When you guys overframe truss valleys where different roof planes intersect, do you always sheath the overframed area first? I’ve got some big gables on this job that would eat up a lot of sheets (yes, I know, I don’t have to continuosly sheet through and don’t plan to) but I’ve seen a few framers in the area framing in with sticks only and sheeting after everything is framed, which seems harder to me. But I’m always looking for better ways to do things.
?
Replies
It's not necessary to sheath first, however it does help to visualize and lay out your valley cleats. On roof pitches steeper than a 9 in 12 I will sheath first, mainly because it makes it easier to get around up there. In addition it does save time because by sheathing first you avoid a second set of valley cuts in your sheathing, which can sometimes eat up as much plywood as sheathing first if your not careful. Sheath it in, but watch your nailing. Then snap it out in chalk, finish nailing off the sheathing, cut away excess and nail your plates home. Now you haven't wasted any plywood and you make your valley cut in one shot.
Boss-man,
You be da ,exspurt on tresses so answer me this.
Is the sheathing under valley trusses taken into consideration in the design/layout or is it to be compensated for in the field by laying out from the valley or are we expected to cut some ply to make every thing copesthetic?
An Older but not necessarily wiser T
Do not try this at home!
I am a trained professional!
Technically, the area under the valley is required to have plywood on it. The reason for that is to brace the top chords of the trusses. Unbraced top chords are in compression and can buckle over time.
I once saw a picture of a house where there was no plywood under a big valley. The top chords of the trusses had buckled so far they literally touched each other. They were fairly big suckers - Like 40' scissors or something like that.
So is it really that big of a deal, or are truss manufacturers just telling everybody to do it because they're paranoid? I think it's some of both. On short span, high pitch, flat bottom chord trusses, it may not matter much. Get into bigger spans, vaulted ceilings, and lower pitches, and you may have some serious problems down the road a few years.
My suggestion would be to go ahead and put the plywood down. Think of it as cheap insurance or something. Fixing buckled top chords can be awfully expensive down the road. And it give you a surface to work off of to build the valley. And less distance to fall. Not that I've ever fallen through a roof. More than once anyway.
Mr. T - To answer your question - Valley truses are figured so many different ways it's hard to say. Some manufacturers try to lay them out from the bottom up, so that they maintain the spacing of the trusses they were based on. Others figure this is futile, since they never fit right anyway. Most seem to run the trusses from the top down and just say hell with the spacing. (ie: They build a 4' valley, then 8', 12',16', etc.)
My suggestion for laying them out is to run a string line where the ridge should be. Then slide the trusses up the slope until they touch the string and nail them wherever they land. Valley trusses always seem to fit so poorly that there's no point trying to calc exactly where they should go.
Personally, I don't like valley trusses. Since there's only one of each size, they are expensive to manufacture. And, as I said, they never fit right. Some truss companies push them, others don't. If you use them see if you can get an itemized price on them to see just how expensive they are.
The only real arguement I can see for using them is that the roof load from above is distributed more evenly over the trusses below. Theoretically, valley rafters are supposed to be supported every 4 feet to distribute the load to the trusses below. But I've never seen it done. That's not a huge deal unless you're dealing with a really big valley IMHO.
So is that more than you wanted to know ?
When I was a kid we had a sand box with quicksand in it. I was an only child... Eventually.
Good detail Boss. These are the worst trusses I've ever seen. Lots of bad sticks, waney edges, wobbly top chords. Two of them broke during shipment, one had a tail come off that looks like it was rotten.
I'm picky about wood, but that's not what I'm talking about here. These are low grade for sure, and the bill was still around $9500.
Dog