We’ve a trussed roof, and as we’ve seen them all go, top chords are up and down from roof plane.
If you want a crisp and straight roof edge line, you of course run your subfascia dead straight, as we are doing. But we don’t want the sheathing edge to track the ups and downs of truss chords, especially at the most extreme wows of up and down.
Is it overkill, or do you pad up and shave down if required, just out at the edge? I’ve been accused enough times on this job of trying to build a piano, and don’t want to do this unless there is payback.
Gene Davis, Davis Housewrights, Inc., Lake Placid, NY
Replies
I don't want to insult you, but I don't know your "skill level". I've never seen trusses far enough out of the roof plane to be that noticeable; are you sure your walls (and the floor they sit on) are level and the walls are plumb and not bowed in or out? I guess if you said your subfascia is straight and level, then the wall plates are level. (Easiest way to check that, at least for up and down or bowed out is to get on a ladder and look with one eye along the length of the top plate). The fascia can be pulled up and down as you nail it to the truss ends, so I would be more inclined to put shims under their bottom chords to get them all into the roof plane than to mess around with the top chords (that or nail 2x4's to the low top chords to get them into plane). I'm no expert on roofs, (or much of anything else!) so see what others here say before you jump into anything!
One more thing: If you run a line that touches all the truss peaks, is it level and straight?
Something else must be wrong - Trusses are built in jigs out of the highest quality lumber by skilled tradesmen, so they should be perfectly straight.
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O.K., I was just kidding. (-:
You don't give any tolerances for how much the chords are up or down, so it's hard to tell what you need to do.
If your sub fascia is straight, the ply should rest on it. That will hold the edge up a hair and make it look fairly straight. (Assuming your subfascia lumber is straight)
If you have dips or humps in the trusses that are more than 1/2" I'd definitely fix them before putting the ply on. But anything less than that, and you get into "piano building", IMHO.
We've had this happen almost everytime we use trusses. You can see it when they are still bundled together. Just one more reason why we hate trusses in most cases.
One advantage of gang cutting rafters in the racks, is that you quickly see the bad stock and can cull it.
How much are you talking with your trusses? What kind of roofing. If it's shake, you can get away with some waves. If it's 40year or higher comp, same thing. Anything else, tile or thinner comp, and we don't let anything bigger than 1/4" go. If you eyeball across the roof plane, you'll notice the big "wows". Don't worry about it at the fascia line.
What size tails did you order? 2x4 is the norm around here for trusses and in the summer time, they will move around.
I should add, that we always use thicker comp and that lets you get away with a little more :-)
Edited 7/19/2005 9:19 am ET by TIMUHLER
> We've had this happen almost everytime we use trusses. You can see it when they are still bundled together.
If the trusses are supposed to be symmetrical, turning the seemingly oddball ones 180 degrees may make them match better. If there are still variations, sorting them out from big to small or high to low may help conceal the errors.
-- J.S.
That's a good idea John, I never thought about that.
That brings up another reason why I don't like trusses. I do not feel safe walking the top plates draggin trusses.
Tim, I'm surprised how much you (being a young buck) and I (being an old fart, who just passed the half-century mark yesterday!) see eye to eye on this. Just beware: the angle-calculating cut-and-stacker is an endangered species, and you're throwing in your lot with a dying breed!
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edited to add parenthetical explanation
Edited 7/24/2005 11:47 am ET by Huck
Huck,
I appreciate your comments. I'm fortunate that this company doesn't like trusses :-) and I get to stick frame.
The other way I look at it is this: We are getting more and more "unskilled" labor around here in the form of workers who don't speak English (Mexican, Russian, etc) who are great workers and people, but who haven't learned some of the more advanced skills like stick framing. I view stick framing (and some of the architectural details) as something to justify my wage :-)
Here's a suggestion to help straighten the roof edge. I still use this method whether trusses or stick framed. Nail a 1x6 pt board on first, then the plywood . If you use 5/8" plywood you don't need to do anything special. If 1/2" is used, feather the 1/4" difference with 30lb felt. Four staggered layers from 36" , 26",16" and 6". This blends in the 1/4" difference. Two benefits to this method, the roof edge will last longer than a plywood edge ,even with the drip. Easier to start the first row of sheathing.
mike
I have seen the up and down on trusses, it usually 1/2 osb that got wet. put 3/4 ply and it will solve this.
Don't know but my WAG would be that you could install runners, or strong-backs in an extreme case, similar to those used to bring the bottom cords in line to flatten ceiling plane without having to strap the ceiling. A real sloppy plane or exacting carpenters might make both the way to go.
I know that gable framing here in sunny, and stormy, Florida often requires similar bracing but run at diagonals from the peak of the gable down to the top plates of the walls.
Given that I would think that what amounts to internal rat-runners would be allowable. The 2by4s would be nailed flat, I would think with two #16s as that seems to be the standard around here.
Extra stiffening could be had by creating a strong-back. Nailing a 2by6 upright to the side of the flat-nailed runner. I have seen this done to flatten ceiling joists, pulling any wild ones into line. Never seen one under the rafter cord of a truss. Best consult with the truss manufacturer or engineer to make sure it doesn't concentrate stress or cause other issues.
But as I said this is just a WAG.
Gene, it's not overkill to be concerned about the planing of your roof. The degree that you want it flat might be overkill.
It's been my experience that the lower pitched roofs tend to have the worst variation. Fortunatly, there is much less roof to fix.
Nowadays, most trusses are flat enough to sheath without much tweaking but occasionally "situations" arise. We tend to keep our eyes open for problem areas. When one is spotted, it usually only takes a minute or two to "booger" it. Boogerin' it might mean sistering a second member to raise a low truss. Other times we rip the high points off. Most of this tweaking occurs after the roof is set but sometimes, the bad apples are spotted when the truss is on the ground. In fact, just last week, I noticed a substantial bow (up) in the top chord of a gable that I was putting together on the table. I simply picked up a straight edge, marked the true plain and shaved off the excess (about 1/2").
Most truss repairs only require small sections (about 8' or less) to fix. Since it only takes about 30 seconds to rip 8', it's really not that big of a deal. Often, a bad spot can be raised by nailing on one stud, so you can see it's not really that bad to get semi-anal about it.
Some of the more serious tweaks occur when the truss configurations change in a substantial way (stepped downs, scissors next to regulars, offsets, stepped downs, transitioning into scissor with pan ceilings, etc). Probably the worst case I've seen involved laminating an entire section with 1/2" ply stips on top, or even possibly 3/4". I think I vaguely remember having to sister 2x4's on edge! That obviously was a design error, rather than a manufacturing glitch.
And finally, we've run into situations that simply couldn't be fixed on site easily. I don't mind doing one minute fixes, but if something is going to take me a lot of time, I'm going to ask for new trusses to be sent out. I've had to have that done two or three times in the past 30 years.
Working with trusses is an acquired art. Since I've seen just about every situation known to man, I don't get flustered anymore. I can booger with the best of them and in most cases, we deliver a fairly nice roof plane. Of course we do our best work in front!
If you are truly anal, you might think about measuring every truss, marking the true heel line, and testing the plane of each top chord with a string line (or just sight it) before it is sent up.
The one comment that you make interests me the most is this: "if you want a crisp and straight roof edge line, you of course run your subfascia dead straight, as we are doing." That statement implies that you are building your subfascia first, which is the way we do it. I find that if I build the straight cornice systems first, then set the trusses to the fascia, I don't have to concern myself with the heel and everything just seems to work out better.
Are you building your overhangs before you set the trusses.
blue