advise on shed roof trusses diy

top gnome

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thank you for all the help. maybe I should add a brace or two on the trusses right now I have the king post and a couple of long screws in each joint along with the pl adhesive and the mending plates. they seem very strong. the will be attached with hurricane braces. I have a couple of them up already. What is the specific issue with sun tuf for the roof? My wife wants a translucent roof and altho expensive the sun tuf fits the bill. I just paid for the suntuf stuff so if someone has had specific issues it would be helpful to know what the issue were.
 

OrangeKrush

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I have a quick question on roof trusses I am building for the small shed so the span is 9 ft wall to wall and 10 ft overall. I am building the truss in the picture that I have seen at a couple of building centers and Menards but realized that most of the pics show the top chord passing by the bottom chord and I have two trusses built and would prefer to leave the bottom chord pass by the top chords. like in this picture. I will use strapping and hurricane braces. the building will have strong wind pressure and some snow. I am using clear plastic Suntuf panels for a roof. 24" inch trusses oc with 24" strapping oc shed is 19 ft long View attachment 86309
This is the best way to do it in my opinion. The top cords run over bottom cords for the wanted overhangs, plus it gives you options of how you want to do your underside soffits on your overhang. How you have it is the way I would prefer it.

Are you saying you are spanning 9' out to out of walls and made trusses 10' leaving you 6" overhang on each side? This will work great with the truss you have shown... no flat spot anywhere!

Probably don't need it but this wouldn't hurt if you have any extra. 722C0095-497A-4969-B855-A40582B7B077.jpeg
Use plywood gussets to all the adjoining 2x4 sections unless you have the cleated type. Sounds like you have this under control though!
 

top gnome

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Those 'mending plates' need to be pressed into the wood, straight down, in one constant press NOT hammered on a zillion times to get them in.
too late i already hammered them in I wish I would have known that -- hammering them in was no fun at all. I have some of the trusses up and will finish putting them up today I am now worried that they will not be strong enough I am thinking about adding plywood gussets after they are up. I have a bunch of work to do before snow flies. I am wondering if I could put a cross pc on the outside of the truss across the top chords. There will be three rough sawn 1x4 across the trusses as strapping. I know the plastic will not add any strength but will also not add much load. I am not sure how strong the PL adhesive is a lot of stuff I build with titebond the glue is stronger than the wood and the fasteners are only there until the glue dries.
 

top gnome

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This is the best way to do it in my opinion. The top cords run over bottom cords for the wanted overhangs, plus it gives you options of how you want to do your underside soffits on your overhang. How you have it is the way I would prefer it.

Are you saying you are spanning 9' out to out of walls and made trusses 10' leaving you 6" overhang on each side? This will work great with the truss you have shown... no flat spot anywhere!

Probably don't need it but this wouldn't hurt if you have any extra. View attachment 86458
Use plywood gussets to all the adjoining 2x4 sections unless you have the cleated type. Sounds like you have this under control though!
I have the mending plates and adhesive and at least one screw on all the joints. I don't really understand the no flat spot sentence . the soffits will be 5 inches on each side and after the roofing is up I will put on the eves. unless I am missing something which is very very possible.

How do trusses fail? I can see the top chords sliding off the bottom chord I dont think the 2x4s are going to break over a 6 ft span. I am worried about the wind as much as the snow we get hurricane force winds pretty often.
 

OrangeKrush

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I have the mending plates and adhesive and at least one screw on all the joints. I don't really understand the no flat spot sentence . the soffits will be 5 inches on each side and after the roofing is up I will put on the eves. unless I am missing something which is very very possible.

How do trusses fail? I can see the top chords sliding off the bottom chord I dont think the 2x4s are going to break over a 6 ft span. I am worried about the wind as much as the snow we get hurricane force winds pretty often.
Do as Old Paint suggested and use some plywood gussets on your 2x4 joints where they meet and use plenty of nails or screws. Very important that you do this as this is what's going to stop any movement of the cords shifting where they meet each other.
 
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Old_Paint

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@DustyRusty , I don't have ANY snow load to worry about, otherwise, there would have been a lot more trusses and purlins, but they still would have been 2x4's. I was going to put them on 24" centers, but since it's a non-residential building, the inspector told me 48" centers was just fine. I'd probably put them on 16" centers as well if I had to worry about snow, but you'll find a truss made of 2x4's is stronger than a rafter made of 2x12's. A LOT stronger. I was impressed with these after I built them. Very impressed. I have a 2x8 connecting the bottoms down the centerline of the shed (under the ridge) and put X braces between them to also improve any chance of wobble. Despite it being open, it's hard to move up there with all the bracing. A truss made with 2x12's could be used to lift a tractor trailer rig or drive one on it, if properly constructed. But one 2x12 truss would weigh as much as all of my trusses put together. Then the load carrying capacity of the walls becomes an issue, real quick. As I pointed out, 2x4 trusses and steeper roofs are becoming the norm for construction down here. Much less expensive materials costs, better profit on the construction.

