Just curious what the current feelings are regarding use of foam board insulation in brick cavity and in metal rainscreen walls.
NFPA 285 testing and the mineral fiber option aside, when using foam board which do you prefer and why?
Does anyone exclude polyiso in rain screen and cavity wall installations any more? Is XPS still seen as being preferable? Presume gyp sheathing, air barrier (your choice), and board insulation.
Thanks.
Our office still excludes iso board in masonry cavity walls. Our concerns stem from the tendency of iso board to absorb water/vapor, thus reducing it’s effective R-value. I realize that the numbers for absorption are small and I acknowledge that a great deal of the information about absorption comparision testing is provided by Dow and Owens Corning so it is somewhat suspect due to the vested interest of these XPS manufacturers. However, I have witnessed iso board in field conditions that has absorbed to much water/vapor to remain effective as an insulator. I had one roof tear-off project where three individuals (myself included) attempted to pick up a 4’x4’x2" thick piece of iso board and had it fall apart under it’s own weight due to the water content. (You could literally wring the water out of the board) This was of course and extreme condition but still it makes you wary. We still spec iso board for “flat” roofs but this is only due to the facts that roofs have a limited life span, leaks are typically discovered & rectified, AND iso board is cheaper. Masonry walls on the other hand are intended to last several decades beyond a typical roof and replacing insulation within a cavity wall is not an easy task. Most or our work is institutional so our cavity walls are masonry back-up and not stud walls therefore the potential issue of fire and the use of XPS is typically not as big of an issue for our work. Anyway those are our thoughts for why we exlude iso board in cavity walls
I allow all the options - XPS for the majority of the work we do, Polyiso occasionally and once in a blue moon rock wool. I have all of these under an article heading CONTINUOUS INSULATION (using the energy code language) and have manufacturer’s installation requirements for each in PART 3 (and there ARE significant differences).
I found BSD and MasterSpec to be woefully inadequate in describing this type of insulation (CI) and its unique installation requirements.
Regarding the question about using polyiso insulation vs. XPS as continuous insulation in a rain screen or cavity wall application, this is what I’ve found to date:
Using polyiso board comes with concerns about delamination of facers, edge cavitation, cupping, bowing, shrinkage, and crushing regardless of use.
a. Facers delaminating is pretty self-explanatory. Unlike XPS, Polyiso board requires a facer. If that facer delaminates, such as where boards are cut or damaged, the insulation core is subject to damage. Hard to imagine that somehow that wont happen on any project.
b. Edge cavitation is exhibited by depressions at the edges of the insulation boards. If the board is not properly manufactured, or if the foam shrinks as polyisocyanurate and polyurethane foams are known for doing, gaps between boards can occur. Loss of insulating value and chances for delamination can increase.
c. Unlike XPS, Polyiso board is prone to bowing and curling, especially at board edges, which can result in gaps and loss of insulating value.
d. Polyiso seems more prone to damage than XPS. XPS is harder to damage and the resulting performance doesnt seem to be affected by damage at XPS boards the way it is at polyiso.
e. When fasteners and anchors used at insulation boards are over-torqued, there is no concern at XPS whereas at polyiso the damage to the facer becomes a real issue.
There is also debate as to what R-value per inch is the real R-value of polyiso over time.
a. Its interesting to see how the R-value per inch seems to increase in some manufacturers literature. With one, it starts at 5.9 for a 1 inch board and goes to 6.7 per inch for a 4 inch board. As a general rule many specifiers seem to use R-5.6 per inch as the aged R-value for polyiso but this varies with whom you ask. Essentially, it will take longer for the R-value to drop in thicker boards as the board ages and the gas migrates and is replaced with air. Also, foil facers help slow the aging process. The question remains, what happens after 180 days which is what polyiso aging is tested at. We presume the owner will keep the building more than 180 days.
b. According to some, the foil facer provides an additional R-value as reflective insulation when adjacent to an air cavity. According to my research, the foil facer must be kept clean. Im not sure how that works in a cavity application.
c. Water absorption seems significantly higher with polyiso than with XPS and that doesnt consider the fact that Polyiso water absorption testing is not based on units with holes (fasteners) in it. Having holes in XPS doesnt matter, you can use it as raft and never sink it. Even EPS seems less water absorbent than XPS. Cant say the same about polyiso. I wouldn’t want my life raft to be a polyiso board.
This is from BIA (www.bia.org) Technical Note 21a:
"There are many rigid board insulation materials that can be installed in the air space of brick masonry cavity walls.
Among the most common are: expanded and molded polystyrene, extruded polystyrene, expanded polyurethane, polyisocyanurate, mineral fibers and perlite board.
Composition. Rigid board insulations are many and varied. They include the various mineral fiber boards and cellular insulation including polystyrenes, polyurethanes and polyisocyanurates. Air, or other gases, introduced into the material expands the material by as much as 40 times. Cells are formed in various patternsopen (interconnected) or closed (unconnected). Most rigid insulation is expanded with hydrogenated chlorofluorocarbons (HCFC), pentane or other hydrogenated gases used as blowing agents. Gradual air leakage into the cells may replace some of the original gas and eventually reduce the thermal insulating quality. Some types of insulation use foil facers. These facers keep air leakage to a minimum and must not be punctured during construction. Aged R-values should be used when comparing different types of insulation."
