Proper Over-Deck Insulating and Vapor Barrier-ing (with pictures)

[canopy]

screws through the foam

Is there any concern about sag especially on say heavy tile roofs with added solar / snow loads? There could be hundreds of pounds of bending force at each screw head with considerable leverage since the screws stick up out of the wood quite far and are only shouldered by foam.

[Don P]

That it a concern, well not the tile part. The 2x strapping was connected together at the peak and that is part of the reason for the steel strapping over the ridge from side to side.

[Joe Hillmann]

screws through the foam

Is there any concern about sag especially on say heavy tile roofs with added solar / snow loads? There could be hundreds of pounds of bending force at each screw head with considerable leverage since the screws stick up out of the wood quite far and are only shouldered by foam.

It could be a concern.  Although if you screw the boards down tight enough there shouldn't be much a lot of force to cause it to sag.  For sagging to happen the boards would have to settle into the Styrofoam to loosen up the screws and then sagging could happen once the screws are no longer under tension.
Although the side eaves and bottom eaves of mine will be supported with lumber to cover the foam so that should reduce the risk of it sliding.  A person could also put in spacers if they felt it was needed.
Also with the more screws a person uses the less likely it will be a problem.  I expect to put a screw every 2 feet in each direction. Each slope of my roof will be 450 square feet that will be 115 screws holding each half off the strapping down.  (putting that many screws in was my plan 2 years ago before prices skyrocketed,  I don't know what long timber screws cost today so my plans my change.)

[Anderson]

Just wanted to leave a link to a very informative podcast I have been enjoying, on building science.
It's with a few guys who worked at Building Science Corp, Steve Baczek and Peter Yost  and a high performance builder Jake Bruton


It's a nice blend of different perspectives, but all aimed at building durability

Here's a episode on air tightness

https://unbuilditpodcast.com/episodes/uig207io63dkdk5fmiwexv78fkinv5

They are very good friends, so they do take every opportunity to give each other a hard time :D ;D ;D