A discussion of air and moisture barriers — hmmm, that's enough to make you stop reading immediately, right? But what if we told you the proper construction materials and techniques could save you big money on energy bills and save your home from mold and other moisture-related problems?
Letting air and moisture penetrate your home has several adverse effects. Mold and mildew grow in dark, damp spaces, even here in the deserts of Utah. Not only can mold destroy a home, it can also make you and your family sick.
If air can get in, it can get out. The result: Your house is too hot in the summer and too cold in the winter. It is also a problem for the environment as your furnace and air conditioner consume excessive amounts of energy trying to compensate for the problems in your home's construction.
The outside walls and roof of your house are called the "building envelop." It is the job of good designers and contractors to understand how to assemble the right building materials in the right order to create exterior walls that will keep you both dry and comfortable. Different types of barriers are available to use in this process, so a little knowledge might stand you in good stead to at least ask the right questions during a remodeling process.
Water can move into and through a wall in several ways:
• Kinetic energy (such as wind) can drive water through the roof, windows or other points of entry in your building envelope.
• Capillary action is when water seeps into cracks or holes in the wall, since the water is naturally drawn to move to drier environments (diffusion).
• A differential in the pressure of the soil and the building can also push water into a wall.
• Finally, water vapor is moisture transported by air moving into your home.
Since water in the environment is committed to trying to enter your house at every opportunity, there must be a barrier to stop leaking, sweating, diffusion, etc. before it can cause any harm.
There are three types of barriers in our antiwater arsenal, so it is important to understand when each type should be used and why.
Moisture barriers are intended to prevent liquid water from infiltrating a wall system. For instance, you may have an underground spring near your home, or you may live on a hill so rain and snow melt will flow down the hill and (hopefully) around your home. A moisture barrier should be placed on the outside of your walls to prevent liquid water from entering.
Vapor is the gas phase component of water — think steam, but it does not need to result from boiling water. Vapor is responsible for the familiar processes of cloud formation and condensation. A vapor barrier will limit moisture in the air from penetrating your building envelope.
Air barriers restrict the flow of air under pressure through the building envelope. Now, here's the really confusing part: Air barriers can be vapor permeable or vapor impermeable. And while vapor and air barriers can be considered moisture barriers (they don't let liquid water through), the opposite is not true.
Beyond choosing the right type or types of barriers, installation is critical in how your home will be protected. These barriers need to be applied to the exterior of the walls of your addition, and they need to be installed correctly and with great care. The smallest hole or tear or an untaped seam can void the warrantee and allow moisture to worm its way into your wall and home.
Window and door suppliers must also do their part, as the whole wall assembly needs to be considered to achieve proper air and water control.
Science and modern technology have provided us with the tools to improve our built environment; now our knowledge and building skills need to step up to ensure we are doing our part in building homes fit for the 21 century.
Architects Ann Robinson and Annie V. Schwemmer are the founding principals of Renovation Design Group, www.renovation
designgroup.com, a local architectural firm specializing in home remodels.