Cedar breather and spray foam

I’ve installed cedar breather over existing roof sheathing prior to installing the cedar roof shingles on a barn. The owner would now like to finish out and condition the barn. Can i install closed cell spray foam on the underside of the decking in order to create an unvented roof system? Please note that we would install a ridge vent to allow the cedar breather to continue to ventiliate under the roof shingles.

I would install a baffle before you insulate so you maintain a normal ventilation system along with the cedar breather.

thanks for the response however the reason we want to go with spray foam and create a non-vented space under the roof sheathing is bec/ the barn construction will not allow for proper ventilation from the exterior soffits/eaves to the ridge. The baffles therefore won’t do much good. There are horizontal timbers in the way that will impede air flow. I just wonder if the cedar breather will allow for both enough ventiliation for the roofing shigles and plywood sheathing.

Barn. Large open space. No mention of indoor air quality? Cedar Breather works as a space between underlayment -as I am sure you used felt or synthetic- and bottom side of wood shingles. Pretty sure this would cancel out venting the plywood as the plywood is under the underlayment. Then of course if you used GAF Deck Armor it may “breathe” a little…

This question may be better answered Forum wise by Jim, big cedar guy I hear.

Yes you can.

The cedar breather has nothing to do with the roof ventilation.

Cedar breather’s purpose is to create an air gap between the decking and the shakes so that the shakes can dry evenly.

If there is no air gap the underside of the shake takes much longer to dry out and leads to curling, splitting, and rotting of the shakes.

IMO this is perhaps the biggest reason why cedar roofs don’t last as long as they used to, roofers have been installing cedar over solid decking with no way for the cedar to breath.