Controlling spa-room moisture
I’m getting ready to build a spa room like the one featured in the article “Adding a Craftsman Spa Room” (FHB #58, pp. 58-61). My biggest concern is moisture control. Here in north Florida it gets very hot and humid. Will I need special ventilation? And with all the hot, moist air in a spa room, how do I keep the windows clear? I’m really concerned about the moisture problem down the road. What will the condition of the room be five years from now? I don’t want the homeowner complaining and having to spend more money later.
Kenneth Bowman, Lanark Village, FL
M. Scott Watkins, a designer and builder in Arlington, Virginia, replies: Like all major issues considered in the design and planning phase of a project, moisture control in a spa room must be integrated with every other aspect of the project. Without an intimate knowledge of these other aspects, I hesitate to recommend any specific strategy for your project. I can, however, share with you some basic spa-room phenomena I have observed.
Excessive moisture in a spa room comes from three sources: water that splashes onto the floor when bathers exit and from the jet action, water vapor that saturates the air and condenses on interior surfaces, and water that leaks from the equipment when draining the spa or servicing the filter. None of these sources is continuous. When not in use, the spa should be covered or drained (primarily for heat conservation but also to prevent evaporation), and under most circumstances, servicing should occur only once every three months.
In developing your strategy for moisture control, ask the homeowners how the spa will be used. Most people are satisfied with a 10-minute or a 20-minute soak (with spa water temperatures over 100°, it is hazardous to remain in the tub any longer than that). In this case toweling the floor and opening windows after using the spa are adequate to vent the moisture on most days in your climate. If the owners use their spa this way on a daily basis, covering the spa with an insulating blanket (bubble sheet) or a customfitted insulated cover (vinyl over foam) should be part of their ritual.
If, on the other hand, the owners use the spa infrequently, say for entertaining once a month, they should drain the spa after each use. I would recommend consulting a local spa retailer/installer for further advice about spas and spa equipment and perhaps a building designer or architect for specific advice on detailing the construction to suit the Florida climate.