Building Science

Building Science Approach in Controlling Moisture in Houses and Buildings

Controlling Moisture

The quest in making homes and buildings more energy efficient without considering the complete structure as a single unit with a number of interconnected operating system has brought a series of negative impact such as poor indoor air quality, moisture condensing on the walls, the proliferation of molds. The uncontrolled movement of air into as well out of these dwellings and improper moisture and liquid water management; ingress, egress and within, of these structures are the two major causes of building failures. The improper management of moisture and water is the main reason for mold growth.

The study of the physical interaction of the operating systems, materials of construction and operating conditions of buildings is called Building Science. The challenges of the design professionals, builders and contractors come from the simple fact that these building are design to have an artificial environment than the outside conditions with ever changing loads, both heat and moisture. In the southern climates, the design is to create the artificial conditions of lower temperature and lower humidity, whereas on the other hand, in the northern climate is to maintain higher inside temperature with lower humidity. Heating and cooling is relatively straight forward. However, the moisture control can be a challenge. In the past, moisture control focused its attention only on vapor barriers. The simplification of using heat flow reduction (insulation) and vapor barrier as the only two barrier design parameters in trying to maintain the artificial environment has resulted in building failures. Litigations related to property damage from improper moisture control resulting in growth of molds and mildew is well known. The plethora of molds and mildew related litigations has force the insurance companies to stop mold protection coverage in many states.

Numerous field evaluations and laboratories studies conducted by building scientists show that air leakage is an important mechanism for moisture transport. In many houses and buildings with excessive mold growth comes from the inadequate control of moisture due to air movement. The quantity of water vapor movement through wall assemblies can be alarming by air movement alone. Studies conducted by the National Research Council of Canada showed that the quantity moisture passing the a single one square inch of opening (air leakage) in a wall can allow as much as 8-10 times the moisture when compared to the moisture passing through a 1000 square feet concrete block wall (diffusion) with two layers of latex paint. The usage of SEALECTION 500 low air permeable spray foam insulation can reduce or eliminate this uncontrolled air movement. There are other documented reasons why the usage of the SEALECTION 500 low air permeable spray foam insulation is the right choice for house and buildings. Here are just a f ew reasons:

• Elimination of uncontrolled air, which can cause up to 40 percent energy loss in residential construction. <Studies done by the Department of Energy>
• Enhanced control over the moisture content of the inside air. Reduced outside dust, pollens, allergens entering houses and buildings.
• Properly sizing of HVAC and air handling systems can be easily achieved.
• The semi-rigidity and cellular structure of SEALECTION 500 offers good noise control.

SEALECTION 500 is a vapor permeable insulation (3.6 perms per inch). This product is not a vapor barrier but it retards the water vapor passing thorough the insulation. Most buildings constructed in the United States are erected on site. Dealing with the initial (construction site) moisture of building materials is of importance to the building scientist. SEALECTION 500 does not trap the moisture within the wall assemblies. In southern climates (cooling zones), the drying of the wall can be accomplished by the moisture removal of the HVAC. On the other hand, in northern climates (heating zones) the low relative humidity of the outside air in the winter shall facilitate drying of the initial construction moisture. Note dry walls always show better thermal response than wet walls.

This brings us to the question of the need of vapor barrier. The general rule of thumb is, place a continuous the vapor barrier (materials having vapor permeance of 1 perm or less) on the warm side of the insulation. The other follow up question is where the warm side of the insulation is? The warm side of the insulation changes with the time of the year. The Department of Energy (DOE) has published a map showing the regions of the United States requiring vapor barrier (8 mils of polyethylene film) be place between the insulation and the dry wall. Vapor Barrier Map. Always check with your building codes officials as to the vapor barrier requirements in your local areas. Nail holes, cuts for electrical outlets and other penetrations compromise the performance the vapor barriers. The combination of low air permeable insulation and vapor barriers as stated in the Vapor Barrier Map is an excellent practical solution in moisture and thermal control of houses and buildings.

The usage of SEALECTION 500 spray foam insulation on the inside of the exterior walls can extend the life of a building by eliminating the flow of airborne moisture into the building envelope, which could lead to condensation, mold growth and building materials decay. Finally, houses and buildings of reduced energy consumption can be durable, comfortable. In addition, building and houses can be built and maintained cost effectively.

Dave Lall , V.P. & G.M. DEMILEC USA

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