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Home Repair - - If it ain't broken, don't fix it. Otherwise look here.
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Posted by John Marsters on June 25, 2006, 11:52 am
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 by on June 26, 2006, 4:01 am
>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.
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.
>Suggestions?
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
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>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.