Page 42 - Green Builder Sept-Oct 2019 Issue

Finding the ‘sweet spot’. There are a
growing number of methods for managing
moisture, driven by advances in material
technology, evolving building codes, and a
growing awareness among end users for
mold prevention, indoor air quality and
energy efficiency.
COURTESY OF TYPAR CONSTRUCTION PRODUCTS

Permeability

Makes Perfect

Advances in technology and increased builder awareness are making the fight
against water leakage more effective than ever.

BY BIJAN MANSOURI
N THE BUILDING INDUSTRY’S ever-increasing pursuit of MANAGING WATER IN MANY FORMS
tighter and more waterproof structures, what are we at risk Water can find its way into a wall in numerous ways. High humidity
of losing? Is there a point at which we build a wall that is too and extreme temperatures can cause vapor diffusion when warm
tight? While a water-tight assembly is vitally important for indoor air causes condensation on colder outside surfaces. Wind-
I controlling issues such as mold growth and protecting indoor driven rain can be forced into small openings in the exterior clad-
air quality, some building practices may be inadvertently making it ding at joints, laps and utility cutouts, and wind blowing around the
easier for moisture-related issues to fester. After all, no matter how building can create a negative pressure within the wall assembly
tightly a wall is constructed, water is inevitably going to find its way which siphons water into the wall.
in. There’s no such thing as a “waterproof” wall, just one that is built When reservoir claddings become wet from rainwater or con-
so tightly it is almost guaranteed to get wet and stay wet. densation and are then warmed by the sun, the vapor pressure of
The highest-performing wall assemblies are ones that have been the stored water increases, driving it inward and outward from the
designed to realistically manage moisture and dry out, not those cladding material. Where that moisture goes from there—and how
designed with the unachievable goal of completely locking out all quickly it gets there—is largely a function of how permeable the
moisture. The good news is that there are a growing number of meth- adjacent building materials are within the assembly.
ods for managing moisture, driven by advances in material technol- Permeability measures the amount of vapor transmission that
ogy, evolving building codes, and a growing awareness among end a building material will allow over a period of time. ASTM E96,
users for mold prevention, indoor air quality and energy efficiency. Standard Test Methods for Water Vapor Transmission of Materials,

40 GREEN BUILDER September/October 2019 www.greenbuildermedia.com

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