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

 

[cj06]

Re: 4" C Purlin Span

probably redid a couple of times till it held !!:thumbsup:

 

[MW66]

Re: 4" C Purlin Span

This is a little off topic from this thread, but I thought that someone might be able to help. I have a new home built with trusses and we are now getting drywall seam cracks in the ceiling. I've discovered that the trusses were not laterally braced according to specification. However, my question is that I saw some sections of bracing that consisted of very short purlins that only spanned the distance between each truss. They used a number of these short purlins and just staggered them down the entire row of where they thought the bracing should be. Is this method of using very short purlins acceptable? For instance, if the gap between the trusses was 16", then they used a number of 17" pulins and staggered them down the entire row.

 

[crash325]

Re: 4" C Purlin Span

With only 4, 3" corner pipe posts, your asking for trouble. Get some wind and your shed will look like a Hula Dancer.

Look at the picture, that guy spans 20' wide by 12' deep. Corners a 2 "C" channels joined into an "L". The corners are 5/8" red heads 4 on each corner. They go into the exsiting slab. Concrete was poured 18" below the slab and 5" above. Re-bar goes through the corners as well.

At the very least put on sway braces as shown in the picture. Those are 1" pipe 4' long, flattened and double bolted at each end.

 

[rambler]

Re: 4" C Purlin Span

More typical to nail a longer wood across the bottom chords, but if you have a pile of 17 inch pieces of 2x I don't see why it wouldn't work, uses more nails. I'd think you wouldn't want them staggered very much, or there will be flex between chords, like an acordian?

As to the old thread part of this, wow, us northern folk sure have to build a lot more than you southern folk can get by with! Four corner posts, 20 foot spans, 1 foot drop on the whole roof - that wouldn't last through most Novembers up here, much less a full winter.

As to the picture of the shed awning; why in the world would someone build a 9 foot high awning in front of a good shed with a (looks like around) 12 foot high door???? What a waste of resources to limit the door to 9 feet.... (As a farmer, equipment keeps getting bigger, shed wall height is always a miserable limiting factor in what you can get inside a shed.)

--->Paul