Rooftop Deck - Rail Posts on Low Profile Frame
I am building a rooftop deck on a slightly sloped roof that will require the joists at the high point on the roof to be only 1.5" deep. What is the best way to attach rail posts on such a low profile deck?
This is a challenging situation but the first thing that comes to mind is using some kind of surface mounted post anchor which does not require a deep joist and which has some kind of engineering guideline or known performance limits.
If the upper part of the deck that is nearest the highpoint is only 1.5" deep it sounds like the other end - where you will be securing your posts might be fairly shallow as well.
If you are not able to use a 2x8 and cannot connect the posts into the framing as a result then this is where a surface mounted post anchor will be helpful. It sounds like you had a wood post and rail in mind although a metal railing which has some building code testing behind it possible choice also.Possible Framing Diagram - Side View
If you want to go with a wood post then something like the Titan Post Anchor
for posts set a 6' post spacing would do the trick.
One thing to keep in mind however, is that if you are connecting your railing to a roof top framed structure and the joist are only four or five feet long you may need to see if the deck lifts up at all when the railing comes under load.
Usually someone would be standing on the deck at the same time and therefore their weight would off set any uplift generated. This may not be an issue at all as the weight of the structure may be sufficient. But it is something to keep in the back of your mind.
Of course this applies to any roof top deck railing scenario.