Frost in vaulted ceiling

Roger Solberg
1/20/2013
Hello,....I am working on an existing Horse Riding Arena with 24' leans attached on either side. One lean houses horse stalls, the other side has a kitchen and viewing area. The building has a steel ceiling,plywood/steel lined walls, and is fully insulated with vapor retarder on the inside and above the ceiling. (6"batt in walls and R-38 in ceiling). The leans are vaulted rafters with ventilation at eave and peak = to or greater than IRC building code, and have a 1inch code compliant nonobstructed path from eave to peak path above the high density R-38 insulation. The owner is heating the arena to just above freezing, but has no air exchange in the building. He is also sprinkling the arena floor periodically to keep dust down. Heavy frost has accumulated underneath the roof steel in the vaulted lean above the 1 inch ventilation path to the extent that large amounts of water leak into the building when the frost melts. The owner insists the roof is leaking. Is anyone aware of documentation that would show that once interior humidity level reach a given level, that mechanical ventilation is required for a conventionally ventilated ceiling with a metal roof to function properly? Thank you.
Todd Miller
Classic Products, Inc.
1/20/2013
I believe it is really a matter of determining Dew Point. http://en.wikipedia.org/wiki/Dew_point
Roger Solberg
1/22/2013
It the dewpoint is high, what does that mean in terms of a solution?
Todd Miller
Classic Products, Inc.
1/22/2013
Dewpoint is a combination of moisture saturation and temperature. Moisture saturation is controlled through ventilation and dehumidification. Temperature is controlled by insulation. Both can be controlled also by blocking any airleaks and other sources of transfer.
Guest User
1/22/2013
Ok. So at what dew point does a metal roof installed as per building code fail to function properly?
Todd Miller
Classic Products, Inc.
1/22/2013
Dew point is a combination of temperature and humidity. The one link I provided includes a graph showing the intersecting points of humidity and temperature at which condensation will occur. It has nothing to do with roof failure.
Guest User
1/23/2013
Ok. The question is, If a vaulted ceiling is installed as per the original post, is there an interior humidity level beyond which the steel roof installed per code will not function properly, (frost over and then rain) and the solution is to reduce the humidity level in the building?
Todd Miller
Classic Products, Inc.
1/23/2013
Roger, I hope you do not think I am being difficult but that is an impossible question to answer. It all depends upon temperature. If you can tell me the coldest temperature at which the surface where the condensation is occurring will be, then I can give you the humidity level based upon the chart included in the link. It's impossible to extrapolate either number without knowing the other number.
Guest User
1/23/2013
I also am not trying to be difficult, just trying to solve a problem and to avoid any similar problems going forward. For purposes of this case, lets say 10 degrees outside and 65 degrees inside when heated dropping to 35 degrees overnight .
Todd Miller
Classic Products, Inc.
1/23/2013
If you have an inside temperature of 35 degrees but a cold surface such as the underside of the roof that hits 23 degrees and the relative humidity is 60 percent, you will likely get condensation and frost. There are some calculators here which can help: http://www.pilotoutlook.com/calculators/temperature-conversion-calculator The way to control this, as you have alluded, is through controlling temperature and humidity. If you can keep that kind of moisture level away from that kind of temperature, then condensation will not occur.

If you would like to reply to this thread, please log in. If you do not have an Ask the Experts forum user account, create one here.

Find a Contractor

Get Started Today

Take the first step to increasing the value of your home with a great looking, durable, fire resistant and energy efficient metal roof. Browse our list of qualified MRA Member Roofing Contractors in your area for a free consultation and estimate.