Condensation Conundrum

[Jessupftw]

Hi All,

Finishing off the interior of my 50' x 80' pole barn located in South Eastern Wisconsin. Side walls are 14' which we spray foamed with 2" of closed cell and added r-19 blankets to get to best of both worlds. I must say, the spray foam really stiffened up the structure and sealed out all the little openings quite nicely. HIGHLY recommend but we just couldn't afford to spray the ceiling ( 6:12 pitch which adds A LOT of surface area, over $12k in cost )

Now its time to start thinking about how to best insulate and air seal the ceiling but do so bit more economically. My original plan was to use R-39 un-faced insulation in-between the rafters and put up a good thick plastic vapor barrier and finish with corrugated white metal from Menards which I think is fairly typical. After thinking (WAY overthinking) I am super concerned about condensation on the underside of the metal roof and having moisture issues down the road due to air leakage into the attic space. My heating/cooling is forced air/AC down a spiral duct located down the center of the ceiling with 3 fans to keep air distributed. Plan to only heat/cool as needed but keep the building above freezing.

After thinking about all my options I think I have a plan but would like your opinion on whether its worth the cost or if I should just accept that all things in life are not perfect....

My plan is still use the r-39 batts but then install 2" foam board on the bottom of rafters, seal/tape all the seams, and spray foam all openings, **** joints, and corners air tight. I would install the metal panel ceiling below that attaching it with longer screws through the foam to the rafters. Yes I would lose 2" of ceiling height but not really concerned with that. Talking $2k in foam board alone not to mention time and labor...

Am I nuts or would this give me the air seal necessary to prevent the moisture issues down the road?

Roof has soffit and ridge venting in place already so the attic would "breathe" much like most residential structures.

Pros/cons of this approach?

Product in question:
(http://www.foamular.com/foam/products/foamular-250.aspx)

 

[Jess]

Is there any roofing felt or underlayment under the roofing? While your plan may work fine, you might want to consider some kind of ventilation immediately under the roofing sheets. The biggest concern would be the batts getting wet and sealing that moisture in. Hopefully, someone with experience with this type of structure will jump in with suggestions.

 

[Jessupftw]

Thanks for the response, Jess

No underlayment, just the steel panels mounted directly to the purlins which is pretty standard construction for pole barns in this part of the world. There is soffit venting along with a ridge vent so the attic space will be able to breathe.

 

[Rookie2]

If the roof is dripping now, it will always drip ! It's a metal to air problem and depends on time of day that the sun hits the metal roof . I'm not sure if it's just building location or if it varies state to state as you go west. I closed and insulated my 14' ceiling, I cut additional vents , I blocked the soffit vents ,nothing seems to help. I need to cover the inside of the roof panels but it's a little late for me.