Shop Roof Insulation - PIC

[Steve Mathews]

Before installing a couple of mini splits for my barn/shop I was advised that at least some roof insulation would help. I planned to use R-19 faced fiberglass batts between the 2x10 rafters and cover it with a layer of white scrim paper. Then I found this double insulated cover that might be a good substitute for the scrim paper. I plan to eventually sheet the ceiling with drywall or tongue and groove wood paneling but not now. Any comments or suggestions?
https://www.homedepot.com/p/Everbilt...LRFL/319738988
Barn 003.jpg

[Jim Becker]

"Technically" the faced fiberglass needs to be covered due to fire risk, so I'm glad you intend to do that with the 'rock or T&G. You might consider using Rockwool instead of the fiberglas because it will stay in place easier, is fireproof and is easier and more comfortable to install. That said, the radiant barrier material you show is commonly used in buildings to help keep things comfortable. It would be more effective if it was on the underside of the roof deck prior to installing the insulation, however.

[Edward Weber]

If you're eventually going to cover it with drywall or T&G, I wouldn't go to the trouble of adding any additional layers of scrim paper or anything. I don't know that it would benefit you.
Depending on your heating/cooling needs, I would simply get the highest rated insulation you can for the rafters you have and where you live. You could go up to R-30 but it may not be worth it.

[Bill Dufour]

Rather than r-19 go r-21 for no more cost. Be careful about venting the underside of the roof deck and requirements for roof warranty. I do not think the bubble foil is any better then the foil scrim.
We need to know your climate.
BilL D

[John S Howland]

Rather than r-19 go r-21 for no more cost. Be careful about venting the underside of the roof deck and requirements for roof warranty. I do not think the bubble foil is any better then the foil scrim.
We need to know your climate.
BilL D

Bill,
I have worked in shops that have covered ceiling insulation with metal roofing. I was concerned about a dew point condition forming on the under side but never did and we have high humidity here. Venting rafters would be key to keeping dry rot out of rafters and sheeting.
John

[John S Howland]

Insulation only slows the heat transfer. If you match you insulation to you region the heat transfer will match the heating and cooling cycle of the building.

[Bill Dufour]

Bill,
I have worked in shops that have covered ceiling insulation with metal roofing. I was concerned about a dew point condition forming on the under side but never did and we have high humidity here. Venting rafters would be key to keeping dry rot out of rafters and sheeting.
John

I have no idea on the latest greatest ideas on roof venting. I just wanted to mention he should do some research before doing something wrong that has to be redone. There used to be quite a discussion about vented or non-vented.
AFAIK All Frank Lloyd Wright roofs sag, leak, rot or all three.
Bill D

[John Pendery]

Hard to tell from the picture, but perhaps reconsider using batt insulation. With that blocking, having continuous venting from soffit to ridge looks challenging. If non vented consider spray foam that will act as an air barrier and prevent rot/condensation issues. Looks like the entire space will be conditioned so that space is a good candidate for it.

[Brian Gouldman]

Disclaimer: Not an expert but have done my own research on modern building science, made my own decisions, and implemented them in my own shop.

My shop has a mini split and I also elected to put in a dedicated dehumidifier, more than anything for comfort and to keep humidity at or below 50% to protect my tools. For my roof, and for that matter my walls, I put rockwool in the cavities. So it is very similar to yours including the cathedral ceiling. What I did next is put up an interior layer of osb and rolled on a layer of liquid applied air barrier (prosoco). Since my shop is not lived in there is nothing other then myself adding additional excess moisture to the air beyond ambient. The prosoco is preventing any moisture laden air transfer to the insulation and roof deck. Lastly, the mini split and dehumidifier enable it to dry to the inside year round without me ever having to think about it.

On top of the osb I have a lay in of green glue, drywall, then a layer of cheap engineered oak flooring glued to that. The extra middle layer was because of my proximity to my neighbors and being in an hoa. It paid off though because you can’t hear anything coming out of my shop beyond 10ft away. So I can happily work away at 12am and no one knows.

[Bill Dufour]

OP still has not revealed his climate so we are shooting blind. Maybe he is in the high desert and not too concerned with moisture only radiant heating through the roof. I see no mention of heating.
Bill D