What is My Building Envelope?

The envelope of your home is a name for the boundaries that enclose the conditioned space.  For your home, the envelope probably consists of some combination of the walls, floors and ceilings.  Another name for the envelope is the building shell.

The conditioned space of your home is the portion of the home you heat in winter and cool in summer.  This typically includes the main living areas.  It typically does not include the attic or crawlspace.  Sometimes the conditioned space includes the basement.

The Well Constructed Envelope

When you spend money (pay the postage) to heat and cool air for your conditioned spaces, you don’t want that air to leak outside and be wasted.  A well-constructed envelope will keep the conditioned air inside the conditioned space with a minimum of leakage.  This is referred to as having an effective air barrier and can really reduce the postage.

Another characteristic of a well-constructed envelope is thick and continuous insulation.  For the climate of the St. Louis area, the applicable code for new construction calls for insulation R-values of R-49 in the attic, R-13 in framed walls above grade, and R-10 in basement or crawlspace walls.  This is referred to as having an effective thermal barrier.

Meeting the code requirements for both new and existing homes can have a drastic effect on the home’s cost of ownership (postage).  Gaps in the continuity of the insulation can just as drastically reduce the total effectiveness of the building envelope.  For example, consider a 1,000 square foot attic with the attic floor insulated to R-49.  If the attic access is uninsulated, then the R-value of the entire attic is reduced to R-36.

Many homes in the St. Louis area lack a well-defined envelope constructed with effective air and thermal barriers.  If this is the case, air sealing and adding insulation may be the most important home improvements you can make.

Air sealing is the work done to establish an effective air barrier along the envelope of your home.  Adding insulation is a different project designed to create an effective thermal barrier.  The final touch is to ensure the air barrier and the thermal barrier are contiguous with each other.

How can you know whether your building envelope is properly air sealed and insulated? 

Schedule a home energy audit or home energy checkup.  A professional energy auditor will use diagnostic equipment such as a blower door and an IR camera to determine assess the state of your envelope.  If you have a problem you can address it by air sealing and by adding insulation.

Want to reduce your postage?  Use a great envelope.