Lean-to rafter beam span charts?

[TimberMan]

Hi folks, I am looking for a span chart that I can use to determine the span length options for the beam that supports the rafter birds mouths of a lean-to. I would like to span 14' with that beam to minimize the amount of posts that will inevitably get in my way but I need to see what that would mean in beam size to see if it is worth it or if i should drop down to an 8'6" span.

Thanks!

 

[WisJim]

Need to know location (for snow loads, etc) and the span of the rafters that are supported by the beam in question.

 

[TimberMan]

Need to know location (for snow loads, etc) and the span of the rafters that are supported by the beam in question.

I am in central NC (Chatham County) and will span 14' from the ledger board on the barn to the beam in question with a 2' overhang.

 

[billconner]

That appears to be 15 psf for design load. How far is ledger beam below eave? Drift load.

 

[TimberMan]

That appears to be 15 psf for design load. How far is ledger beam below eave? Drift load.

I am still working on my elevation drawings but let’s say top of ledger will be 24” below the eave of the barn roof.

 

[billconner]

9' of roof at 20 PSF (5 dead and 15 live) and I'm going to suggest the drift load is all on the ledger end of rafters - which would mean rafters are designed for maybe 25 or 30 pounds to accommodate drift load. 180 PLF or 2520 uniform on the header between lean to posts. I believe a triple 2x12 will span 14' with that load. Also what southernpine.com table 15 says for no 2 SYP. A triple 2x10 might and a double 2x12 might but I wouldn't without an engineer's review.

 

[TimberMan]

9' of roof at 20 PSF (5 dead and 15 live) and I'm going to suggest the drift load is all on the ledger end of rafters - which would mean rafters are designed for maybe 25 or 30 pounds to accommodate drift load. 180 PLF or 2520 uniform on the header between lean to posts. I believe a triple 2x12 will span 14' with that load. Also what southernpine.com table 15 says for no 2 SYP. A triple 2x10 might and a double 2x12 might but I wouldn't without an engineer's review.

Thanks! I just looked at the plans for my house and 30 pounds was the total design load used for the roof.

 

[billconner]

Thanks! I just looked at the plans for my house and 30 pounds was the total design load used for the roof.

I suspect very conservative for you but it's the difference of a triple 2x12 vs 2x10.

Don't underestimate you're ledger beam supporting a drift load. Make sure it's well anchored.

 

[PWC Repair]

Looks like one single 2x12 LVL is plenty sufficient for that.

 

[mike93lx]

Looks like one single 2x12 LVL is plenty sufficient for that.

Are you saying a single ply lvl can replace a 2-3ply dimensional lumber beam of the same height, or thay bill's recommendation is oversized?

I had always thought that you could go with a shorter beam with lvl but that you would generally need the same number of plys (e.g. 2x12 down to a 9.5" lvl)

 

[billconner]

Are you saying a single ply lvl can replace a 2-3ply dimensional lumber beam of the same height, or thay bill's recommendation is oversized?

I had always thought that you could go with a shorter beam with lvl but that you would generally need the same number of plys (e.g. 2x12 down to a 9.5" lvl)

I thought it would be the other way. Same depth for reflection but narrower because it's f of b was greater.

How does a lvl compare cost wise with sawn lumber? And in this region, fine to use rough dawn, near half the cost of lumber kiln dried and finished. And in this case, is pressure treated lvl required?

 

[mike93lx]

I thought it would be the other way. Same depth for reflection but narrower because it's f of b was greater.

How does a lvl compare cost wise with sawn lumber? And in this region, fine to use rough dawn, near half the cost of lumber kiln dried and finished. And in this case, is pressure treated lvl required?

Its been a bit since I have priced an lvl, but last time I looked, it was in the $5-7/lf area. Probably a lot higher now.

A 2x12 is going to be around $2-2.50ish/lf

 

[PWC Repair]

Are you saying a single ply lvl can replace a 2-3ply dimensional lumber beam of the same height, or thay bill's recommendation is oversized?

I had always thought that you could go with a shorter beam with lvl but that you would generally need the same number of plys (e.g. 2x12 down to a 9.5" lvl)

According to these charts........a tripled up (3ply) #1-2x12, spanned 14ft, has a Total Load capacity of 355# per lineal ft.
A single 2x12 (1-3/4x11-7/8) LVL 2.0 spanned 14ft has a capacity of 494# per lineal ft..........considerably MORE than THREE 2x12's. That's why they are used to span large openings. And if you figure the cost, it might even be cheaper to go that route.
I've recently learned ALL ABOUT this stuff trying to build my son's cabin.

