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Attaching dimensional rafters to round header beam

 
John weren
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Hey there, I’m a newbie from western Canada and working on a greenhouse project.  I’m wondering how best to connect my girder truss and rafters to the round header beam?  I could use a J bolt if I offset the rafters a bit from the top of the vertical posts.  Not sure if it’s best to have the girder truss(3 ply) resting on the header beam and vertical post joint anyways?  Could fashion up some sort of metal bracket as well. Any thoughts would be greatly appreciated!
JW
Figured pics would help to explain easier
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Mike Haasl
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So the bottom of the truss is flat and would be sitting on your round beams and you're wondering how to attach them?  

I would be tempted to just cut a small flat on the top of the beams.  Maybe 2-3" wide so they don't remove too much wood but give a flat spot for the truss to rest.  Then once the truss is sitting on them, toenail them in place or use some big hurricane ties to connect them.  I don't thing huge J bolts would be needed since they won't really want to move in any direction once the roof is on.  

Will you be doing one tripled up truss and then framing rafters radially from there to cover the rest of the building?  

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John weren
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Mike Haasl wrote:So the bottom of the truss is flat and would be sitting on your round beams and you're wondering how to attach them?  

I would be tempted to just cut a small flat on the top of the beams.  Maybe 2-3" wide so they don't remove too much wood but give a flat spot for the truss to rest.  Then once the truss is sitting on them, toenail them in place or use some big hurricane ties to connect them.  I don't thing huge J bolts would be needed since they won't really want to move in any direction once the roof is on.  

Will you be doing one tripled up truss and then framing rafters radially from there to cover the rest of the building?  



Yes planned on making a small smooth flat surface about  1-1.5” deep on top of round beams and slight knotch in rafters to make smooth connection.  Tend to overbuild and was alsothinking the J bolts would look better that storm ties. Storm ties would wrap around the round beam and be visible.  Thoughts on the three ply girder truss sitting directly above the vertical pole, on the two connecting header beams?  Yes re rafters to G truss. I will add pic.  It’s a non symmetrical greenhouse.  Need to figure how best to connect the 4 rafters at the peak on each side of the girder truss. A hanger similar to pic probably works best but needs to be fabricated.
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Mike Haasl
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Wow, that is a funky shape!  Looks like you have some engineered plans, might they have specified a connection at the peak?  

The triple truss likely can hold the weight of the whole roof.  The other rafters just need to be solidly tied to the peak and the perimeter beam so they don't shear down into the building.  Normally with rafters you have to worry that snow load will push them down and blow out the walls of the house.  Here the truss is probably designed to hold them up (if connected well enough) and keep the wall beams from getting pushed outward.

All those words don't resolve the need for a very good connection between the rafters and the central truss.  

One thought could be to bolt through the vertical central 2x6 of the truss to add a block of wood (dark red) on either side.  Then the rafters (green) can rest on that block as well as be nailed/timberlocked to the truss.
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John weren
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Mike Haasl wrote:Wow, that is a funky shape!  Looks like you have some engineered plans, might they have specified a connection at the peak?  

The triple truss likely can hold the weight of the whole roof.  The other rafters just need to be solidly tied to the peak and the perimeter beam so they don't shear down into the building.  Normally with rafters you have to worry that snow load will push them down and blow out the walls of the house.  Here the truss is probably designed to hold them up (if connected well enough) and keep the wall beams from getting pushed outward.

All those words don't resolve the need for a very good connection between the rafters and the central truss.  

One thought could be to bolt through the vertical central 2x6 of the truss to add a block of wood (dark red) on either side.  Then the rafters (green) can rest on that block as well as be nailed/timberlocked to the truss.




Ya it’s shaped to conform to existing oval garden.
That’s a good thought with block and would be less obstructive than a longer board running in same place but from both edges of truss, but may exert excessive pressure on that piece of GTruss (may be overthinking it)  Would still be nice to tie the rafters to the GTruss for lateral movement, even though posts are solidly in the ground.

Yes the engineered drawings (for permit) specifically hurricane ties but not significant detail as was trying to save on cost
 
Dan Parker
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For the truss to header connection I would consider a piece of steel angle as a seat.

Depending on the diameter of the header, a size of steel angle with equal length legs could be specified. This approximately 8” long piece could be placed on the header with one leg oriented parallel to the truss or rafter to creat a seat.  Four holes in the angle could pass lag screws to secure it, two vertical screws and two horizontal.
 
John weren
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Dan Parker wrote:For the truss to header connection I would consider a piece of steel angle as a seat.

