Metal roof condensation

[Arky217]

I have a metal carport and sometimes condensation on the underside of the metal roof is so much that it 'rains'.
Since I only have vehicles in the carport, it's no big deal.

However, I am planning a low cost garage using the same type of roof, only over wood trusses.
I would like to eliminate the expense of sheathing and just use the metal on the trusses,
but I am concerned about the condensation.

Would this product  http://www.lowes.com/pd_409814-56291-BP48100_1z0uk7m__?productId=3775461&pl=1 
solve the condensation problem ?  It is just two layers of reflective material with a 1/4" layer of plastic bubbles between.

Arky

[John Raabe]

Condensation happens when there is warm moist air next to a metal roof that is exposed to a cooling night sky. The surface of the metal drops below the dew point.

Unless you can bond a good insulation air-tight to the bottom of the roof you will still get condensation (now between the roof and the top of the bubble sheet). That is not a good insulation for your garage roof. Spray foam or a paint on felt might work...

See if this search is a help: https://goo.gl/jWfb26.

John

[JRR]

Our cabin porch's metal roof has never demonstrated this phenom ... that I have noticed, and I have touched the underside of the metal when I thought it would have occurred.  Of course, our porch is wide open, not very large and and has no heat source.  However, I can imagine that engine exhaust, or warm house air coming through a doorway, would cause the rain to happen straight away.

[Dave Sparks]

The drought out west caused us to start looking at data from our rain catchment system. We started saving the first 15 minutes of rain to garden only tank 2 years ago. It use to just go down the hill so we really did not know the data. The thing that we learned was not what we expected. There was close to 40 gallons a night on some of our cool spring and fall nights coming off our metal roof from condensation.

I sure would not want anything like that happening underneath the roof!

[MountainDon]

............There was close to 40 gallons a night on some of our cool spring and fall nights coming off our metal roof from condensation.

I sure would not want anything like that happening underneath the roof!

Wow!!

That helps to understand how the guzzlers in the UT desert backcountry always seem to have water in them for the wildlife. (Google guzzler if you don't know what they are. )

[Dave Sparks]

They also keep rattle snakes alive in a burlap bag and eat them when they are hungry.