “training”) in regard to connections (ESPECIALLY roof and foundation) and penetrations to insure they are air tight as well as moisture tight. I cannot stress the importance of a “system” to provide an acceptable air barrier include the roof and foundation details. Failures of foam panels such as SIPs has been found even without air movement through the material. Convective loops can occur within the material at the gaps within the joint system driven by natural convection and heat differences.
Second, outboard insulation is the best approach to a thermal barrier, but with our inherited practices for the need to stuff the walls with pink stuff, we tend to fill the stud bays even though it may not be necessary. Yes, this provides more R-value, but also pulls the condensation plane into the interior of the building, sometimes within the stud bay itself causing condensation problems. A building will always leak some air causing potential condensation. Fluffy stuff will not prevent air movement and therefore not block convention. Filling the stud bay with insulation and including exterior insulation such STYROFOAM SIS™ will slow energy transfer from the interior (in cold climates) thus pulling the condensation plane inward, possibly causing condensation within the fluffy stuff. The designer must look at hygrothermal modeling to ensure this will not happen in the climate where constructed and the contractor keep from filling the stud bays when specified otherwise by the designs.
Thanks so much for the information Scott.
 


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