Really good tips. I’m getting ready to build my first roof, a lean-to addiction on my barn, and am glad I decided on 2x4 purlins. Love the block on gable end - I probably would have thought of that after I was all finished!😂
I just did the purlins on my post frame woodshop - I'm sure that's why they recommended this video. Mine are on edge and the trusses are 8' on center, but the concept is the same. They sure cover quickly when it comes time to tin the roof 😊
Hey Jack, thought I invented the purlin end support. This is my first project, pergola porch with metal roof. Can I ask, how did you attach the purlins where two ends meet? It looks like one purlin end spans the entire width of the joist, what is the other purlin end attached to? Both ends have 2 screws in the end. Thanks
For this project the purlins meet on the rafter, joint centered on the rafter, and screw in (screws angled so they aren't too close to the ends of the purlins). However this is not the best way to do it because it puts a lot of screws in one spot on the rafter and won't have good pullout resistance against uplift. Need to make sure to stagger the purlin joints when doing it this way so that they alternately fall on different rafters. If uplift is a concern, the best way is to have the purlins meet halfway between two rafters and put a 2' section of 2x4 underneath them that you can screw into with spread out screws. That keeps the joints off the rafters and avoids having too many screws in one spot.
Thanks for the idea of matching purlins between the rafters, I'm dealing with eastern red cedar, thats why I'm wringing my hands over so many screws in the edge of 2 of my rafters, I'd been toying with attaching a nailer 2x4 to both rafters ending one purlin on the rafter and the other on the nailer but this is a pergola, and appearance is a consideration. Thanks again.
Great video, and thanks for the recommendations! Do you recommend using pressure treated for the same application or can you get away with untreated 2x4? Thanks!
I use pressure treated for roof framing on boat house roofs that are over water, but it's not necessary on land. If you use pressure treated, be sure to put a membrane material between the roof panels and purlins to prevent corrosion of the roof, and use hot dipped galvanized roofing screws.
Cupping toward the bark side is a general rule, but 80% of my rough hewn pine purlins cupped toward the bark side. When I contacted the local sawmill the old man there said it all has to do with specie and drying process. He said smaller pine boards will cup towards the bark as the tension and compression is released. @@edwardbowles8613
I have seen some post/frame buildings with decking on top of purlins and some with only a plastic barrier between the purlin and the metal. What is the determining factor in that choice? Thanks!
Different scenarios to the two methods you cite, and they generally are not comparable choices. The plastic you saw is probably a bubble wrap radiant barrier to reflect heat out and provide a minimal insulated vapor barrier to ward off condensation problems. This is done when the metal shares airspace with a closed area that generates moisture and/or has limited use climate control. In stick-frame consruction (trusses or rafters but no purlins) a metal roof is often installed over OSB sheathing with a roof membrane. Under the OSB would be a traditional attic or ceiling construction with appropriate insulation.
I'm trying to decide between purlings and osb sheathing for my off grid woods cabin. It'll have an insulated attic ( I made trusses instead of just rafters) with poly as a vapor barrier between the attic and living space and a steel roof. There will also be 4' air chutes either stapled to the osb or the underside of the purlings so the insulation dosen't block the attic ventilation to the soffit overhangs. I heard from somewhere that there can be condensation dripping from the steel with purlings, but I'm not sure if that applies with a normal insulated and vented attic
I think the main condensation risk is from warm/moist interior air getting to the metal. So proper vapor barriers and venting will prevent that. However, most metal installers still want some sort of barrier between OSB and metal panels, usually an adhesive membrane/shield product (there are many nowadays, most common is the blue stuff). That will prevent any sort of environmental moisture that condenses under the metal from causing rot/damage to the OSB. No matter what you do, metal surfaces can sweat under environmental conditions. I occasionally see it on my open pole barns with metal roof and purlins. It's rare but happens. And think about all the other metal objects that can sweat under particular conditions. I've even seen my sawmill sweat when we get a sudden increase in temperature/humidity after it's been cold. It's under a roof and well ventilated, but if the metal is cold and the air is moist, it will sweat.
