Tyvek homewrap question
i am using tyvek homewrap on my house and was wondering about water getting behind the tyvek.
i know there is a decent vapor permeability rating with tyvek that allows water to escape out that happens to get behind it, but when following all of tyvek’s recommendations, like taping horizontal overlap joints, and taping at the bottom of the wall to my metal flashing, the only way for water to escape at that point is through vapor permeation.
my concern is this: the hundreds of staples are certainly not water tight. They are bound to let water behind the tyvek. And considering I will have a rainscreen system, which allows me to not be so caulk reliant – water just will get behind my siding and I don’t want to have to worry about it so much.
is the vapor permeability alone sufficient to allow water to pass back through the tyvek to the outside given the amount of water that potentially could make it through the staples’ holes.
to alleviate my concern I could tape over all of the staples, but that would not be fun.
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Replies
Kevin,
The short answer is that if enough bulk water gets behind your WRB that it can't easily dissipate through diffusion something has gone terribly wr0ng at the cladding layer.
The said, Tyvek installation instructions show taping, both at the flashing above windows and doors, and at the base of the wall, as optional. if you are more comfortable doing so, you can leave a path for moisture to drain.
Consider using Commercial Tyvek. It is a lot harder to tear, or rip at staples.
I expect that a fully adhered WRB (like Blueskin) would outperform Tyvek HomeWrap in multiple ways (less water, less air and less vapor entry, more durable).
A bit of an aside:
I've noticed that both Tyvek and Henry Blueskin WRB installation guides show the window-head "flashed" with tape, but no metal flashing. They seem to rely on the head-frame itself. That doesn't meeting building code here, but I wonder if it is becoming standard practice elsewhere?
The key to bulk water management for any WRB is free drainage; you have that with any rainscreen cladding system. In order for the bulk water to make it past fasteners, it needs to either sit there for a very long time or be driven in by pressure. If installed properly, the amount of bulk water that makes it past your WRB can be managed as vapor (drying).
Peter
I agree with the other posts, I think the best alleviation to your concern is to not tape the bottom to allow for drainage.
Otherwise, staple the Tyvek in vertical passes, then run a long stretch of tape over them. I do that, it's not hard nor is it a big deal.
The hardest part (if you're not doing the work) is asking your framers the arduous task of stapling somewhat neatly instead of like a kid with a crayon. They will whine like a kid as well.
Another thing to remember is that Tyvek installation instructions require cap-nails or cap-staples. Regular staples can only be used at the corners for temporary support during installation.
You have to draw the line somewhere. Do you plan for water to get behind the sheathing? Do you plan for water to get the drywall wet? Do you plan for water to drip down through your ceiling? The WRB is the line that's drawn where we decide that that's the last line of defense against water. If water gets past that in any substantial quantity, it's going to be a problem. That's why it's so important to detail it correctly.
Um. If we're going to use Tyvek as temporary cladding material, as is often the case on the jobsite?
Why don't they alleviate this concern entirely and use Tyvek in a lapped fashion so that you can't actually see any staples from the outside? After you tape down the flaps there would be zero penetrations (before you put the final cladding on).