Vapor Barriers part 1 in a 3 part technical series
Pool Design article by Kevin Ruddy, SWD Master
The correct selection, placement and installation of suitable vapor barriers and insulation are critical to avoid deterioration of building materials. Warm, humid air inside a pool building naturally migrates to the cooler, drier air outdoors. As it does so, moisture condenses in the exterior wall cavity, causing mold, rot and deterioration of the exterior wall materials. This effect is especially pronounced in colder climates where the contrast between the humid indoor air and the dry exterior air is greater. Proper selection, placement and installation of a suitable vapor barrier can minimize this unwanted moisture migration.
With vapor barriers, permeance is critical. The permeance rating measures the amount of moisture that can migrate through a particular vapor barrier. A vapor barrier with a permeance rating greater than 0.1 (the kind typically used in standard construction) will allow too much moisture through it and is not recommended for use in indoor pool construction.
The exact placement of the vapor barrier is also an important element to understand. All materials on the pool side of a vapor barrier are highly susceptible to moisture damage. For this reason, the vapor barrier should be placed as close as possible to the inside finish surface of all exterior walls and ceilings. Use only waterproof or highly moisture-resistant materials on the poolside of the vapor barrier. Vapor barriers should be used on all walls around the pool enclosure, even if there are common walls shared with other living areas. Also, all passages to other living spaces should be weather tight; exterior grade doors and windows.
When installing the vapor barrier, be sure envelope the entire perimeter of the pool enclosure. All seals, gaps and punctures should be overlapped and sealed tightly. Use a suitable sealant material to accomplish this. The manufacturer of the vapor barrier material would be able to provide this. The following pages provide additional information with images to help explain in further detail.
Controlling Humidity Through Proper Air Distribution
Efficient dehumidification will not take place if the air distribution system is designed improperly. Careful consideration must be given to the location of supply air ducts, the location of the air return grill, use of moisture barriers and door and window insulation values. The objective of an air distribution system within a high moisture environment such as an indoor pool facility is to maximize airflow of warm, dry supply air over any surface that is prone to condensing temperatures, including all walls, windows and skylights.
An indoor pool requires space air heating 70% to 90% of the year. Therefore, the most effective air distribution system is one that takes advantage of hot air's natural tendency to rise. This type of system will supply the air "low" and return it "high.
- Efficient dehumidification requires a well-balanced and properly placed ducting system.
- Never position ducts in a way that will result in short cycling of the supply air.
- Position the return inlet(s) so that all of the moist, warm air flows efficiently back to the dehumidification system, eliminating dead areas where air stagnation can occur.
- Locate a single return duct about 10- 15 feet above the floor to capture the rising moist air.
- Airflow over or too near the pool will speed evaporation and limit the dehumidification system's effectiveness. The greater the velocity, the greater the evaporation process.
The next segment in this series will be published next week.
Omega Pool Structures, Inc.
2091 Church Rd.
Toms River, NJ 08753
T (732) 255-0231 F (732) 255-2883