Cathedral Ceiling

[surfsupinhawaii]

Hi everyone, I am building a log home, the second story is dimensional wood with a  roof system being a Cathedral ceiling. I have a 3 1/2 x 16'' psl ridge with 2x12x24' long rafters. My question is what type of rafter grade you would use for a cathedral ceiling. I am worried about twist and cupping since I will be applying a wood ceiling to the bottom of the rafter. I priced out L.V.L lumber but it runs around $4.35 a foot. I think If I ordered #1 grade for the rafters I would get the same amount of cupping and twist out of my boards that I would get out of #2. I wish I could cut it myself with my norwood mill. Unless I pick the wood myself, the lumber company I buy from usually sends at least 20% boards that are twisted or severely cupped. Anyone have any comments or suggestions for my cathedral ceiling. The cost for the  2x12 is around $2700 the L.V.L boards would come to around $5400. Should I spend the money to get a flat ceiling. I really need to be careful with my money, but also need a flat ceiling. Thanks

[Furby]

Check out the wooden I beam joists.
They can also be used as rafters in some applications and are cheaper then LVL, but more $ then solid wood.

[beenthere]

surfsup...
I put up a similar addition, with cathedral ceiling and 2x12 rafters. The room was 24x30. The 24' ridge was 3 1-3/4 veneer lams nailed, with the rafters sitting on top. As you mentioned, the twisting would be a problem, but our rafter material was not a problem.
There is 10" insulation between the rafters, and 3/4" cedar board panelling nailed on the room side of the ceiling. Standard sheathing plywood above, with asphalt shingles.

If a yard sends unusable junk lumber, like 20%, I'd order more than 20% extra and return the scrappola for credit.  ;D ;D  I often do that, but I also sticker and stack all lumber that I get from a yard, so it dries evenly on both faces. 

[surfsupinhawaii]

Thanks Furby and Beenthere. I have used the T.J.I. for my floor and will use it for the second floor. It's too late for me to take my plans to the county and try to have them re-engineered with TJI. I have a snow load of 78 here and the snow is coming. The length on my rafters is around 21' long. Beenthere I was wondering if you did anything such as any type of blocking on your rafter to keep them from twisting. I still have to allow for ventilation in each bay, . Did you have a soffit under the rafter then applied to that or just to the bottom of the rafter and had good straight boards ? thanks again

[Don P]

One more thing to check is select struc doug fir, its the grade above 1 and usually pretty stable. I went the TJI route for rafters... once.

[beenthere]

surfsup
The 10" insulation was fiberglass batts, and they were up against the thin styrofoam venting that went all the way from the top plate to the ridge vent. I looked at my pics and don't see where there was bridging installed (think there was but not sure).  I'll load a pic or two of the rafters going up, and the cedar paneling going up. The sheathing was on the top of the rafter, and the paneling on the bottom. No additional attachment, and the lumber was straight. 

[beenthere]

Here is what the addition ended up looking like inside




and from out




and...its been great!!  Why we call it the great room.  ;D ;D

[Mooseherder]

That's a nice addition BT.  I like the wide open space.

[Roger Nair]

I would stick with the dimensional lumber and add  two courses of x bridging to stabilize the rafters and roof deck.  You can buy metal bridging from a building supplier, better yet cut the bridging out of 1 x 3 and toe nail with 8 penny nails.  Solid bridging is a lesser option, due to cupping tendency of the rafters.  Any conventional carpentry text should illustrate the technique.  Why two courses?  I think the extreme length of span requires it.