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Old 08-25-2009, 08:12 PM   #1
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someone who is pretty knowlegdable about IRC see if you can tell me when you need to acount for sheer wall protection. My inspector is making me run my garage header from wall to wall, and put 1000 lb straps at either end of the garage opening. My walls on either end of the garage wall are just over 2 feet long. Can someone explain to me what circumstance and why I need this protection?

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Old 08-25-2009, 08:25 PM   #2
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He's right on. The garage wall with the door has more opening than it has sheathing, so it is unable to resist shear forces like a wall with less openings (the code is 25% openings or less). The header moves lateral forces across the opening. Making it full length and fastening the heck out of it to the sheathing allows the short portal walls on either side of the door to act as shear collectors to get the lateral loads managed. The hold-down straps are required to anchor the wall to the foundation because simple 1/2" anchor bolts won't resist the moment (overturning) forces.

The code actually diagrams this. Sheathing layout and nail pattern are very critical as well.

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Old 08-25-2009, 08:31 PM   #3
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ok, my walls are onle 2 feet 2 in on either side. So even if my walls were seven feet on either side I would still need shear protection? At what length of wall do I not need the header to travel the whole length of the garage. Others in my office are giving conflicting information, stating that since the walls are over 2 feet that code does not require the protection.
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Old 08-25-2009, 09:00 PM   #4
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I'm not a carpenter, or a code official by any means, but I sat thru HOURS of lecture on shear walls as part of my continuing education credits for licensing. (And I thought I would never use this stuff!)

From what I recall, the inspector is requiring you to install a "Portal Header" above th egarage door. There are many variable that contribute to sheer wall requirements, including:
Total wall height.
Actual clear height of door opening.
Aspect ratio of sheer wall width : height.
Wall sheathing used.
Total wall area sheathing : openings.
And, I'm sure there's many other variables.

From what I recall in the UDC (may be similar to IRC sheer codes?) code that we use here, there is an exception for garage walls at OH doors, which allows a 4:1 aspect ratio. That means if your wall is 2 feet wide, your wall can be no higher than 8 feet total, without additional requirements, such as the hold downs & portal header your inspector mentioned.

In all honesty, the shear wall codes are somewhat complicted & require a lot of detail to understand completly. For that very reason, you are normally required to submit a shear wall plan before obtaining a permit, at least in my area. The intent is to get the archis/designers/engineers to do the detail end of the shear walls, leaving a clear & simple plan for those "constructing" in the field to follow. With that being said, if KC has dealt with these codes for years (as I assume he has), he should be able to answer any of your questions if given more detail. Good Luck.
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Old 08-25-2009, 10:07 PM   #5
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I don't have a 2006 code book handy but here's the applicable section that you can check from the 2003.
R602.10.6
The 2006 goes a lot more in depth on this. I can't summarize three pages of code much better than I already did.

The scope of the '03 code only recognizes walls in excess of 2'8" for alternate braced panel designs, which this is. In our area the prescriptive code is rarely met and therefore most jurisdictions require an alternate braced panel engineered design as part of the plan. Some cities provide their own prescriptive design. From your description of his requirements, your inspector's requirements are actually not even as strict as the 2003 code which requires 1800lb hold downs. The '06 made it even tougher.

The only information that matters is what is required locally in your area, and what (if anything) your designer put on your plan. These things vary quite a bit depending on the structure itself, the seismic design category you're in, etc.

Your home resists incredible lateral loads in even moderate wind events. The garage wall is a major weak point in most homes. Many people don't have an understanding of the forces at work in a 50mph gust, let alone sustained peripheral winds of a tornado or hurricane. Wall bracing works to save the structure...We as codes officials saw proof of that in hurricane Katrina.
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Old 08-25-2009, 10:11 PM   #6
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Here's what a google search yielded. Maricopa County AZ's design....Right in line with the modern IRC code aside from the hold-downs...Good diagram!
http://www.mag.maricopa.gov/pdf/cms....acing21659.pdf

Its an APA design FOR ONE STORY STRUCTURES ONLY and that is what a lot of engineers and jurisdictions are using. Two story designs usually require hold-downs and are more dimensionally restrictive.
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Old 08-25-2009, 11:01 PM   #7
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OR... you could take some of the gold bullion you have stashed away and buy a couple of these: http://www.strongtie.com/products/st...age-portal.asp
Be safe, G
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Old 08-26-2009, 09:19 AM   #8
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I truly hope a lot of folks see this thread, and walk away realizing that there really is a lot more to building a structure than 2x4 stud framing. I run into so many people (homeowners and "contractors" alike) that look at me like I have a horn growing out of my forehead when I try to explain what they really need to be doing.

Nice thread.
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Old 08-26-2009, 02:07 PM   #9
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Quote:
Originally Posted by Aggie67 View Post
I truly hope a lot of folks see this thread, and walk away realizing that there really is a lot more to building a structure than 2x4 stud framing. I run into so many people (homeowners and "contractors" alike) that look at me like I have a horn growing out of my forehead when I try to explain what they really need to be doing.

Nice thread.

Agreed -

I built a relatively simple 24x30 workshop a few years ago here in SoCal, did the shear walls - anchors, bolts, nailing, etc. Was an excellent education. The city inspector folks were a huge help along the way.

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