Build your own roof trusses -advice ?

gabeancounter · Sep 7, 2011

Project 28x50 pole barn with first 3 bays enclosed and other 2 will remain open. Want to use standard shingles for roofing instead of metal. HOA will not let the siding be metal etc.

Roof trusses @ 24" OC. 26 trusses total. I have calculated the cost to build (w/ free labor) the trusses at $33 each versus $68 plus delivery. $900 savings equals worth the effort!

28' trusses with 1' overhang is the largest I can build with 16' lumber. According to the plan below, I will need 5 1/2 - 2x4x16 and a little more than a half sheet of 1/2" plywood.

I am able to purchase 2x8x16 SYP for $8 versus 2x4x16 Whitewood for $6 -Is it better to rip the 2x8's in half? Any problems doing this? The boards will be a little thicker than a standard 2x4 by using this method. The southern yellow pine is heavier and seems stronger than the whitewood? I have a good tablesaw to rip them with. My other question is that the plans show not cutting the inside braces with any angles just letting the plywood gussets hold it together- any problems?

Thoughts?

EddieWalker · Sep 7, 2011

I'm not an engineer, so I'm not qualified to tell you what to build or how to build it. I do have some experience with building, and make a living as a General Contractor/Remodeler.

If it was me,
I would use 2x6's for the top runs.
I would cut all my angles so the ends are flush and tight with each other.
I would add a 2x4 in the middle from the peak to where your bottom chords come together.
I would make the top, middle, plywood gussets bigger. Probably 12 inch square
I would use deck screws on the plywood gussets
I would run two 2x4's the full length of the building on the bottom chords to tie them all together at an equal distance apart by deviding the span into thirds
I would be sure to overlap my decking
I would cut one truss and write the length and angles on the ends of every board, then cut and built them all at the same time.

That's just me and what I would do.

Eddie

massey990 · Sep 7, 2011

There is a big difference in grades of SYP, most truss engineers require "#1 dense" for the key members. Less expensive grades can be used for the webbing.

schmism · Sep 7, 2011

As a previous truss engineer.

Look up how gradeing rules are done. You can NOT rip graded #1 2x8 into a 2x4 and expect the 2x4 to also be #1.

as #1 eastern spruce is not a grade of material you can get today. you will likely need yellow pine instead. SYP or SP. Today the grades are #1/#2 SPF. and yellow pine grades from stud to #2, #1, select structural and dense.

Look for a larger lumberyard that builds trusses. they will have MANY MANY more grades of 2x4 than lowes. you should be able to buy SP #1 from them.

the grade of the material is very important. You can always go up in grade without having to recalc the design but never go down.

You dont HAVE to cut angles on webs, but for compression webs (the outer 2 short webs in the W pattern) you can rely on direct contact pressure to transfer some of the compression force instead of haveing to rely entirely on the plywood gusset and nails. The other issue is you may have difficulty finding enough room to put all the nails if you dont include the tips of the angles.

Another mistake that is commonly made is someone will find (or get) a truss drawing showing "real" press-in-plate sizes and instead go the a big box store and buy nail on plates of the same size and use those instead. WRONG. dosnt work that way. the holding value of nail on plates is FAR less than that of machine-press-in-plates.

The size of the nail, 3" common as called out in the drawing, greatly affects the number of nails needed in each joint. the smaller the nail the less holding power it has. as im shure you dont want to spend all the time to clinch all the nails over with 3" nails and 2.5" of material, i suggest you upsize the gussets to 3/4" plywood. You cannot simply downsize the nails to 2.5" nails and use the same number as shown in the drawing.

Id ask the truss manufacture to price out an 8' OC truss instead of a 2' oc truss. you might be surprised to find its cheeper to go that route as there are only 8 required for your 50' building.

