Help Insulating the roof?

[Jeepbeater]

I have a Adam's Truss building, (similar to a Miracle Truss). Normally these buildings would have a steel building insulating blanket put down over the purlins and then the steel roof would be screwed down on top.

My Roof is plywood, felt paper and shingled like the house. I have vented soffits all the way around and a ridge vent that runs the length of the building. I realize now that I should have put some 2x4s perpendicular to and on top of the purlins and then put the plywood down to vent the roof, but I am a little late for that now. Roof is finished and I'm not tearing it off.

Based on these pictures how would one go about insulating this roof and do I need to be concerned with airflow beneath the plywood?

Was thinking about drilling some 2" holes in the 2x6 Purlins to provided airflow? Necessary?

What about framing down using a 2x4 nailer attached to the underside of the purlins run perpendicular with a 2x6 tied on the side. That way I have the airflow and can then fill the framed down section with batts and cover the underside with drywall or some lighweight paneling.

Just fill it in with batts as it sits now and forget about it?

Ideas, suggestions?

I'm located in Maryland near the Bay.

Thanks,

John

 

[Dragster Racer]

It's a hard one to explain to someone I understand...or maybe it's just me. LOL.
But I think my answer would be...no, I would not just fill in with insulation and call it good. That will leave no air flow from what I am seeing, and you don't want that. My preference would be to put a flat ceiling in. You are going to need space between whatever insulation you put in and the gap that you leave for airflow.
I almost never suggest this because I'm not a big fan price wise. But, I think you could in this case avoid the extra framing, seal off the vents, and spray foam the entire thing. I think you can get by without the ventalation. But there are other experts here on that.

 

[Jeepbeater]

I have a 24" exhaust fan in the wall above the door. You can see it in the second picture.

http://www.teksupply.com/contractor/supplies/prod1;;pg109845_109850.html

Put it in there mostly to clear out the welding fumes and whatever else.