# Venting and Roofing an enclosed pool area question

• posted on June 25, 2006, 3:52 pm
I have a pool area that I have enclosed in its own building. I'm running into humidity issues with the roof and am looking for some advice.
I put a directed air vent every other beam but am still having condensation issues inside the roof during the winter months, resulting in water damage to the beams and the underroofing.
Suggestions?

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• posted on June 26, 2006, 8:01 am

I'm surprised you are more concenred with roof condensation than condensation on indoor window surfaces, which are likely to be cooler than a roof in wintertime, if the roof has any insulation.

Add more roof insulation with a vapor barrier below to raise the ceiling temp above the dew point of the room air, or raise the ceiling temp with some fin-tube heaters just under the ceiling, with no air circulation, and/or reduce the room air dew point temp by circulating dry outdoor air in wintertime or using a pool cover or a dehumidifier that pumps heat back into the pool.
For instance, if it's 30 F outdoors and the room air is 80 F and the roof has R10 insulation, including an R2/3 slow-moving air ceiling surface film resistance, (80-30)1ft^2/R10 = 5 Btu/h will flow from the room out through each square foot of roof, making the ceiling temp 80-2/3x5 = 76.7 F. To avoid ceiling condensation, you might keep the max room air dew point 5 F lower, ie Tdp < 71.7 F, with a vapor pressure Pa < e^(17.863-9621/(460+Tdp)) = 0.793 "Hg, approximately. The vapor pressure of 80 F air at 100% RH is P80 = 1.047 "Hg, so you might keep the room RH < 100Pa/P80 = 76% to avoid condensation. With less roof insulation, the RH would have to be lower.
Nick