The effort to control the building envelope and to manage its' interior climate for comfort and efficiency has gone through years of mutations as various climatic effects were dealt with using a variety of products and schemes. Today the concept of exterior air barriers is being experimented with and even being adopted by code agencies as the latest answer in this challenge. As we do these experiments on real buildings we can measure the energy efficiency change almost immediately. Unfortunately we cannot measure the building longevity and human health impacts until years later. Some climates do help us along however. In Wisconsin, air/moisture retarders were placed on both sides of glass fiber insulation in walls, a situation known as Tri-State Homes. The houses rotted - fast. Recent reports from Seattle and Vancouver report more moisture problems than ever in new construction since the 1984 energy code was passed, while most older buildings somehow escape moisture damage.
We continually believe that we can correct a given problem without considering secondary effects which may flow from that correction. I have identified six mechanisms of heat loss or gain that must be considered all at once with each material change in building practice. They are Conduction, Radiant, Air Convection, Air Infiltration, Air Intrusion, and Moisture Movement and Accumulation. These are recognizable by their various marketing remedies: R-value, radiant barriers and window coverings, air/vapor retarders, house wrap (air barrier), venting, drainage plane, etc. All of this and all the other variations is attempting to effectively separate two antagonistic climates yet may have contradictory purposes such as venting vs R-value.
The problem has been solved for years in the agricultural, refrigeration and roofing industries using spray-in-place and pour-in-place polyurethane foams and polyiso board.It is likely that the potato, carrot or apple you eat in the wintertime has been stored in
polyurethane spray foamed storages. These are so well air barriered by the closed cell spray foam that in the case of apples, the air is replaced with nitrogen. Refrigerator manufacturers moved from glass fiber to closed cell polyurethane pour foams in the 1960s. Then consider roofs. The differences between an unvented commercial flat roof - and a residential cathedral roof are two: 1) one is flat and the other sloped, and 2) the one is commonly insulated with closed cell polyiso or spray polyurethane and the other typically insulated with glass fiber. The first has successfully isolated the climates apart in all of the six mechanisms through the roof systems entire thickness, a condition I call "climate isolation" when used in the context of our installed Corbond system. The other system has failed to isolate the climates apart in all of the six mechanisms excepting conductive losses to varying degrees, depending on moisture load and air movement.
There are other differences that follow on the insulating system choice in the cathedral roof. The air/moisture retarder behind the interior wallboard is the dividing line between interior and exterior and divides the climates by just 6 mils. This becomes the condensation plane in the air conditioning season. We intentionally breach the air barrier created by the roofing to carry off moisture but regrettably this becomes the conduit for moisture in summer. Slope, rafter length, heat loss, ambient temperatures, dew point, sunshine and snow cover affect roof system performance in infinite variations. We put fiber in cathedral roofs and attics and vent like crazy. We put fiber in walls and are now promoting sealing them up. Is a wall so different than a cathedral roof? Would anyone promote air barriers for stopping up soffit and roof vents and claim there would be no negative consequences? There would be severe negative consequences in winter and positive consequences in summer. This raises an important question. Which do we build for in what climate zones?
The Climate Isolation System is Thermal Control (R-Value), Air Control, Moisture Control and Reversibility all-in-one. An air barrier system that performs all four of these functions will work. An air barrier that does not perform all four functions will work to control air, but cause building damage and health problems resulting from moisture accumulation or entrapment. Seasonal climate change and the advent of air conditioning require that the system be viable in both directions. A system with a O^breather' on one side doesn't qualify because of seasonal vapor drive reversals. A system with a vapor retarder on either side does not qualify for the same reason. A system with air in its' insulated core doesn't qualify because where there is air there is moisture which will move to the dew point. To control all the six mechanisms all the time, the system must do all four - thermal, air and moisture control, in both directions - all the way through - displacing air and moisture while developing significant R-Value.
The necessity for an air barrier cannot be overemphasized. However, unless thermal, air and moisture isolation, as well as reversibility are integrated within and throughout the air barrier, failure of one nature or another will occur in time. Spray-in-place, closed cell polyurethane answers all these criteria in all types of buildings in every climate in North America. The indoor climate is controllable mechanically without a negative impact on the building envelope. The insignificant costs of this high efficiency product are more than offset by construction simplicity, high R-value in very thin spaces which eliminates oversized framing and venting, human comfort and health, building longevity without continuous reconstruction, and of course, super energy efficiency.