I didnt think purlins could be joined like that. my neighbour who is a building inspector told me that theyhad to be overlapped etc if they werent one single length. This seems much more reasonable
This way is fairly standard practice, but your neighbor is 100% right. When there is a higher risk of wind uplift loads (say for an open structure, or a high-risk location), I instead join my purlins in between rafters, because I do not like concentrating fasteners from two purlins into the a rafter if there is a higher load. When doing that, an additional short block goes between the rafters, under the purlin joint. You just need to think about fastener placement to keep them spread out.
I have seen some forums calling for 60d ring shank nails to attach purlins. 6 inch seems overkill. Noted you used 3.5 structural screws and mentioned ring shank as an option. Any comments on 60d vs 16d?
60d are for purlins on edge. They have to go through 3 1/2" of wood before getting to the rafter. I just finished the on-edge purlins on my building yesterday - one hell of a job!
@@Smoothjaswi I usually do 2' on center from eaves going up, and then the last spacing near the ridge might have to be less since the rafters are rarely a multiple of 2. But it really doesn't have to be exact or specific unless you are needing to calculate for fasteners and uplift resistance.
Joints should be staggered but no need to have long purlins. This roof is 24' long, and I've built pole barns up to 80' long, so inevitably it involves stitching the roof together with shorter pieces of lumber.
Can't give a good answer without knowing your local roof load requirements, but I'd suspect not if laid flat. Even with no snow load a 2x4 can sag under it's own weight over time when laid flat on a 4' span. For 4' span most people put the 2x4 on edge, but that adds other complications.
@@bandmasterjf If it's a conditioned space then you need a plan to deal with condensation. That will be dependent on the type of insulation, the roof structure, the local climate, etc. There is a lot to it. The current state of the art is sheathing, roof underlayment, then the metal. It has to be a system that works together.
Great job, 2x4 is an excellent idea. I was just watching video of nails and screw which made a lot of sense to me. Nails should be used. Structures move sway and settle, nails can bend a little, but we know screws just snap off and break. Are you screws that allow for that, if there is any ?
If using screws, it's important to use structural screws, like these GRK screws I use for framing. Do not use deck screws, as they will crack as you noted -- they are only meant to hold wood down and don't do very well with shear loads or bending loads. I have also used glue-coated ring shank nails shot in with a nail gun which hold roof purlins very well.
@@Lumber_Jack Thanks for clearing that up for me. I been out the game for awhile. Excellent information. I will be purchasing some of those screws soon.
Your foundation would have to be very poor for the building to move enough to break screws. I’ve seen many roofs blown off because the nails just pull out though
The Purlin overhang 2x4 attachment was fantastic!
Agreed
Meh rather do it on the roof or it’s way harder to straiten out the gable truss
This recommendation helped a lot. Thanks for sharing this info!
thanks for sharing... I'm also a big fan of the structural screws.
End block is a good tip, thanks.
Very nice, well built architecture!
Really good tips. I’m getting ready to build my first roof, a lean-to addiction on my barn, and am glad I decided on 2x4 purlins. Love the block on gable end - I probably would have thought of that after I was all finished!😂
Great idea with the facia blocks
I noticed the tree branch on the end of your ridge beam. Nice to see others "Topping out"!
😊
I just did the purlins on my post frame woodshop - I'm sure that's why they recommended this video. Mine are on edge and the trusses are 8' on center, but the concept is the same. They sure cover quickly when it comes time to tin the roof 😊
I love those GRK R4 structural screws.
What length?
@@reasons04 I always used GRK #9 3-1/8 inches long
Good advice on the Lathes. Save you from running a saw to align them up on the Eves.
Thank you for the recommendations.
What is the max overhang you would recommend on those purlin ends with blocks attached?
