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Diagonal Bracing: Does it matter later?

A

Amish Electrici

Bronze Member
Joined
Apr 24, 2012
Messages
39
As I get into the remodel of my well-worn home, I find a board in an inconvenient place. Let me explain....

1957 single-floor ranch, with 2x4 studs and 5/4x8 plank sheathing. At the corners of the house, set into notches in the framing, are 5/4x8 boards set at perhaps a 45 degree angle.

I can see how these braces would 'square' the wall during assembly, but I am not sure whether they add anything once the sheathing boards were added; I would think the sheathing can't help but add a lot of shear strength to the wall.

So, here's the question: Is one allowed to simply cut away any offending parts of this diagonal brace... or should other bracing be provided?

[it is my intent to instal an air conditioner in that location. I am also looking into alternate locations for the A/C]
 
Initial answer would be no.

Your wind and seismic zones would determine the amount of shear bracing required. Seimic zone "D" does not permit diagonal bracing.

The 5/4X8 boards may not provide adequate shear

If you can provide your wind, and seismic loads maybe some one else would have a more input
 
Diagonal let-in-bracing is not very effective. If this is what is resisting lateral loads you may have a problem.

Straight sheathing is not much better but if there is enough of it might be better. Diagonal sheathing could be fairly decent. Preferred is plywood or OSB sheathing.
 
The effectiveness of diagonal bracing varies.

Diagonal bracing is very effective in preventing the twisting of frames in both wood and steel framing.

As stated by mtlogcabin

Your wind and seismic zones would determine the amount of shear (lateral) bracing required. Seimic zone "D or E" does not permit diagonal bracing.

Is it as effective as solid sheathing, No.

Is it effective in your ranch house, Maybe, wedon't have enough information.
 
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Diagonal let in bracing has been an affective means of bracing houses for hundreds of years or longer. Please don't sell it short. Even modern timberframes use similar methods. Find another place for the HVAC.
 
I chose the route of caution, though it appears to me that this let-in bracing was intended only to keep the walls square while they were assembled - rather than to provide any wind or seismic resistance.

In any event, I left the bracing 'as is,' and moved my hole over another stud bay - where the brace is well below the work area. I notched my jack studs to fit around the brace.

When I cut the stud that passed through the middle of my hole, there was absolutely no movement or settling. Still, I constructed a proper header, then 'pre-loaded' the header by driving a shim between the header and the stud.
 
if it was "let-in" bracing as opposed to surface mount bracing, it was placed with the full intent that it remain for the long haul.
 
OK, this topic has arisen again, in the course of my remodel. Here's a clean pic of the opened exterior wall:

DiagonalBrace.jpg


In this instance, I might be lucky, in that this particular wall is at the gable end of the roof, so it might not be a 'bearing' wall. Anyway, you can see the brace quite well. What you can't see is that I'd like to put an exit door right in the middle of it.

I do not know why the stud spacing is so irregular. General appearance of the framing is that, when in doubt or when convenient, they just threw more wood in.

Is there an approved method to cut this brace, to substitute for it? Perhaps, by sheathing the inside of the wall with shear panels? Does it matter whether the wall is bearing or not?

Otherwise, my intent is to remove several studs, instal a header, and mount a door for direct access to the backyard. (There's a special place in heaven for the inventor of the multi-master!)

My remodel is going slow, but sure .... in part, because I'm thinking so much before I hack into things :)
 
By no means am I an expert on bracing but I am learning more about it little by little and there are a couple items to consider to start. One, since it's the gable end, if it's a one story house that's a lot less of a load coming down on it then if the roof rafters and ceiling joists are landing on top of it.

That particular let in brace is at a steep angle, so steep that it's not providing nearly as much resistance as one that is closer to a 45 degree angle; I think the minimum used to be a LIB had to cross three bays (@ 16" o.c.) but it's been a long time since LIB bracing has been allowed in the part of California where I work so my memory could be wrong. That one looks like it's crossing three bays but the angle looks to be more than 60 degrees.

You could shear the inside of the wall as you mentioned but If you center the door between the wall and window with the two big holes in the diaphragm I don't think you're going to get much shear value. One thing we do when there are discontinuities in the diaphragm is to run continuous blocking along the headers and sills, put on the ply and then run continuous metal straps we get from Simpson and that makes the shear wall ratios work better by making the areas into a bunch of little rectangles that are all tied together (that is how one of the engineers I work with explained it to me, not sure if I remembered it correctly but we do it all the time).

If you could stick the door to one side you could get a nice size shear panel between it and the window. Of course, depending on where you are has a tremendous influence on what is required.
 
