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TOPIC: Ventilation

metal roof condensation

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I have a small cabin (683 sq feet) that was built this summer (2010) and a metal roof installed over 1x4's 24" apart. no osb or felt, the ceiling has 19R insulation. no soffit overhang, but the ridge's on the metal left open with a mesh screen to keep out critters. gable vents were installed (15"x20") there is only about 15 ft of the roof sweating underneath, which is on the south side of cabin. that is over the bath and bedroom. the bathroom vent is vented to the outside. there are no leaks in the roof, only condensation. I do have vent free fireplace in the living area, but the living area has no condensation. any suggestions? would there be anything to put underneath the roof rafters to keep warmth from getting to the metal? thanks for any help and advise
tom anderson

12/28/2010
It is not the warmth that is condensing but the moisture and higher than ambient relative humidity that creating issues. You need to stop the moisture (air) from reaching the roof. You can install some sort of sealed vapor retarder/barrier. You can look into plastic that is sealed up tight or spray foam the rafters. Those are you two options. Easier option is to get a circulation fan to vent some of the humid air out of the living space and control the humidity in the space during the cold months. Eric Novotny
Eric Novotny
An informed customer is the Best Customer!

12/28/2010
thanks, Would a dehumifier for a small bedroom/bath take out enough humidity to help? I do leave a window raised a little. I have been told that humidity in a house should be around 45 to 50. Also I am thinking of taking the trim down from the bedroom ceiling and caulking then reinstall. would this help? I also was thinking of using a foam insulating board with the aluminum side down to living area. I would take up the insulation between the ceiling joist and laying it between the joist, caulking the edges, then put the insulation back down on top of this. Does this seem logical? would it help? thanks again
tom anderson

12/29/2010
You would be better served to enclose that bathroom and vent it through the roof deck and out of the home. The humidifier will help for certain. Eric Novotny
Eric Novotny
An informed customer is the Best Customer!

12/30/2010
In addition to previous responses please understand that your vent free fireplace is pumping a lot of moisture into the home. Todd Miller
Todd Miller
Isaiah Industries, Inc.

1/6/2011
+1 Good catch. I breezed over that section. I would never, repeat, never use a vent free fireplace. I have been in homes and observed dangerously high CO levels as a result of the failure and/or poor design of these units. Get rid of that unit and get a properly vented unit if you value your safety. Eric Novotny
Eric Novotny
An informed customer is the Best Customer!

1/6/2011