Post frame roof only questions.

[lennyzx11]

Guys, I'm in the preplanning stage for building a 24 ft wide by 20 ft deep metal roof only with a 9 ft eave height.
The trusses will span the 24 ft.

I am planning on using 6x6 posts but wish to have a 10-12 ft centered opening on one of the 20 ft side walls if possible.

This is going on front of my shop and slightly behind the house so the area can't deviate much from that.

The questions.

What should the trusses be made of? 2x6? Is a butt connection allowed on the bottom chord with plywood gussets? I can't find a clear answer on this. We are in SE Oklahoma so minimal snow load is expected.
I want to build them. And the minimum spacing that should be done between them? I was thinking 4 ft spacing but that may be too wide with purlins every 2 ft.

What should the top band be made of in the 10-12 ft open area of the sidewall? I am trying to keep an 8 ft underneath clearance to back my tractor with ROPS through there occasionally.

Should the top band be set into a notched post top and doubled up with one 2by? In the notch?

Here's the pictures of where I am planning. I plan on making it freestanding but up against the front of the shop with about a foot drop in vertical height under the original overhang.

That garage door is a 9x12 and the roof is a 4:1 for reference. Building is 24 ft outside to outside.

Any comments and criticism welcomed.

PS the backhoe arrives Monday to dig the stump out. I plan on starting the layout and postholes the week after.

 

[RNeumann]

Trusses are an engineer product designed for each individual situation. If you are planning to "make" trusses you would need to have the design engineered. Most folks buy trusses- they included the engineering for your opening etc.

I'd also be concerned about the posts. The sheer and wind loading on an open sided structure is far different than most would expect or understand.

Btw- a 20' 2x6 is a common length at most lumber yards. If you wanted to "make" the roof yourself just use what's called "conventional framing" with a ridge beam and hand cut rafters. Those specs and designs are a part of most building codes. Google something like "UBC rafter span tables"

 

[Rustyiron]

I'd also be concerned about the posts. The sheer and wind loading on an open sided structure is far different than most would expect or understand.

:thumbsup: I've heard it can get a little "breezy" in OK.
Fwiw, a "truss" on the 20' wall needs no post in the span. You'll need a beam in the 24' wall front & back.
From your post's "language", I'd seek out a bit of local help & advice on this build.

 

[jaxs]

I have a similar size building in Tx near Hugo that has stood straight and tall for 25 years. 24' trusses on 48" centers are home made with 2x4. Splices are allowed by code but should be near centered between web contact points. (look at homes under construction). Put marks at 80" and 160" on 20' bottom cord. That's where W sit's on bottom cord. I don't recall math for top cords but mark bottom cord 40" from each end then with top cords set in position,use a square to transfer marks 90 deg from bottom cord to top cords. If you have overhang I wouldn't run bottom cord past plate unless using large gusset above plate. Naturally top cords can have tails for overhang. My side posts are on 16' centers and plate is double 2x8 with 1/2" plywood sandwitched. 24 guage metal can sub for plywood.

 

[lennyzx11]

Thanks to all.

@RNeumann
Your concern over the posts? I had thought 6x6 would be adequate. I planned on either using uplift protection in the post holes.
I understand about engineering trusses but have read and heard a lot of information regarding home builds. I have a narrow window of time home to work and the first two quotes for trusses can't have them delivered before I leave again. I have done stick framing and do know what a rafter square is so I'll relook at that.
I did plan on using gussets glued and nailed at all web intersections.
@Rustyiron
Not quite sure on what you mean on a "beam in the 24' wall front and back." You mean a post supporting the top band/plate? (Forgive me if wrong terminology) or a vertical post centered from top of horizontal "band" to apex of roof?

@jaxs
Perfect! Thanks for the details. Do you know what length the splices are overlapped or are the butt jointed with plywood gussets on both sides?
Also you mention having a 20 ft bottom chord. But I'm spanning the 24' length. At first I thought you maybe be raising the 20' bottom up until it fit the triangle, but then you say don't extend it past the plates. Which would be 24' apart.
What did I misunderstand?

Is your 2x8 sandwiched plate lying flat or edgewise on top of posts? Or nailed bolted to the outside or inside of the posts?

Thanks everyone for all the tips.

 

[KennyG]

For a small building like this the 6 x 6 posts are more than adequate, in fact they are overkill. I would suggest 4 x 6. 4 x 4 would be strong enough but, as has been noted in other threads, it's hard to get them straight. In our area, 4 x 6 are available that are very straight and stable. In fact, my 40 x 48 building has 4 x 6 on 8 foot centers and it's fine after 40 or so years.

I would definitely go with a stick built rafter roof on a building this size. No need for trusses on this size.

 

[3Ts]

My preference would be engineered trusses from a truss company. However, I see that you've already gone this route and that the timing is a problem. I found that they could engineer & build the trusses for less than I could buy the wood if I made them myself. 20 & 24 foot spans are not that much. Check with the building department and they can tell you what size for joists & rafters based on local weather conditions.

 

[M5farms]

do you not have engineered metal trusses in your area ? that's practically all that is used here for open barns . Mine is 8x8 post with truss every 10 foot (60'L) and it spans 50'w.

 

[jaxs]

Lenny,questions like " Is your 2x8 sandwiched plate lying flat or edgewise on top of posts? Or nailed bolted to the outside or inside of the posts?",I must agree with Rustyiron.
"From your post's "language", I'd seek out a bit of local help & advice on this build"
.

 

[jimmysisson]

If you're opening is under a truss it doesn't need too much of a header. Not the same with stick built. Why not align the new opening w your current garage door - more storage area for attachments!
Jim