Metal Deck Perpendicular to Short DIrection Drainage

[reverbz]

Hey Guys,

I have a job I'm working on which is a long rectangular building. I am using open web steel joist connected to CMU walls. I have metal deck perpendicular to the joists and am wondering how drainage is dealt with when the deck is perpendicular to the short direction. Wouldn't water "pond" in the deck grooves? How have you guys dealt with this in the past or am I supposed to have subframing?

Thank you!

 

[KootK]

I'm in a northern climate but, here, the deck's corrugated profile would never be exposed to the elements as you've described. Rather there would be a roof buildup that would render the roof plane a flat surface.

 

[Beginning-Bear]

Can confirm what KootK posted above is similar in southern US climates (Texas). Maybe just thinner insulation layer on top.

 

[HTURKAK]

I have metal deck perpendicular to the joists and am wondering how drainage is dealt with when the deck is perpendicular to the short direction. Wouldn't water "pond" in the deck grooves?

You have two options,
- The metal deck will be supported on purlins. In this case, roof deck could be a single deck or sandwich metal deck ,
- The metal deck directly supported on roof joists ,or roof frame . In this case the height of the ribs would be different to span btw frames . In my zone , typically heavy density rock wool used with membrane roofing. The roof would be walkable. This option is more expensive .

 

[XR250]

You have two options,
- The metal deck will be supported on purlins. In this case, roof deck could be a single deck or sandwich metal deck ,
- The metal deck directly supported on roof joists ,or roof frame . In this case the height of the ribs would be different to span btw frames . In my zone , typically heavy density rock wool used with membrane roofing. The roof would be walkable. This option is more expensive .

I don't understand. 99% of buildings are constructed as a version of what KootK has presented. Canopies and un-heated buildings would be the exception in my area.

 

[ANE91]

The purlin approach is common enough in parts of TX and LA. I may have pics…

 

[XR250]

The purlin approach is common enough in parts of TX and LA. I may have pics…

But why would you need to do that unless your decking is exposed?

 

[ANE91]

You wouldn’t otherwise. Some commercial owners prefer the exposed decking, and some contractors prefer not to muck about with topside insulation and membranes. It’s unfortunately all too common for rainwater or water residual from cleaning to become entrapped thereover as the roofing progresses over multiple days.

 

[XR250]

You wouldn’t otherwise. Some commercial owners prefer the exposed decking, and some contractors prefer not to muck about with topside insulation and membranes. It’s unfortunately all too common for rainwater or water residual from cleaning to become entrapped thereover as the roofing progresses over multiple days.

Makes sense.

 

[Ron247]

As described, you most likely will have water issues forever, with no real good cure other than replacing the roof. Many I have seen cross-framed the joists with hat-channels or some other product and then sheet the roof with panel run parallel to joists. This is generally an unheated building.

Also, the built-up system as already described are popular. It is definitely more common when the building is climate controlled and needs insulation.

I have never seen what you describe. If it is a screw down roof, a slightly blown rubber washer, poor screw installation and numerous other things that tend to happen will lead to a bunch of leaks. If you are using vinyl backed insulation, finding the leaks gets a lot harder.

 

[ANE91]

If you are using vinyl backed insulation, finding the leaks gets a lot harder.

Long stick + nail on the end, poke the vinyl, set up a bucket. IR survey optional.

 

[JAE]

Note that decking and metal roofing are two different things.

The OP stated "decking" but not sure if that's what it is or not.

Decking leaks and is not meant to be a water barrier system.

 

[Ron247]

ANE91, we used to use a pellet rifle on taller buildings, but that is good to drain the leak, not find the leak. Of the ones I have dealt with, really bad leaks are easier to find than smaller leaks. As you know, most leaks occur uphill of where you see them come out and you are also seeing where it is ponding on the somewhat loose insulation.