It may not be a wall bearing much vertical load but it does take horizontal wind or seismic load. The vertical studs with horizontal sheathing can be racked fairly easily, by forming a triangle with the permanent let in bracing they have locked the frame in place. Think of a horizontal load pushing from the left side of the picture trying to shove the top of the wall to the right. That force follows the brace to the rigid floor rather than allowing the horizontal sheathing to slide board by board to the right and racking the frame. As the brace becomes more vertical it becomes less effective... but still much more effective than no brace.

Google fachwerk architecture for some pics of historical pre plywood bracing methods

Yeah they didn't unfold their stick rule unneccessarily and the level was a bucket of water back in the day. No mud tunnels or water stains, sweet!
 
Yankee said:
The shear is unrelated to the bearing (or, , , am I mistaken???).
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No, you are not mistaken. The bearing is the vertical load and the shear is referring to the lateral loads.
 
I want to thank, again, Francis Vinyard for this link:

http://www.ce.udel.edu/courses/CIEG407/Class_17/Wood%20Chapter%2023%20-%20IBC.pdf

There's the code. It discusses, among other things, different types of bracing.

Reading 'between the lines,' it's possible that I could suppliment the diagonal let-in bracing by sheathing the inside face of the wall with plywood or OSB. It's also possible that I could 'get away with' simply cutting the brace and closing in the wall.

I'm not willing to take the chance, considering the variety of openings I wanted to make. I last encountered this sort of bracing in mounting an air conditioner in the wall - and solved that issue by shifting the A/C over a bit. Had I adopted a cavalier attitude towards the bracing, I would have soon had one end of the house witout any bracing at all. Would it fall down? Twist? Be OK? Who knows?

Nope, my decision on this one is to -first- have a chat with an engineer. I suspect that the easiest course (again) will be to reduce the size of the window I wish to add, and shift the door a bit, so as to leave the bracing alone.

Those who asserted that diagonal let-in bracing wasn't very effective are correct I see that the code accepts it for only the lightest of loadings.
 
It occurs to me that I have probably confused everyone with my 'alternate' plan.

My alternate plan is to eliminate the window you see, and place a door in that location. A new window will be placed to the left of the diagonal brace.
 
Sounds like you are headed in the right direction. You are correct that diagonal let-in bracing is one of the least effective forms of bracing that was ever allowed. In your situation it is further complicated by the fact that the angle of the bracing provided is much less than optimum. 45 degree angles are the preferred method. If it were me I would be most reluctant to interrupt the existing brace. Consulting with an engineer is a very good decision.

Good Luck
 
I don't know why some are eager for you to squander money on an engineer. They must be engineers.

I get the idea that permits won't be required so it's up to you.

If you have 4' of wall left over, what more do you need?

Not convinced yet.

Install 3x framing and blocking where needed.

Shear on both sides

Nail it with 10d 2" edges and 6" field.

Don't forget the anchor bolts that aren't there now.

Look on the internet for examples of shear transfer at the raised floor and roof. It's simple stuff really.

If you are still leary of going it alone, sheath the entire wall with blocks at the headers and sills.

CS16 over the sheathing at the blocks and header/sill. (Be smart enough to miss the window flange if there is one)

I'm only trying to help and if I still haven't convinced you, look into buying a Hardi-Frame.

As a last resort, go ahead and give an engineer money for the numbers that go with all the stuff listed above. Better yet, get it value engineered so you don't waste any nails.
 
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Let-in diagonal bracing may still be used today. It is an effective method. Its used in lots of structures that are still in good shape.
 
Where in the code does it state that work that impacts the structural integrity of the building is exempt from a permit?

I agree that Table R602.10.2 does show let in bracing. However, when I go to Table R602.10.3.1, it doesn't appear that it is listed there even for Seismic Desing Category 'A'.

Perhapos what you really mean is that gypsum wallboard can be used if properly sized and placed. At that point, the let-in bracing is just extra insurance.

Even if permits are not required, you are still obligated to build to code. Section R105.2.
 
Big Mac said:
Where in the code does it state that work that impacts the structural integrity of the building is exempt from a permit?
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I didn't mean to say that the code doesn't require a permit for what he plans. I meant to say that it sounds as if there won't be a permit for whatever reason. It could be that there is no adopted code where he lives or it might the most common reason of all, he might not get caught.

The last one is the reason that I use. (That's for you fatboy. Now that didn't take long did it?)
 
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Mac said:
Let-in diagonal bracing may still be used today. It is an effective method. Its used in lots of structures that are still in good shape.
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It depends on your SDC (Seismic Design Category) In the 2010 CRC (California Residential Code) look at Table R602.10.1.2(2) 'BRACING REQUIREMENTS BASED ON SEISMIC DESIGN CATEGORY' (AS A FUNCTION OF BRACED WALL LENGTH) (Caps from the book) . It's on page 217 and 218.
 
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