4" C Purlin Span

[DTCOOPER]

4\" C Purlin Span

I am building a basic little pole shed for the tractor and mower..
I am setting some 3" pipes I have for corner posts, and was thinking of just spanning the 20' with 4" C Purlins that I also have and just screwing the tin to the top. Will the 4" purlins hold a span that long, or do I need to go to a larger purlin?
My tin is 26" x 12'. I was thinking of going 10 sheets wide x 1 sheet long. With like a 1' drop from rear to front. I want to just use the 4 posts on the corners without putting any posts in the middle to keep all of my space open if possible.
What say you folks ?

 

[caylor]

Re: 4\" C Purlin Span

What gauge are the 4" purlins? I have a little book that tells me some purlin spanning guidelines.

 

[EddieWalker]

Re: 4\" C Purlin Span

Daniel,

I'd say your pushing it with that large of a span. The purlins might hold it, but any bad weather, especially wind, and you'll have some flexing or worse.

If you build a truss instead of the C channal, you should be able to make the span fairly easily. Think along the lines of two horizontal purlins reinforced with a bunch of triangles along the length. The triangle shape gives it all the strength.

Eddie

 

[DTCOOPER]

Re: 4\" C Purlin Span

I think they are 11 guage (I THINK)..
Eddie, I have a 15x30 building existing, I want to make this shed kind of a lean to.. it will be totally separate from the existing building, just butted up against it (if that makes sense)
If I do a truss like you are saying, at the back side nearest the existing building, and then another purlin only on teh front edge, do you think THAT would work ?
I am just concerned with making the trusses, will I have to make the posts too high... My existing building is only about 9' high at the wall. So my high side will need to be 9' or less.
Whatcha think ??

 

[caylor]

Re: 4\" C Purlin Span

How about 12 ga? I have not seen and 11 ga purlin manufactured in our part of Texas. Anyway, I would have to agree with Eddie on this one, the span is much too large to span with a 4" C Purlin.

For reference purposes, I recently designed a chemical storage building for a water treatment plant in East Texas and the span between the roof trusses was approximately 17 feet. I used 8"x2.5"x16ga Z-purlins at 4'-0" O.C. to support the metal roof. The only load on the roof was that of wind and 20 psf live load from "snow." Ha yeah right snow in Texas, silly building codes.

So the Z-purlin used in my building is about "double" the size of your 4" C purlin and could only go around 17 feet in span.

 

[DTCOOPER]

Re: 4\" C Purlin Span

WELL DARN IT !
How about if I do some 6" on 4' centers ? Would that hold it ??

 

[wushaw]

Re: 4\" C Purlin Span

</font><font color="blue" class="small">( 20 psf live load from "snow." Ha yeah right snow in Texas, silly building codes. )</font>

You shoulda been in San Antonio in 1984-5 when they/we got 13" (record) there wasn't too many leantoos, awnings, cheesy carports and several roofs didn't hold up either.
It really can happen....just not too often /forums/images/graemlins/smirk.gif

 

[wroughtn_harv]

Re: 4\" C Purlin Span

Your purlins most likely chances are nine times out of nine and a half, fourteen guage.

If I recall correctly fourteen gauge C purlins you need a minimum of six inch for a twenty foot span.

This Saturday, the twenty fourth, we'll be building a fifty two by forty building using four inch C purlins and two inch (two and three eighths O.D.) pipe in Josephine, TX. It's a north Texas TBN get together.

 

[bucmeister]

Re: 4" C Purlin Span

We built a large shed at the camp a few year back and it was recommended we use 8" C purlins on the 20' spans, that has worked well for us. We did place them on 5' spacing which was pushing it for the tin sheeting, but again it has worked well.

As far as rain loading it up, wouldn't that as much a function of the pitch of the roof?

 

[aczlan]

Re: 4" C Purlin Span

We built a large shed at the camp a few year back and it was recommended we use 8" C purlins on the 20' spans, that has worked well for us. We did place them on 5' spacing which was pushing it for the tin sheeting, but again it has worked well.
As far as rain loading it up, wouldn't that as much a function of the pitch of the roof?

Being as the last post was in 2005, I would hope that the OP has finished the project by now.

Aaron Z