Building science is a systems approach to home building that considers relationships between a home's components and its environment. The goal of building science: to optimize occupant health, comfort and safety; maximize energy efficiency and structural durability and reduce builder and contractor callbacks.
Part three of the Building Science series will examine moisture and moisture flow — where moisture comes from, sources of moisture as well as problems and solutions associated with moisture and moisture flow.What is moisture flow?
Because of its association with health concerns, moisture flow — as it relates to mold and mildew growth — has been a popular topic among homeowners. Problems linked to moisture flow, or an excess of moisture flow, include:
Moisture flow comes from a variety of sources, including exterior moisture and/or internal problems. With exterior moisture, rain can soak into the ground and seep into the house through the foundation. Rainwater can also come up through the slab, hence why vapor barriers are used under slabs.
An often-overlooked source of moisture within the house comes from people and activities in the house. People bathe, clean, cook, perspire — all sources of moisture. Plants and pets also serve as sources of moisture as well.
Additional examples of moisture inside the home include clothes dryers, which can contribute five or six pints of moisture to the house per load. In addition, missing vapor barriers, which prevent ground moisture from migrating into the conditioned space, can add 105 pints of moisture a day into the house. Needless to say, moisture is unavoidable.Excess moisture flow problems and solutions
Moisture is unavoidable; however, it is controllable. The following will provide a top-to-bottom review of moisture flow problems and solutions.Roof/Attic/Ceiling Systems
Problems associated with roof/attic/ceiling systems include:
From the outside, condensation and surface staining can be seen by snow melting in a specific spot on the roof.
With material deterioration, the plywood, underlayments and shingles can all deteriorate if they become wet. Surface condensation may be the cause of material deterioration. Additional causes of material deterioration may include ice damming or high humidity.
How can a builder solve roof/attic/ceiling system problems? The following tips offer some helpful solutions:
When examining wall systems, it is important to consider that wall construction should be treated differently in different climates.
There are several solutions for combating problems relating to wall systems, including:
Reservoir systems must have the ability to dry so that they won't cause moisture problems. It is up to the architect or designer to plan for this.Permeance of building materials
Permeance, commonly referred to as "perms," is a measurement that refers to the ability of products to resist water vapor passing through them. The higher the number, the greater the perm. For example, gypsum board, mineral wood and fiberglass are very permeable and have high perm values. On the other hand, some products that can be used as vapor retarders — such as asphalt-coated kraft paper or vapor retarding latex paint — have low perm values.
Builders should know there exists "smart" vapor retarders, which have the ability to vary perms depending on moisture conditions. How exactly does it work? In cold, dry weather, smart vapor retarders work like a poly film to repel moisture. If moisture builds up inside a wall cavity, for example, the smart vapor retarder senses the moisture and increases its permanence, permitting the moisture to leave the cavity and allowing it to dry out.Windows
Much like roofs/attics/ceilings, common moisture flow problems related to windows include condensation and staining. Other problems include:
Solutions for combating problems related to moisture flow and windows include:
Probably the area most often associated with moisture flow problems, poorly planned basements and crawlspaces can wreak havoc on a house.
Problems associated with moisture flow in basements and crawlspaces include:
Solutions for combating problems relating to excess moisture in basements and crawlspaces include:
If there are moisture problems that occur after the house is built, there are some additional fixes, including: