How to install purlins, quick question

[JohninCT]

One more quick question, He has a couple large pole barns on his property and did not putting any sort of barrier between the metal roof and the purlins. I have been over to his place a number of times and have never seen any condensation on the under side and/or the ceiling "raining". With a non sealed, non conditioned building in a mostly shady area, do I need to worry about condensation? The joists/rafters are 2x10x12's flush with the ridge joist, but attached to top of side plates with simpson hurricane straps. So there will effectively be about 10in gap on the side walls between the roof and the wall. http://s98.photobucket.com/user/rholmes69/media/20140708_144542_zpshb37k7vz.jpg.html

I'd run them across the top of the rafters and leave ends long to give you a roof overhang front and back.

 

[ace10]

You're going to screw the tins onto the purlins, right?

To prevent uplift, I would use some construction screws on the purlin-to-rafter connection. Especially if you're going to have open sides or big gaps under the eaves.

 

[KRBrouwer]

On my outdoor deck by the pool, I ran my purlins across the top of the joists (wide side down), 2 feet between the joists, with the purlins spaced about 16 inches apart on the advice of the person installing the metal roof. I attached the purlins with 3.5 inch screws (2 at each joint). Very sturdy.

View attachment 382188

Building my first pole barn, old timer across street is giving me pointers. He said to install purlins like the picture shows I have done. 3.5in 16d nail. Joists/rafters are about 40 in space between them. Putting purlins 24 in on center. Do I need to redo the purlins just straight across on top of the rafters? It would certainly by a he'll of a lot faster than cutting so many boards... at this point I've only cut 6 2x4's

 

[bigtiller]

If you want to do it like Morton, the 2x4 purlins are spaced every 2ft on top of the rafters and stood on the skinny side, then nailed in with a 6 inch ring-shank nail.

Them guys can shake your hand and you won't forget it.

 

[Gary Fowler]

I have always seen them place on top of the rafters, sometimes tall side down sometimes narrow side down but always on top and on 24" centers. I think if I were building and put them narrow side in the vertical plane I would buy some of the galvanized steel hangers that nail or screw into the rafters and then to the purlins. I always hated toe-nailing even with a pneumatic gun.

 

[bigtiller]

I have always seen them place on top of the rafters, sometimes tall side down sometimes narrow side down but always on top and on 24" centers. I think if I were building and put them narrow side in the vertical plane I would buy some of the galvanized steel hangers that nail or screw into the rafters and then to the purlins. I always hated toe-nailing even with a pneumatic gun.

Morton does't toe-nail the purlins, they pound that 6 inch ring-shank nail all the way through the center of the purlin 3.5 inches and the remainder of the nail goes 2.5 inches into the rafter.

 

[buckeyefarmer]

purlins are put on edge when the trusses are larger and spaced further apart. It all depends on the design, you can have fewer trusses, but they have to be heavier and the purlins have to be able to span the increased distance, or you go with closer, lighter weight trusses, then you can use smaller purlins, even lay flat if the trusses are closer. Or you can put trusses on 16" center and sheath it. There are many options, it all depends on the design and load calculations per that design. I would not do it the way the OP shows, by nailing pieces of 2x4S between the trusses.