Head Flashing over Water Table / Skirt Board w/Rainscreen
jamesboris
| Posted in Green Building Techniques on
My project: Single-story, 1/2″ D rainscreen with 1″ D live-edge cedar siding (projects ~2″ at overlap) + 3″ D cedar skirt, in Zone 2A. 2 questions:
1) Rainscreen details usually show a rigid head flashing (aka drip cap) above the water table (aka skirt, aka trim at bottom of wall), going back to the battens (not the sheathing). Is this necessary if I instead rip the top edge of the skirt on a 10° bevel? I’ll leave a 3/8″ gap above the skirt / below the siding.
2) Do I need a drip kerf cut in the bottom edge of the skirt? It’s 30″ above the ground. Behind it is ~3″ of dead air space, then the web of a steel I-beam.
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Replies
James,
I would say you still won't get anything like the water intrusion you would with an open cladding, and particularly as it's at the bottom of the wall, a small amount of moisture getting in is pretty inconsequential.
I'd be tempted to leave the bottom of the water table alone.
Thanks Malcolm. How's about the top? Metal head flash or bevel?
I've always used flashing, but that's because I could get matching colours as the cladding was painted. I think the bevel would be my choice with cedar.
We don't have a much leeway with rain-screen design here as our code mandates a lot of the detailing - right down to the length of flashing drip edges, and their distance from the cladding behind.
Gotcha. I've used your code as a reference pretty often. I have a bunch of paint-grip galv that I could spray paint to match other metal details, just seems like overkill to use a drip cap just to protect the skirt. 3" thick, rot-resistant wood, soaked in Cutek, with a 10-deg bevel... I always like to check here before I go beyond the usual details on stuff like this, but in this case bevel seems ok to me too...
James,
A couple of photos of the last water table I did with a cap flashing. The trim and siding were Hardi. Apologies that the printing on the WRB is upside-down.
I find that finish on any painted horizontal surface does not last. Even if beveled, chances are that is where the paint will start to fail first.
The way I look at it, the flashing above is mostly just to protect the top edge, so going only back as far as the rain screen is good enough.
I had planned to take it only back to the rain screen too, but now I'm thinking, per Tyler below, that the flashing's main purpose is blocking insect entry... in my climate, a much worse fate than stain wearing out... I've pulled off so much vinyl siding only to find a house 50%+ encased in mud dauber tunnels.
I'm not sure i have your detail pictured correctly in my head, but wouldn't a 3/8" gap allow for insect entry?
Yes, it would! Insects could crawl through the gap between [the top edge of the skirt] & [the bottom edge of the siding's starter strip]... thanks!! Can't believe I didn't think of that... thoughts, anyone? 3 ideas:
1) run a double layer of Zip tape across the rainscreen battens, centered on the 3/8" siding-to-skirt gap
2) same, but with a 3" strip of sheet metal... i.e. keep the "wall" leg of the drip cap, just for insect-shielding
3) caulk the gap after installing siding, though I have never seen this on any detail. Seems like a bad idea for a belly band, but for my water table I dunno...