Metal building roof question

[loudhornsrule]

I am building a 30x30 metal building over concrete in North texas. Can i lay the perlins on top of the rafters flat? I'm a one man show and it would be so much easier. I've looked at a few done that way and they seem ok. Bad idea or good idea? I know they get their strength from standing up, just looking for something easier for me. Thanks

 

[747driver]

Depends on how wide it is between each truss. Is it 4' 8' 10' On Center trusses ? If they are 4' O/C trusses then maybe you could use 2x4s on the flat. Otherwise I would install them on edge. How tall is the building ? Maybe you could go rent a scissors lift for 2 days to install them.

 

[Xfaxman]

The metal building that I had used metal trusses and metal purlins.

What are you planning to use for purlins?

 

[jfh28]

the purpose of the purlin is to transfer the load from the roofing material to the rafter/truss/frame depending on your system....the load will be mainly live load and depending on your area could be driven by wind/snow/hurricane/tornado......check with your local codes to find out the value....that weight usually in pounds per square foot is applied to the roofing material which then is transferred to the purlin and from there to the supporting structure so the purlin has to be able to carry that weight along with the contributing dead load weight of the roofing material and anything else laying on top of it such as insulation or sheathing as well as the weight of the purlin itself....whoever designed the structure of the roof should have run the calculations to determine the required size of the purlin.......if we're talking about 2x wood purlins then laying it flat essentially makes it a 1 1/2" piece of wood and there will not be much load carrying capability to it....even if the span is only four feet a knot or other imperfection in the wrong place on the purlin could cause it to fail.......metal c or z shapes are not designed to be load carrying laid flat....the purlins could also be part of the roof structure design contributing to bracing the trusses/rafters/frame so that could effect the sizing and fasteners required too as well as any uploads from wind for example......your question should really be directed to the person who designed your building structure as they will be the ones who know what was factored into the design.........if you are a one man construction show then you might want to build a jig that will hold the purlin in place hands free while you fasten it.....you won't set any speed records but it will get the job done........Jack

 

[ovrszd]

You can also buy metal hangers to place the purlins. Makes installing them much easier.

 

[Deere Dude]

Depends of joist distance. I had one PB with joists 9' apart and used 2x4 on edge. I built a 26x40 addition with joists 2' on center so I put 2x4 purlins flat. It was a 10/12 pitch roof and I weigh 265 and was using them like a ladder. It worked great.

The farthest I would even consider running them flat would be 4' on center. Some depends on snow load also. Don't know where you are. Caution, I am not an engineer.

 

[EddieWalker]

I personally like to put my trusses on 4 foot centers and then use 2x4's on the flat, every four feet, for my purlins.

 

[strum456]

Nearly every building I see here in PA has trusses 4' OC and 2x4 purlins laid flat 2' OC.

BUT, all of our buildings have the same setup with the trusses 3' OC. This may sound unusual, but we have done several buildings this way, and I would do it the same on the next one. A few extra trusses don't cost that much, and we think 3' OC is a much better job.

I suppose this could create an issue for some applications with 8' lumber. It has not been a problem for me. Most splice purlins on the trusses with 3/4" overlap. I splice them BETWEEN the trusses, using splicing blocks cut to fit in between the trusses.