I have an approximately 100 year-old bungalow in climate zone 4A (Maryland).  It’s time to replace the roof (gable with front and back dormers).  The roof is unvented.  My question is whether we should vent the roof as part of our roof replacement project?

The complicating factors are that in 2012-2013, we had central air installed and the air handler and ductwork were installed in the kneewall attic space adjacent to our second floor (this space is directly under the roof).  We also had open-cell spray foam (Icynene LDC50) installed up to the roofline and in the kneewalls.  The open cell spray foam was covered by painted drywall on the second floor but not in the kneewalls (the exposed foam in the kneewalls is separated from our second floor living space by doors, as shown in a picture).  The second floor living space is conditioned but the kneewalls are not. The air handler and part of the ductwork are in the kneewalls and thus are in unconditioned space.  The kneewalls can get very humid in summer.  Shortly after the installation, on days with big temperature changes (eg from the 30s to 60s), we noticed brown staining on our north-facing wooden porch ceiling (the porch ceiling eventually cracked/warped and needed to be replaced).  This seemed like a sign that the open cell spray foam had caused a condensation problem.

To create a vapor barrier, in 2016-2017, we painted the drywall adjacent to the open cell spray foam with a vapor barrier primer.  The Icynene installer sprayed Henry Air-Bloc 32 directly on most of the open cell spray foam in the kneewalls (however, the air handler and ductwork blocked access to some of the open cell spray foam so not all of the foam was covered by the Henry product).  Despite this, we still have the condensation problem, although it has been somewhat better in recent years, perhaps due to use of a better dehumidifier in our wet basement.

Over the years, to address the condensation problem, some inspectors and engineers suggested creating a vented roof to add ventilation, while others advised against creating a vented roof.  Would you have any advice on whether we should ask a roofer to create a vented roof as part of our roof replacement project, or stick with an unvented roof? Thank you.