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Can I my own rafters instead of using roof trusses?

Can I my own rafters instead of using roof trusses?

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  #1  
Old 04-21-13, 03:05 PM
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Can I my own rafters instead of using roof trusses?

We have a 20 ft deep single car garage that we are converting to a two car garage. There is no second story above it, just a roof. We have already built the rough opening for the 16 ft garage door, the walls are up, and its time to add onto the existing roof to extend over the new garage space. Having widened the garage 9 ft we need one end truss and 3 common trusses but I am wondering if I can just build roof joists myself. Slope is 6/12 and 20 ft deep with 2 ft eaves. Seems to me I could just start with a ridge joist, run long properly sized 2X lumber down to the new top plate, extend it to match the existing eaves and call it good. Am I missing something or is that basically it? One thing that concerns me with doing it that way is a need for a horizontal tie between the front and back walls. Do I need that? I know I wont have a way to add a ceiling to match the existing one but Im not too concerned about that.
 
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Old 04-21-13, 03:32 PM
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Welcome to the forums! You say "20 ft deep". Is that the length of the garage, or the length of the rafter you will need? Maybe a picture or two of the garage in its present state would help us help you better. http://www.doityourself.com/forum/el...your-post.html
 
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Old 04-21-13, 04:30 PM
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Working on getting a pick or two for you. Thanks for the welcome. The garage is 20 ft deep. That is 20 ft from the garage door to the back wall. In this first pic, we are digging footings for the extension. The north wall of that garage was extended out 9 ft. All walls are now up and its time to roof it. The rafter lengths I can determine from a chart, but I just am unsure if I can do it that way. What keeps the front and rear walls from spreading apart in the new addition? (besides the existing roof trusses) I have redlined the rafter locations I am talking about doing, rather than buying premade trusses.
 
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Last edited by Jammer864; 04-21-13 at 04:37 PM. Reason: added red areas
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Old 04-21-13, 04:52 PM
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Here is a pic of the garage in its present state. Right side of the pic is north. North side of garage has been extended to create two car garage. The roof now needs extended north to cover it. I know I can order trusses for it but it seems quicker for me to just make joists myself.
 
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  #5  
Old 04-21-13, 05:06 PM
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You said you "won't have a way to add a ceiling . . . ." Actually, you do--simply install ceiling joists from front to back, one under and (attached to) the rafters where they sit on the top plate. In addition to having a nailing surface for a ceiling, they also serve as tension members, keeping the walls from spreading when heavy snow is pushing down on the rafters.
 
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Old 04-21-13, 05:11 PM
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Thanks BridgeMan45, I had thought of that but didnt know if it was required or not. Seemed to me there has to be some way of providing tension. I found a span chart for ceiling joists. Seems I would need a 2x10 for the 20ft span I have. With the 6/12 pitch roof sitting on a 2x4 top plate, I would have to trim off quite a bit of that 2x10 to fit above the top plate. Do the charts take that into account?
 

Last edited by Jammer864; 04-21-13 at 05:52 PM.
  #7  
Old 04-21-13, 06:23 PM
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There is bearing under the ceiling joist (top plate) so imo trim away.
 
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Old 04-21-13, 06:38 PM
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For no more trusses than you need and considering the cost of the large dimensional lumber you are proposing to use, trusses would be a given factor. You may find as I did on a job, certain companies are not as busy as they once were during the "boom", and welcome any business you can throw their way. I needed 50 or 60 extremely long trusses on a job once. Had the truss guy measure and give me a quote. I asked how much lead time.....he said he would have the first load to me the next day....I fell over. So it won't hurt to investigate trusses. Labor savings are built in.
 
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Old 04-21-13, 08:10 PM
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I agree, trusses easier. OTOH, page 33; Troubleshooting Good Residental Construction - Google Books

Last table at bottom page; Chapter 8 - Roof-Ceiling Construction

Gary
 
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Old 04-21-13, 09:25 PM
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An advantage of rafters and joists is the fact that the result is a built-in storage area for bulky items, especially with the OP's steep roof pitch. Can't do that with trusses, as their diagonals always get in the way.

Cutting off the top ends of ceiling joists (to fit within the roof's profile is) is never an issue. Shear loading at the ends is minimal, while the more important working areas of the joists are the middle one-third of the span, where bending moment is greatest, and is the reason for needing (deeper) 2 x 10s for the 20' span.
 
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Old 04-21-13, 09:36 PM
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Thanks guys for the help. Gary the troubleshooting link was very informative. I love to study stuff like that. This house is near Omaha, NE. Times are good there. The local truss manufacturer wants 3 weeks and the big box stores are telling me 2 to 3 weeks. Im torn about what to do now. I like the idea of setting my own schedule and not relying on someone else by making my own rafters. On the other hand, like chandler mentioned, cost on the lumber is close to what the trusses cost. My wife wants it finished so she can get the garage door up. I dont blame her. Anyway, you guys have helped a ton. Thank you all.
 

