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Old 02-08-2011, 04:54 PM   #1
OIIIIIIIO
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Default truss spacing...?

Hi,

I'm pretty sure I know what the answer will be from the guys on this board...I did search a little bit, but just want to confirm...

What are your thoughts on having trusses set 24" on center with 7/16" OSB sheathing an H-clips vs 16" OC...one side of the garage with have nearly 7/12 pitch (scissors trusses)...the other will be 4/12 (storage/spreadweb trusses)...I'm in south central Wisconsin...

My father-in-law (licensed contractor in IL) and I (no construction knowledge of any kind) am concerned about a potential wavy-roof with the extra span of 24 OC (sagging of the sheathing between the trusses)...but everyone else (truss designers, local building inpsector, etc...) seems to think it shouldn't be a problem with good sheathing....both say 90-95% of houses going up are going up 24" OC...but those same people say it's tough to find quality building supplies...things like sheets of OSB with not enough glue that they fall and flake apart and stuff...

Thoughts?

Thanks!
Patrick

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Old 02-08-2011, 05:03 PM   #2
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Default Re: truss spacing...?

I'm no expert,but you do see a lot of homes with the wavy roof syndrome with the trusses on 24" centers,new and old ones.
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Old 02-08-2011, 05:08 PM   #3
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Default Re: truss spacing...?

When I built my Garage, the engineer spec'd 24" oc, for the extra $104.00 I went for the 2 extra trusses I needed to put them 16" oc i makes for a much nicer finished job!
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Old 02-08-2011, 05:12 PM   #4
Addrock
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Default Re: truss spacing...?

I just built mine with a 10/12 roof 24 OC in southern WI. A steep pitch cures a lot of ills. It has had no more than 6" of snow all winter. The other thing taller pitch gives you is a room upstairs. When I ran the numbers it cost nearly nothing for the extra room. Because I built it myself I payed $17.33 per square ft. Good luck.
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Old 02-08-2011, 05:12 PM   #5
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Default Re: truss spacing...?

Quote:
Originally Posted by FRANKIEWHIPIT View Post
When I built my Garage, the engineer spec'd 24" oc, for the extra $104.00 I went for the 2 extra trusses I needed to put them 16" oc i makes for a much nicer finished job!
Put that way, I would too. But, 7/16ths or what ever you call it, is not enough for 24 OC. So, if the 5/8ths you need is more than the extra trusses, you found your answer.
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Old 02-08-2011, 06:16 PM   #6
OIIIIIIIO
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Default Re: truss spacing...?

According to my calculations for my garage (one run is 36'...the other is 20')...24 OC vs 16 OC results in 28 trusses vs 42...
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Old 02-08-2011, 06:26 PM   #7
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Default Re: truss spacing...?

2ft. centers is standard with 7/16 osd. Have seen allot of roofs with asphalt roofing look wavy when frost is on top. Most of time problem is caused by lack
of good roof and soffit ventilation. Condensation on underside of osb causes
swelling of panels. Framer
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Old 02-08-2011, 07:05 PM   #8
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Default Re: truss spacing...?

If it is an option,you should upgrade to 5/8 sheathing with clips , or better yet, 5/8 t&g sheathing.
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Old 02-08-2011, 07:11 PM   #9
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Default Re: truss spacing...?

Most homes around here (southern Illinois) put trusses on 24's with 5/8 osb roof deck, if you have your heart set on using 7/16 then plan on buying a few extra trusses and put them on 16's dead over the studs. If your worried about snow load or any extra weight on the roof system 16 inch centers is a good idea anyway.
That said i have seen some use 3/4 plywood and trusses on 16's before, talk about a solid roof!
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Old 02-08-2011, 07:12 PM   #10
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Default Re: truss spacing...?

I used 1/2" ZIP Roof which doesn't require clips at 24" OC. That stuff is heavy, it's OSB with a laminate on top. It's weatherproof for 30 days.
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Old 02-08-2011, 07:17 PM   #11
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Default Re: truss spacing...?

I too, live in Illinois. Back about 13 years ago, I personally built my garage. It's a 40' x 30' with 6-12 pitch trusses on 24" centers, with 7/16"OSB and H-clips. Mine shows no signs of dipping between trusses.
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Old 02-08-2011, 07:45 PM   #12
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Default Re: truss spacing...?

I used 1/2" OSB with clips on mine, along with 4/12 pitch.
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Old 02-08-2011, 08:19 PM   #13
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Default Re: truss spacing...?

My 24x36 is built with scissor trusses on 24" centers...The trusses were engineered for a tile roof, as well.
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Old 02-08-2011, 08:41 PM   #14
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Default Re: truss spacing...?

Quote:
Originally Posted by Doug B View Post
If it is an option,you should upgrade to 5/8 sheathing with clips , or better yet, 5/8 t&g sheathing.
I agree. I will use 5/8" ply with h-clips when using 24" centers. With 16" oc spacing I will use 1/2" CDX. If you do use the OSB for sheathing, just be sure you put the rough side up, or you may be looking at your roof on your back, from the ground.
Ken
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Old 02-09-2011, 12:54 AM   #15
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Default Re: truss spacing...?

I have mine on 24" spacing with 7/12 pitch. Used 1/2" plywood with clips. No waviness yet. Located in Northern Illinois.

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Old 02-09-2011, 01:50 AM   #16
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Default Re: truss spacing...?

Quote:
Originally Posted by framer View Post
2ft. centers is standard with 7/16 osd.
I take it you don't live in heavy snow country...

In MN many cities require 1/2 plywood as a minimum for code for snow.
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Old 02-09-2011, 02:06 AM   #17
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Default Re: truss spacing...?

1/2" CDX 24" O.C. with a 5/12 pitch. No real snow load worries to speak of.
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Old 02-09-2011, 07:17 AM   #18
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Default Re: truss spacing...?

O, 36'(12")= 432" divided by 24"= 18+1=19. 20'(12")=240" divided by 24"=10+1=11.
36'(12")= 432" divided by 16"= 27+1=28. 20'(12")=240" divided by 16"=15+1=16.
So, at 24" on center you will use 30 and with 16" centers you will use 44.
My figures are not including any extra truses if needed.
Ok, now let me explain how i learned constrution. My Dad tought me, we tore down houses for the materal to fix up other houses. In doing so, I learned what worked and what didn't (time tested). The one thing that always stood out was carring the "load" from the peak to the foundation. This is something that I try to pass on to everyone that I can.
Can you set them on 24's, ya. Would I, for 14 extra trusses, no. I tend to over build but, I can walk away from a job knowing it is there to stay and not having to worry about comming back to fix something. This is just MHO, so take it or leave it, your shop, not mine.
I hope i gave ya something to think about, little d.
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Old 02-09-2011, 09:26 AM   #19
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Default Re: truss spacing...?

Another consideration is what type roofing material (metal or shingles) are you using? If shingles I would go with 16" OC. If metal I would be fine with 24" OC IMHO.
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Old 02-09-2011, 09:52 AM   #20
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Default Re: truss spacing...?

When we installed the metal roof on our house and my shop, the metal roofing manufacturer specified 5/8 plywood on 2' centers. These used hidden clips to hold the standing seam roofing, held in by screws. I'm quite sure the plywood thickness was to increase the screw engagement and thus wind removal resistance. I'm also quite sure the Dewalt drills we used to screw in the clips would have stripped out holes in OSB. As usual, I went with overkill, the 5/8 plywood on 16" centers. Never have been a fan of OSB on a roof, or 2' centers.
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