| Introduction
If everyone on the prairies tried to maintain comfortable winter levels of humidity in their homes, condensation would be a serious problem. Leakage of humidified air through ceilings and exterior walls would result in damaging amounts of condensation. Fortunately for the condition of their houses, most people put up with sore eyes sore noses, itchy skin, cracking floors and furniture, and higher than necessary energy bills. The advent of the R-2000 house brought this potential problem to the fore; not only were reduced leakage levels needed to reduce energy consumption, increased amounts of insulation aggravate condensation problems.
As insulation levels increase, making outer components of the enclosure colder, condensation amounts due to air leakage also increase, without any change in rate of leakage or humidity.
There are four common basic approaches to air leakage control:
Traditional (no special measures to control air leakage)
Poly (fold, lap, staple, tape, and seal the vapour barrier to make it airtight)
ADA (Airtight Drywall Approach; uses the drywall as an air barrier, with gaskets and seals at edges and penetrations)
EASE (Exterior Air System Element; uses a vapour-pervious spunbonded polyolefin paper between layers of pervious sheathing as an exterior air barrier)
The Poly and ADA approaches place the air barrier at the interior surface, and thus have to address more penetrations than the EASE approach, which places the most airtight element on the exterior, where it is not affected by stair stringers, bathtubs, or electrical outlets.
Each builder, faced with a fan door test to be passed to achieve R2000 status has to figure out what to do to get adequate tightness, but there is little published information to guide neophytes, or to allow builders to consider easier but equally effective details as alternatives to their own.
Most efforts to improve airtightness have focused on the vapour barrier (the Poly approach), but the functional requirements for an effective air barrier make this difficult; they are different than the requirements for a vapour barrier, a job for which poly is well suited. An air barrier must be continuous, air impermeable, and supported so that it can resist wind loads. A vapour barrier need only be impermeable to vapour diffusion, and reasonably continuous. Both must be durable. The ability to resist wind loads, with stagnation pressures sometimes on the order of 1 kPa, and suctions even higher on the lee side of a building, is the requirement which most dramatically contrasts the two sets of functions (see CMHC's report on "Structural Loads for Air Barriers").
Most of the details devised by R-2000 builders to reduce air leakage have not been tested, except as part of a whole house. Since the R-2000 house is perceived as appealing to a niche market, there is less pressure than there might be to make details cost-effective as well as functionally effective, yet all buyers are being advised by newspaper housing experts and health advisors to humidify their homes. If the housing industry responds to demands for lower energy consumption and greater winter comfort without taking steps to reduce air leakage substantially, serious condensation problems will be the result. | 
