Continuous Insulation – Part 3
Sorry for the delay in posting. I had to work out some legal and liability issues on some of the information in this post before publishing . . .
When I left the last post, I was about to give away the final and best solutions I have found to providing Continuous Insulation (CI) in a metal-framed wall with the widest variety of cladding materials. I also want to leave you with some outstanding issues I have yet to resolve so you can be aware of them and press cladding and insulation manufactures to get the issues resolved. I’m also going to provide a list of links to manufacturers I have spoken with that have been helpful in one way or another, or are now aware of the issues . . . With that, let’s wrap this up . . .
The first solution I found is a proprietary system. I’m not against proprietary systems, but they often come with a price-tag. I would much rather find a solution that uses materials my contractors are familiar with, and if possible, construction methods with those materials that are simple and make sense to my contractors.
The first solution, a proprietary system, uses a specialized girt, appropriately named a “CI-Girt,” by Knight Wall Systems. The biggest advantage to this system is that the primary girt runs vertically and attaches through to the stud, and if necessary, a horizontal girt is added for cladding attachment. Therefore, the system works for both vertically and horizontally attached cladding systems. These guys are definitely on the right track, but I was not looking forward to specifying a proprietary system from Washington state in by Baltimore buildings . . .
Finally, I found what I was looking for all along . . . someone who has done testing with “normal” stuff and made it work. In fact, they used standard metal hat channels, wood furring, screws, and similar products. They went so far as to format their data for inclusion in future Model Building Codes. Since the research is not yet in the codes, you will need to have a structural engineer verify it and specify according to the specifics of your project, but here it is . . .
I highly suggest reading most of the data, process, etc . . . but for a quick run, skip to PDF page 70 (document page 62) for a simple chart.
So there you go . . . there’s the solution . . . but there is still one major problem . . .
Fire codes . . .
In IBC 2009 and other model building codes, there’s information about materials and how they should be used, tested, etc. For Continuous Insulation boards, particularly Foam Plastics, one of these tests is NFPA 285 (IBC 2009 2603.5). From what I understand, this test provides standards on how a product should perform within an exterior wall assembly when a fire on the inside of the building laps up the side of a building through an opening such as a window.
In a masonry cavity wall, the thermal mass of the masonry veneer generally allows most Rigid Foam products to work without any problem. Expanded Polystyrene (EPS), Extruded Polystyrene (XPS), and Polyisocyanurate are all viable solutions, along with Mineral Fiber, some spray-foam products, and more.
However, with thin cladding, such as metal panels, lap siding, etc . . . plastic foam products do not seem to fare well. One manufacturer I talked to actually pointed me to their biggest competitor as one of the only products that will pass this test.
Mineral Fiber Boards seem to work and are commonly used in CI rain screen type wall systems. The specifier needs to understand the particular water-related issues with mineral fiber, but it is an option if installed correctly.
Dow’s Thermax (ci) is a specially formulated polyisocyanurate that has been tested with a variety of thin cladding material, and seems to be performing well on the NFPA 285 test. In fact, if you’re willing to spend a small amount of money getting your building envelope right, the entire Thermax Wall System shows some great promise that I may address in another post.
I haven’t found definitive answers to whether or not any other Continuous Insulation Product will work with thin cladding materials. I haven’t quite figured out what this article is saying, but other than that, I invite anyone to leave their findings of acceptable products in the comments below.
So, that concludes my series on Continuous Insulation with thin cladding materials. Where would you like to go next?
Andrew Kulp, AIA is Senior Project Architect at Curry Architects in Towson/Baltimore, Maryland. Please feel free to contact us for all of your design needs.