Author Topic: Horizontal sheathing seam blocking code req  (Read 574 times)

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Offline Naildrivingman

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Horizontal sheathing seam blocking code req
« on: March 26, 2020, 06:54 PM »
I can’t seem to locate the answer to this in the IRC. I am located in MN, so I believe we are relatively low on the seismic reaction spectrum.

Does anyone know when/where/if blocking of seams is required?

Thanks,
Chris
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Offline Peter Halle

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Re: Horizontal sheathing seam blocking code req
« Reply #1 on: March 26, 2020, 07:22 PM »
I might suggest some explanation  of your situation for better responses.

Respectfully.

Peter

Offline Naildrivingman

  • Posts: 504
Re: Horizontal sheathing seam blocking code req
« Reply #2 on: March 26, 2020, 07:49 PM »
I might suggest some explanation  of your situation for better responses.

Respectfully.

Peter
I’m doing a project that requires moving of window openings. I will be unable to span from plate to plate with vertically installed sheathing.  Therefore, I will have horizontal seams where the old openings were. Just blocking these seams isn’t such a big deal (25-30 total).  what is a big deal is blocking all the other seams of this 1990s addition that weren’t blocked by that builder (75-100 additional to the above). 

I feel that if I block my seams, I’ll have to block the other guy’s, too.  If I block nothing, possibly I’ll get by or at the least have to block only mine. The way I interpret the code is that I’m not required to block the seams, but some are telling me I have to. Very confused.

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Online Bob D.

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Re: Horizontal sheathing seam blocking code req
« Reply #3 on: March 26, 2020, 07:59 PM »
You (actually the HO, unless that's you) might be required to bring the rest of the structure up to current code IF over a certain percentage of the structure is being remodeled/altered. So it may be that even though when the house was built it met the code in affect at the time it may be now that all those horizontal seams will need to be blocked to be in compliance with current code.

Grandfathering can be nullified(lost) if a significant percentage of the structure if altered. Varies by state so best to check with the AHJ to know what they want to see.
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Offline DeformedTree

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Re: Horizontal sheathing seam blocking code req
« Reply #4 on: March 26, 2020, 08:51 PM »
You don't block those (or you don't have to), your sheathing runs horizontal (cross studs, not parallel to studs).  If you run it with the studs as you are describing you will see some buckling in the plywood and you reduce the ability of the plywood to brace the wall.  The blocking you talk of would also be another thermal bridge. (unless your put it flat to the outside (you need to notch insulation around it).

Now you definitely should go and seal/tape those seams as a level of air sealing, but also you should have house wrap going over the exterior too, sealed back to the existing house wrap, and wrapped into the new window opening.

Offline Naildrivingman

  • Posts: 504
Re: Horizontal sheathing seam blocking code req
« Reply #5 on: March 26, 2020, 08:53 PM »
You (actually the HO, unless that's you) might be required to bring the rest of the structure up to current code IF over a certain percentage of the structure is being remodeled/altered. So it may be that even though when the house was built it met the code in affect at the time it may be now that all those horizontal seams will need to be blocked to be in compliance with current code.

Grandfathering can be nullified(lost) if a significant percentage of the structure if altered. Varies by state so best to check with the AHJ to know what they want to see.
I’m not opposed to doing the right thing.  Unfortunately with the current health situation, getting answers from inspectors is nearly impossible. I realize the “and other” situation could apply to my work “and other”.  Basically if I don’t have to block the seams, great.  If I do, well, marshal on.

The resolution as to whether I have to or not, may take longer than simply doing the work. I’m hopeful that someone who reads this can help me interpret section 602 of the IRC.
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Offline Brush

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Re: Horizontal sheathing seam blocking code req
« Reply #6 on: March 26, 2020, 09:04 PM »
I'm in Michigan and here our wind speed requires a greater amount of braced wall then the seismic does.  With that said you're only required to block horizontal joints if its counted as a braced wall panel (R602.10.10).

