The goal of the Building Performance Knowledge Community (BPKC) is to promote architects as leaders in the application of technical design for building performance; in the use of high-performance design criteria, codes, and standards; and in programming, designing and managing building performance. To advance, disseminate, and advocate—to the architecture profession, AIA members, building owners, the construction industry, the academy, and the public—design practices that create buildings that are healthy, energy efficient, and durable.
Building envelope performance issues and concerns for energy use and human occupant comfort evolved with the addition of insulating materials (thermal barrier) as part of the exterior wall and roof (attic) systems, as well as the design and installation of mechanical systems for cooling and heating human occupied buildings. My first experience with building envelope performance reality and concerns began very early for me.
I grew up in the 1940s and 1950s in Dallas, Texas. My parents bought their first house in 1947, in which my younger brother and I mostly grew up. The house was only two years old at the time they bought it. We moved in on Christmas day, and I was six years old. I began elementary school and graduated from high school living in it.
Initially, our back fence and rear property line was the Dallas city limits, and I could see my first school (Walnut Hill) from our back yard. It was a mile to the north. The land was totally agricultural or wooden areas in the beginning, but it began to grow houses after the first two years.
Our heating in the winter was by gas space heaters, fueled with butane in the beginning, but later with Natural Gas when the gas lines were extended into our neighborhood. The house was built in 1945, and there was no insulation in the walls, floor (pier& beam foundation), or attic. The first cooling that we had was by an evaporation cooling fan installed in a rear window. Later, two window air conditioners were installed, insulation was blown into the attic, and the exterior walls got insulated aluminum siding.
Before the window unit air conditions and insulation was installed, we would occasionally sleep outside in the back yard during the hottest days of the summer. It was cooler under the open clear sky than inside the house at night. So, this is about the building envelope thermal barrier, which has evolved in both materials and design since what that house had.
Today the building codes require higher thermal resistance (R-value) than before, and the R-value requirements vary over the several climate zones throughout the country. Most recently, the building code requires that insulation must be continuous over the total opaque building envelope (the six sides of the building excluding windows or skylights).
There are many types of insulation materials available today, but the real thermal insulator is the still air contained within those materials. The main design consideration, regardless of material type, is its continuity over all exterior opaque envelope surfaces, and eliminating thermal bridging.
Heat movement or thermal energy transfer is only in one direction, from a hot location to a cold location. Heat transfers occurs by three means, conduction, convection, and radiation. Insulation reduces the ability of heat to transfer.
Air movement over and thru, and water saturation of, the thermal insulation material is a concern that must be recognized and addressed in the envelope insulation design (detail drawings and specifications). How the insulation is installed is of equal importance and should be addressed by the specification. Verification of the insulation performance, in both design and installation are important. Reviewing the design, inspecting and documenting the installed insulation installation methods and means should be done at various times and locations during installation. Using a thermographic cameras for observing the building envelope insulation as installed is an effective method in verifying performance, or detecting defective conditions.