Given that buildings are generally constructed “tighter” today than they were 50 years ago, the importance of eliminating water intrusion into wall assemblies has increased substantially. Contractors are always on the lookout for any advantage that technology might provide.

Given that buildings are generally constructed “tighter” today than they were 50 years ago, the importance of eliminating water intrusion into wall assemblies has increased substantially. Contractors are always on the lookout for any advantage that technology might provide.

A breathable, spray-on waterproofing/air barrier in the wall assembly can mitigate or eliminate one of the major forces that cause water infiltration into walls: pressure differential. The barrier, in combination with venting and compartmenting, enables the pressure behind the cladding material to equalize with the pressure outside and prevent rainwater penetration caused by pressure differentials.

By designing and constructing an airtight building envelope, the risk of moisture problems – mold growth, decay, corrosion, loss of insulation value and Indoor Air Quality (IAQ) problems – that can occur due to air leakage and condensation are minimized. Controlling moisture helps to control mold growth in wall assemblies.

Air leakage is a significant potential source of condensation and moisture accumulation in building envelope assemblies, according to several studies completed in the last decade. One such study compared potential moisture contributed by air leakage vs. vapor diffusion over a period of one year¹. The results: infiltration/exfiltration proved to be a significant potential source of moisture accumulation in walls and/or high relative humidity levels in interior spaces.

Water vapor diffusion, on the other hand, was shown to be a much less significant potential source of moisture than previously thought. The study showed air leakage was 228 gallons (863L) which equals 45.6 five gallon (19L) buckets vs. less than six ounces (.18L) of vapor diffusion.

At the same time, airtight construction is likely to be less capable of drying than “air-porous” construction in the event of water leakage or other unforeseen circumstances that cause water to enter a wall assembly. The contractor must strive to prevent rainwater penetration into the wall assembly, constructing an airtight building envelope assembly of compatible air barrier materials and enhancing the drying potential of the wall assembly in the overall design strategy. Luckily, a number of connecting air barrier materials are on the market to make transitions from one material to the next.

Construction detailing is a critical component for the success of any wall assembly. Aside from minimizing and controlling the condensation that may occur via air leakage or water vapor diffusion, the contractor must also create construction details to prevent rainwater penetration.

The traditional choice for moisture protection has been asphalt-saturated felt paper, which can tear or be incorrectly lapped during construction. It also must be covered quickly, whereas a spray-on air-and-moisture barrier may be left uncovered during the construction process. Traditional house wraps and building papers, depending on brand or type, measure water resistance in hours and, in some cases, may allow water penetration within the first few minutes of exposure. A spray-on structural moisture barrier can help minimize the risk of damage from water intrusion during and after construction.





¹Extrapolation of data from: Preventing Indoor Air Quality Problems in Educational Facilities: Guidelines for Hot, Humid Climates by CH2MHill in cooperation with Disney Development Company.