Sealing windows in a metal building

[CowDoc1]

This is a new construction (next month), red iron building. The windows will be framed with C channel and J channel trim is available. I'll be using new construction vinyl windows, and I'm unsure what style to buy.

What type of window is easier to seal and keep sealed long term; those with an integral J channel or those without? Oddly, those with an integral J channel are $50 cheaper. Does any one have a preference and why?

On a house, because of house wrap and the way windows are flashed, no caulking is needed. Well... maybe some tape. I'm still a bit ignorant on how a window is sealed on a metal building. J channels funnel the water, but the window still needs sealed. I'm hoping there's a method that doesn't rely entirely on caulk to keep water from behind the wall panels. Would someone please expound some of that good learnin' on how to seal metal building windows?

 

[Walter_TA]

Mine had the integral j channel. They were nice in that they held the sheet on the outside. I used screws to hold the sheet in place. And lots of caulk. The windows were held firmly in place with the screws. I used J channel trim to trim around the window. Make sure the cut the sheet larger that the opening. The j channel will cover, and it is easier. I have had no leaks. I will try to take some pics.

 

[CowDoc1]

Thank you Walter. I am a bit confused by your explanation though.

An integral J channel is just a slot that is pre-formed in the window frame. The window has to be placed at a wall panel seam. The wall panel(s) is notch from the side, "smaller" than the window frame. So the panel slides into the channel with maybe 1/4" wiggle room. Then all of it is screwed down together. The integral channel hides the panel edges and no additional J channel is needed. In fact, additional J channel can't be added because the edge of the wall panel is hidden. There isn't access to slip J channel behind the wall panel.

From your description, as I understand (or mis-understand) it, the hole in the panel was cut "larger" than the window frame. So the metal fit over the entire window (less the nailer strip). Then, metal J channel was slipped in behind the wall panel as usual. It sounds like the integral J channel, if it was there, wasn't used. Maybe you were referring to the nailer strip rather than an integral J channel. This kind of sounds like a normal metal J channel installation... with a lot of caulk.

Scratching my head here. Yes, a picture would be great if you don't mind the bother.