| Author |
Message |
Ronald L. Geren, RA, CSI, CCS, CCCA, MAI
Senior Member
Username: specman
Post Number: 265
Registered: 03-2003
| | Posted on Monday, May 22, 2006 - 06:12 pm: |    |
We received comments back from our envelope consultant suggesting that we provide through-wall flashing at each floor level (there are 6 floors) where we have vertical metal wall panels. Expansion and contraction have been taken into consideration.
The metal wall panels are applied to non-loadbearing metal studs with exterior gypsum sheathing and a spray-applied air barrier. The metal panels are actually attached to a continuous, horizontal, metal strap that is in-turn attached to the studs. Bottom closure pieces with drip edge are to be provided at the bottom of panels and over openings.
Has anybody out there ever been asked to do this, or have done this? Seems to defeat the purpose of having vertical metal wall panels if you're going to require a horizontal line every 10-12 feet. |
Wayne Yancey
Senior Member
Username: wyancey
Post Number: 130
Registered: 05-2005
| | Posted on Monday, May 22, 2006 - 07:06 pm: | |
Ron,
I do what you describe all of the time. I am currently doing this with metal wall panels, but my thru-wall flashing is every second floor. My building is 12 storys.
Your envelope consultant wants a rainscreen cladding system. The metal wall panel is the water or weather barrier; the air barrier and the thru-wall flashing are the waterproof layer which direct water out of the cavity and provide redundancy. Think brick veneer wall with cavity and weep holes over support angle every floor. In the metal wall panel system, the vertical leg of the thru-wall flashings will ideally have a 2 inch vertical leg plus 3/4" (+/-) hemmed drip edge at 45 degrees.
As part of the envelope consultant's service, request some design assist details (at 3"=1'-0").
You are correct about the aesthetic implications but it it best practice.
The continuous, horizontal, metal strap needs to be sloped to drain (15 degrees) and perhaps also perforated with slots.
Add an insect screen to the bottom of the cavity. Perforated stainless steel is good for this.
Wayne |
Ronald L. Geren, RA, CSI, CCS, CCCA, MAI
Senior Member
Username: specman
Post Number: 266
Registered: 03-2003
| | Posted on Monday, May 22, 2006 - 07:20 pm: | |
Wayne:
I understand where masonry cavity wall is used and there's a shelf angle that blocks water from draining all the way down to the bottom of the cavity, but what is the necessity in a metal wall panel? There's nothing to block moisture, such as a shelf angle, from reaching the flashing at the bottom of the panel run.
The straps are flat so I don't see how perforating them will achieve anything. The specs do note to slope, but I'll add the 15 degrees as you suggest. I'll look into the insect screen as well.
Thanks. |
Jim Brittell
Senior Member
Username: jwbrittell
Post Number: 23
Registered: 08-2004
| | Posted on Monday, May 22, 2006 - 07:20 pm: | |
Ron,
I recently attended a presentation on ASTM E 2266 regarding prevention of water intrusion in wall construction. Wayne's comments agree with everything I heard in that presentation. The only thing I would add is that rainscreens are more advantageous in areas with higher rainfall (40 inches or more per year).
You can contact RCI SoCal Chapter for a copy of the presentation. (They were charging $40 for a CD with all the PowerPoint presentations...) Go to www.rcisocalchapter.org |
Ronald L. Geren, RA, CSI, CCS, CCCA, MAI
Senior Member
Username: specman
Post Number: 267
Registered: 03-2003
| | Posted on Monday, May 22, 2006 - 07:25 pm: | |
Jim:
Thanks, I'll take a look into that.
The project is in Phoenix; our annual rainfall is almost 1/6 of that you mentioned (and that's during a wet year; however, we've been kind of dry lately). |
Phil Kabza
Senior Member
Username: phil_kabza
Post Number: 174
Registered: 12-2002
| | Posted on Tuesday, May 23, 2006 - 10:10 pm: | |
Let's not lose track of Ron's comment above, though, that arbitrarily requiring additional weep elements in the metal panel system when they are not required by intervening structural members (shelf angles) or by analysis of the volume of water anticipated in the cavity is irrational. The added weeps guarantee more complicated and expensive detailing, added potential for waterproofing and visual screwups, and the likelihood of streaking on the exterior of the metal panel system over time. |
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