Hey Jack, thought I invented the purlin end support. This is my first project, pergola porch with metal roof. Can I ask, how did you attach the purlins where two ends meet? It looks like one purlin end spans the entire width of the joist, what is the other purlin end attached to? Both ends have 2 screws in the end. Thanks
For this project the purlins meet on the rafter, joint centered on the rafter, and screw in (screws angled so they aren't too close to the ends of the purlins). However this is not the best way to do it because it puts a lot of screws in one spot on the rafter and won't have good pullout resistance against uplift. Need to make sure to stagger the purlin joints when doing it this way so that they alternately fall on different rafters.
If uplift is a concern, the best way is to have the purlins meet halfway between two rafters and put a 2' section of 2x4 underneath them that you can screw into with spread out screws. That keeps the joints off the rafters and avoids having too many screws in one spot.
Thanks for the idea of matching purlins between the rafters, I'm dealing with eastern red cedar, thats why I'm wringing my hands over so many screws in the edge of 2 of my rafters, I'd been toying with attaching a nailer 2x4 to both rafters ending one purlin on the rafter and the other on the nailer but this is a pergola, and appearance is a consideration. Thanks again.
What if you're building a 24x 35 rv cover how many do i need
Great video, and thanks for the recommendations! Do you recommend using pressure treated for the same application or can you get away with untreated 2x4? Thanks!
I use pressure treated for roof framing on boat house roofs that are over water, but it's not necessary on land. If you use pressure treated, be sure to put a membrane material between the roof panels and purlins to prevent corrosion of the roof, and use hot dipped galvanized roofing screws.
Ok, what's the structure? What gauge roof panels?
All flat boards should be bark side down to resist cupping and raising the metal roof.
Wood does not cup toward the bark. So bark side up.
Cupping toward the bark side is a general rule, but 80% of my rough hewn pine purlins cupped toward the bark side. When I contacted the local sawmill the old man there said it all has to do with specie and drying process. He said smaller pine boards will cup towards the bark as the tension and compression is released. @@edwardbowles8613
@@edwardbowles8613nope, that is incorrect. A board will always cup opposite of the growth rings.
I have seen some post/frame buildings with decking on top of purlins and some with only a plastic barrier between the purlin and the metal. What is the determining factor in that choice? Thanks!
Different scenarios to the two methods you cite, and they generally are not comparable choices.
The plastic you saw is probably a bubble wrap radiant barrier to reflect heat out and provide a minimal insulated vapor barrier to ward off condensation problems. This is done when the metal shares airspace with a closed area that generates moisture and/or has limited use climate control.
In stick-frame consruction (trusses or rafters but no purlins) a metal roof is often installed over OSB sheathing with a roof membrane. Under the OSB would be a traditional attic or ceiling construction with appropriate insulation.
I'm trying to decide between purlings and osb sheathing for my off grid woods cabin. It'll have an insulated attic ( I made trusses instead of just rafters) with poly as a vapor barrier between the attic and living space and a steel roof. There will also be 4' air chutes either stapled to the osb or the underside of the purlings so the insulation dosen't block the attic ventilation to the soffit overhangs. I heard from somewhere that there can be condensation dripping from the steel with purlings, but I'm not sure if that applies with a normal insulated and vented attic
I think the main condensation risk is from warm/moist interior air getting to the metal. So proper vapor barriers and venting will prevent that. However, most metal installers still want some sort of barrier between OSB and metal panels, usually an adhesive membrane/shield product (there are many nowadays, most common is the blue stuff). That will prevent any sort of environmental moisture that condenses under the metal from causing rot/damage to the OSB.
No matter what you do, metal surfaces can sweat under environmental conditions. I occasionally see it on my open pole barns with metal roof and purlins. It's rare but happens. And think about all the other metal objects that can sweat under particular conditions. I've even seen my sawmill sweat when we get a sudden increase in temperature/humidity after it's been cold. It's under a roof and well ventilated, but if the metal is cold and the air is moist, it will sweat.
@@Lumber_Jack Yep, even firearms will sweat laying in the glove box or on a gunrack.
