condensation on metal roof

[Joseph Hammel]

I cant figure out what forum to put this under. I own a 16 unit apartment building in Hammond Minnesota near Rochester. It had a flat rubber roof over about 2/3 of the building. It was needing replacement and as more of a long term fix I decided to have a truss system built and put a steel roof on the building. However we didn't sheath the roof the steel is on purloins. We vented the soffit and ridge. Now we thought we had leaks but it turns out its condensation forming inside on the steel dripping on the rubber and finding a way in. We had to cut the rubber around the perimeter to install the Lam beam to set the truss system on. I looked into spray foam. The spray foam guy suggests a 1 inch layer on the back of the steel and totally closing up the system. So we would block off the soffits and foam it all in tight including the ridge vent. This would be about $5000. My other Idea was to use cellulose to put a r-30 (or more) layer on top of the old rubber. We could reseal the edges with rubber scraps to act as a vapor barrier.  R-30 would be about $1300 for material plus labor but I can hire some $20 hr guys to do that. Any other suggestions/ comments? I wish I would have done this differently. Oh the other advantage to the blow in is I can do it now where the foam would have to wait till spring.   

[Joseph Hammel]

I wanted to update everyone on this. First. Yes I talked to the contractor. I don't put any blame on him. We have a good relationship and he has done several projects for me. This was a rather ambitious project and he did it for a very fair price. To cut costs I did 4 foot truss spacing and used purloins for the tin. (steel) If we would have sheathed it we might have a slow problem instead of a obvious one. It Is the lack of insulation under the old roof that is causing the problem. I wish the inspector or the multiple people I spoke with/ brainstormed with on this project would have warned me about this problem but no one did. @Tim Swieczek I get what your thinking. but there is no "attic" between the rubber and the ceiling. There may be some fiberglass in the ceiling joist and some foam under the rubber. Its a tapered rubber roof. To me with the new truss system and roof "capping" the old system now the rubber is effectively a high mill vapor barrier. there is also a regular pitched shingled roof that the new roof tied into. I believe there is a lot of heat loss coming through the holes they cut under the new roof to tie into the structure.  So the solution I selected. The cellulose.  I will update with results.