Flashing 4x4 railing posts on roof deck


What is the best (strongest & most weather resistant) method to fasten 4x4 posts on a waterproof deck? Deck is constructed with a waterproof membrane and aqua-stop over plywood.

I’m looking to replace the existing railing with a stainless cable rail.


Depends upon the type of post and its attachment to the deck. Are the posts metal? Generally, a deck coating requires that you mesh and coat up the post a few inches.


We weld a pin to a 12x12 piece of steel plate, set it in flashing cement ( on asphault based roof) and bolt it down and flash it in. Then take the 4x4 and route the inside out to the diameter of the pin and slide it over.


Once I cover a deck with TPO or EPDM, the carpenters put the post, into the rim joist. The outside of the deck, that way we don’t penetrate the membrane. It’s an option to look at.


They are surface mounted wood 4x4 posts. Are there any special brackets or flashing products that should be used?


Here is a picture


There really are no special brackets avalible. In a setup like yours posts penetrate the roof and roof deck and are connected to the framing.

If you are looking at replacing the railing, either reuse the existing posts or you are pretty much getting into replacing the roof. If they are not leaking or rotted, you can just slide post sleeves over them and they will look brand new.


I think my posts are just surface mounted with a metal bracket.


It appears they are. With a ridgid railing like you have that will suffice, the railing sections attached to the house are keeping them ridgid. Switching to a tensioned steel cable railing the posts will likely need to be mounted in a different fashion.


That’s what I was afraid of. I was hoping something like this might work to achieve a strong surface mount solution. The weatherproofing makes it that much more complicated.



That is basically what I was referring to in my first post. We fabricate our own with a 12"x12" plate with a 12"x12" tall pin.