What did my boss find in his attic?
I am and Engineer who designs stream restoration and fish passage projects. It has been nearly twenty years since I took my structures classes, and I am rusty to put it mildly.
My boss came out to my office today, and drew a sketch on my white board, of his attic structure, and it has two “L” shaped members, that neither of us can identify. He wants to know if they are load bearing, because one of them is directly over where he wants to install an new bathroom fan, and he wants to cut it out.
They are made up of two 2X6s, nailed into an “L” shape, and run the length of the attic, nailed to the roof joists. They are not connected to anything else. The only thing I can think of that they could be doing is keeping the roof joists from rolling over.
I have attached a quick sketch of how the roof is framed, and the things in question are in blue.
Any insight into what they are, and what they do would be greatly appreciated.
Thanks, Randy
Replies
Those are called strongbacks. I wouldn't cut it. They give strength and rigidity to the framing.
No blue colour but I know what you are referring to. They keep the bottom chord of the trusses from twisting under load. You do need them but I think they can be moved a little without worry. Check with a truss manufacturer to be sure.
I needed room for some can lights a few months ago, made a new strongback long enogh to span four ceiling joists - bridging the section I wanted to cut away. I installed it with screws (to avoid hammering and maybe cracking the drywall), then cut away the section of the strongback that was in the way.
When I was done, I had the clearance I needed with doubled strongbacks on either side.
do what dave45 did, it is strong
Dave,When I was replacing some ductwork in the attic, I found where the electrician had simply cut out flat part of the strongback for the light. Not just one, but two were in the layout of his light. This in a 22' span of 2x6 on 16" centers running the 17' length. There is about a 3/4" sag in the center of the ceiling.Pete
Pete -
My all time favorite was the guy who cut away parts of the trusses to build an attic playroom for his kids. He actually did a pretty good job - cut down door in the bedroom wall, carpet, drywall, paint, lights, etc, but he was really POed at the builder because his kitchen ceiling had sagged about 2".
He was rather annoyed when I pointed out that the sag resulted from him whacking away at structural parts of his house. - lol It cost him plenty to have us jack up his kitchen ceiling, demo the playroom, and rebuild the trusses. It cost even more because I had to do it in July when it was over 90* up there by 10:00 am.
Where's Boss Hog when you need him
To me, it's just a brace, or "strongback", as others have said. They aren't structural. They're just designed to help keep the ceiling joists in line. So I don't see any reason to worry about cutting them.
It takes months do devolop a good customer, but only seconds to lose one.
The good news is that we'll be out of them in no time.
In Horsetralia we refer to these members as 'ceiling hangers'. While MarkH's identification is also correct, the OZ variant accurately describes the function. These members keep the ceiling in plane, preventing any point loading from distorting the line of the ceiling,
particularly along the length of the room.
Of course, cutting these at any point may release any residual stress,
and cause the distortion they have been installed to prevent. However,
if bridging members were fixed, say 12 inches away on both sides before the original was cut to make way for the desired fitting,no significant
movement would result.
As a 'belt-and-braces' approach, a vertical tie between the original member and overhead rafters would be good insurance.
I hope this helps.
Eric.
the Dave-45 method works...
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming
WOW!!! What a Ride!
Forget the primal scream, just ROAR!!!
Dave45's method is the correct one for repairing strong backs.
As far as the above recommendation to add a verticle member - I wouldn't do that. Basically you may be transfering load where it shouldn't be.
Generally, truss bracing of this type is not required to be in a real specific location and therefore can be moved a foot or so in either direction. For that matter, it may have not been required (by the truss manafacturer) at all. It might have been just installed as good practice to help keep the ceiling flat.
Now all we need is someone to say "you need an engineer for that". :-)
I posted the reply below without really studying the drawing. I wrote it thinking this was a truss roof, having re-read the Op and looking at the photo's again now I am not sure. If it is not a truss roof it clearly does not apply.
My Apology
Almost all the simple, low slope (-6/12)trusses (like you have drawn) that I have installed in over 30 yrs call for bracing in that location as part of the engineered requirements. UNLESS you have a RIGID CEILING applied to the bottom chord.
The location at roughly 1/3 points is to prevent the lower chord of the truss from developing an "S" configuration under loading and failing due to lateral load at those points. Truss Joist and Others used to have a great little tutorial handout on just this scenario.
I often install them even when I am having a rigid ceiling installed, not to meet the truss installation requirements to to align and straighten the lower chords of the trusses to their spec'd. o.c. dimension for the trades that follow me. Fastening trusses to interior walls in a no-no here unless you use truss clips , so it is common to "float" the trusses and use the pictured bracing to keep them in alignment. Nothing like having the plumber, electrician or hvac crew fasten their stuff to a truss that was floating in the breeze and have a truss or two 1-2" off for the drywall crew.
Trusses that not installed in a vertical potion are significantly weakened.
Permanent bracing is more apt to be found at specified locations on the webs.
Having said all this, and with no access to the original engineering , I would do what others suggested, add some bracing to each side of what you want to remove and carry on. Or make a call to a local truss manufacturer and simply ask them the question.. they of course won't really want to answer because of liability , but if you approach them right they might give you some insight.
Edited 12/13/2006 12:23 pm ET by dovetail97128
Edited 12/13/2006 8:40 pm ET by dovetail97128
Edited 12/13/2006 8:41 pm ET by dovetail97128
You're close in your guess. They keep the joists evenly spaced, prevent twisting, and keep them from warping vertically. Take them out, and the ceiling will gradually warp.
What he can do, though, is cut one out where he wants to run the fan and add a similar "L" to one side of the fan duct. This new "L" should span more than the cut out section. For example, if he cuts out the "L" between two joists, the new "L" should span three joists.
Install the new material with screws. Driving nails into the joists will bounce them and pop the nails holding the ceiling sheet rock up.
George
In my neck of the wood we use something like this to transfer lateral wind loads on a gable end wall, through the length of the building ( plate to plate) . We have to attach it to an external plate with bolts. If you could see what I've been working amongst lately ( Cat5 Hurricane damage ) you would appreciate the need for them.
regards
Mark
It maybe just a strongback for overspanned ceiling joists, but I have also seen them used as floating headers. Typically they will have a leg from the rafters down to the header.
If they don't have the legs up to the rafters then put in a new one across a half dozen ceiling joists, then cut out the old one. I learned the hard way. I cut one and the ceiling joists dropped an inch. A free drywall repair was now on me.
Thanks, everyone for the input. I've done some concrete designs, but never any wooden structures.
I told him to install two parallel to the one he wants to cut, and bridge them across three joists either side.