 

[mike93lx]

According to these charts........a tripled up (3ply) #1-2x12, spanned 14ft, has a Total Load capacity of 355# per lineal ft.
A single 2x12 (1-3/4x11-7/8) LVL 2.0 spanned 14ft has a capacity of 494# per lineal ft..........considerably MORE than THREE 2x12's. That's why they are used to span large openings. And if you figure the cost, it might even be cheaper to go that route.
I've recently learned ALL ABOUT this stuff trying to build my son's cabin.

No ****. Thanks.

I had no idea the disparity was that significant.

I havent had a need to spec one, so haven't dug into it, but that's pretty impressive

2.0 is on the high end of lvl spec, right?

 

[PWC Repair]

No ****. Thanks.

I had no idea the disparity was that significant.

I havent had a need to spec one, so haven't dug into it, but that's pretty impressive

2.0 is on the high end of lvl spec, right?

1.9 vs 2.0 has to do with the elasticity of the LVL. The 2.0 is stiffer and commonly in stock. A 1.9 may be spec'd if there will be normal times of higher moment load where the LVL may NEED to move a bit according to some engineer that understands that stuff LOL!

 

[billconner]

A 2x12 is going to be around $2-2.50ish/lf

$1.20-1.50 around here from the Amish mills. NY code says same as no. 2 SPF. You're probably right that a single lvl would make more sense. I do, however, like the uniform rustic appearance of my totally rough dawn pine garage.

 

[mike93lx]

$1.20-1.50 around here from the Amish mills. NY code says same as no. 2 SPF. You're probably right that a single lvl would make more sense. I do, however, like the uniform rustic appearance of my totally rough dawn pine garage.

What species are you getting from the mill?

 

[billconner]

According to these charts........a tripled up (3ply) #1-2x12, spanned 14ft, has a Total Load capacity of 355# per lineal ft.
A single 2x12 (1-3/4x11-7/8) LVL 2.0 spanned 14ft has a capacity of 494# per lineal ft..........considerably MORE than THREE 2x12's. That's why they are used to span large openings. And if you figure the cost, it might even be cheaper to go that route.
I've recently learned ALL ABOUT this stuff trying to build my son's cabin.

Am I misreading this or is that for no. 1 grade? I looked for no. 2 in my post suggesting triple 2x12. Number 1 grade would likely allow double 2x12.

 

[PWC Repair]

Am I misreading this or is that for no. 1 grade? I looked for no. 2 in my post suggesting triple 2x12. Number 1 grade would likely allow double 2x12.

That chart is for #1.......BUT, there's not much difference in that and #2 grade........at least not for pine.

 

[billconner]

That chart is for #1.......BUT, there's not much difference in that and #2 grade........at least not for pine.

True, but close. Table shows double 2x12 at 205 for my calculated 180. I'd use the triple and not worry about a knot or other flaw, and maybe use all 16s as long as no joint close to center of span. I think that would be a lot more likely to stay in line than a joint on every post. And I'm fine with the lvl. I do think it's more weight to lift and as noted different appearance if that matters. All thoughts also based on me working solo.

 

[Firebrick43]

For a pole barn lean to you really shouldn’t exceed 8’ in span between post.

The minor issue pop is needing larger holes for bigger pads/cookie to spread out the almost doubling weight placed on the soil if you go 14’, especially with snow loads

The major issue that would need some engineering to solve is uplift. By reducing the post count your reducing the number of up lift anchors at the bottom of the post. Lean to’s already have uplift issues due to being open sided allowing wind to get under them, one shouldn’t exacerbate the issue

The increased point loading at the top of the post due to uplift would need some kind of strapping as well.

Uplift forces will be so concentrated that significant strapping will be needed from the beam to the post. In 8’ spacing the header beam is attached to the side of the post with large pole barn spikes. By making a larger beam to handle the loads it’s to thick to nail or bolt and would need to be set on top of the post.

The size of strapping is not your standard stocked Simpson strong tie hardware, stress will be too concentrated for that.

 

[billconner]

2500 pound is maybe a little over a square foot at most depending on soil. Not a very big footing. Yes, may need a hole larger than 12" but nearly half of them.

 

[TimberMan]

2500 pound is maybe a little over a square foot at most depending on soil. Not a very big footing. Yes, may need a hole larger than 12" but nearly half of them.

Yes, I was thinking about footing size and lift resistance over the weekend. 8’ spacing would give me 4 posts vs 3 posts at 14’ which makes be more comfortable structurally. Only downside is that I plan to access this lean to from 3 sides so the fewer posts the better from that standpoint.