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Moisture Control | Roof
Decks | Rigid Insulation
| Roof Membranes
Design Requirements: Each of the three types of structural concrete roof decks; cast in place, post tensioned cast in place, and precast panels have different characteristics and performance properties. Designers shall evaluate the properties desired from a structural concrete deck by consulting specialists such as the Portland Cement Association. The primary design criteria to be specified for structural concrete decks are as follows:
| 1. |
Drying times that are commensurate with the design mix, the environment, and climate conditions so that the roof system may be installed over a dry deck. |
| 2. |
Roof deck slope for positive drainage. |
| 3. | Structural support to allow for short and long term deflections so as to prevent ponding. |
| 4. | Allowance in the design to accommodate seismic events, settling, and thermal movement. |
Surface Condition: Prior to installation of the roof system, the deck shall be smooth, and free of surface moisture, including frost. Sharp fins, ridges, depressions or other irregularities in the concrete surface shall be removed prior to installation of the Fields BUR membrane. Voids or joints greater than .25" between individual concrete panels shall be grouted.
Drying and Venting Cast in Place Structural Concrete Roof Decks: Concrete roof decks shall be dry and hydrated prior to installation of the Fields roof system.
If a dry surface cannot be obtained within a reasonable period of time, the roof system installation shall be postponed and the designer, general contractor, roofing contractor, deck manufacturer, and any other involved parties shall be consulted for acceptable remedies. Due to residual moisture in some mixes of concrete, even after an adequate drying time, a vapor retarder may be required so as to protect the roof assembly from the effects of latent moisture.
Certain drying agents are incompatible with some roofing components. The designer shall consult with Fields to ensure that the concrete drying agent planned for use in the deck is compatible with the BUR membrane components specified. Designers are advised that drying techniques sometimes employed to reduce surface cracks in certain design mixes of concrete are often counterproductive to installation of the roof system. For example, if roofing is to occur soon after the deck dries, the technique of using polyethylene film for keeping concrete damp during drying is not recommended because it inhibits surface drying of the deck. In such cases, additional time is required to allow for sufficient drying.