Last edited by Jammer864; 04-21-13 at 10:19 PM.
  #12  
Old 04-21-13, 09:49 PM
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If you go with trusses, don't forget to factor in the cost of crane rental, with operator. Can be several hundred $$$ an hour, plus travel time.

Rafters and joists can be set by hand, with just you and a grunt helping. Most grunts are happy with $12 or so an hour.
 
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Old 04-21-13, 10:19 PM
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Its gonna be rafters using Pine, Birch, or Fir from our local Menards. They do not stock Southern Yellow Pine which would of been my first choice. Going with 2x10 ceiling joists, and 2x8 on the rafters. 16 in centers are gonna be required, cant do 24 or going to need timbers (just kidding). Iowa snow load is up to 40lbs psf. Think I got it all figured out. Will probably get started on this Thursday or Friday, weather permitting. I'll post some pics!
 
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Old 04-22-13, 10:54 AM
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Another question with this project guys...

Does the ceiling joist in this garage project actually have any live load? Im looking at the table link supplied earlier and the very first table shows "uninhabited attic, no storage, live load of 10psf, 5psf dead load". That seems to be my instance. Using that table I can span 20ft with with a 2x10 using pine spruce fir and can go 24 inch on centers. This is for Iowa, which wants a 40 live snow rating for the roof, but it seems to me there is no load at all on the ceiling joists in this instance. Am I correct?
 
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Old 04-22-13, 12:10 PM
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We all know you'll eventually be storing stuff up there, or even just climbing around doing electrical and/or insulation work. So in that sense, yes, the joists will be subject to live load.
 
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Old 04-22-13, 07:04 PM
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If I hung 1/2 inch drywall for a ceiling, any idea what live/dead load I would be looking at on the tables?
 
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Old 04-22-13, 08:04 PM
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As you enjoyed those links so much, here are a few more to read;

Fig. 8.32; Residential Construction Academy: Carpentry - Floyd Vogt - Google Books

Fig. 7, from a lumber manufacturer; http://www.google.com/url?sa=t&rct=j...,d.cGE&cad=rja

Funny how they are all the same; http://www.google.com/url?sa=t&rct=j...hd6WkAK8Q2d9ew

City Code in CA, pp.7; http://www.google.com/url?sa=t&rct=j...-4uLrg&cad=rja


Now I'm repeating myself (but a lot more info), lol; http://www.google.com/url?sa=t&rct=j...Au_GhA&cad=rja

With your 9' high garage, trusses would just trucked out, a good non-union residential carpenter could lift them up alone, no crane time... over 28' are a little heavy to carry alone after 55 years old, I find. OTOH;pp. 179; Plans, specs, building - Jack P. Jones - Google Books

From north of me; https://docs.google.com/viewer?a=v&q...6fTirapfPwoKzA

Wood Truss Information

Enjoy!

Gary
 
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Old 04-22-13, 08:45 PM
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Single Doug-Fir #2, (repetitive use)1500 Fb, 16"o.c., will carry 37# per sq.ft. including 2# per sq.ft. drywall (1/2"), I think you'll be fine...that's over 1000# total per joist with a l/360 deflection. Check with local AHJ for the required paper trail your H.O. Insurance carrier may want if every a claim.

Gary
 
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Old 04-22-13, 08:53 PM
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I'd suggest using 5/8" drywall for your ceiling, as it's not as likely to sag like the 1/2" does. Better fire resistance too, slowing down a garage fire from getting into the common attic and then the house. Your local building department may require it.
 
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Old 04-22-13, 09:14 PM
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Good point there! If you get the permit, they may require it. Depends on if the gable truss on the house end is closed-off per code in the garage attic.

If you add attic pull-down steps for storage on the new area; add material on the face to make them code-acceptable. Add blocking for the auto opener and run the wires for the opener/safety reverse sensors before you drywall.

Gary
 
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Old 04-22-13, 10:05 PM
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Awesome knowledge linked there Gary. Thank you very much. I will be owning a copy of the Residential Construction Academy book by Floyd Vogt just as soon as I can find one.

One thing I learned reading thru those links is the ability to be able to stagger the rafters. The thought had never occured to me. For a guy with no nail gun, being able to end nail those rafters at the ridge board is gonna be nice. For me, toenailing with a hammer gets old real quick. I also learned about joist hanger nails.....I always thought those nails were used in all holes and have done it that way in a few decks I have built. Not now! I will be using a joist hanger to mount the ridge board to the existing structure and that info came in very handy. dgeman, the 5/8 in drywall on the ceiling is a good idea. The current garage has a drywalled ceiling and I have no idea if the attic space is open to the house structure.
 
 

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