Offline Naildrivingman

  • Posts: 504
Re: Horizontal sheathing seam blocking code req
« Reply #7 on: March 26, 2020, 09:15 PM »
You don't block those (or you don't have to), your sheathing runs horizontal (cross studs, not parallel to studs).  If you run it with the studs as you are describing you will see some buckling in the plywood and you reduce the ability of the plywood to brace the wall.  The blocking you talk of would also be another thermal bridge. (unless your put it flat to the outside (you need to notch insulation around it).

Now you definitely should go and seal/tape those seams as a level of air sealing, but also you should have house wrap going over the exterior too, sealed back to the existing house wrap, and wrapped into the new window opening.
The 1990s has 8’ ceilings below and 10’6” ceilings above.  The stories are separated by 2’ tall floor trusses.  The builder vertically installed 9’ OSB about halfway up the truss from the mud sill below, then continued up the sidewall, so the existing upper horizontal seam is about 3’ down from the top plate.  The addition is 40’ long with a vaulted gable end at 18’, so I have more seams at about the 15’ level on the gable end.

I am removing 6 windows and their corresponding framing, in-filling new king studs and creating 10 new openings.  Therefore I will have my own horizontal seams to deal with.

@DeformedTree I believe you are saying that turning sheets perpendicular to the studs is stronger than vertical.  This is what I was taught and the way I did it until I started working for a guy in the early 2000s.  At that time, 10’ tall sheathing had been introduced in addition to 9’ tall.  From that point on, I never ran my sheets perpendicular to studs again.  I’m sure I’ve built something with horizontal seams in the last 20 years, but honestly I can’t remember an inspector ever calling me out about it.

Bottom line is I don’t have a lot of discretionary money in this one.  If I have to block all the seams, I will have to eat the associated costs of that work. Not high on my list of fun things to do.
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Offline Naildrivingman

  • Posts: 504
Re: Horizontal sheathing seam blocking code req
« Reply #8 on: March 26, 2020, 09:19 PM »
I'm in Michigan and here our wind speed requires a greater amount of braced wall then the seismic does.  With that said you're only required to block horizontal joints if its counted as a braced wall panel (R602.10.10).
@Brush thanks for your reply.  This is where I get confused.  I can’t make heads or tails of what constitutes a braced wall panel. I’ll go back and study that section again.

I’m kinda embarrassed, because after nearly 30 years in residential remodeling, I should know all these issues, but I don’t.  Thanks for your patience.
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Offline Brush

  • Posts: 8
Re: Horizontal sheathing seam blocking code req
« Reply #9 on: March 26, 2020, 09:54 PM »
I'm in Michigan and here our wind speed requires a greater amount of braced wall then the seismic does.  With that said you're only required to block horizontal joints if its counted as a braced wall panel (R602.10.10).
@Brush thanks for your reply.  This is where I get confused.  I can’t make heads or tails of what constitutes a braced wall panel. I’ll go back and study that section again.

I’m kinda embarrassed, because after nearly 30 years in residential remodeling, I should know all these issues, but I don’t.  Thanks for your patience.

Its a bit confusing, but a braced wall panel is just a section of wall that is braced.  I believe there is a minimum amount of braced wall for each wall line, don't remember off the top of my head and I put my book away.  The section covers a handful of different ways to create a braced wall panel with different materials and nailing schedules, we mostly use continuous sheathing.  Your wind and seismic requirements determines the maximum spacing and the length of braced wall panel per wall line.

Offline Naildrivingman

  • Posts: 504
Re: Horizontal sheathing seam blocking code req
« Reply #10 on: March 28, 2020, 08:38 PM »
I got the answer (more or less).  The inspector for my project told me that the code doesn’t enforce blocking of horizontal seams unless it is a seam that occurs in a wall that is less than 4’ wide (ie single car garage with narrow walls adjacent to the OHD would be an example of a braced wall and therefore required) or if an engineer/architect calls out specific construction.

In my case, these walls don’t classify as braced walls, so technically no blocking is required by code.  However, sheathing manufacturers require specific panel nailing for minimum shear strength. Generally, panel nailing requires one fastener every six inches and if there is a horizontal seam, meeting that requirement is not possible, therefore a block is required to meet this requirement.

Long story short, if you have an exposed seam, install a block. It’s cheap and easy when done at framing.

Thanks for all input.
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