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Truss plates for Segmented Roof Vaults

 
gardener
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I've been working on an idea for making Segmented Roof Vaults from whole pallets.
I don't have any legible  drawings yet, but picture an octagon with equal sides, now, cut off 4 sides in a strait line and that is what this vault should look like in profile.

I was trying to design a plywood truss plate that would align each pallet to the proper angle with no cutting of the pallet.
While researching I saw that  that most trusses uses plates that were simple rectangles and the lumber itself was cut to fit at the proper angle.
Now I'm thinking I should follow suit and cut the ends of my pallets to fit at the right angle.
I'm not sure about using rectangular truss plates.


The thing is, I'm trying to have a clear span with no bottom cord or webs.
Because of that I'm thinking I should keep a 135 degree corner in my truss design.
A rectangle would have a lot less material in contact with the joint.
Right now I'm considering an  obtuse triangle, a short squat pentagon and a "boomerang shape".
I've also considered abandoning any predesign for the truss plates whatsoever.
By cutting each pallet stringer to 67.5 degrees on each end, I could fit them together, and fasten pallet deck boards across them till I'm satisfied.
Any excess board would be cut off with a sawzall latter.


 
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If I'm understanding correctly, I'd cut the ends of the pallets to 135 degrees so they butt together fully.  Then I'd use triangular plates of plywood to connect the pallets to each other.  Pallets may warp/twist as they dry out so your building may change shape a bit over time.

Remember that the metal truss plates attach pretty well to pine lumber but if your pallet runners are hardwood it might be a struggle to pound them in.
 
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My experience with well seasoned pallets is that a decent nail gun should be able to do the job. The question now becomes if the investment is worth it.
 
William Bronson
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I think if each pallet is cut to 67.5 degree an angle   they will join to form 135 degree angles.
I want a framing nailed anyway, though my compressor has a rather small capacity.

I was looking for the photo that inspired me,  and sure enough,  someone posted the story  here on permies.

https://permies.com/t/6306/Slumtube-Affordable-Housing-Shipping-Pallets

It features an arch shape that is a dodecagon, with 5 sides cut off.
There seem to be two arches,  one either the other.
I was thinking of a second outside wall,  but vertical,  with the space between filled with leaves, for a compost that develops into a leaf duff, and eventually a green roof.
 
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I liked this last night and I still like it this morning.  I was thinking about it in bed before I got up, and I don't think it wise to cut the pallet ends.  In my experience they are stuck with horrid nails and it would be a nasty job anyway.  I would consider splitting a 10(?)inch pole though to make 8 segments and use these at the nodes, like the wedges in the link you give above.  Possibly they could be pre-nailed so the pallets knock on, although this might be tricky at the last pallet.  Assembly will be a bit awkward without help, since pallets are pretty chunky to lift around.
You'd probably still need buttressing or other support at the wall tops, to cope with the spreading loads.
 
pollinator
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I've usually used obtuse triangles in my homemade trusses; lot less cutting than the pentagons, and the boomerang would be even worse imo..


But.. you sure give up a lot of strength skipping a bottom chord.

A compromise option would be raising the bottom chord... you could also do something like a scissor truss..
 
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The two arches in the photo are connected to form a truss. This gives it actual strength to stand varying loads. A single arch of pallets would depend on very strong joining plates and/or geometry to spread the load best (not semicircular but catenary).  If you put the arch on top of walls, you would need either buttresses to keep the walls from spreading, or slanted walls to counteract the spreading force.

The triangular plates to join the double arches only need good nails/screws to fasten the parts together. They function as the "wedges" mentioned previously.

A double pallet truss as shown would also require diagonal bracing from inner to outer layer for best stiffness. A series of rectangular frames requires rigid joints for strength, while subdividing the rectangles into triangles with diagonals makes an inherently rigid structure.
 
William Bronson
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Excellent points.
After noodling about it,  I'm leaning towards cutting 2x4  lumber into  inverted equilateral trapezoids , 4"  on the top,  about 1" on the bottom, and roughly 3.75" on the equal sides.
In practice I would cut 22.5~ angles on either end of a 4" length of 2x4.
This should give me the angle I need between pallets.
It's better than plywood because short pieces of 2x4 are commonly discarded, and easily cut.


Now for strength... I would rather not double up on the thickness of the wall, and I still want to keep the inside of the span as free as possible.
Pallet deck boards are roughly 3.5" x 40".
If I screw a deck board to one of the trapezoids the combination can align the the pallets at the proper angle, and act as a truss plate.
After this first truss I plate is in place,  I should be able to add two more deck boards under the first.

This would create a rectangular plate made up of 3 boards, with 165 square inches of material in an obtuse triangle between the two pallets.
 
