Engineered Roof Truss - Catwalk in the Way of Bathroom Vent Duct

I've got an engineered roof truss system - a scissor truss. 

I've also got big long "catwalk" that goes across the trusses. It's a 12' 2x4. I've got several of them crossing the entire length of roof from gable to gable. They aren't really catwalk though - not wide enough to easily walk. 

In reading across the web, it looks like these 2x4's were likely installed when the house was built to maintain proper distance between the trusses (24" OC). I've also read that there should be no issue in removing them, or relocating them.

I've got a bathroom duct vent that in order to best route I need facing a center direction - the outlet being right next to one of these catwalks. I would only need to move the 2x4 over about 10" to make room for a 3" 45º elblow. 

As we've got a few folks who are knowledgable on these topics, I thought I'd ask the GRM hivemind. 

Can I remove, or at least relocate truss-to-truss catwalk?

Shouldn't be an issue to relocate.  You could almost certainly remove it, now that the framing has been sheathed, but moving it over a foot or two to make clearance won't be a problem.

We would typically call those "rat runs".

Like Duke said- relocation is no problem.  But I wouldn't remove them.  They keep the bottom chord of the trusses spaced evenly, and make the entire roof system act as 1 system, instead of individual trusses.  They don't do a lot now that the roof is sheathed, but they are still part of the engineered design.

Thanks all! 

Those are longitudinal wind bracing and there must be more of them than what you show and are very important (each individual engineered truss build and load drawing will show exactly what load and stiffing bracing needs to be attached and where to place them). You can cut out a truss or two of them, but as close as you can, place a new one that grabs at least two trusses on each side of the cut-off truss brace. All bracing laps need to span two truss chords because the nails at the end of the braces don't count as real attachment points.

Feel free to add a 2x10 plank or 7/16" OSB cat walk anywhere you want.

Wind Bracing Diagram

In reply to VolvoHeretic :

I actually don't have anything like the green and red lines in that picture. Definitely nothing like the red or purple. 

The green lines (continuous lateral restraint) might be my "catwalks" but they aren't as close to the truss joint as that example shows.

Either way, I'll replace whatever I cut out with something similar. 

Even if you just drop an 8' 2x4 over a little bit and screw it to the bottom chord before you cut you'll be fine.  I've always done that in these cases.  Chances are you're ok to just cut it but at the same time it's all part of the roof system and is there for a reason.  You're also tying the house together end to end at the top of the walls to prevent walls trying to move outward, which while highly unlikely at this point it is a definite concern during construction and i've seen it happen when temporary wall braces were removed before the entire roof structure system was finished.  

pheller said:

In reply to VolvoHeretic :

I actually don't have anything like the green and red lines in that picture. Definitely nothing like the red or purple. 

The green lines (continuous lateral restraint) might be my "catwalks" but they aren't as close to the truss joint as that example shows.

Either way, I'll replace whatever I cut out with something similar. 

Maybe those are for location where high velocity wind is a thing? I am pretty sure mine has them, but I am in live in hurricaneland.

I put those in when building the garage and was told to use furring strip instead of 2X4s.  The purpose was to keep the trusses happy until the roof went on.  I would think there's enough bracing now that everything's up, but to sleep better at night, box around it.  Put parallel braces 18" to each side and cut the piece out.

Those are just generic diagrams. Different bracing members will be required depending on wind load locations (Tornado Alley, Hurricane Alley, top of a hill...) and snow loads. Each different truss in the roof system comes with a specific bracing location marked on the truss data sheet and if you have a hip roof, there will be one for each different truss which will be a lot of them. The main braces will be longitudinally along king pin at the ridge line and at the bottom at various locations on the bottom cord. Vertical X bracing is also required with no more than 20' of space between X's.

Lot's of builders don't put all of them in and when I drafted for a forensic engineer for 20 years, the insurance companies hired us to to assess blame when someone's roof either collapsed or blew off. Pole barns are the worst and we were busy.  Nail sizes and diameters along with nailing patters as well as splicing design are very important and must be capable of withstanding 90 mph (or is it 115 under the newest code?) wind in tame locations and much more in high wind places. ND is the safest place in the US for earthquakes so I have no experience on that, but that's another can of worms.

Your building permit municipality should have records that will indicate where the trusses came from and you should be able to find the engineering on your trusses without too much trouble.

Just replace anything you cut out and span across multiple trusses.

See page 12 for member bracing which doesn't say much: Alpine Truss Design