Thread: Sheathing Flashing

When using Tyvek over OSB sheathing are you still required to install flashing at the OSB horizontal butt joints?

Sorry, this is my Socratic day.

Similar Threads:

• Jack flashing shingles at edges.
• Skylight flashing new construction
• Fastener type for flashing
• Roof flashing
• Chimney Flashing

This poor question is still languishing after 35 lookers!

Originally Posted by A.D. Miller

This poor question is still languishing after 35 lookers!

I guess that means no one knows the answer.

The question becomes, does OSB require that horizontal flashing you are referring to when not covered with a WRB?

And when you you NOT use a WRB?

Originally Posted by A.D. Miller

When using Tyvek over OSB sheathing are you still required to install flashing at the OSB horizontal butt joints?

Sorry, this is my Socratic day.

Flashing and Tyvek perform two differant jobs. I guess it would all depend on the location of the joints.

What no siding? unless your OSB is exposed, which would be a bad thing, why would you need to flash the horizontal joints?

This building will be clad with stone veneer and Portland cement stucco.

Originally Posted by Scott Patterson

Flashing and Tyvek perform two differant jobs. I guess it would all depend on the location of the joints.

SP: Very true. Tyvek, which is not a favorite product of mine anyway, is not a vapor barrier. It allows moisture to pass through it. How then they can hawk this as a "secondary water barrier" is so much smoke and mirrors to me.

I say the poly flashing must be on the OSB horizontal joints with or without the Tyvek.

When there is a WRB installed over OSB sheathing, I can't think of any reason why flashing would need to be installed behind the WRB. The drainage plane will be (should be?) outside the OSB. I can't say I've ever seen any install instructions showing flashing installed behind the WRB on the horizontal sheathing joints, nor can I think of any reason it would do any good. I didn't answer originally, because I was not sure I understood the question.

Originally Posted by Brandon Whitmore

When there is a WRB installed over OSB sheathing, I can't think of any reason why flashing would need to be installed behind the WRB. The drainage plane will be (should be?) outside the OSB. I can't say I've ever seen any install instructions showing flashing installed behind the WRB on the horizontal sheathing joints, nor can I think of any reason it would do any good. I didn't answer originally, because I was not sure I understood the question.

BW: In my service area AHJs require that 6-mil ploy flashing be installed as a flashing material at all horizontal OSB sheathing butt joints. The question is why would the installation of a house wrap, which is not a vapor barrier, obviate the builder's responsibility to install the OSB flashing?

Originally Posted by A.D. Miller

I say the poly flashing must be on the OSB horizontal joints with or without the Tyvek.

Now we are getting to the crux of the question: *YOU* say that there must be a flashing on the horizontal joints - Why do you say that?

Back documentation please, not just "feel good" thoughts.

BW: In my service area AHJs require that 6-mil ploy flashing be installed as a flashing material at all horizontal OSB sheathing butt joints.

Hi Aaron,

I've never heard of that before. Did they require this back before WRB's became commonly required? I'm wondering if it's something that used to be required, and they still roll with it. Question is, what purpose does it serve when a WRB is installed?

Do you have any literature I can read up on regarding this installation? I'm quite curious. Are the local AHJ's citing code, or is this a local requirement only?

Say water leaks in behind the WRB, and the flashing prevents the water from seeping in at the horizontal OSB seams. Will the wall sheathing not rot out whether or not flashing is installed at the horizontal OSB joints?

Originally Posted by A.D. Miller

BW: In my service area AHJs require that 6-mil ploy flashing be installed as a flashing material at all horizontal OSB sheathing butt joints. The question is why would the installation of a house wrap, which is not a vapor barrier, obviate the builder's responsibility to install the OSB flashing?

The question really becomes three things:

1) Why do the AHJ in your area require that - what code, listing, installation instructions, etc., are they basing that on?

2) Why would you install a flashing behind a WRB?

3) Under what installation conditions would the OSB be the exposed layer (talking about regular OSB here ... there are several OSB products out which - not my words, theirs and their listing - *do not require* a WRB over them, and those installations *DO* require the flashing you are speaking of, but for regular OSB which is not going to be left exposed ... why?).

I think your AHJ have looked at and read those product installation requirements and have gotten confused, applying the requirements for OSB with a treated surface which is supposed to be the WRB (I don't buy that, but that is what they are listed as) and which ALL joints, both vertical AND horizontal are to be sealed with tape flashing ... the AHJ are applying those requirements to regular OSB, and you are following them down that road.

Originally Posted by A.D. Miller

SP: Very true. Tyvek, which is not a favorite product of mine anyway, is not a vapor barrier. It allows moisture to pass through it. How then they can hawk this as a "secondary water barrier" is so much smoke and mirrors to me.

Aaron,

You need to stop, take a deep breath ... hold it ... hold it ... hold it ... now slowly ... I said slowly ... release it.

Now go back and re-read and think about what you just wrote.

You are talking about:
1) vapor barriers
2) water barriers
3) moisture barriers

And EACH of those has difference uses and different properties.

First and foremost, Tyvek is not, and is not intended to be, a "vapor barrier". It is a "water barrier" to an extent.

6 mill plastic sheeting is a vapor barrier, moisture barrier, and water barrier, of course, though, the vapor, moisture and water trapped on each side WILL condense on it, so it has its limitations of use too.

You DO NOT WANT a "vapor barrier" to be wrapped around the house. Do you realize what that would do to the interior environment? O-M-G YUCK!

You need to stop, take a deep breath ... hold it ... hold it ... hold it ... now slowly ... I said slowly ... release it.

Dr. JP: If you were not so concerned with providing a therapy session for me you would read my posts and see that I am not advocating vapor barrier installation on exterior walls, but only a vapor barrier material to serve as a flashing at OSB butt joints.

Originally Posted by A.D. Miller

Dr. JP: If you were not so concerned with providing a therapy session for me you would read my posts and see that I am not advocating vapor barrier installation on exterior walls, but only a vapor barrier material to serve as a flashing at OSB butt joints.

Aaron,

And if you were not so in need of that therapy session you would have realized that what you just posted proved you have not read, or at least not understood, what is being asked.

"but only a vapor barrier material to serve as a flashing at OSB butt joints."

Why?

Why would you do that?

Why would you need that?

Why would you even consider that?

Why oh why?

Originally Posted by Jerry Peck

I guess that means no one knows the answer.

Or we are all out on jobs....

Originally Posted by A.D. Miller

This poor question is still languishing after 35 lookers!

Originally Posted by Dom D'Agostino

Or we are all out on jobs....

My guess is not because they READ the post. If they were out on job and knew the answer I would expect the answer to have been posted.

Oh, that's right, there are some who know the answer but do not post, waiting for someone else to post so they can comment on that post.

Keep up the good work, Dom.

Originally Posted by Jerry Peck

Keep up the good work, Dom.

Sorry, I forgot the obligatory "smile icon" in my first post. It was meant as a light hearted jab.

But thanks anyway...