❤️🇺🇸💙 THANKS FOR SHARING ❤️🇺🇸💙
so it looks like you don't install short 2x4's running vertically between the purlin 2x4's?
thanks again
Only at the gable overhang if needed, but typically there is some other type of gable framing use to brace or box-in the gable ends.
Alright! Thanks for clarifying that!
How many inches do the purlins overhang on your gable ends?
It can be anything up to about 18-20" but the longer you go with overhang the more support you will need to keep the gable ends from drooping.
What type screws do you suggest
Is the fixing of your purlins right?
great video thanks
I didnt think purlins could be joined like that. my neighbour who is a building inspector told me that theyhad to be overlapped etc if they werent one single length. This seems much more reasonable
This way is fairly standard practice, but your neighbor is 100% right. When there is a higher risk of wind uplift loads (say for an open structure, or a high-risk location), I instead join my purlins in between rafters, because I do not like concentrating fasteners from two purlins into the a rafter if there is a higher load. When doing that, an additional short block goes between the rafters, under the purlin joint. You just need to think about fastener placement to keep them spread out.
I have seen some forums calling for 60d ring shank nails to attach purlins. 6 inch seems overkill. Noted you used 3.5 structural screws and mentioned ring shank as an option. Any comments on 60d vs 16d?
I'd pick 16D for sure. 60D seems insane.
I “think” that’s for if you are doing purlins one their sides.
60d are for purlins on edge. They have to go through 3 1/2" of wood before getting to the rafter. I just finished the on-edge purlins on my building yesterday - one hell of a job!
what is the distance between each purlin?
Nominally 2' here but it really depends on the wind loads and fastener requirements. Some locations might need more purlins.
@@Smoothjaswi I usually do 2' on center from eaves going up, and then the last spacing near the ridge might have to be less since the rafters are rarely a multiple of 2. But it really doesn't have to be exact or specific unless you are needing to calculate for fasteners and uplift resistance.
Good video, are you using all treated lumber for your roof?
This is all rough sawn yellow pine, not commercial lumber. It has no treatment.
Love video thanks helped
Is it not advisable to use one perlin the whole length, say 16' long? Thanks
Joints should be staggered but no need to have long purlins. This roof is 24' long, and I've built pole barns up to 80' long, so inevitably it involves stitching the roof together with shorter pieces of lumber.
@@Lumber_Jack alrighty.. appreciate the quick reply
my trusses are 4ft on center. Do you think a 2 x 4 purlin will span 4ft?
Can't give a good answer without knowing your local roof load requirements, but I'd suspect not if laid flat. Even with no snow load a 2x4 can sag under it's own weight over time when laid flat on a 4' span. For 4' span most people put the 2x4 on edge, but that adds other complications.
Do you put a vapor barrier between the wood and metal?
Not in this application.
@Lumber_Jack I'm building a living space with a gambrel roof. Would you in that case?
@@bandmasterjf If it's a conditioned space then you need a plan to deal with condensation. That will be dependent on the type of insulation, the roof structure, the local climate, etc. There is a lot to it. The current state of the art is sheathing, roof underlayment, then the metal. It has to be a system that works together.
Great tips.
👍😎
Great job, 2x4 is an excellent idea. I was just watching video of nails and screw which made a lot of sense to me. Nails should be used. Structures move sway and settle, nails can bend a little, but we know screws just snap off and break. Are you screws that allow for that, if there is any ?
If using screws, it's important to use structural screws, like these GRK screws I use for framing. Do not use deck screws, as they will crack as you noted -- they are only meant to hold wood down and don't do very well with shear loads or bending loads.
I have also used glue-coated ring shank nails shot in with a nail gun which hold roof purlins very well.
@@Lumber_Jack Thanks for clearing that up for me. I been out the game for awhile. Excellent information. I will be purchasing some of those screws soon.
Your foundation would have to be very poor for the building to move enough to break screws. I’ve seen many roofs blown off because the nails just pull out though