Drying reserves? Call it a safety buffer. When we’re waiting for the subway we don’t stand on the track’s edge. Getting hit by the train is like getting hit with mold damage. To be safe we need a buffer of drying reserves.
As Anton TenWolde, retired physicist from the U.S. Forest Products Laboratory, and cellist, says “You need to assume that the building will get wet, somehow, at some point in time. Stuff happens. So you need a moisture-tolerant design.” Lothar Moll, Executive Director of MOLL bauökologische Produkte GmbH, parent of Pro Clima, says also, “There is always moisture risk present, but if we can maintain drying reserves that are greater than the moisture risk, then safety can be assured.” Is it safe to stand on the edge of the subway platform? Safety really requires a buffer: in this case, moisture-tolerance. We want to stay well away from conditions conducive to mold growth.
Per ASHRAE 160P, Criteria for Mold Growth: Mold growth can occur when the relative humidity (RH) of the material is above 80% while the surface temperature is between 41 and 104 F on a 30 day running average. That definition is the cliff’s edge, not a safety buffer. We make a safety buffer, we establish drying reserves, by saying we’d prefer that the RH never goes above 80%, no matter the temperature. Then in analyzing assemblies with WUFI Pro and real-world data collected, it may not be reasonable to stay completely below 80% at the coldest points of the year. The question becomes: how much risk is acceptable risk? How far can we reduce the safety buffer? Is a spike above 80% okay? Probably. Are weeks or months above 90% okay risk? Likely not.
Just as drivers increase the safety buffer space between cars when traveling at higher speeds, the drying buffer shouldn’t shrink as the insulation levels grow. With highly insulated assemblies, their exteriors are colder, will have less interior heat flow available to dry them out and consequently are more likely to stay wet. Consequently, greater airtightness* and intelligent vapor control are required. Both are easily achieved with Pro Clima’s INTELLO PLUS smart vapor retarder.
INTELLO PLUS can be an excellent tool to increase the safety of insulated envelopes and increase its drying reserves. It can then provide maximum protection from moisture damage, as it limits wetting while maximizing the drying potential. INTELLO PLUS inboard of the insulation layer does this by providing airtightness and unsurpassed smart vapor variability – a perm rate variation of 100 times – significantly retarding vapor movement in wintertime conditions (0.13 perms) – while opening up and allowing vapor to dry inward in summertime conditions (over 13 perms). See our blog post: Why The Vapor Curve Matters
When planning drying reserves, here are 8 situations made for INTELLO PLUS:
- Assemblies with significant outboard vapor retarding or a vapor closed profile. In assemblies that have limited outward drying potential such as vapor closed roofs (flat or asphalt shingles), foam insulation boards or exterior sheathing (OSB, plywood) including double-stud walls. See our blog posts: The 8 Golden Rules for Foam-Free Unvented Asphalt Shingled Roofs and The Ten Golden Rules for Foam-Free Flat Roofs and Keeping Sheathing Dry in High-R Double-Stud Walls – a WUFI study.
- Metal framed buildings: Fully insulated metals stud walls can greatly benefit from INTELLO PLUS to prevent condensation in insulated cavities, when tailored for use and climate.
- Historic Masonry retrofit with interior insulation. We’ve devoted a whole book to this subject: High Performance Historic Masonry Retrofits and are gratified to see very similar solutions now by the Building Science Corporation in How Buildings Age.
- Assemblies with batt insulations. The combination of air barrier and vapor control with INTELLO PLUS can transform walls insulated with batts into a high-performance solution. See our post: Yes, Unvented Roof Assemblies Can Be Insulated With Fiberglass – A WUFI Post
- Non-toxic fibrous insulation (the ideal cost efficient match). INTELLO PLUS in combination with non-offgassing, non-ozone depleting, recyclable/high-recycled-content insulation materials is a robust solution that is just as efficient, and far more sustainable than foam. See Is Foam Evil? A New Paradigm of Foam – Less is Best and Foam Fails.
- Super-insulated assemblies that need risk mitigation. In analyzing different levels of insulation, you will see risks rise or fall. INTELLO PLUS can be a powerful lever in making the assembly attain the desired drying reserves.
- When interior airtightness is required. Interior airtightness has many advantages. See our blog post An Interior Air Barrier Does It Better. And with INTELLO PLUS you also get vapor control built in. See also 5 Reasons Why Airtight Drywall Is Obsolete.
- Meeting Code for Class II vapor retarders. INTELLO PLUS can handily meet the code demands of a Class II vapor retarder.
Let’s limit the wetting and increase the drying. 475 can help. See our INTELLO PLUS Resource Library for more information. INTELLO PLUS is part of a complete airtightness and moisture control building system that includes membrane and sheathing tapes, window and penetration tapes, pipe and wire penetration gaskets and other accessories.
* Airtightness should always be confirmed with a blower door test. Pressurize and depressurize. Find leaks and make as tight as possible.