35' spaced brace wall lines for a 40x40' structure

[xenovacivus]

The 2018 IRC code allows braced wall lines to be placed up to 4' from the associated braced walls. I'm building in Seismic Design Category D1, which means 35' max spacing on braced wall lines (with the 1.4x adjustment factor). As far as I can tell, I could place the exterior walls up to 4' each from the 35' spaced brace wall lines, and create a structure up to 42' by 42' without needing interior braced wall lines - is that correct?

 

[steveray]

Sounds close...does not really add up though...

 

[mtlogcabin]

Have you used this?

Wall Bracing Calculator - APA – The Engineered Wood Association

www.apawood.org

APA Wall Bracing Calculator​

You must be signed in to access the calculator.
Welcome to the APA Wall Bracing Calculator. This tool is intended to simplify the design of residential structures that comply with 2009, 2012, 2015 or 2018 International Residential Code (IRC) wall bracing requirements.
This calculator is intended for use by experienced designers that are familiar with wall bracing.
With the APA Wall Bracing Calculator:

1. Create a project and identify its pertinent details.
2. Pictorially identify and calculate the bracing requirements of each braced wall line.
3. Pictorially identify, qualify and locate each bracing segment on a given wall line.
4. Export the results to a printable document.

Download the APA Wall Bracing Calculator Quick Start Guide for a tutorial.

 

[steveray]

Simpson has a good one too...

 

[SDS]

Your BWL's would be at 35' apart...offsetting 4' further beyond this line would only be 39', not 42'

However, the exception to the rule of offset BWL's defined in table R602.10.1.3 states that this 35' rule only applies to an area not exceeding 900sf (assuming we're not talking about a 1-room, single-story Townhouse here)

39x39=1,521sf

So...no. You cannot design a building in the manner you're describing. As I understand it, the 35' exception is to allow flexibility in designing prescriptively...not to provide an 'allowable max building footprint' definition.

That said, the largest footprint you can design (square) prescriptively is 30x30=900sf...placing BWL's at 26' apart and offsetting 4' further to 30'...or simply locating bwl's at 30' apart. Arguably, placing BWL's at 26' would require less BWP than locating BWL's at 30'...the APA Wall Bracing Calculator another poster linked to is a great tool for working out these scenarios.

 

[SDS]

Your BWL's would be at 35' apart...offsetting 4' further beyond this line would only be 39', not 42'

However, the exception to the rule of offset BWL's defined in table R602.10.1.3 states that this 35' rule only applies to an area not exceeding 900sf (assuming we're not talking about a 1-room, single-story Townhouse here)

39x39=1,521sf

So...no. You cannot design a building in the manner you're describing. As I understand it, the 35' exception is to allow flexibility in designing prescriptively...not to provide an 'allowable max building footprint' definition.

That said, the largest footprint you can design (square) prescriptively is 30x30=900sf...placing BWL's at 26' apart and offsetting 4' further to 30'...or simply locating bwl's at 30' apart. Arguably, placing BWL's at 26' would require less BWP than locating BWL's at 30'...the APA Wall Bracing Calculator another poster linked to is a great tool for working out these scenarios.

Bad math...its early...the 900sf rule still governs

 

[steveray]

However, the exception to the rule of offset BWL's defined in table R602.10.1.3 states that this 35' rule only applies to an area not exceeding 900sf (assuming we're not talking about a 1-room, single-story Townhouse here)

Seismic....We don't get that here....Until we do...

 

[SDS]

Seismic....We don't get that here....Until we do...

Well he did mention SDC D1...I (think) I got that part right at least *cross fingers*

 

[xenovacivus]

Hey, thanks for the great answers so far. The 2018 IRC Figure R602.10.2.2 gives an example with BWL 1 offset from the rightmost exterior wall:

I figured I'd extend this to all the brace wall lines - each line is offset inward 2' 6" for a total of 5", which spaces them 35' apart. This might also shorten the effective length of the brace wall lines to 35' instead of 40', because they're defined to end when they intersect a perpendicular brace wall or exterior wall. Theoretically I could offset them both 4', for a BWL spacing of 40-8=32' (or alternatively a maximum building size of 35+8=43' ...which is what I meant earlier, 43', not 42').

Anyway, here's another example where BWL's A, 1, and 2 must be offset inward to include bracing in the jogged exterior walls:

And thanks for pointing out that APA Brace Wall calculator - those results match my by-hand results. The calculator allows me to enter 40' brace wall lines with 35' spacing; but I suspect it wouldn't be able to detect brace wall location issues anyway.

 

[mp25]

I read the guide to bracing from one of the handbooks that ICC publishes. They specifically stated there (but not in the code itself) that the intent of that 4' rule is not to artificially reduce your BWL spacing when the actual entire wall length is 4' away from it - such as along BWL1. The intent for the 4' was to cover situations similar to BWL 2 - where you have some bump outs that are close together as such close proximity allows the segments to act similarly to a continuous wall.