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Weather Resistant Barriers


Bryan
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In Indiana a majority of the state is still under the 2003 IRC with Indiana amendments. With that, and if I am reading the code correctly, the use of a weather resistant membrane is not required under most exterior finishes. However, a weather resistant membrane or water repellent sheeting is required under masonry veneer.

On a large number of the new homes in our area they are using foam insulation board for the exterior sheeting (water repellent sheeting). Therefore, how does one go about properly detailing wall penetrations and windows? I typically see 4 inch butyl flashing tape used around the window; however, it is just adhered to the foam board. I am of the opinion that the tape will fail much sooner than later and then you have a leaky window, door or wall penetration. Additionally, this same theory can be said about all horizontal sheathing joints that have been taped.

I have seen somewhere; however can't remember where, where the sheathing board should have a "Z" type flashing at all horizontal joints. This could be as simple as a piece of house wrap tucked under the upper board and draped to the exterior side of the sheet beneath. Should this same principle be utilized at all windows, doors and wall penetrations?

Bryan

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Most mfg's. want to see a membrane pan under the window with an interior dam, and drip caps or other flashing over the window, similar to (or the same as) under an exterior door.

The pan should extend out over whatever sheathing is applied, so I figure that must include foam board.

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Most mfg's. want to see a membrane pan under the window with an interior dam, and drip caps or other flashing over the window, similar to (or the same as) under an exterior door.

The pan should extend out over whatever sheathing is applied, so I figure that must include foam board.

Very true. Let me phase it a different way. How do you flash the head of a window or door when there is nothing to lap over the head flashing? The same would go for a pipe penetration.

Bryan

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Here is a photo of a through wall penetration that is not flashed or sealed to the exterior sheathing. What really has me intrigued about this is there was a dark spot on the floor below the clothes dryer that started at the band board and went inward. The spot tested about slightly wetter than the surrounding sub-floor materials.

The homeowners, for whom I am working, indicated that the washer has never overflowed, and the stain is adjacent to the washer, not below it. What I am speculating is happening is moisture is penetrating the masonry veneer, running down the back side of the veneer or the sheathing, following the dryer vent into the wall cavity, then sinking to the sub-floor.

Given the visible penetration of the HVAC exhaust it appears that exterior wall penetrations were not sealed to the water resistant sheeting. Also if you look at the photo you can see where water has made its way in at the HVAC exhaust.

Bryan

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Very true. Let me phase it a different way. How do you flash the head of a window or door when there is nothing to lap over the head flashing? The same would go for a pipe penetration.

I have no idea what the manufacturers require, but I would let in flashing above windows, etc. With pipe penetrations, I would make sure that there is a trim block at all penetrations and let in flashing there as well.

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Very true. Let me phase it a different way. How do you flash the head of a window or door when there is nothing to lap over the head flashing? The same would go for a pipe penetration.

I have no idea what the manufacturers require, but I would let in flashing above windows, etc. With pipe penetrations, I would make sure that there is a trim block at all penetrations and let in flashing there as well.

When you say "let in" are you referring to extending the flashing to the interior side of the sheathing? Cause that is the only way I see to keep the water out of the wall assembly.

Bryan

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When you say "let in" are you referring to extending the flashing to the interior side of the sheathing?

Depends on how thick the foam board is. You could run flashing all the way behind the foam, or just cut grooves part way into the foam.

I'm surprised that they are using sheathing on all of the walls. In this area, if they build with something like Dow foam board, they don't have sheathing behind it.

Of course, a WRB over the foam board with conventional flashings is a better approach in my opinion, and may be recommended by the foam board manufacturer. It's been a while since I've studied up on this foam board stuff-- they don't use it much around these parts.

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When you say "let in" are you referring to extending the flashing to the interior side of the sheathing?

I'm surprised that they are using sheathing on all of the walls. In this area, if they build with something like Dow foam board, they don't have sheathing behind it.

I may have miss used the sheathing term for there is no structural panels on the exterior of the house, only foam board.

Bryan

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Maybe I missed it, but what's the cladding? They can't be using foam panels for the cladding.

Exterior is full brick with lap siding above. If you look at the photo I posted above you can see the back side of the masonry. That along is what got me thinking about this.

Bryan

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Well, if it's at the brick, there should be full through wall flashing above and below the windows with end dams, weeps, and wicks, with the flashing lapped out over the foam.

If it's at the siding, the pan flashing should be detailed into the WRB and over the foam, w/a drip cap over the window detailed via shingling into the WRB.

I think that's it, but unless I saw a better picture, I'm not absolutely sure what the correct method would be.

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Well, if it's at the brick, there should be full through wall flashing above and below the windows with end dams, weeps, and wicks, with the flashing lapped out over the foam.

If it's at the siding, the pan flashing should be detailed into the WRB and over the foam, w/a drip cap over the window detailed via shingling into the WRB.

I think that's it, but unless I saw a better picture, I'm not absolutely sure what the correct method would be.