Depending on the diameter of the header, a size of steel angle with equal length legs could be specified. This approximately 8” long piece could be placed on the header with one leg oriented parallel to the truss or rafter to creat a seat.  Four holes in the angle could pass lag screws to secure it, two vertical screws and two horizontal.



Thanks for the thoughts.  Not sure I entirely follow.  Could you send a pic or do a basic sketch on phone?
 
John weren
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wrench weren wrote:

Dan Parker wrote:For the truss to header connection I would consider a piece of steel angle as a seat.

Depending on the diameter of the header, a size of steel angle with equal length legs could be specified. This approximately 8” long piece could be placed on the header with one leg oriented parallel to the truss or rafter to creat a seat.  Four holes in the angle could pass lag screws to secure it, two vertical screws and two horizontal.



Thanks for the thoughts.  Not sure I entirely follow.  Could you send a pic or do a basic sketch on phone?

. Header is anywhere from 6.5” to 7.5”



 
Dan Parker
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wrench weren wrote:

Dan Parker wrote:For the truss to header connection I would consider a piece of steel angle as a seat.

Depending on the diameter of the header, a size of steel angle with equal length legs could be specified. This approximately 8” long piece could be placed on the header with one leg oriented parallel to the truss or rafter to creat a seat.  Four holes in the angle could pass lag screws to secure it, two vertical screws and two horizontal.



Thanks for the thoughts.  Not sure I entirely follow.  Could you send a pic or do a basic sketch on phone?


Yes, I will try to post one here. If not I can send it to you with your address.
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Dan Parker
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Well there it is!

For the diameter header you indicated I would recommend a  L5x5x3/8“ or possibly a L6x6x3/8”.

The section drawing I made shows two lag screws but four screws, one in each corner is the intention here.
 
Dan Parker
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If you extend one of the legs you may be able to fit  fasteners that will secure the rafter to the beam. Here I am showing a L8x6x3/8 with two additional screws or bolts with nuts.
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John weren
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Dan Parker wrote:If you extend one of the legs you may be able to fit  fasteners that will secure the rafter to the beam. Here I am showing a L8x6x3/8 with two additional screws or bolts with nuts.



Thanks!  That seat may work well at the girder truss to header joint, 3 ply/4.5” wide.

I guess could rotate the angles 90 degrees and add one to each side of the truss as well as per pic.

4EAD34D5-224D-433B-9FBC-FD590DE9BA15.jpeg
[Thumbnail for 4EAD34D5-224D-433B-9FBC-FD590DE9BA15.jpeg]
 
Mike Haasl
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I think it could work for the rafter to beam connection as Dan drews but I'd prefer a flat on the beam and orienting two bracket the way you just came up with.  There shouldn't be much side load on that connection but more metal always looks more secure and helps people sleep better.

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Dan Parker
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wrench weren wrote:

Dan Parker wrote:

I guess could rotate the angles 90 degrees and add one to each side of the truss as well as per pic.



Yes, welding or bolting two additional L brackets as in your drawing to the structure I drew earlier would be ideal.

 
Peter Ellis
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You're building under a permit issued based on engineer's drawings and specifications, correct?
Are your building inspectors going to look at whatever you invent in collaboration with people on the internet and just accept the alternative solution, when the engineer's drawings that were approved specify something different?
I'm actually facing exactly that issue in a build I am working on. The engineers specified a particular kind of scarf joint, but apparently forgot that this structure is being built with round wood. The scarf joint they specified works great in rectangular milled lumber, but tapers away to an unacceptably small cross section in round wood. I'll be substituting a scarf joint that is better suited to round wood and functionally equivalent to their call out. It's a readily explained adjustment that I fully expect the inspector to accept.

On the other hand, where the engineers have called for simpson strongties to anchor the posts to the foundation, I'll be using precisely what they specified, because I can't make a valid argument that what they called for won't work and I don't need to provide areas for the inspector to question the build.

In a sense, if it ain't broke, don't fix it. especially if big brother is looking over your shoulder watching what you are doing.
 
Glenn Herbert
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It would definitely be best to locate the girder truss seats directly over the posts at the header joints, with a suitable flat for good bearing. A small notch in the bottom chord of the truss may help with alignment, but I would be wary of reducing the cross section of members in tension, especially if engineered at full dimension.

I would use the pair of "L" oriented angle brackets sitting on top of the headers, bolted together through the truss and down through the headers on each side of the post.

JIIIL

III is the girder, J L are the angles.
L4x4x1/4 x 4" long should work fine.
I would use two bolts through the girder, staggered horizontally and vertically so they distribute the load in multiple planes and do not stress one grain line. Nailing plates on the girder faces at the bolt locations would help reduce the possibility of the girder lower chords splitting, not that they would have great splitting stress normally.
 
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