What’s the REMOTE wall and how does it work?
One of the great conundrums of building in a cold climate is how to achieve an energy efficient building envelope that is safe from moisture trouble. Why do they so often go hand in hand? Because in cold climates, you have lots of warm, moist air inside that desperately wants to escape outside. How? Through your building envelope. When you get moist air on a cold surface, which is bound to exist somewhere inside your wall, that’s when the problems start. (More on this concept in “The Moisture Issue”)
The REMOTE wall (Residential Exterior Membrane Outside insulation TEchnique) was developed specifically to address this problem. Adapted from building techniques used in northern Canada, the REMOTE wall moves the majority of the insulation to the outside of the wall in order to keep all the wood components of the assembly warm and dry.
The REMOTE wall manages moisture much differently than a conventional cold-climate wall. A standard wall is based on the premise of not allowing moisture into the wall. To achieve this, a vapor barrier is placed on the inside of the studs (plastic sheeting, in most cases). However, this plastic sheeting never works perfectly, because inevitably it will be punctured by plumbing and wiring penetrations, or even just someone hanging a picture frame. Moisture-laden air will find a way into these leaks and holes and, when it hits a cold surface, will condense into water. This typically happens on the plywood sheathing. If the sheathing is not able to fully dry out during the summer months, it will eventually develop mold and structural rot–an inherent weakness of a traditionally framed wall in an extreme climate like Fairbanks.
The REMOTE wall is based on a totally different premise. Rather than blocking moisture with an interior vapor barrier, it allows moisture from inside the home to travel freely into the wall and instead focuses its attention on keeping all the wood surfaces warm. If this moist air never makes contact with a cold surface, it will never condense. So how do you keep all the wood framing warm? With a thick layer of rigid foam board on the outside of the plywood sheathing. This foam keeps all the wood components of the wall above the dew point (the temperature at which vapor condenses into water): in other words, warm and dry. This creates a super-efficient wall that nearly eliminates heat loss through the wood studs.
The critical element of this system is to use enough foam on the outside to ensure the wall actually stays above the dew point. If not, you may actually be creating a greater risk for moisture problems: if the sheathing gets wet, it will have a hard time drying out when encased in vapor-impermeable foam (this is called the “double vapor barrier effect.”
The amount of exterior insulation needed depends on your climate. In Fairbanks, the accepted standard is to put at least two-thirds of the total wall R-value on the outside of the sheathing. For a 2×4 wall with fiberglass insulation (approximately R-11), this means using at least R-22 on the outside (equivalent to six inches of EPS foam). For a 2×6 wall, you would need even more. Milder climates can get away with less on the exterior. In Anchorage, for example, the recommended ratio is 60% of the R-value outside the sheathing (equivalent to 4 inches of EPS foam on a 2×4 wall).
Supported by extensive research and testing, the REMOTE wall is an excellent choice for cold climates, but it’s critical to follow the rules to achieve a durable, safe system.