That is where I am having the challenge. How does one install flashing for a window, door, or other penetration in a shingle fashion when the sheathing is your WRB? The only way I can see it being done is to cut through the foam board and install a "Z" type flashing to cap off the flashing detail. Currently around here builders are relying on self adhering flashing tapes to do the job; however, my personal opinion is the tape will fail much sooner than later especially on the horizontal details.

Bryan

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Well, if it's at the brick, there should be full through wall flashing above and below the windows with end dams, weeps, and wicks, with the flashing lapped out over the foam.

If it's at the siding, the pan flashing should be detailed into the WRB and over the foam, w/a drip cap over the window detailed via shingling into the WRB.

I think that's it, but unless I saw a better picture, I'm not absolutely sure what the correct method would be.

That is where I am having the challenge. How does one install flashing for a window, door, or other penetration in a shingle fashion when the sheathing is your WRB? The only way I can see it being done is to cut through the foam board and install a "Z" type flashing to cap off the flashing detail. Currently around here builders are relying on self adhering flashing tapes to do the job; however, my personal opinion is the tape will fail much sooner than later especially on the horizontal details.

Bryan

What ever could you mean?

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Hi,

Well, I'd never seen the stuff before so I googled "Structural Insulated Sheathing." Man, this stuff is being pushed by Dr. Joe and PATH and a bunch of folks. Apparently, Dr. Joe tested the stuff in a test home for at least a year before he endorsed it.

Here's some helpful links:

The Dow Structural Insulated Sheathing home page

The Dow SIS installation instruction page

The ICC Evaluation Service Code Report (Shows some flashing details).

The Build A Better Home - Avoiding Moisture Accumulation in Walls instructions (Referenced by P.A.T.H. as being the proper technique for weatherproofing and flashing walls where SIS is used - wherever the diagrams show "structural sheathing" just substitute SIS.)

Enjoy.

ONE TEAM - ONE FIGHT!!!

Mike

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I've never seen it either.

Why wouldn't one detail the flashing into the foam board in the same manner as they would any other WRB? It's thicker, but it's still the WRB, right?

It would mean Z flashing instead of tape, and I'd probably want a good sheet metal guy on site to customize channel in whatever profile was necessary.

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Tape was never intended to replace flashing details, it was meant to be used in addition to proper flashing. Another best practice thing that is misused and misunderstood. I don't see any problems with structural foam sheathing, but there still needs to be a WRB and proper flashing systems. They're inter-dependant not inter-changable.

Tom

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No one said they were.

Tape is the required means for sealing WRB, i.e., Tyvek, in all sorts of applications. Tape is good when used as designed.

Peel and stick is just fine for door pans, if one knows how to install peel and stick door pans. Sure, I have my guy solder up copper pans for some jobs, but some jobs can't afford copper pans. For all practical and useful purpose, peel and stick is tape and flashing, no?

If I'm reading the mfg's. stuff correctly, the SIS can be the WRB. It doesn't say you have to use housewrap over the SIS (clearly stated as "optional"), and they also indicate you have to tape the seams with Weathermate, the same stuff that goes on housewrap. Meaning, tape is part of the WRB, therefore it has to be detailed into flashing.

So, I'm not sure your statement is correct.

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If the foam is intended to be the WRB then why does Dow manufacture a house wrap? This is no different than any other discussion about the differences between minimum standards and best practice. When there are builders out there that still think that nailing flanges are adequate flashings, a sheathing material that functions as a WRB is an invitation to disaster. If I were going to build new I'd be looking at advanced framing and SIS, but ther would be appropriate flashings and a WRB in the wall system too. Far less costly than detailing windows and doors to the back side of the sheathing, which is a concept that will escape the grasp of most builders out there.

Tom

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I think the real challenge is keeping the flashing properly shingled into and behind the WRB when utilizing foam board. Yes the easiest way would be to do a layer of house wrap on the exterior; however, it is additional cost and we all know that will not happen.

I also found this detail on BSC web site. It shows utilizing "tape" to seal the flashing to the foam board. In my opinion this still creates a reverse shingle flashing application that will fail over time.

Bryan

Download Attachment: icon_word.gif WindowFlashingdetail.doc

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I think the real challenge is keeping the flashing properly shingled into and behind the WRB when utilizing foam board. Yes the easiest way would be to do a layer of house wrap on the exterior; however, it is additional cost and we all know that will not happen.

I also found this detail on BSC web site. It shows utilizing "tape" to seal the flashing to the foam board. In my opinion this still creates a reverse shingle flashing application that will fail over time.

Bryan

Download Attachment: icon_word.gif WindowFlashingdetail.doc

83.38 KB

I guess you didn't read what I'd posted very carefully; Joe Lstiburek is endorsing this method and has tested it.

Going up against an opinion of Dr. Joe's is a pretty risky thing to do in my opinion. They guy lives and breathes for building envelope challenges.

ONE TEAM - ONE FIGHT!!!

Mike

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