The biggest concern with trusses is that all joints are well fastened. There are so many different designs that it makes it easy for one person to argue the benefits of one over the other. I was originally going to use the mesh, too, but when I saw that it's not as effective if it can't be applied with a flat surface press, I elected to use gussets. I glued the gussets and put three screws in EVERY timber joined by a gusset on both sides. I also used 'weather proof' screws to get the maximum corrosion resistance, but now that the glue is set, it probably doesn't matter if the screws are there or not. I would have used stainless fasteners, but when I figured up how much that was going to cost, I couldn't justify it. Corrosion of fasteners due to damp/wet timber is one of the worst enemies in the South. While worse on outdoor installations like decks, just the humidity here can make a timber stay damp enough to make a Fastener corrode and fail. I've got a deck to rebuild this autumn at a second property because of this very problem. The builder that installed that deck did not use outdoor rated fasteners, so most of them have failed. It's just a really neat stack of lumber, not a deck. More like a Jenga game.

A metal roof will shed snow a lot better than a composite/asphalt roof simply because it's smoother and has less friction, especially if any heat can get under the metal. My guess is that's why you always see doors and windows under gabled ends up north, or brakes to divert the snow around potential pedestrian traffic areas. A steeper pitch can also help with snow load, but it's a lot harder to stay on a slick painted metal surface for putting in the fasteners or any roof maintenance. Ya don't have to go very much further south from here to have roof pitches down in the 2:12 range, just enough for rain to run off.
 

Old_Paint

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The pyramids analogy does not really apply to truss design.
But triangle theory applies to both trusses and pyramids. That was my point. EVERYTHING can be solved with triangles. They're the strongest structure known to mankind. Pythagoras was a pretty smart dude.
 

fried1765

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But triangle theory applies to both trusses and pyramids. That was my point. EVERYTHING can be solved with triangles. They're the strongest structure known to mankind. Pythagoras was a pretty smart dude.
Pyramids sit flat on the ground.
Pyramids are dead load structures.
There is no load carried by a pyramid.
 
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Russell King

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If you are worried about the strength of the trusses then just make a second set and put them double at each location. The weakest point of the trusses won’t be the same place so you get more safety and strength with the double trusses.

You can also just place more single trusses closer together so that less load is on each truss.
 

GreensvilleJay

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I KNOW one way a ROOF truss can fail....
Keep adding 'stuff' on top of the bottom chord (aka 'garage attic space ') and you'll destroy a 40' long truss ! There USED to be 7 of them in the shop (12' OC), One 'snapped' as someone had kept putting stuff ON TOP of the bottom chord.
 

top gnome

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thank you

I ended up putting a 3/4" plywood gusset on the top and each end of the truss with about 15-20 nails. glued along with the mending plates and just a mending plate on the other side. I think it is enough the wind is strong enough the snow will not likely be on the roof long. Looking at the suntuf documentation the want a 2x purlin so I will add that. I do not intend to hang anything from the bottom chords.
 
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Old_Paint

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Pyramids sit flat on the ground.
Pyramids are dead load structures.
There is no carried by a pyramid.
Again, I think you missed my point. But, ok, you made your point, you're the expert. I get it, experts must be righter than anyone else, whether or not they are on target.

I'm not going to hijack the thread to argue with an expert. I'll just have to accept that I was lied to in geometry class about 50 years ago, and everything I've used triangles to solve strength issues was wrong. I'm disappointed that I let someone mislead me with Pythagoras' theory. According to you, pyramids are not triangles. Gotcha.
 

fried1765

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Again, I think you missed my point. But, ok, you made your point, you're the expert. I get it, experts must be righter than anyone else, whether or not they are on target.

I'm not going to hijack the thread to argue with an expert. I'll just have to accept that I was lied to in geometry class about 50 years ago, and everything I've used triangles to solve strength issues was wrong. I'm disappointed that I let someone mislead me with Pythagoras' theory. According to you, pyramids are not triangles. Gotcha.
Perhaps a bit past high school geometry class!
Civil engineer here!
Obviously, I know just a little about building design/construction, and the Pythagorean theorem as well.
 

Old_Paint

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thank you

I ended up putting a 3/4" plywood gusset on the top and each end of the truss with about 15-20 nails. glued along with the mending plates and just a mending plate on the other side. I think it is enough the wind is strong enough the snow will not likely be on the roof long. Looking at the suntuf documentation the want a 2x purlin so I will add that. I do not intend to hang anything from the bottom chords.
Yes, your trusses will work just fine, especially now that you added the glued gussets to them. They're probably overkill, depending on snow load you might see. I didn't need to, but I put gussets on both sides. That just makes sure I mitigate any flexing effects on the joints. 9 feet isn't a long span in the grand scheme of things, but that bottom chord will eliminate any outward force on your walls. Nails or screws for assembly doesn't matter, other than keeping the truss flat in its plane while handling it. I.E., don't let it flex side to side. But you shouldn't have much trouble with those considering how small and light they are.

