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Spraying exterior walls Post New Topic | Post Reply
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Daniel Vinyard
Posted: Dec 11, 2007 09:27 PM
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Spraying exterior walls
I am remodeling a 50yr old home and will be tearing out the interior to the studs. The siding is cypress which was applied without a vapor barrier. There is no existing insulation in the walls either. My question is, can CC foam be blown in without first applying a Tyvec style vapor barrier? I don't want to have to remove all of the sidding as well. Thanks.
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mason
Posted: Dec 12, 2007 07:41 AM
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It is not a good idea to spray directly to the siding. At some point the siding will be replaced and the foam would have to be re-installed. Plus this type of siding is not typically recommended as a suitable substrate for SPF. As for what to put in the wall cavity. You don't need a structural sheathing or a vapor barrier membrane if you are using closed cell foam. So you can use any type of lightweight sheathing or membrane that is water vapor permeable but also sheds water. |
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Posted: Dec 12, 2007 08:44 PM
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tyvek is not a vapor retarder.. it is a house wrap,,,,a feeble attempt at an air barrier...it is a marvelous external drainage plain (sp?)... also consider,,you would not want a vapor retarder on the cold side of the wall in your cold climate area of philly... indeed it would not be a good idea to apply to the siding directly...(so this place is framed and sided with no sheating or clab boards or nuffin???) necessity is the mother of invention...why not put a 1" piece of board stock in the stud cavity and use the spray foam to seal it in place.. you would obtain an air barrier as well as achieve additional r value... the board stock would give you the layer of interference between the siding and the foam insulation... the best system,,,probably not,,but it would work just fine,.... hope this helps... |
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Daniel Vinyard
Posted: Dec 14, 2007 05:36 PM
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I don't know why my great-grandfather did not use any kind of sheathing before he installed the siding, but now I have to deal with it. I like the idea of using a transition material between the foam and the siding. It should be easy to make work. What material to you mean by "board stock"? Thanks again. |
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mason
Posted: Dec 15, 2007 04:02 PM
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Board stock is a generic term for polyurethane foam sheathing. Before polyiso board, you used to use polyurethane foam that was cut into the thickness that you wanted. Now, it is used for any type of foam sheathing, such as EPS, XPS and polyiso board. |
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Nicholas Cioffi
Posted: Jan 29, 2008 09:44 AM
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I have a similar question regarding the lack of exterior sheething and house wrap. Can the foam be sprayed directly to a hardiboard type siding (cement based product)? I like the idea that you can eliminate as much wood as possible with the spray foam application, but will the structure be strong enough to resist shear forces without the plywood sheething? |
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mason
Posted: Jan 30, 2008 07:44 AM
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Check with your supplier to determine if a primer is needed for adhesion. But the foam will enhance the racking strength of the wall, dependent on how strong the wall is to begin with. There has been a lot of research on how much racking strength 2 lb sprayfoam provides to different substrates. SPFA conducted racking testing at NAHB Research Center 1992 and 1996 between wood studs and metal studs and at Architectural Testing Inc. in 2005 between wood studs. Results: SPF installed between metal studs: (3.5 inches) • Increased racking strength of drywall sheathed walls: 2400 lbs to 5300 lbs •Increased racking strength of OSB sheathed walls: 4800 lbs to 6000 lbs SPF installed between wood studs: (3.5 inches) • Increased racking strength of vinyl sheathed walls: 913 lbs to 2800 lbs • Increased racking strength of plywood sheathed walls: 2890 lbs to 5,300 lbs • Increased racking strength of polyiso sheathed walls: 1,109 lbs to 2,159 lbs SPF installed between wood studs: (1.5 inches) • Increased racking strength of polyiso sheathed walls: 1,109 lbs to 2,257 lbs Details are available from SPFA |
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Circle-D
Posted: Jan 31, 2008 07:48 PM
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Mason, Is there a publication number for these test results? |
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mason
Posted: Feb 05, 2008 02:52 PM
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The specific test reports can be obtained from SPFA. Or email me and I can send you the reports. |
