Building In Fall & Winter?  INTELLO Will Protect You

Building in Fall & Winter? INTELLO Will Protect You

So you’re building a high-performance, low energy building - maybe even a Passive House. What's the Problem?


INTELLO PLUS Double-Wide intalled in a new build on Prince Edward Island, Canada. Owner: Fred Schreiner; Project Manager: Village Vista Construction; Contractors: Don DesRoches Construction & Greenfoot Energy Solutions

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 vapour drive is going outward 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?*


INTELLO X can be exposed to UV and weather during construction, allowing for assemblies such as this one in Vermont by Robert Swinburne.

Luckily the answer is simple too: Install an INTELLO smart vapour retarder. There are two varieties, each with identical vapour characteristics: 1) INTELLO PLUS, an interior grade membrane, with its reinforcement layer suitable for doubling as a dense-pack netting, or 2) INTELLO X, a commercial-ready version that can stand exposure to the elements for up to 2 months and double as a temporary WRB.


INTELLO PLUS is stapled to studs. A reinforcement grid allows INTELLO PLUS to double as a dense pack netting.

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 vapour drive, the enclosure builds drying reserves and a safety buffer. In fact, INTELLO provides the most powerful protection available on the market today.

INTELLO smart vapour retarders are the best at what they do because, among other reasons, it’s the only vapour 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.


Intall INTELLO PLUS at ceilings to provide lasting protection against mold and rot, even in unvented assemblies.

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 vapour 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.


Builders from CedarValley Passive Homes install wall panels in Wasaga Beach, Ontario, using INTELLO X as an air barrier / vapour control / temporary WRB.

Next, the question is the drying potential – and with the greatest vapour variability on the market at a factor of 100 – INTELLO provides maximum drying capability when warmer months arrive. So the range of the vapour 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 vapour control?

Some ideas:

  • vapour 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 vapour retarder? Bad idea
  • Allow it to open up quicker? Let's not go there – you don't want to load your assemblies with vapour when the interior is at a healthy 50%RH
  • Give the vapour permeability a direction? Nyet, Vladimir. (And don't install it backward or the non-improvement can have unintended negative consequences.)
  • Make it vapour 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.

Continue the conversation on social media

x