Basics of Water Management

The building envelope is the physical separator between the conditioned and unconditioned environment of a building including the resistance to water, air, heat, light, and noise transfer.

Often, people think the building envelope only refers to the cladding—the exterior of the building—including the roof line. While in some cases that is true, sometimes the building envelope goes below grade or it can follow the inside of the attic or walls. It can be part of the crawlspace if there is one, or maybe of an elevated space.

For proper performance, we need to ensure that we control everything from the weather on the outside to anything that infiltrates the wall systems to the heat that hits those systems, all of which are related to moisture management.

The goals for a building's design are for it to be durable and long-lasting; energy-efficient; and comfortable, healthy and safe to work and live in. Moisture, it should be noted, represents the greatest threat to sustained achievement of these goals. Moisture management, therefore, is key.

Energy and water management work hand in hand with a few factors impacting the wetting and drying rates of building assemblies. How this wetting and drying take place within a building is based on some building science fundamentals that state:

Bulk water intrusion is typically a source of weather and site conditions. It can enter through cladding deficiencies, and then it's absorbed by materials through capillary action.

Also, both air-transported and diffused moisture can contribute to moisture-related issues as well. We’ve previously learned that moisture moves from wet to dry, but how? Bulk or liquid water (which is the most severe) can move by various forces, including gravity, wind-driven rain, and capillary action, which is aided by pressure differentials. Water vapor moves via air currents, infiltration, exfiltration, and diffusion.

In terms of priorities, protect against bulk water first (water control layer, flashing, drainage, capillary breaks); protect against air entrained moisture second (continuous air barrier, internal air seals); finally, protect against diffused moisture (vapor permeability of materials, location).

Good designs include water-resistive barriers (WRBs), flashing, drainage, redundancy and compatible materials. Moisture issues can start at ~15 percent moisture content and that can cause corrosion of metal fasteners. At 16 percent, it may lead to fungal growth.

The issues found here could have been avoided by simply having a properly designed water management and drainage system capable of managing the typical moisture that penetrates behind stucco cladding systems. Stucco, along with other absorptive claddings like brick and fiber cement, require enhanced drainage protection to avoid moisture related issues.

In Moisture Management, we organize our thinking around the four Ds: deflection, drainage, drying, and durable materials.

We know that wall assemblies dry slowly, so it is critical that everything is done to avoid complications. This is accomplished through proper design, material specifications, construction, and maintenance.

Moisture Management – Types of Wall Systems

There are three main types of wall systems in moisture management:

When you are designing a moisture management system, there are a number of key details to focus on, including the following:

Drainable Wraps provide a cost-effective enhanced drainage by creating a drainage channel behind the cladding system. For best results, use a non-compressive gap material that is non-directional to ensure that a drainage gap is present, and that moisture will be able to drain out efficiently. Enhanced drainage is required behind stucco, fiber cement, and other absorptive claddings but can also enhance the sustainability and resilience of other cladding systems. As wall systems get tighter and tighter the need for a consistent draining plane channel becomes crucial to the success of the wall. This is where having WRB with these capabilities comes in. By creating non-compressive gap of at least 1mm it allows 90% drainage efficiency or better in the wall system.

Author: Milton LozanoMilton Lozano is a Product Specialist at Tamlyn. He is based out of Houston, TX and serves on the Specifications Team with an emphasis in Moisture Management and Building Envelope. He holds a B.S. in Mathematics from the University of Houston and brings 13 years of experience in Education. During his many roles he has acquired skills in leadership, planning, teaching, active problem solving, presentation, team management, business development, and many more that translate into his current role. Milton's job emphasizes architect/builder presentations, job site walkthroughs, interactive mock installs, and product solutions.