General Question on Flashing
Last Post 27 Oct 2013 09:59 AM by FBBP. 12 Replies.
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joe bobUser is Offline
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20 Oct 2013 01:31 PM
Hey All, My name is Joe Martino and I am a student at the Evergreen State College. I have been working to develop plans for a hybrid solar aquaponics greenhouse, and managed to obtain a permit two weeks ago. As a student, I do lack some basic understandings on the location of certain elements. The N wall of the structure sits about 3' from the exterior of a dorm building, and the county official has asked that that wall become a 2-hr fire wall. How do I set the flashing between the concrete and wall for this? If the layering from the studs to the exterior works as such; 15/32 ply, house wrap, two layers of 5/8ths green board, and finally a 5/8ths layer of lap siding, will I want to place the flashing between the studs and the ply, have it run out below the other layers so they are protected from rain splashing up, then caulking the joint? I just want to try to stop the greenboard from getting wet and wicking into the studs and insulation. Thanks all! Joe


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20 Oct 2013 06:40 PM
Posted By joe bob on 20 Oct 2013 01:31 PM
Hey All, My name is Joe Martino and I am a student at the Evergreen State College. I have been working to develop plans for a hybrid solar aquaponics greenhouse, and managed to obtain a permit two weeks ago. As a student, I do lack some basic understandings on the location of certain elements. The N wall of the structure sits about 3' from the exterior of a dorm building, and the county official has asked that that wall become a 2-hr fire wall. How do I set the flashing between the concrete and wall for this? If the layering from the studs to the exterior works as such; 15/32 ply, house wrap, two layers of 5/8ths green board, and finally a 5/8ths layer of lap siding, will I want to place the flashing between the studs and the ply, have it run out below the other layers so they are protected from rain splashing up, then caulking the joint? I just want to try to stop the greenboard from getting wet and wicking into the studs and insulation. Thanks all! Joe



a posted sketch (cross section) would be beneficial instead of a verbal description,
what is you 2 hour wall made of?


Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br />
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21 Oct 2013 02:53 PM
Joe Bob - assuming the two layers of green board are your fire rating.

The lap siding is designed to handle the majority of the moisture coming at the wall from outside. The house wrap and flashings are the true water barrier.
As such your stack up should be studs, sheathing, rated drywall, house wrap and flashings, 1/2" air gap and then siding.

The house wrap and flashing must be installed such that they always over lap from the top down, i,e, the higher material always is outside the lower. When the house wrap and flashing are in place and before strapping and cladding, you should be able to run a hose at the top of the wall and at no time should water be able to migrate into the wall on its way down.

Then install the strapping to provide the airspace, then the siding.

Install cor-a-vent (or similar material) at top and bottom to prevent insects from entering the venting gap.


joe bobUser is Offline
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21 Oct 2013 11:26 PM
Hey All! Here are the pictures. Firewall is the green board. 2 layers of 5/8ths. The main question is, where does the flashing go? More importantly, in my mind, how do I ensure that the flashing protects the bottom of the green board in such a way that it doesn't get wet due to water splashing back up, then wicking into the wall? Our thought was to install it behind the sheathing, then caulk it where it meets the lap siding so that it runs underneath all exterior components, and doesn't allow water to run back up and around itself into the green board. Check sketch 2 for an idea of what that looks like. ThingofBeauty, you may have a point, but again, until we're all clear on what I'm askin', I gotta wait. Also, house wrap or felt? Again, I do appreciate everyone's time, and your responses. Looking forward to hearing back sirs. Thank you. Sincerely, Joe "Bob" Martino

Attachment: Flashing.pdf

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22 Oct 2013 05:44 AM
Posted By joe bob on 21 Oct 2013 11:26 PM
Hey All! Here are the pictures. Firewall is the green board. 2 layers of 5/8ths. The main question is, where does the flashing go? More importantly, in my mind, how do I ensure that the flashing protects the bottom of the green board in such a way that it doesn't get wet due to water splashing back up, then wicking into the wall? Our thought was to install it behind the sheathing, then caulk it where it meets the lap siding so that it runs underneath all exterior components, and doesn't allow water to run back up and around itself into the green board. Check sketch 2 for an idea of what that looks like. ThingofBeauty, you may have a point, but again, until we're all clear on what I'm askin', I gotta wait. Also, house wrap or felt? Again, I do appreciate everyone's time, and your responses. Looking forward to hearing back sirs. Thank you. Sincerely, Joe "Bob" Martino



Bob,
1. as shown the green board will wick as the bottom edge is not protected
2. Green board is for interior use and is not even allowed in our loacation even for interior use.
3. Unless you have a tested and approved 2 hour rating for that assembly?, the building official may not let you use it. I have not seen a 2 hour rating set up in that fashion


Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br />
joe bobUser is Offline
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22 Oct 2013 11:36 AM
You may be correct about the greenboard however the cbo in my county suggested and permitted that design. also, were you able to look at image 2? it looks like its gunna be fine because the flashing runs under the greenboard, and we caulk where the flashing finally meets with the lap siding.

let me know what the thoughts are.


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26 Oct 2013 04:56 PM
Posted By joe bob on 22 Oct 2013 11:36 AM
You may be correct about the greenboard however the cbo in my county suggested and permitted that design. also, were you able to look at image 2? it looks like its gunna be fine because the flashing runs under the greenboard, and we caulk where the flashing finally meets with the lap siding.

let me know what the thoughts are.



The flashing and tyvek should be over the green board to protect it, you may want to consider exterior gypsum sheathing that is made to be used outside
regardless, your flashing is in the wrong place


Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br />
joe bobUser is Offline
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26 Oct 2013 06:43 PM
kavala, we will work to replace the greenboard. however i do have a concern that if the flashing is on the outside of it, there wont be anything underneath to protect it from water splashing back up. does that make any sense or am i just imagining something different from what your telling me? thanks for the responses, they have been helpful.


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26 Oct 2013 07:02 PM
Posted By joe bob on 26 Oct 2013 06:43 PM
kavala, we will work to replace the greenboard. however i do have a concern that if the flashing is on the outside of it, there wont be anything underneath to protect it from water splashing back up. does that make any sense or am i just imagining something different from what your telling me? thanks for the responses, they have been helpful.



I am not sure what you are thinking? but the you basically have three layers of sheathing , flashing always goes over the wall sheathing, then gets covered with felt / tyvek over the top edge of flashing, then finally with siding/cladding,
if you have the flashing behind any of the layers of sheathing then the bottom edge is susceptible to water/ moisture wicking at the bottom edge


Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br />
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27 Oct 2013 01:19 AM
bob - just have a J trim made up for the two layers of drywall and slip it over them prior to mounting the flashing where it belongs on the outside.


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27 Oct 2013 07:44 AM
Posted By FBBP on 27 Oct 2013 01:19 AM
bob - just have a J trim made up for the two layers of drywall and slip it over them prior to mounting the flashing where it belongs on the outside.




Why not do it right the first time?


Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br />
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27 Oct 2013 08:03 AM
there are plenty of do's and do not's examples on the web


Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br />
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27 Oct 2013 09:59 AM
Chris - OP's wall is wood to a stem wall. This puts the drywall out overlapping the concrete. His thought was to put the flashing before the drywall so that the flashing would cover the bottom of the drywall protecting it from ground splash. Of course, that is the incorrect location for the rainscreen. So put the rain screen behind the lap siding where it belongs and install an independent flashing to protect the drywall.

And yes, he would be much better off using an exterior grade type X or C drywall.


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