sweating steel

[bob96]

Have steel tubes ceiling/roof joists that are supporting an exterior canopy. On top of the steel tubes, plywood deck is attached. Between the tubes is rigid insulation/blue board. The bottom of the tubes is carsiding for a ceiling finish (carsiding = old railroad car look, a type of 3/4" decking arch'l finish). The roof is a shed roof. Midwest climate. So cool nights and humid days result in sweating of the steel and staining wood supporting beams and carsiding. Any ideas how to help mitigate the sweating? At this time, it would preferable to remove the plywood deck due to the ceiling finish is already installed.

Thank you.
Bob

 

[JoshPlumSE]

One summer I interned for a company that specialized in "building envelope" work. It was an interesting mix of roofing, water protection, and structural. This would be the type of investigation that would be right up their alley.

In fact, I can still remember my boss diagramming out a similar issue for a project. Showing me a diagram of temperature drop through the roof or wall system and how this led to a dew point right between the insulation and the ceiling material.... resulted in a ton of moisture damage.

I think they ended up specifying some type of more advance moisture barrier. But, I'm not knowledgeable enough to recommend any remediation procedures.

There are companies out there that specialize in this. The ones I know of are:

http://www.gainc.com

http://www.abbae.com

You might have some more success consulting with one of them than trying to reinvent the wheel yourself.

 

[msquared48]

I would remove the stained material and install new material after you have created a space below the steel tubes and insulation with furring strips and soffet end vents for the spaces created by the furring strips. You could further protect the underside by installing a liner of visqueen below the furring strips. This should solve the problem.

You need to vent this.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com