September 21, 2017

Building In Fall & Winter?  INTELLO Will Protect You

You’re building a high-performance, low energy building – maybe even a Passive House.

What’s the Problem?

Easton+Combs Architects

Easton+Combs Architects – Massachusetts

You started construction in the summer, but by late Fall or Winter the finishes are being installed and the indoor relative humidity (RH) is high – reaching 90%.  You know the vapor drive is going out and the wood framing was delivered wet to begin with, the concrete is still drying, and the tiling and drywall spackling is making you worry about the potential for moisture loading of the enclosure.

The question is simple: How do you protect your high-performance assembly from moisture damages with a humid interior, during construction, in colder months?*

Luckily the answer is simple too: Install an INTELLO smart vapor retarder.

Why? Because INTELLO provides reliable performance – preventing moisture loading of the enclosure in colder months and allowing inward drying in warmer months. Through seasonal changes in vapor drive, the enclosure builds drying reserves and a safety buffer. In fact, INTELLO provides the most powerful protection available on the market today.

Chris Corson, Ecocor

Chris Corson, Ecocor – Maine

It’s a fact that INTELLO is the best, not because we’re saying it, but because among other reasons, it’s the only vapor variable membrane to meet the stringent standards of the German Institute of Construction Engineering (Deutsches Institut für Bautechnik, DIBt), which is the body responsible for technical approval for construction products in Germany.  In fact, INTELLO is so good, DIBt has also approved it for use in unvented hot roofs.

A critical aspect of meeting the approval is the shape of the variability curve (how quickly the membrane opens or closes under increasing or decreasing humidity), and how the material works under construction stresses.

Why is INTELLO Best in Fall & Winter?

During construction in colder months, when the interior of the building is at 90% RH, and the RH inside the insulation directly outboard of the INTELLO might conceivably be as high as 50%, the average RH at the membrane is 70%.

The German building code standard DIN 68800-2 requires that at 70% average RH, the vapor variable membrane’s permeability should not exceed 2.2 perms, yet not fall below 1.3 perms.   At Pro Clima and 475 we call materials meeting this threshold HYDROSAFE.

We call it HYDROSAFE, because even in these challenging conditions, a 2.2 perm rating is retarding enough to avoid further damaging levels of moisture loading.  And it must not be below 1.3 perms, to guarantee the long term protection and durability during occupancy of the building.

INTELLO is HYDROSAFE, with an optimized perm rating, at the sweet spot of 1.6 at 70% RH – providing maximum protection during construction and then during occupancy.  So the shape of the curve is important.

Paul Dowling Architect - Ontario

Paul Dowling Architect – Ontario

Next, the question is the drying potential – and with the greatest vapor variability on the market at a factor of 100 – INTELLO provides maximum drying capability when warmer months arrive. So the range of the vapor permeability curve is important too. We see this drying capability in real life experience.

Don’t Go The Wrong Way

So INTELLO is reliable and proven by data – but you can’t help asking: Okay, can we improve on this vapor control?

Some ideas:

  • Vapor closed, like poly?  Forget about it (a recipe for mold and moisture damages, when the impermeable poly doesn’t allow inward drying in the summer)
  • Reduce the variability, making the maximum drying capacity less than 5 perms, so when it’s fully open you’re trying to dry through the low range of a class III vapor retarder?  Bad idea
  • Allow it to open up quicker?  Let’s not go there – you don’t want to load your assemblies with vapor when the interior is at a healthy 50%RH
  • Give the vapor permeability a direction?  Nyet, Vladimir. (And don’t install it backward or the non-improvement can have unintended negative consequences.)
  • Make it vapor open?  Better not to un-protect your assemblies

*Opening windows and dehumidifiers should be employed to try to limit interior RH to 50-60%, however spikes are most likely unavoidable and need HYDROSAFE protection.

In the meantime, don’t make problems for yourself. Get the best protection. Get INTELLO.

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2 Responses to Building In Fall & Winter?  INTELLO Will Protect You

  1. John November 3, 2017 at 5:38 am #

    “Reduce the variability, making the maximum drying capacity less than 5 perms, so when it’s fully open your trying to dry through the low range of a class III vapor retarder? Don’t think so.”

    So this is saying you don’t want a permeability less than five because it won’t dry, but Intello, at 70% humidity (very high) only has “an optimized perm rating, at the sweet spot of 1.6 at 70% RH – providing maximum protection during construction and then during occupancy.”

    This confuses me, and seems contradictory, given the fact that, to achieve a perm rating of 5, there must be a relative humidity level at the membrane of over 75% as far as I can tell ( This can only really occur with a higher interior humidity than wall cavity humidity (if the wall cavity has an RH high enough to create those conditions at the membrane, the wall is already screwed).

    “The German building code standard DIN 68800-2 requires that at 70% average RH, the vapor variable membrane’s permeability should not exceed 2.2 perms, yet not fall below 1.3 perms. At Pro Clima and 475 we call materials meeting this threshold HYDROSAFE.”

    This is so the wall cavity is protected from excess moisture correct?

    So how, bearing all this in mind, does 5 perms fit into this conversation? It seems to me, and perhaps I am wrong here, that calling those perm ratings higher than five “drying capacity” is misleading, because if the humidity is high enough to cause the membrane to open all the way, it is, in all likelihood doing the opposite of drying, and allowing vapor to drive into the wall. This is why you have DIN 68800-2 to protect the wall from excess permeability in high RH conditions.

    I would love to hear your thoughts as I sort through this.

    • Ken November 4, 2017 at 10:51 am #

      Dear John,
      Thank you for the comment. Yes, it is a confusing subject and it seems we are even struggling to get the concepts across succinctly and clearly. Hopefully this helps:

      The 5 perm reference is hypothetical – that if a membrane were to stop opening at that level of vapor openness, it isn’t providing a very big pathway for drying to occur if moisture levels got to 80%, the threshold for moisture damages.

      It would be very hard for the membrane to reach an average (note that it is the average value of both sides of membrane) RH of 75% in the winter, given that any moisture in the assembly in the winter would be headed outward, away from the membrane. As we note we want the permeability lower at 70% (average) RH so that even in relatively high stress conditions like construction it is relatively retarding.

      BUT in summer, particularly with central air-conditioning, the vapor drive is headed inward and any moisture that may be in the assembly is piling up at the membrane – so the membrane is the “canary in the coal mine” – at the point of maximum moisture. And as the RH moves from 70 to 80% the vapor profile opens up rapidly, heading over 13 perms…. 13 perms, as opposed to 5 perms, allows substantial drying capacity and keeps the assembly out of the danger zone.

      Of course the whole process is dynamic and it is the cycling through seasons and permeability ranges that builds substantial drying reserves.

      Hope that makes some sense. Happy to get on the phone too!

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