Horizontal vs Vertical Joists/Rafters - Help with terminology please!

[CA_Tallguy]

Hi folks -- I'm trying to research something but for the life of me I can't come up with search terms that bring up what I'm talking about. Usually I can muddle around and eventually I'll stumble on what I'm looking for but I'm stuck on this one.

Basically, I'm wondering if there is a term to describe "horizontal" rafters or joists that are perpendicular to the "normal" direction of eve to roof peak. Something like the pic below, except NOT on a flat roof (this is NOT a pic of my building).



See how there are major beams and then the rafters/joists hanging off them? Basically I'm trying to understand if I can have a roof like this where the major beams are inclined rather than kind of flat as in this pic, and they would then be "major rafters" or something and then between them there would be 2x6's strung on simpson joist hangers to form the roof of my building. On top of this will just be some furring strips, then rigid foam and then R-Panel. I'm doing this to provide a foundation for the foam and insulation space on the interior, plus some framing in case I want to drywall it all in or something.

I don't think you'd call them purlins would you? These would not be running across the "major beams" but rather be hanging off of them/between them. And in my case, the 2x6's would also be supporting the roof deck whereas in this pic they seem to just be ceiling joists.

I'm building out a structure that already has structural steel tubing forming the overall structure. If I orient these 2x6 rafters/joists/purlins or whatever they are perpendicular to the steel "major rafters" then the span is less than if I did the normal low-to-high orientation and it just seems like it is going to be easier to frame out (since I don't need them for structural support as the steel is doing that).

Still, I'd like to do some research on this and any pros/cons but without the key terminology I am having no luck finding examples of this. (Unless it is just such a stupid idea that nobody would do it this way, hence the lack of search results!)

Thanks in advance for any help.

 

[johndeereman]

Look like ceiling joist to me.

 

[rburke65]

I would think you could Google carpentry framing terms and find out a lot of info.

 

[CA_Tallguy]

I've looked at tons of diagrams and even have reference books. The issue is that nothing looks like what I'm thinking about doing. Framing diagrams always seem to talk about rafters spaced 12 to 24 inches apart, running from eve to roof peak, and then ceiling joists as a separate thing running parallel and below the rafters.



Here's a pic of my metal frame. I'm currently thinking about boxing in the metal on each of the 5 "frame" sections going down the long length of the building (they are 10 to 12 feet apart) to create "super rafters" -- then running 2x6's between them, 24 inches apart, stepping up to the roof peak. So the only things I have resembling the "rafters" in most diagrams is what will be these things that are more like BEAMS or trusses every 10 to 12 feet. Unless you would call my 2x6's going down the building the long way either rafters or joists.

 

[msherrow]

It does't look like the metal structure is strong enough to support the weight of all the wood you prpose to hang on it. How large are the metal rafters? Or the horizontals? How far apart is each section?

 

[David C]

Roof framing members perpendicular to roof rafters or roof joists are called purlins, regardless of whether they are on top of or hung from the main spanning framing.

In the photo it looks like your steel framing will make a very nice support for a canvas tent.

David

 

[CA_Tallguy]

The tubing is 3x3 structural steel on each section. I know it looks more like 1x1 in this pic! But still, I do wonder if they have enough strength to be the primary load bearing members. My contractor says it will be fine but he isn't exactly the "licensed" type so I'm trying to research it myself too.

The outer walls (and a large section of the center run under the peak) are also going to be framed with 2x6's on 24" centers. In that process, I should be adding a lot to the strength of the vertical posts.

If needed, I COULD make the outer and center walls load bearing if I wanted to run a normal rafter orientation and create a structural ridge beam. It would be a lot more work and seems like a waste of the pre-existing metal frame as I'd basically be framing up a normal stick building so the metal wouldn't be doing all that much.

So I wondered, how can I leverage what steel frame I have? If I can beef up the sections as the primary load members for the structure by be sistering in 2x6's on each side of the steel 3x3 and also boxing in the top and bottom. That should greatly increase their capacity, right? My thinking is they should have strength greater than a 6x8 beam, which will be their approx outer dimension when all is said and done. Or I could sister in up to 2x12's along those if I really need more strength. They are only spanning 14 or 15 feet from eve to peak.

Each "section" of the structure is about 11 feet apart, and the last section is a bit wider, maybe 13-14 feet. There are now 2x2's for purlins running the length of the building spaced 48" apart (not all were welded up before this photo was taken).

I have a feeling that someone is about to post a reply saying "call an engineer!" Before I do that, I'm just trying to get some idea myself on how sufficient or insufficient the basic ideas are. And actually, if I can't come to a SWAG about the sufficiency of running the 2x6's lengthwise, I guess as purlins, then I probably will just end up going the conventional route and have eave to peak rafters using span tables and such. Just seems like a waste of the steel that is there right now.

 

[CA_Tallguy]

This is a pic of the pre-existing building that I'm trying to extend and frame in the walls to create a workshop. It gives you a better idea on the steel framing members.

 

[kbs2244]

DavidC has it right.
They are called purlins.