Matching existing roof

[spebby_92]

I am adding an attached garage to my house and will be tying into the existing roof. I think I have the framing figured out (hip roof). My question is the about the roof sheathing. The existing roof is sheathed with 3/4" 1 x 6 planks. If I used 1/2" plywood would the

1/4" difference show when the shingles are applied? I'm reroof the whole roof. Would 3/4" plywood or 23/32 tongue and groove OSB be a better choice? Would the thicker material add significantly to the dead load (10 psf)? My rafter span is very close to the limit for a 2x6 without purlins. Since there are no load bearing walls in the garage, I can't use purlins. Any comments will be appreciated.

[marson]

What kind of shingles are you applying? Something like a 40 year Timberline will cover a lot of sins as we say. At any rate, why use

1/2" plywood? Most roofs are sheathed with 5/8's. 3/4 plywood or OSB would be better yet, though it would be heavy to use on a roof.

[Robert Allison]

Just build the framing up an extra 1/4", then add the 1/2" plywood to bring it up even with the existing roof.

[<moo]

where I am all sheathing is half inch osb on the walls plywood on the roof

some people use osb on the roof too but i dont like it

all you have to do is get the first 2 rafters right and the ridge beam

watch how you cut the birds mouth where it sits on the top plate of the wall

when it all lines up just duplicate it

[DT]

Yes, this method will work for you. What counts is the dimension from the birdsmouth cut to the top of the rafter. Make a template from your existing rafter and allow another 1/4" height to make up for the difference in the deck thickness.

[spebby_92]

Thanks all for the responses. I will build the framing up 1/4" assuming I use 1/2" plywood. I am also considering using 5/8" rated sheathing and if I go that route I will build the framing up 1/8". The existing roof uses 2x6 rafters with purlins. The span of the garage I&#39;m building is borderline for 2x6 rafters at 16" o.c. and since I don&#39;t have any load bearing walls in the garage I can&#39;t use purlins. I thinking 5/8" rated sheating for 16" o.c. and 1/2" plywood for 12" o.c.

[Kickstart]

you&#39;re just guessing Aren&#39;t you ?

[spebby_92]

What do you mean I&#39;m guessing? The span is 14&#39; - 6". According to the span tables for 20 lb live load and 10 lb dead load, a 2 x 6 span is 14&#39; 1" for 240 deflection and 14&#39; 4" for 180 deflection. (douglas fir #2)

[Wayne Whitney]

Using thicker sheathing won&#39;t allow you increase the joist spacing. The sheathing&#39;s job is (among other things) to distribute the load to the joists. So the (minimum) sheathing thickness required depends on the joist spacing. The load those joists have to carry is pretty much independent of the sheathing, as the extra dead load from thicker sheathing is negligible.

Cheers, Wayne