Id also inquire at the truss manufacture about putting together a kit for the building including all the purlin material for the roof and for the sideing as well as posts. You may find his price on material for a kit for the complete building (with all materials delivered) is very comparable to what you can buy the materials yourself. you can see significant savesings if he uses a composit posts plating treated material on the bottom and regular material on the top. a 3 ply 2x8 post will be MUCH less expensive than a 6x8 post

nickel plate · Sep 7, 2011

I agree with Eddie who suggested you use screws on the plywood gussets-I would also use a good exterior water based wood glue or subfloor adhesive where the gussets cross the webs and chords. You will need to flip the trusses and gusset the other side.
At the gable end trusses, attach a 2x4 in a hanger or 2-90 degree angle clips running from the top of the GE truss diagonaled down and attached to the king post of the first common truss or at least to the 2x4 lateral bracing.
Use some kind of a metal hurricane tie at each common truss end and attached to the two top plates.
Be very particular of your choice of grade stamped truss lumber. If you can locate 1750f or better MSR (machine stress rated) lumber in your area, will cost a bit more but right for the job. Avoid any boards with wain (bark edged).
I hope you have a large enough flat and firmarea to built on such as a conc slab.
Cut your square or plumb o'hangs after the trusses are set and braced off using a chalk line running the full distance of the roof. Although it's ladder work, it turns out eyeball in line.

gabeancounter · Sep 7, 2011

Eddie,
I gather you are referring more to the design below instead of the "W"?
Going to 2x6 for the top chord almost doubles the deadload. Hmmmm.

Yes, cutting the boards angles to make them flush seems more correct, but I am not a truss designer either.

I was thinking about using PL400 construction adhesive and ring shank nails. I have a framing gun and really not wanting to screw that many boards. I do prefer screws most of the time. The sizing of the gussets allow a good yield out of each sheet of plywood.
Thanks for the thoughts.

MikeD74T · Sep 7, 2011

When I build trusses (which is often faster & cheaper than having them delivered and I'm selling my time after all) I cut the brace angles because it aids accurate assembly. I use 2" ring nails with a nailgun because they make it easier to turn the half assembled trusses over. If you can rip 2x8's in half to save $2 you have too much free time.

Since you'll save a bunch of money making your own trusses consider using the 19 3/8" spacing (5 per 8') to get a little stronger roof. MikeD74t

gabeancounter · Sep 7, 2011

schmism said:
The size of the nail, 3" common as called out in the drawing, greatly affects the number of nails needed in each joint. the smaller the nail the less holding power it has. as im shure you dont want to spend all the time to clinch all the nails over with 3" nails and 2.5" of material, i suggest you upsize the gussets to 3/4" plywood. You cannot simply downsize the nails to 2.5" nails and use the same number as shown in the drawing.

Steve,
Thanks for the reply. I did notice the 3" nail requirement. Was thinking the same thing. Why require a nail that long? I was acutally going to use the ring shank with 2" nails on both sides.

Being that I am doing an ashpalt shingle roof, I don't want to go over 2' OC. I was actually going to use 5/8 plywood sheathing to cut back on sagging between the trusses.

The 1100lb rating below was the lowest on the chart. Would #2 SYP not reach this rating? Thanks Paul

gabeancounter · Sep 7, 2011

MikeD74T said:
When I build trusses (which is often faster & cheaper than having them delivered and I'm selling my time after all) I cut the brace angles because it aids accurate assembly. I use 2" ring nails with a nailgun because they make it easier to turn the half assembled trusses over. If you can rip 2x8's in half to save $2 you have too much free time. Since you'll save a bunch of money making your own trusses consider using the 19 3/8" spacing (5 per 8') to get a little stronger roof. MikeD74t

Mike,
What type lumber are you using? (HD and Lowes #2?). The advantage to ripping in half was saving $4 per cut

and the wood possibly being stronger than standard spruce. Would you use 7/16 osb and 19" spacing or 19/32 osb and 2' spacing?

slowzuki · Sep 7, 2011

1. Grade of wood required should be on drawing outdated grades means the drawing is way old.
2. Check age of drawing, design loads and wind loads have changed and lot of the free truss drawings are no longer valid.
3. Shop around for trusses, there is a 50% variation in price around here. One supplier 2 hrs away can beat the local supplier by a big margin even with shipping.
4. Can't substitute a brittle screw for a malleable nail without reengineering. Might work, likely won't.