Breaking Down the Building Envelope & A Word of Caution
“Shut the door! We’re not paying to air condition the whole neighborhood” ~ Mama Mitchell circa summer 1998 in Houston, Texas.
The building envelope consists of the 4 walls, roof, foundation, doors and windows that are responsible for keeping the good air in and the unwanted air out. It’s what keeps you cool in the summer and warm in the winter and is your main line of defense in keeping your home comfortable and secure from surprisingly high utilities bills. In addition to these parts of the home there are a few other terms to know re: the building envelope.
Attic (or other) Knee Walls. These are common offenders for energy loss partly due to the difficult nature of proper air sealing and insulating. These are typically short walls used to create living space in attics as an afterthought. The problem occurs when the other side of the knee wall is 100% unconditioned attic space.
Cantilever. Cantilevers are the parts of the house that overhang the foundation, like a bay window or second story bump out. These are great for adding space without needing foundation directly under but they tend to leak in unwanted air and lack insulation. Easy fix.
Shared Walls. These are very important to address when updating the building envelope. The walls have unconditioned air on one side, and living space on the other. A prime example is the wall between your garage and your living space. Insulation drill and fill for these is easy, as the garage drywall is typically not expected to be pretty. Pro Tip – Be sure to air seal where the drywall meets the foundation in the garage. This is a huge source of heat leakage and toxic air quality.
A Word of Caution. Energy efficiency retrofits on the building envelope can have unintended negative consequences and/or amplify pre-existing problems as well as create new issues. Air quality, moisture control, envelope durability and combustion appliance performance are all a function of a healthy home. Building science is real so be sure to work with qualified niche professionals.James Mitchell Energy Efficiency, Green Education, News