Rabbeted joint under new metal roof. Bad idea?

Hi all,

I’m about to have a new standing seam metal roof installed and with it 2″ of rigid insulation where we only had 1″. The attached image is not my home but shows the type of roof we have.

The current roof is just the wood you can see in the pic with 1″ insulation on the other side, then two old layers of asphalt shingles. This roof needed to be replaced 10 years ago. The main problems for us have been the lack of insulation, ice dams, and general water intrusion (which has picked up recently to the point of finally getting us to pull the trigger to fix it).

We’re all ready to go and were planning on using something like the insulation backed Zip panels with tape to create a decent barrier for the water. However, I had mentioned my concern about the roof suddenly being much tighter and the possibility of us getting condensation on the inside of the roof. I grew up in a home where this had happened and our home is on a large pond.

Hearing that, and my contractor knowing that as we remodel parts of the house over time I’m opting to make everything as air tight as possible, he suggested using the Hunter HB Shield panels instead due to the rabbeted edge of the panel allowing for at least a bit of air flow under the roofing materials. I know they have even better products for this but they are not within our budget.

So I’m wondering:

1) I assume that bit of air flow would be a good thing, but while that might be good for the roof, it’s not going to have any impact on my interior condensation concerns, right?

2) I’m assuming since they are rabbeted that these joints don’t get taped up like the Zip system, which makes me wonder about the lack of a consistent seal and essentially wide open joints on the roof that is currently leaking on me. Wouldn’t it be better all sealed up?

3) What options do I have if we seal the daylights out of this thing and get condensation inside? Ridge vent won’t really work here, right? Is there some type of roof vent that could be installed later?

ANY and all thought/tips/ideas would be very welcome! Thank you!

 

Are your 2 posts the same question for the same project?

For max insulation should I go for snow covered asphalt over metal?

 

Same project, but if you read them I think you'd see it's very clearly a different question.

 

Only way there would be condensation is if the inside of the home was to moist.
I'd be concidering SIP roofing panels attached to the outside roof decking before I messed up that pretty ceiling.
https://www.sips.org/about/frequentl...ed-panels-sips

 

You get condensation from air leaks and air exchange so I don't think I would purposely want / or create air spaces. If you are worried about condensation between the sandwich, I would put a self healing ice and water on the existing roof deck before you added anything new (insulation or sip) on top of it. That way you would be sure of no leaks. Self healing so that all the penetrations / fasteners used on the future roof will be largely sealed.

 

> Only way there would be condensation is if the inside of the home was to moist.

Right and that's what I'm worried about. We're 50' from the water, all windows.

> I'd be concidering SIP roofing panels

That's exactly what we are doing here, my question is about the rabbeted joint on the Hunter panels.

> I don't think I would purposely want / or create air spaces

This is what I was thinking too, but then what's the point of these Hunter Panels. It would seem they are always going to have some sort of gap, right?

> I would put a self healing ice and water on the existing roof deck before

Hmm, that's an interesting thought, but keeping in mind I'm not a roofer - won't I then end up with two vapor barriers, which I've heard isn't good?