How and/or Why does ArmorWall work in cold climate zones?

The first impression of many reviewers is that the system design of ArmorWall places a vapor barrier on the exterior or that the insulation is interior of the air barrier component, so let’s talk about it:


We have been building structures for thousands of years, but we have only been introducing conditioning within those structures for a relatively short period of that time. As we advance the means and processes that we use to condition these buildings we must adopt better measures in making the buildings perform and efficient.  Our current philosophy in conditioning buildings and efficiency depends a great deal on designing high-performance building enclosure elements to handle infiltration and exfiltration.  However, as we try and make our buildings “as tight as possible” we also introduce other “unintended consequences” within our building’s walls.  We saw this with the previous requirements in Climate Zones 6 and higher that required a Vapor Barrier behind the interior gypsum as we wanted to control the interior vapor from the conditioned environment from hitting the cold surface of the sheathing in the back of the cavity.  However, we have since learned from our flaws that with the use of continuous insulation (especially those of low permeability) that the use of this vapor barrier on the interior actually wasn’t good practice as we were introducing multiple vapor barriers into the assembly that would no longer allow our walls to dry.  Thus we have now introduced the exemption into the I-Codes to allow the designer to eliminate the interior vapor barrier and practice good building science.  This exemption and use are encouraged by MaxLife within our designs to allow the physics of vapor to drive to the correct surface and allow the wall system to work at its utmost performance potential.

Within the ArmorWall design, we place the foam insulation behind the structural sheathing and supplemental air barrier for several reasons.  One great benefit of having the insulation behind the sheathing is that ArmorWall benefits from having the lack of wind washing of airflow from behind the cladding or air cavity actually reducing the R-Value of the intended insulation.  This seems like a minor point, but the other reason that the air barrier is on the exterior is to allow for better observation and installation of the air barrier.  Since air movement carries 100x more vapor than vapor drive, it is much more critical to get the air barrier sealed and tight rather than overly concerning the vapor drive of an assembly.  Stopping exfiltration and infiltration into a wall cavity is much more important than concerning with vapor, although we should not completely ignore the concern of vapor drive either.  Having the air barrier on the exterior allows the trades, and subsequently, commission agents, to ensure that the air barrier is sealed at all of the penetrations rather than hoping it was sealed before the cladding was installed and cannot be observed.  The significant breakthrough with ArmorWall is that most cladding attachments don’t need to fully penetrate the system and thus allowing for a better chance at controlling extraneous air leakage and a much better performing system.

Another theory to consider is based upon the system that we have been building commercial low slope roofing systems.  This system is dependent upon placing the vapor barrier in this case, and insulation behind the membrane at the deck of the roof.  When installed continuously and thoroughly this system works in multiple environments, and especially in a northern cold climate zone.  Effectively if you take the low slope roof assembly and turn it on edge, then you have an ArmorWall assembly with one critical difference.  The crutch of any roof membrane working is that it has to stop water from entering the system so it has to be 100% non-permeable by nature as my good friend Dr. Joe Lstiburek would say.  Being that a wall is in a vertical fashion, our system doesn’t have to be non-permeable to stop the flow of bulk water as we use gravity to aid us in our efforts.  With ArmorWall we are able to use a vapor permeable membrane on the exterior face so that should water or vapor become entrapped within the system then it can dry to the appropriate surface based upon environmental conditions.  The further uniqueness of this assembly is that the sheathing itself, Magnesium Oxide (MgO), does not degrade, mold or crumble when wet as other traditional fire rated sheathings may do when construction moisture accumulates.  The board itself being vapor open allows the free flow of the construction moisture to gain access to the exterior wall surface in the vapor permeable option and often the cold surface in the upper climate zones.    This systematic approach entails better overall performance and forgiveness of construction errors than a traditional wall system that has been utilized up until now.

Since air movement carries 100x more vapor than vapor drive, it is much more critical to get the air barrier sealed and tight rather than overly concerning the vapor drive of an assembly.

Further exemplifying the performance of ArmorWall is demonstrated by calculations with known modeling software such as WUFI.  ArmorWall has shown demonstrated performance in cold climate zones such as the attached example in Minneapolis.  As can be demonstrated within the model, the dewpoint doesn’t occur within the insulation as it can’t because it isn’t a surface.  It would occur on the cold surface, IE the exterior and thus the risk is greatly reduced.  To further prove the condition, there have been many projects installed within the difficult environment of Minneapolis for several years and the assembly has proved its effectiveness. A few installation photos are provided below.

Obviously, there are a lot of assumptions of basic building science involved within this simple explanation with many complex conditions to explore.  These would be difficult to discuss within this simplified document and if we can be of any further assistance please feel free to contact Technical Services for design assistance with your specific project.

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