|
History Pro Affiliations |
|
RMS
Services Certification |
|
Coatings/Mastics Hot Asphalts Organic Felts BUR Sheets |
|
Ad
Images CO/OP Info |
|
Design
Criteria |
|
Moisture Control
Moisture control within the roof assembly includes
such factors as moisture migration, dew point, condensation, ventilation,
and vapor retarders. Some migration of interior moisture is allowed due
to the natural downward drying cycle that occurs in most climates; and
therefore, the criteria for determining the need for vapor retarders shall
take this into consideration. The term vapor retarder refers to a Fields
waterproof membrane installed prior to the BUR membrane so as to surpress
the flow of moisture vapors from the interior of a building into the roof
assembly. Moisture from the interior of a building generally comes in
the form of water vapor from the following four sources:
| 1. | Construction processes which include the drying of interior concrete, cementitious roof fills, plaster compounds, water-based finishes, and fuel burning space heaters. |
| 2. | Operational sources such as swimming pools, greenhouses, laundries, textile manufacturing, food processing, and paper plants. |
| 3. | Occupancy sources which include kitchens, shower facilities, exercise rooms, and even breathing from high-density occupancies. |
| 4. | Cool climate regions where moisture vapor generally flows upward through the roof system from a heated, more humid interior toward a colder, drier exterior during the winter months. Such a climate condition causes vapor to migrate into an insulated roof system where it can cool and condense into water. |
Buildings with high interior relative humidity require vapor retarders, as well as buildings located in the Central and Northern regions of the United States. For such buildings, the designer shall calculate the roof assembly dew point so as to determine the correct location to install the vapor retarder within the roof system. Included in the calculations shall be the R-value of the roof assembly components, anticipated interior and exterior temperatures, regional temperatures, the building's planned relative humidity, and any other pertinent data.
The Three Primary Moisture Control Factors| 1. | Ventilation is the exchanging of air in a given space. Passive or mechanical ventilation is designed to control moisture and reduce heat buildup. Exchanging the air in a given space is accomplished by venting moisture-laden air to the outside, while inducing fresh outside, or conditioned drier air to the inside. |
| 2. | Insulation provides R-value and aids in temperature control within a building. Insulating a roof reduces the amount of energy required to heat and cool a building and can also reduce the potential for condensation on interior surfaces or within the roof assembly. |
| 3. | A vapor retarder is a Fields two or more sheet waterproof membrane adhered and coated with Fields asphalt. The vapor retarder is generally installed somewhere between the deck and the insulation. Vapor retarders are installed to inhibit the flow of moisture vapor into the roof assembly from the interior of a building. |
