Double ridge - Contractor Talk - Professional Construction and Remodeling Forum

straightline · 10-18-2009, 04:53 PM

Got a question about double lvl ridge. Will be framing using 2x12 with double 14"LVL ridge boards over a cathedral ceiling below. To gain the air flow from the soffit to the ridge would you guys let the rafters sit 3/4" higher than the ridge boards to allow air flow to the ridge vent? What have most of you being doing in this instance?

Warren · 10-18-2009, 05:07 PM

I usually tack a 2x4 flat to the ridge and purlin the rafters to this. Don't forget to remove it when you sheath the roof.

straightline · 10-18-2009, 05:11 PM

so you allow 1 1/2 for ridge vent flow above the top of the ridge boards? Do you use 11 1/4" ridge vent?

Warren · 10-18-2009, 05:15 PM

Ridge vent can be whatever you or your roofer prefers. Having a structural ridge has no bearing on what ridge vent product you use. Our engineer usually calls for minimum of one inch airspace whenever we use 2 ply LVL. I just go 1 1/2 because I have plenty of 2x4 blocks laying around.

**framerman** · 10-18-2009, 05:18 PM

Quote:

Originally Posted by Warren

I usually tack a 2x4 flat to the ridge and purlin the rafters to this. Don't forget to remove it when you sheath the roof.

That's what I do also. If it's a single 2x, I rip something down to 1" high. Anywhere a ridge vent is, this is done.

straightline · 10-18-2009, 05:22 PM

Thanks for your advice. do you let your sheathing overshoot the end of the rafters some on each side to take up some of the open space left by the lvl's 3 1/2" or how do you deal with that wide of a gap at the ridge?

straightline · 10-18-2009, 05:24 PM

I agree lone framer on a single ridge. Just never dealt with double ridge over cathedral use trusses most of the time.

straightline · 10-18-2009, 05:31 PM

sorry meant framerman not loneframer. Anyway how do you deal with the wide gap left at the ridge when using double ridge lvl's?

**loneframer** · 10-18-2009, 06:18 PM

I do basically the same as Warren and Framerman. I usually use a 2x ripped to 1" to gauge the rafters above the beam. The sheathing is then cut back no more than 1" from the centerline of the roof, leaving no more than a 2" opening at the peak.
We have done the same thing with hips in some cases. Drop the hip 3/4" to 1" to allow airflow to the ridge. Some architects specify full venting of the hip, in which case the hip would get vented in the same manner as the ridge.

straightline · 10-18-2009, 07:15 PM

Thats how I will do it, figured you would have to let sheathing extend past end of rafters at ridge just better to have someone verify it. Thanks for the info.

Timuhler · 10-18-2009, 09:39 PM

Hold the rafters 1" tall and then sheathe 1" past and this will leave airflow for the ridge vent

sorry for the huge size, but you can see the ridge was a tripled 2x12 so we held the rafters 1" high (lowered the ridge 1")

Timuhler · 10-18-2009, 09:40 PM

jeffatsquan · 10-18-2009, 09:43 PM

The most important part of this detail after you allow for the air is make sure that over shot seathing is rugged enough to nail the ridge cap I often will make little 2x triangles to go on top of the lvl to make the seathing more ridged

Timuhler · 10-18-2009, 09:44 PM

dos mas

**framerman** · 10-18-2009, 09:58 PM

Tim, is that siding in the last picture? It almost looks like gyp board.

Timuhler · 10-19-2009, 12:00 AM

Quote:

Originally Posted by framerman

Tim, is that siding in the last picture? It almost looks like gyp board.

It was 4x10 LP Smart Side non grooved. We added 1x3 batts later to make it board and batten. That was one of my favorite houses to frame.

http://picasaweb.google.com/TimothyU...eat=directlink

straightline · 10-19-2009, 09:33 AM

Thanks Tim for the pics, I see what you did with the rafters that will work for me. Do you guys usually cut your seat cut on your rafters to sit completley on your top plate on a 2x6. I do but have read in code where heel cut should not be more than 1/4 of lumber depth which on 12/12 pitch would have you cut more than a 1/4 depth to get the 5 1/2" to sit completly on top plate of 2x6?

WNYcarpenter · 10-19-2009, 04:31 PM

What are you guys using for insulation? We're at r-38....I might be wrong, but we can't fit bat insulation in our cathedrals with an airspace so we've been using spray foam.

I'm not an advanced roof framer, but I was taught to cut rafters that notch over ply'ed LVL's so the long points meet at the actual ridge....I like the x-tra cut if we're using 20' DF 2x12's makes installing easier.

Edit: 800