How to install purlins, quick question

[rholmes69]

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

 

[ace10]

Are the the rafters notched for the 2X4 purlins or the purlins cut down?

 

[David Wayne]

I would run them across the top, not only faster but I believe stronger. Just dont have all the purlins butt together on the same rafter, you need to alternate the joint (like a block wall). And when you put the fascia board on use a 2x(dont know what width you need) not a 1x, it will give more meat for hanging gutters on.
Hope this wasnt confusing

 

[rholmes69]

No, the rafters are not notched, I cut each purlin individually.... took me like an hour to hang 8 40in purlins....

I wasn't planning on hanging gutters, but I will use 2x4 on fascia in case I decide to at a later date. Thanks!

 

[Texasmark]

I have a Morton building and a BCI, both commercially constructed of wood structure. The Morton uses pre cut vertical 2x6 purlins on 2' centers between the 10' rafter spans, best I can recall. The BCI uses 12' horizontal 2x4s on 2' centers on 5' rafter spans giving you a foot of overlap on each 10' of support which makes for a sound joint....no split ends. The BCI way you just buy the board and nail it up. Goes real fast and on my self built wooden pole barns that's the way I did it. One of my first is over 35 years old and shows no sign of giving up.

HTH,
Mark

 

[rholmes69]

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.

 

[s219]

If the only thing holding the purloins is a nail into the end grain, that is very lousy support. And slow going. Normally they get nailed across the top. The long length and the nailing across grains gives lateral bracing. Sitting on top of the rafter gives vertical support. Right now you have neither.

 

[ace10]

No, the rafters are not notched, I cut each purlin individually.... took me like an hour to hang 8 40in purlins....

I wasn't planning on hanging gutters, but I will use 2x4 on fascia in case I decide to at a later date. Thanks!

Oy. I've seen 2X purlins laid on their sides attached to the top of the rafter/truss. I've seen 2X purlins attached between trusses with narrow side up. I've seen 2X purlins on their edge on top of trusses/rafters. But never something like you've desribed and shown.

Seems like a terrible idea... from both strength and time to build perspectives. Did the neighbor offer any reasons why he would suggest going this route?

You've got a relatively wide span between rafters for laying 2X4's down for purlins. If you have any risk of snow load, and given that 2:12 or 3:12 pitch, I would get some 2X6's in there for the purlins.

$0.02

 

[rholmes69]

Reasoning was a wider surface to nail into and I could nail along the entire edge of the joists as well. I will remedy the situation though. At least it is only like 12 bucks in wood worth of a mistake.

No snow loads really to be concerned with. We might get a dusting to a couple of inches if we are lucky. Last winter we had around 5-6 inches in one snowfall and that was an anomaly. We had 12 inches over 15 years ago, that was the most in like like 30 years. Not really worried about snow here....

 

[gphil12873]

I would run them across the top as said earlier. Stagger the joint locations. The couple I have help build put two nails and a 3" to 3 1/2" screw at each rafter. With the condensation, If you are not going to insulate it I wouldn't worry about a thing. Google garage journal and there is a website like this one with a wealth of knowlege.