Roof Penetrations- Proper Installation

I am currently having a snap-lock standing seam metal roof (Drexel Metals 450SL, 24ga, fastened with clips) installed on my house. The original asphalt shingle roof is being stripped off and the metal roof installed directly to the deck.

For the first pipe penetration, the installer screwed the pipe boot to the metal panel AND the roof deck. My understanding from everything that I've read is that the panels need to float to allow thermal movement and pipes boots should never double pin the panel to the deck. It appears that the proper method is to cut the deck opening to a slightly larger diameter than that of the boot so that the boot screws penetrate the metal panel but not the deck.

The installer came highly recommended--by a salesman at Drexel Metals and 5 previous clients who I spoke with. I also went to see their previous work (3 houses). They have a lot of experience and it shows in the way that they work. What they have done so far looks great and I am pleased with them. My only concern is how they installed the boot appears to contradict the proper method.

I politely raised this concern with the installer and asked him to speak with the manufacturer to see which is the preferred method. It was a cordial conversation in which he confirmed that this is how they have always installed boots and he agreed to check with Drexel Metals.

I have 6 more pipe penetrations, some which they will get to tomorrow and I don't know if he will have a resolution from the manufacturer. I called the salesman at the manufacturer who recommended him; he said that the installer's method was correct and that not screwing the boot through both the metal panel and deck would void the no leak warranty, but I do not how well versed he is on installation details or was, in essence, deferring to the installer.

Is the installers' technique correct? If not, what is your recommendation in how I should proceed? Thanks

Eric, it is a hip and valley roof covering an approximately 100'x70' house. The longest panels will be 40' long.

Fastening the boot to the metal panel and deck isn't a concern to you?

BTW, the info on this site was influential to my decision to go with a metal roof. Thanks

A 40' run is pretty substantial. We live in snow country and split the panels at penetrations and use murphys to divert snow. If you are using decktite type boots you can ask the installer to remove the deck tite, round out the holes made in the panel(not the wood deck) to a bigger size and reinstall the boot. This will give some additional wiggle room for the panel to move.