Mold and Fungus Prevention: Avoid Moisture Problems as You Build

Mold and fungus are big problems on construction sites. Of course, mossy growth, black splotches and OSB resembling bark mulch are effects, not causes. The cause is almost always water intrusion into the building envelope.

Solving a mold problem may require professional mold remediation, but meanwhile the issue of water infiltration needs immediate attention. On the other hand, if mold is caught early enough, remediation may not be necessary.

That’s because mold is like a three-legged stool. Remove one of the legs and the stool tips over. Mold’s “legs” are moisture, a cozy temperature and a food source, such as drywall paper.

To combat moisture, builders and installers need to know “how to think like a rain drop,” said building scientist Mark Parlee of TheBuildingConsultant.com. How is water going to get in?

“The top three problems I see are kick-out flashings, window flashings and installation, and transition details between dissimilar materials. Builders fail with amazing regularity to get water away from the building envelope with simple details. As a result, water gathers, gets in, and when it can't escape via proper weather boarding of flashing integration with the weather resistive barrier or proper drain planing, it causes damage.”

In builders’ defense, there is an ocean of information available for window installation, and then there are local codes and warranty requirements from manufacturers, and they don’t always agree. One resource that may help is Construction Instruction, an app (and consulting company) from building scientist Mark LaLiberte. With extensive instruction in video, podcast and written form on design and layout in multiple categories, it can help solve — by preventing — mold and fungus problems.

Within the building industry, mold problems can reach marquee status. The next problem brewing, according to Parlee? “The dual-clad wall system with adhered stone veneer on the bottom and another cladding like vinyl on the top,” he said. “It’s being installed everywhere, and many builders are doing it wrong. It’ll make mold’s last big movie, the EIFs problem, look like a straight-to-DVD drop in the bucket.”

Water will get into a building envelope, said every building scientist ever, notably Josepth Lstiburek from Building Science Corporation. And since “raindrops” will find their way in despite best efforts, it’s critical to give them a way out, for example by caulking the tops and sides of a window flange but not the bottom, using a stucco-style drainage plane for ACMV and leaving weep holes in brick siding.

If you can keep moisture out and let it escape when it does enter, mold problem solved. No cause, no effect.   

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Mark Clement