Not sure why you would need a 2x purlin on a roof that small and with trusses on 16" centers, but if that's what the manufacturer wants, you should probably heed that. I used 2x purlins as well, but laid them down rather than standing them on edge. If I had it to do again, I would double the number of purlins I used instead of just putting the minimum recommended by the roofing manufacturer. Your roofing manufacturer may have a minimum fastener penetration in their design. In the event of a severe windstorm, the plastic sheeting is going to tear away before a purlin fails, which might actually be a good thing (to prevent complete destruction), except for anyone downwind of you (flying plastic debris). Just make sure to follow all the instructions for the fasteners. Usually on stuff like that polycarbonate roofing, there's additional or larger washers required to prevent it from tearing out easily.

That's gonna be a very strong roof, structurally. Don't doubt your design. It will likely hold up anything your walls will support. Your trusses will tie the walls together and make the whole structure very rigid, especially with the bottom chord going all the way to the ends of the top cord. If you're putting sheathing on the walls, that's when you'll really notice it getting rigid. Believe it or not, that's still triangles at play. Sheathing prevents the structure from racking and twisting, as well as makes vinyl siding installation much easier.

Short soffits and eaves will do a good job of mitigating lateral wind drag that normally lifts a roof. The hurricane ties will certainly add to that protection. I would still recommend a vent on the ridge if you're not going to put any climate control on it. Obviously you're not putting a ceiling in it, otherwise there would be no point in translucent roofing. A ridge vent will equalize any pressure in the event of a tornado or high wind to prevent implosion or certainly blowing out any windows you put in it.

Is this going to be a growing/planting shed, or are you just using the translucent roofing for daytime lighting? A small solar system would be a great addition if you need lighting.

I'll point out again, if you want 5 ONLY ways to build a truss, just ask 5 experts. I'm not trying to be an expert, just lending my design and experience. I tend to put a lot of overkill in what I do to make something strong. What I do might cost more than what someone else might do. It's just what I think I want at the moment, whether necessary or not. I used to build doll houses for the girls in the family, and I'd build the roofs strong enough for me to stand my 200 pounds on. Simply because I know what kids will do when you're not looking. I didn't want the roof to cave in and hurt the kids if they decide to climb on them. Overkill? Certainly for a doll house, but not for the kids' safety.
 
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Old_Paint

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Perhaps a bit past high school geometry class!
Civil engineer here!
Obviously, I know just a little about building design/construction, and the Pythagorean theorem as well.
I grew up on a farm in podunk rural Alabama, and education was my escape. Little did I know how much education I was getting while roofing/repairing barns, digging wells, and reinforcing machinery, even driving a tractor in a straight line with nothing but parallax and triangles to guide me. I got a lot of the practical knowledge about triangles long before I understood the math, and the practical experience is exactly why I decided I'd rather work with my head than my back and hands. I certainly learned a lot about gravity down in those wells and using my head to stop a falling bucket was not the best lesson.

I became an electrical engineer and put in 45 years in heavy industry services in just about any industry you can think of in just about any discipline you can think of, so I'm just a little bit past geometry, too. You'd be hard pressed to name a single industry I haven't been in, and a large percentage of that service work included a lot of mechanical knowledge, especially in motors and generators. I know a thing or two because I've seen a thing or two that used a whole lotta triangles to solve the problems at hand, even some triangles that couldn't be seen. But that's just it, it was still using triangles. The use of triangles in both our professions is exactly what makes the two very different applications of Pythagorean Theory so very similar. But if pyramids are not triangles, then I was certainly taught a lot of fallacies in geometry, and all those lies were reinforced for lot of education and a very long time. The world is flat, and you'll probably never get a civil engineer and an electrical engineer to explain something the same way. I can live with that.

Just goes to show you, if you want 5 ONLY ways to do something (or explain it), just ask 5 engineers.
 

OrangeKrush

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thank you

I ended up putting a 3/4" plywood gusset on the top and each end of the truss with about 15-20 nails. glued along with the mending plates and just a mending plate on the other side. I think it is enough the wind is strong enough the snow will not likely be on the roof long. Looking at the suntuf documentation the want a 2x purlin so I will add that. I do not intend to hang anything from the bottom chords.
When you get a chance you should throw a gusset on that bottom cord where the upright 2x sits on it.
This could be the last thing you do to the building.. scrap 2x, plywood or 1x unless you already have the metal gussets on them.👍
 

top gnome

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thank you all for the help. I am using board and batten siding with 1x4 strapping on 24" centers. the 2x4s will be on the flat for the purlins I will add the pc at the bottom when the building is closer to complete. I realize both sides would be better but I think this will suffice. thank you again for the help
 
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awesome

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FWIW: I built a garage this summer and ordered trusses. They were factory made and approved by an engineer. I'm in a region where we get lots of snow.

They are 30' long with a 6/12 pitch. All built with simple 2x4s. I have 1 truss every 24".
I actually had to build and extra one myself since my design changed and I made the garage 2' wider. Like @Old_Paint said, I used little pieces of plywood instead of the metal things on every joints. The metal ones are expensive.