I am in a bit of a panic and need some advice.
I am in the third year of building a large shop .. finally putting the roof on. Just over 3000 sq ft on the bottom … 1200 sq ft of attic storage above. I have put every nail in myself.
Standing seam metal over purlins.
Way back I asked the question, can I put metal over purlins. I was assured by the supplier this was not an issue. No moisture barrier of any type needed. Just need good ventilation and insulation.
Installing purlins was a lot easier for me that 150 sheets of wood … plus it was cheaper so I could go with the standing seam roof rather than shingles.
Just a home shop so the moisture load is small (not like a horse barn).
Anyway … there is always dew on the roof … no issues. Today for some reason, I reached under the roof as I was putting up panels … WET!
Now I know I don’t have any insulation in yet but you can not get more ventilation than completely open!
Concrete floor 20 ft below …. It has been there for 10 years … no rain in the past two weeks.
I am not about to rip the roof off and put down sheets of wood … I have to work with what I have.
I will be insulating the ceiling. The soffit and ridge are vented along the entire length. There is at least a 6” air gap under the roofing.
Is there more I can do?
Spraying foam on the roofing is out of the budget .. plus the roof moves to I am not sure if that would work.
I could put something like Tyvek on the bottom of the top truss member to stop moister from going up.
I had planned on putting the insulation just on above the ceiling (as on the left side of the picture). It would be a pain in the butt but I could put in closer to the roof to cut out the large air volume about the two shop wings (as in right side of picture).
Just trying to figure out where to go from here.
Here is a link to a short video I put up a few weeks ago … This side of the roof is now almost done. There are more pictures and videos on my facebook page.
https://www.facebook.com/michael.csele/videos/900649032083441
Thanks …. Mike
Replies
Hey Mike,
It sounds like you're dealing with condensation buildup under the metal roof, which is pretty common in metal roofing without a moisture barrier, especially in open, uninsulated spaces. Since tearing off the roof isn’t an option, I'd suggest focusing on improving the insulation and airflow.
One option is to add a radiant barrier or breathable underlayment between the purlins and the roof panels to help control condensation. Since foam is out of budget, perhaps using Tyvek or similar material might help limit moisture rising from the floor. Placing insulation closer to the roof, like you mentioned, can reduce the air gap and might also help manage the temperature difference that leads to condensation.
You could also try increasing ventilation to keep air moving, but since you have the soffit and ridge vents, improving insulation could be your best shot. Make sure any concrete or uninsulated areas aren't contributing to the problem, as moisture can rise from them over time.
Good luck! Let us know how it goes!
Definitely agree it sounds like a condensation issue. Obviously a little late now but, while metal roofing can go directly on purlins, in most cases, you'll still want to use a moisture barrier or underlayment beneath the metal roofing. This helps with insulation and prevents condensation from forming on the underside of the metal panels.
No picture, link is dead.
Sorry .. had it as friends only ... just set it to public, should work now.
Thanks!