The way I see it, there is no way to attach the board to the backup system and anchor the veneer without puncturing the facers. We typically require anchors at spacing as close as 16 inches OC (see Masonry Code and manufacturer guidelines). If the board relies on the foil facer to maintain its R-value, I suppose that might pose an issue as well.
Bottom line: I have yet to see a compelling reason to use polyiso in lieu of XPS in a rainscreen/cavity wall application.
Frankly, mineral fiber is looking better every day.
Please continue to let me know your thoughts on this subject.
Thanks for providing me additional amunition against the iso board in cavities, very handy. On a related note: what is everyone’s opinion on the full height cavity drainage system installations. Our office has been specifying Mortar-Net or similar at the base of cavity walls for almost as long as it has been available. However in our area there is now a big push (by the sales reps) of the full height systems (CavClear or similar). We do not see the need or justification for this step but I wonder what opinions the rest of you have.
I’m with you on that Scott.
I like the MortarNet Total-Flash system using the copper flashing and stainless steel drip edge. After reading that same BIA Technical Note, I’m wary of using PVC inside walls just as I would never use aluminum or galvanized steel. I’m not a big fan of rubberized asphalt having dealt with melted goop in the past. If they made it of butyl rubber, maybe I’d change my mind. Still, it’s too easy to accidentally cut through the membrane flashing products with a trowel.
As to the mortar control systems, as long as the flashing extends sufficiently above the top of the mortar catching product, I’m comfortable. I see no benefit of creating mortar bridges all the way up my wall where water in the winter can freeze and migrate along the ties as it thaws. The whole idea is the keep the weeps free. Using Total-Flash or something similar, that’s a non-issue. Sounds like these folks are displacing the free air space with their product for monetary gain, not added value.
This discussion also needs to address NFPA 285 testing. Any “plastic foam” insulation must used in the exterior wall assembly must be tested unless it is Type 5 construction (see IBC Chapter 26). Mineral wool board has some issues, but does not since it is not plastic. I don’t think it has been formally adopted yet, but it seems like a done deal that many air barrier products will also have to be tested.
Ken: Peel and stick plastics have the “goop” issue but my real concern is durability. I am stubborn when it comes to flashing. I like old fashioned 7 oz. copper fabric, with the fabric extended out of the wall of course. I used to always say “it needs to last until I’m dead” of course I am getting older so now I tell the mason “it needs to last until everyone in my office is dead”
J. Peter: you make a good point and it raises a question we have been asked more than once. In a brick and block wall (with the foam in the cavity) we contend that the masonry constitutes a thermal barrier (2603.4.1.1) and thus we are okay to use the foam how we always have. Not sure if we are correct in this assumption and would appreciate some feedback.
Personally, I spec mineral wool from Thermafiber or Roxul first for a variety of reasons. Mineral wool has been used in Canada (blah blah blah from the expat Canadian again) for roofs, walls, and below grade installations for years.
US designers and specifiers are just learning about mineral wool’s advantages. And, no it does not store water (like a sponge) nor aid in mold growth. Two uban myths. Yes, it must be used in greater thicknesses. Get over it.
Is your Wall Assembly NFPA 285 Code Compliant?
What Air Barrier Materials Are NFPA 285 Code Compliant?
This is not an advertisement for Grace but Grace provides both permeable and impermeable solutions that pass NFPA 285 as part of the wall assemblies containing foam plastic insulation.
Perm-A-Barrier Aluminum Wall membrane: 40-mil self-adhering air & vapor barrier membrane, which provides up to 1 year UV exposure and improved sealant adhesion to the film
Perm-A-Barrier VPS System: Self-adhering vapor permeable air barrier membrane and primer. Excellent adhesion to typical construction substrates.
Grace is not a new kid on the block pumping out products to get on the air/vapor barrier bandwagon. They have been in this market (along with Henry / Bakor) for over 30 years in Canada EH.
As I noted in my first post, I’m just looking at XPS vs. Polyiso head-to-head, NFPA 285 notwithstanding.
OK, here is a better question…
Why would you want to use board insulation in cavity wall applications in the first place?? Espcially with masonry veneer. Even with fibre cement, wood veneer composite or metal panel walls my firm typically specifies spray-in-place foam insulation. Even under metal siding. Install veneer ties or girts as the case may be, then spray! No cutting, no pasting.
Not sure about differences in codes between Canada (eh?) and the US, but with most SIP products, flame spread is less than 500 and they are self-extinguishing and do not promote combustion.
The added benefits, in my humble opinion, are that there is reduced labour (or labor for my US friends) for cutting around girts, veneer ties etc., it is easier to insulate non parallel/perpendicular faces of substrates, you can insulate the underside of roof decks protruding past the face of the wall or structural members sticking out of the wall substrate AND most SIP Products are also tested and pass requirements for air barriers (again to Canadian requirements and at no additional material or labour costs!!!)
