On roof raises, why do people tuck the sheet metal behind the rub rail?

[Truffles]

On most Blue Bird roof raises I see, people put a lot of work into tucking the sheet metal under the drip awnings up top, but then also tuck it under the rub rail below the windows. It seems like water would sheet off better if the metal went inside the drip awnings and then OUTSIDE of the rub rail down below, so that no water worked its way inside the rub rails.

Also, this would be much easier for me to do than try to bend the metal to get it inside both the awnings and the rub rails.

Is there a functional reason why I shouldn't overlay the new metal over the rub rail?

[UnicornWizard]

I'm looking at this exact situation right now on my Thomas bus. It seems like I can take the sheet metal either over or under the rub rail. If I take it under the rub rail, then it slips in nicely with some of the vertical trim pieces. Otherwise, I'll have to cut and notch it where it corners. So, it might just be a convenience thing. I'll also be using sealant in all the seems, so I'm not that concerned with water ingress at this point.

[musigenesis]

Originally Posted by Truffles

On most Blue Bird roof raises I see, people put a lot of work into tucking the sheet metal under the drip awnings up top, but then also tuck it under the rub rail below the windows. It seems like water would sheet off better if the metal went inside the drip awnings and then OUTSIDE of the rub rail down below, so that no water worked its way inside the rub rails.

Also, this would be much easier for me to do than try to bend the metal to get it inside both the awnings and the rub rails.

Is there a functional reason why I shouldn't overlay the new metal over the rub rail?

I would think just aesthetics and a slight angle problem in terms of lining things up (your new sheet is basically going to be its own thickness plus the thickness of the rub rail stock farther out than the side sheeting). I would put it under the rub rail and rely on seam sealer to keep the joint watertight (my bus is already 1/3 Dynatron-550 so I'm done for if the stuff fails anyway).

[EastCoastCB]

You get a better seal putting it under the rub rail. On top wouldn't be proper at all.