2.5/12 unvented roof w/ problems

I've got house built in the 70's w/ 2x6 rafters at a 2 or 2.5/12. She has intake vents in the soffit on one side, which has a rafter lentgh of about 44' The other side is only about a 10' run. Kind of like an upside down checkmark. NO EXHAUST currently.

Anyhow, her decking is rotting from the underside. She has a mod bit roof now, but in ALOT of area's the decking is GONE! Other areas it is just super weak, and some areas are fine.

I'm definitely going to remove all of the decking. From there, I'm just a bit unsure until I open it up

-Should I plan on removing all fiberglass insulation and install a vapor barrier??

OR

-Should I plan on replacing wet/missing fiberglass insulation and adding enough to fill the rafters, install decking, install 1.5" ISO w/ single ply roof??

OR

-Should I plan on installing baffles the whole way up to create a vented system?

Also, we couldn't find any source of moisture that wasn't venting outside such as fart fans.

I've thought about going w/ a criss cross of purlins to create a breathing metal system, but it would have to be exposed fastener. She won't pay for standing seam.

Any thoughts??

Humidity issues are complex some times. You roof a house for the grandma and grandpa that have their weekly bath and do laundry once a week and everything is fine. They sell to the family with 3 teenagers who have steamy hot showers twice a day and the dryer is going 24/7 and they are boiling up Mr. Noodle and the humidity problems are now an issue. Heat loss combined with moisture becomes a killer for the underside of any roofdeck that does not have proper ventilation.

I hope people stay around shingling 1:12's forever. Makes the sale easy.

Natty: Your probably right, but there is no bathroom near the worst of the problem area. There is however a kitchen, but it doesn't have a range hood. There is a chimney right below where the problem is the worst, and that chimney has had a fire before. I'm wondering if they didn't replace all the insulation right there, but I don't see that causing a widespread problem.

Rotflmao!!! Good one, Tom. Well said. ("Peepo eat, peepo eat!")

clover83 Said:

Also, we couldnt find any source of moisture that wasnt venting outside such as fart fans.

Back in the '70s, all they use to put in around here was a couple of gable vents. In the '80s, common practice was to throw in a couple of wind turbines and be done with it.

In '81, I roofed a small 2.5/12 that had been leaking- used tabbed shingles like what had been on there. The owner did not want the turbines. 10 years later his ceiling falls in over the bathroom and a lot of the decking went bad and most of the staples on that side of the house were rusted away. I learned the hard way about moisture problems.

She doesn't want to change the general style of the house and I don't blame her.