It seems like such a no-brainer to me eh?
SIP is still going to have to comply with NFPA 285.
Feedback I’ve received is that spray-applied costs more than XPS which costs more per R than polyis board (based on manufacturers’ claims).
That might change as spray gets more popular south of the 49th parallel. Of course we would require two passes at 2 inches to get a 4 inch thick application so that may be why we’re getting push-back.
Paul, I liked your comment in another thread about limiting application thickness to 1 inch when applying SIP over peel-and-stick membrane flashing at openings. I was wondering how to handle the heat generated from a full 2 inch thickness.
Ken:
I find it hard to be believe that the cost for SIP is more than polyiso board when you consider adhesive, labour to properly cut and fit around any protrusions from the substrate and the material and labour cost to provide a separate air barrier.
As I stated before, most SIP products are tested and comply with air barrier requirements. Other than “transition membranes” (i.e. peel & stick) that we insist on at changes in material or at window bucks/door openings, we do not specify an air barrier. We have it built into the SIP.
I am not aware of any issues with transition membranes delaminating due to the exothermic reaction of the SIP curing process.
Something NEW we are implementing on a current project, due to Ontario Building Code/National Energy Code for Buildings changes (which essentially reproduce requirements of ASHRAE 90.1-2010) is the addition of a 25mm girt/hat section between the substrate and the z-girts for panel/siding installation. Due to the fact that this additional girt is enclosed in the SIP, the thermal bridging of the Z-girt is reduced dramatically (one of the PA’s went to a presentation by Enermodal Engineering with respect to the new Code requirements and there was data testing an assembly with the second level of girt that showed dramatic improvements in thermal bridging). This all but resolves the issue of continuous insulation requirement in 90.1.
Scott: As a manufacturer of copper flashings I am happy to read your thoughts on good old fashioned 7oz. copper fabric flashing. With all the talk about sustainability in construction, there isn’t a more sustainable flashing than copper. There are some very good non-asphaltic copper flashings on the market that are also compatible with many of the air barriers systems currently available. If specified together, this would make for an unbeatable system.
I also read a note regarding all-wall mortar deflection systems. As a mortar deflection manufacturer too, both all-wall and standard mortar deflection methods have a place in cavity wall construction. When building with a smaller airspace (i.e. 1-inch),using a all-wall mortar deflection with a heat bonded filter fabric keeps the entire airspace clear from mortar droppings and mortar bridging at wall tie locations, which greatly increases the drainage and ventilation within the narrow airspace. This clear drainage channel will help keep moisture and other surfactants from lingering within the wall system, which in time could hinder the performance of other building materials within the wall system. When building with an airspace of 2-inches or more, I agree that the standard 10-inch high mortar deflections are sufficient.
Please visit www.mortairvent.com to view installation videos of all-wall and standard mortar deflection options. This will give better insight into the debate.
My opinion: extruded polystyrene, spray polyurethane, or mineral wool are the best choices in a cavity. I think SPF is probably cheaper when considering the air barrier.
I specified continuous morter deflection for limited locations where the cavity gets a bit small, as mentioned by Keith Lolley. The typical condition would be at areas where the backup wall had a protrusion around a column, or where the brickwork stepped in.
To play the devil’s advocate: I think the BIA recommendation about 2 inch air cavities is completely outdated. At the time that this recommendation was made, a typical cavity wall had no insulation or air barrier in it. The weather barrier wasn’t really one - it was “tar paper.” In this condition, mortar bridging was most definitely a concern. Now our walls are almost waterproofed with a high-performance air barrier, which is covered up with rigid insulation. If there is some mortar bridging, it would seem to me to be of practically no consequence. That leaves only the potential benefit of venting and drying. I don’t believe either ofd these concerns very thoroughly studied since wall construction has changed so dramatically.
Today I received a copy of Commercial Building Products magazine, June 2012.
In it is a full page ad by Hunter XCI introducing, and I quote, “Energy Efficient Xci Polyiso” for exterior rain screen type wall cladding and face sealed systems. Go to www.hunterxci.com for further information. The add illustrated 4 type of polyiso, each with a unique facer on the cavity side.
Wayne
It’s been a while on this post, but I do want to respond to Ken’s comment about XPS vs ISO (NFPA 285 not withstanding).
NFPA 285 is exactly why I hardly use XPS, unless your building is only masonry veneer, you are forced to consider another product and I typically like to stick to one insulation if possible. XPS is great, but if you have anything other than brick or stone, SPF/MW/ISO is required.
Sprayed poyurethane foam and polyisocyanurate are also subject to NFPA 285 testing if part of an exterior wall assembly.
The use of masonry veneer does not provide an exception to NFPA 285.
Ron, I didn’t mean to suggest otherwise. I only meant to explain that XPS has only been approved behind masonry assemblies. Thus if one has a finish other than masonry, one must look beyond XPS to other insulation systems.