Glenn Herbert
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Those trapezoids should work fine as spacers, though they will have pretty much zero strength for fastening anything - they will split from the first nail driven, and if predrilled they would split at the first load placed on them. I think cutting boards, or pieces of pallet rail, to about 16-20" long tapering to points at 22 1/2 degrees (long skinny triangles/trapezoids) and fastening those to the sides of each joint would give a reasonably strong arch. How wide a structure are you looking to get? If you do not use curved sheets of roofing material, you would want an even number of segments so there was not a flat top to worry about shedding water.
 
D Nikolls
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Glenn Herbert wrote:I think cutting boards, or pieces of pallet rail, to about 16-20" long tapering to points at 22 1/2 degrees (long skinny triangles/trapezoids) and fastening those to the sides of each joint would give a reasonably strong arch.



I would bet on dimensional lumber of any sort having a tendency to split if used as truss plates; my understanding is that plywood or steel is the standard for exactly this reason!


I took this pic of the truss framing in the barn at my friends former property. I think the builder was working with shorter lengths of salvaged roofing, and this was how he managed a larger span.. it seemed applicable to your goals.

The building is of unknown age and probly never met a permit or engineer... but the trusses seem sound at least a couple decades later.
20201209_131951.jpg
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Glenn Herbert
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Yes, I was thinking after posting that plywood would be the best type of salvaged material for truss plates... it was late and I didn't have time to get on again. I would think any sort of plywood say 32" long x 8" wide in a trapezoid with 22 1/2 degree acute angled points would do a fine job.
 
William Bronson
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The strength of pallet decking is a real issue.
This article from Mother Earth's News was part of what started me looking into doing an arched roof.
http://builderswithoutborders.org/publications/pub6.htm

Its about parallel chord pallet trusses, built using pallet wood and round wood poles.
Owen Geiger is the author,  and he refers to Alfred von Bachmayr, who pioneered building trusses from nothing but pallet wood.

Both of these guys were/are involved with appropriate technology development work  with Builders Without Borders.

Von Bachmayr has passed away,  but he developed the pallet truss as way to reduce the expense of roofs on stawbale buildings, for which he was a great advocate.

The article above referenced  von Bachmayrs article in The Last Straw Journal, issue #38, The Pallet Truss: A Low Cost Alternative Roof Structure, but The Last Straw Journal website is rather janky, and I did not find that article yet.
I did find some other nice articles about his work with pallets.
Here is a memorial to him that has some nice photos of pallet trusses being used:
https://www.thelaststraw.org/tribute-alfred-von-bachmayr/
Here is his article "The Pallet Truss: A Low Cost Alternative Roof Structure" from the Builders Without Borders website :
http://builderswithoutborders.org/publications/pub6.html

The thing is, both of these guys pre-drilled the pallet wood and at least  one of them used glue as well.
Glue is not something I'm eager to do , it means more things purchased.
Pre-drilling isn't so bad,  but I do have another method that might work.
Brads and staples from an air nailer don't seem to split pallet decking.
I say this because I've clad 20 feet of fence in decking board, using these fasteners.
No splitting to speak of.
Now clearly the holding power and shear strength of a few brads or staples is not going to be enough, but fortunately, they are very cheap, easy, and fast to use,  so using 20 of them is an option.

Assuming that this works,  I will still need to adjust downward my expectations for the strength of this roof design.
I'm not against using plywood, but I am inspired to investigate ways to build with salvaged pallets adding only a minimum of purchased materials.


On the subject of using plywood, another consideration is using a CNC to make the cuts.
This could save labor and material while making precise and  complex shapes viable.
The boomerang shape,  for example,lends itself to being nestled closely together with very little waste.
Truthfully I'm not sure if that is good shape, it creates beneficial geometry, no triangles, instead it seems heavily reliant on the strength of the plate material.
bldgtrusses.jpeg
 Building pallet trusses using jig
Building pallet trusses using jig
settrusses.jpeg
 Setting pallet trusses on a strawbale structure
Setting pallet trusses on a strawbale structure
 
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there is the lamella style roof makes use of shorter sections timber planks
house-roof-idea-lamella3.jpg
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house-roof-made-from-wooden-plank-sections.jpg
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lamella-rafter.jpg
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lamella-roof5.JPG
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pollinator
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I just have to say, tony, I love the look of that on it's aesthetic merits alone. It looks structurally beefy, and yet I bet some iteration might be made to work really well for greenhouse glazing structure.

I love the department of ag publications, specifically the older ones, at least the ones that haven't been anathametized for being based on bad practice.

-CK
 
tony uljee
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giant beehive anyone
bee-hive-roof-full-of-bees.jpg
[Thumbnail for bee-hive-roof-full-of-bees.jpg]
gift
 
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