Moisture management is one of the most important aspects of building design. It’s impossible to build a perfectly dry wall assembly, but there are ways to minimize moisture damage and maximize assembly durability.
Insulation is an essential part of moisture management. Insulation decreases the flow of air and can lower the temperature in areas of a home that are not heated.
Air Sealing
Air leaks waste a significant amount of energy in homes, and they also create drafts that can make the home uncomfortable. Leaky windows and doors, attics and crawl spaces are particularly problematic. Air sealing can help prevent these problems by reducing drafts and making the house more comfortable.
A properly installed air barrier system can reduce energy costs significantly. It also helps to prevent the build-up of moisture that can lead to mold growth and wood damage. Several types of materials can be used to form an air barrier, including foam insulation, rolled fiberglass, rigid foam and spray on polyurethane. The type of material used will be dependent on climate, construction method and other factors.
The most important part of an air barrier is the proper installation. The seal must be carefully made and all gaps and holes must be filled with durable caulk or other materials. The material must also be carefully selected for its ability to retard vapor diffusion. This selection is usually based on hygrothermal analysis results.
Insulation and air sealing work best together to stop energy waste and provide comfort. Insulation locks in warmth in the winter and cool air in the summer, while air sealing stops excess airflow and heat loss. A high level of attention to detail in both areas will improve the results of each, and will result in a more comfortable home that is easier to keep clean and free from unwanted pollutants and allergens.
Insulation
From thick blankets of fiberglass batts to meringue-like mounds of spray foam, insulation helps slow the movement of air into a home in winter and out of it in summer. Its effectiveness is measured by its R-value, and it’s a major contributor to a home’s energy efficiency.
In addition to its insulating properties, proper insulation can also play a role in reducing moisture intrusion. It does this by preventing vapor from entering wall cavities. The average family creates two to three gallons of water vapor a day through everyday indoor activities such as cooking, bathing, washing dishes and laundry. When vapor passes through a home’s insulation and condenses, it can lead to mold and mildew growth. Persistent moisture intrusion can also cause rot and structural damage.
Moisture control is a critical component of any home improvement project. It can make your home more comfortable and energy-efficient, less expensive to heat and cool, healthier to live in and prevent costly moisture problems.
While the building industry primarily measures a product’s R-value and thermal performance, it must be considered along with its ability to resist moisture intrusion. When wet, many insulation products lose their ability to perform as designed. In fact, independent laboratory Stork Twin City Testing found that EPS and XPS insulation lose a significant percentage of their R-value after just 30 days of immersion in water.
Vapor Barriers
Vapor barriers are materials installed under a building that prevent the passage of moisture vapor. They are most commonly installed in crawl spaces and under concrete slabs, though they can also be used in walls. They work best in conjunction with sub-slab vapor depressurization systems.
They can be made of materials as simple as plastic film, and can include asphalt-impregnated tar paper, foil skrim kraft, or asphalt-coated fiberglass batt insulation. They typically have a low perm rating (0.1 or less) and are intended to impede the movement of moisture vapor through wall assemblies during cold weather, protecting them from condensation.
Using the wrong barrier or placing it in the wrong location can lead to serious problems. For example, when a plastic barrier is placed against the studs of a wall in an unconditioned climate, mold can develop within the wall. Similarly, when a low-perm vapor barrier is installed under a concrete slab, moisture may migrate through the slab surface to the flooring, where it can cause a variety of problems.
Another common problem is when a vapor barrier is punctured or torn, allowing moisture to escape into the air. This can be caused by mistakes during installation or by poor construction practices. It can also be exacerbated by improper ventilation. When moisture makes its way to the concrete floor, soluble alkalies can change the pH of the concrete, which can destroy adhesives and result in flooring failures.
Vapor Retarders
As part of a comprehensive moisture management plan, it’s critical to use vapor retarders correctly. Also called vapor barriers, these are specialized materials strategically designed to obstruct the flow of moisture through walls and floors. When used properly, they prevent excessive moisture from migrating into a home or building and help control humidity effectively.
Smart vapor retarders have permeance rates that allow a very small amount of water vapor to pass through them while preventing the majority of moisture from passing through. The permeance rate is determined by the test method and is typically specified in terms of vapor diffusion through thickness (perms). Vapor retarders must also meet other requirements for construction use, such as tensile strength and puncture resistance.
During conditions of low relative humidity, smart vapor retarders maintain their impermeable state to protect the wall system from moisture ingress and condensation. When relative humidity increases, the vapor retarder opens up and softens, allowing moisture to penetrate into the wall cavity. This allows the wall to dry and eliminates the possibility of mold and mildew forming in the drywall or concrete slab.
Depending on the design, climate zone and codes, vapor retarders can be installed along, in or around walls, ceilings and floors as part of the metal building insulation. In cold climates, they can be installed in the wall assembly, while in heat-dominated climates, they can be installed on the exterior side of the insulation.