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TOPIC: I Have An Existing Metal Roof and Have A Question

Condensation problems

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Hello. We have recently built a new cabin with a metal roof and are experiencing condensation issues. Water is forming on my mdf encasements all along the length of the ceiling beam, but mostly in the center. The roofers used a ridge cap instead of a vent. I'm not sure if this is an issue or not. There is no attic involved here. Underneath the metal, in order, to the t&g pine ceiling is: synthetic felt, 7/16 osb,2x8 rafter cavity with foam vent inserts, r19 insulation, 3/4" t&g stained pine. Humidity in the house is running 54% w/ temps set @73. I don't live there but have been going up regularly and it SEEMS that the condensation forms on only sunny days. Any ideas or help would be greatly appreciated. I'll attach more pics if necessary. Thank you!
Eric Brooks

10/11/2017
Is there a way to ventilate the rafter cavity with intake vents and the bottom and then ad a ridge vent to the roof? Todd Miller
Todd Miller
Isaiah Industries, Inc.

10/11/2017
Probably yes to both. I just wanted to hear from a pro before we did that. The ridge vent is obviously going to be a pain. So, you think it may be radiant heat somehow getting to the cool mdf beam on the interior? Here's a pic of the exterior, if it helps. Also, note the a/c vents in the ceiling in the first pic. I thought they might be cooling the beam too much so I put air defectors on them to make sure the air was all traveling downward.
Eric Brooks

10/11/2017
I am a little uncertain as to why this would happen only on sunny days. Condensation though occurs when warm moist air from inside the living space hits a cool surface. Warm moist air migrates upward in homes. My thought is to provide a means for it to ventilate to the outside ... and hopefully the condensation will stop. If you have ceiling fans, you may try running them and seeing if stirring up the air inside the home some works to diffuse the moisture and prevent condensation. Todd Miller
Todd Miller
Isaiah Industries, Inc.

10/12/2017
House is brand new? Moisture is potentially coming from the home it self and the structure is a cold spot. I am guessing this is only happening on the North facing roof section? Eric Novotny
Eric Novotny
An informed customer is the Best Customer!

10/12/2017
Moisture is only coming from the main family area ( beam) w the vaulted ceiling. The attic area over the bedrooms is fine. See pic. The place is about 1 yr old. We don't live there so it's hard to pinpoint when this started or occurs. The humidity, as noted above, is only about 50% inside.
Guest User

10/12/2017
How would I provide that? Cut a vent in the ceiling and then run it all the way through the roof? I tried a floor fan upstairs pointed to the vaulted area to "dry it out" and it dripped worse. I figured it might be chilling the beam even more. I haven't tried running the main ceiling fan constantly. Should I consider a dehumidifier inside? As stated, the humidity in the house is already at an acceptable level. So, you're thinking it may have nothing at all to do with the heat transferring down from the metal roof?
Guest User

10/12/2017
What are the exterior temps right now? Its not uncommon to have it not happen in a bedroom (shorter ceiling and more head circulation) vs. a tall vaulted ceiling. You need to get the interior humidity down in the meantime. 50% (54% is what you mentioned before) is way too high. Eric Novotny
Eric Novotny
An informed customer is the Best Customer!

10/12/2017
So, this chart and most of the ones I can find, are incorrect?
Guest User

10/12/2017
Here is a better calculator for you to use. http://www.dpcalc.org/ You will note that if you have a 70 degree interior temperature, 54% RH, and a rafter surface temperature of 52 degrees (very easily done if you have some overnight lows), you will have dew point. The other reality is that unless you are actively stirring the air, humidity can concentrate in areas that are otherwise stagnate. Eric Novotny
Eric Novotny
An informed customer is the Best Customer!

10/12/2017
Todd, replied to you under the wrong message. Sorry.
Guest User

10/12/2017
I really don't think this is from heat from the outside. Ventilation would require bringing outside air in at the bottom of the air cavity and then a ridge vent at the top. Moisture inside the home will migrate to the cavity and be carried out as well. Keep in mind that your humidity levels may be even higher at the ceilings. A great source of ventilation information is available at www.airvent.com Todd Miller
Todd Miller
Isaiah Industries, Inc.

10/12/2017
Ok, I purchased a dehumidifier on the way to the cabin this morning. When I arrived, the humidity was up to 61% near the beam. It is now 45% after a couple of hours of the machine running. It is a sunny, hot, and humid day today and there's no sweating on the beam yet. I will know more later this afternoon. My builder still thinks we need to go ahead and replace the ridge cap with a vent, just in case. He thinks it can't hurt. Maybe Plan on adding a humidity system to my hvac, if this works? Any thoughts? Thank you both so much!
Guest User

10/12/2017

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