2x6 tongue and groove as roof sheathing

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Old 06-08-14, 07:01 AM
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2x6 tongue and groove as roof sheathing

18x16 gable roof over my deck with exposed rafters and no ceiling. Plan is to use 2x6 T&G sheathing, since it would require no plywood or OSB overlay and 1" roofing nails wouldn't penetrate beneath.

Can I span place rafters 4 to 6 ft OC using the 2x6 plank sheathing, and would rafter ties every 6 ft be sufficient for the latter? I like the idea of fewer rafters and ties underneath to look less cluttered, since I'm not doing a cathedral ceiling.

Thanks in advance.
 
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Old 06-08-14, 07:31 AM
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These are really questions to ask an architect or engineer, since his okay is what a building inspector would respect as being trustworthy. Based on the size of the roof, IMO rafters 4' OC and 4' rafter ties would probably be wise. An architect could probably run the numbers and come up with a solution to keep things more open... perhaps doubling up the rafter ties, putting one on each side of a rafter and through bolting them. (same amount of rafter ties, but with a farther distance in between). But that sort of thing is outside our pay grade. (this advice is free).

http://aitc-glulam.org/shopcart/Pdf/aitc_112-93.pdf
Chapter 8 - Roof-Ceiling Construction
 
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Old 06-08-14, 08:51 AM
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What Xsleeper said. As far as experience, we have done v-joint t&g 2x6 decking so the v-joint showed below for effect. BUT our architect plans would only allow 4' oc beam rafters, not standard 2x lumber. IIRC, we had to sheath it with OSB prior to roofing material.
 
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Old 06-08-14, 10:43 AM
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What do you mean by "...not standard 2X lumber" for the rafters?
 
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Old 06-08-14, 11:35 AM
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Beam rafters are 3" thick, not 1 1/2" thick.
 
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Old 06-08-14, 11:43 AM
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Do you mean 2 pieces of 2X lumber nailed together for the rafter?
 
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Old 06-08-14, 12:20 PM
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You said you had exposed rafters. What are they made of? Two pieces of dimension lumber would not look good, unless you planned on later boxing it in for decoration. But, yes you can do that as long as the two rafters are identical top to bottom. You can't just sister the rafter leaving off either end.
 
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Old 06-08-14, 12:26 PM
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I haven't calculated rafter sizes for 48" OC. For 24" OC, I was planning to use 2X8 for rafters. I would possibly need 2X10 or 2X12 if I go to 48" OC.
 
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Old 06-08-14, 01:05 PM
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You can use this calculator for your figures. Maximum Span Calculator for Joists & Rafters
 
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Old 06-08-14, 01:23 PM
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Thanks. That's very handy. However, it does not calculate spans for 48" OC. I haven't found any tables for this online. It makes sense that the rafters would have to be beefed up since there woudl be half as many with 48" OC.
 
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Old 06-08-14, 08:11 PM
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I found this table for open beam ceiling from a local building code. I also found this same table in another code published by an independent city. I don't know where those value are derived from.

A 4x6 Doug fir beam can span up to 9'4". Apparently sheer is another factor that needs to be taken into account using T&G sheathing. I.e., the need for to overlay plywood over the T&G, but I'm not sure that's a significant issue here in Alabama.

http://www.chulavistaca.gov/City_Ser.../form_4602.pdf
 
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Old 06-08-14, 08:59 PM
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Our owner-built log home in SW Colorado had trusses at 4' centers, made of framed 4 x 6 (I think) Doug fir. The roof/ceiling was exposed T&G 4 x 6s, with standing seam metal on the outside. Never had any kind of bowing or deflection, even with a few feet of heavy, wet snow on it, and it looked good as well.

And I think the word is "shear."
 
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