Roof purlins for truss roof question
drptop70ss
| Posted in Construction Techniques on
Finally moving along on my 40×60 pole barn shop, trusses will be 40′ clear span, 4/12 pitch and 4′ OC. My question is for the roof purlins, believe the truss drawing called for 2x4s 2′ OC. Do I nail 2x4s flat across the tops of the trusses, or on edge? If on edge, do they sit on top of the trusses or do I nail pieces on edge between the trusses with the tops flush to the top of the truss? Also if on edge either way does simpson make a tie for this? I bought 12′ 2x4s already so I can do this either way. Rookie question, this is my first pole barn. 🙂 thanks,
Dave
Replies
First off, check your local codes. They may say strange things about what you can and can't do which have no apparent basis in logic.
For trusses 4' O.C., I'd suggest putting them flat. Gives you a nice wide surface to hit with screws or nails. Fasten them to the truss well, as this the only bracing the top chords of the trusses have.
For trusses more than 4' O.C., you'll probably have to stand the purlins on edge. I have some purlin span charts I can fax out if any of you are interested. (Don't have a scanner, so no pictures)
IMHO, purlins that are dropped between the trusses are far superior to purlins on edge over the top. You get a much better connection that way. I've used some real neat saddle hangers for this before but don't remember who made them. (Wasn't simpson)
It should show you how the 2x sits on your trusses on the profile drawings of your truss.
That being said. I would think that they were meant to lay flat across the trusses.I also agree with Ron that the best way would be to put them on edge in between each truss.
my two cents, Dave
"It should show you how the 2x sits on your trusses on the profile drawings of your truss.
"
As far as the truss design is concerned, it doesn't make any difference where the purlin is. But the truss design program assumes a good connection at each purlin location to keep the top chord from buckling in compression. I don't personally believe that purlins on top of a top chord (and on edge) can provide a good connection.
But a 2X4 laid flat with a couple of 16D nails ain't bad.......
The roof itself consists of the roof trusses, roof purlins, metal building insulation, truss bracing, roof steel and screws. While the weight can vary greatly, depending upon loading requirements, it will rarely be more than four pounds per square foot. With this said, most customers ask this question because they have concerns about unloading a truck. In most cases, our vendors will be equipped to offload materials they are delivering themselves.
Do you realize you're trying to answer a question from 2002 - - 12 years ago?
Doesn't matter to a spammer.
The roof itself consists of
Yes. At the eave not only is trim provided to fit tightly at the top of the wall steel up against the roof steel, but we also provide reflective building insulation to aid in filling the voids at the steel ribs. At the ridge, we provide closed cell foam closure strips to fill the gap between the roof flashing and the ridge cap. These closures are UV-resistant and because they are closed cell, they will not soak up moisture like a sponge.