Venting Over Wide Ridge Beam
Hello, we are mostly through with framing, and had a realization that we don’t have a good vent path to the ridge cap. Our roof is carried by a girder truss that is 4 ply 2x material. So 6″ wide. The rafters/trusses are parallel chord 24″ deep. The intent is to vent the sheathing and fill the remainder of the truss with dense pack. Today the framer and I were looking at it and realized there isn’t a path past where the rafter/truss meets the beam. Being a 6″ wide beam, it’s a little different than typical. How would you handle this situation? Picture is attached to show what I mean. I’ll grab one of the actual truss when I can.
Ideally, we would have held the beam an inch lower, but that’s in the past now.
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Replies
You could go with shingle vents on either side of the ridge. You can also build a larger ridge cap ie:
https://buildingscience.com/sites/default/files/figure_4_0.png?itok=B917Pi5o
This is what I would do, it will look better imo
This seems pretty straight forward. It doesn't need to be very big I think, just 1x3 laid on side to make a little cap even. Hold the 5/8 sheathing short of the beam by 2" and then cap with the 1x3 and another layer of OSB at the top.
Make sure there is enough overhang over the roof deck to be able to tuck the top row under the ridge cap. Also get some ridge vent material and cut it to fit between the 1x3 to block bugs and blowing snow.
If you want to keep it low profile, I don't think you even need the 1x3s. Just nail on cant strips to complete the triangle at the ridge, shingle the roof up to the vent openings, then run a roll-out vent along each side of the roof and fasten the second layer of sheathing through that. Or if roofing with metal, you could skip the sheathing and just get someone to bend you an extra-wide ridge cap. An extra 3" on each side should suffice. Your roofers might have some better ideas, and may even have come across this situation before.
Tim_O
I would do one of there two approaches:
- Build a vent space above the trusses, which is a lot easier than installing baffles below the sheathing.: https://www.greenbuildingadvisor.com/article/building-a-vaulted-high-performance-and-foam-free-roof-assembly
- Strap the roof horizontally with 2" x4"s before sheathing.
I do like Josh's method from a performance standpoint. But I think it seems a bit dangerous to install on a large steep roof. The peak of our house is 30' up and it's a 12/12 pitch.
Tim_O,
The ridge cap/over-roof Akos linked to in his first post look a lot better than most ordinary ridge caps.
I don't have a better suggestion than the ones above. But in case it's not obvious, for others reading, the best way to handle this is to hold the ridge beam 1-1/2" down from where it's shown. I'm surprised your framer didn't catch it. If your ridge were a solid beam, you might be able to shave off the top corners on an angle to provide a vent path, but you'd need an engineer's approval.
He pointed it out after, but by then it was too later. I'm not sure we could have done much though, being a truss design, I don't think we had much choice at this point. Dropping the beam would potentially be an issue for the hangers used. I should have caught it in truss design review.
Tim,
"I should have caught it in truss design review."
I definitely would have caught it if it was rafters, but as part of a truss package I might well have missed it too.
Without knowing more about the structure and aesthetic considerations, here's a few brainstormed suggestions in order of cheapest/easiest:
-Shingle vents. I've seen them work for intakes where there is no soffit for venting, so possible they could work for ridge venting too. Check the specs and hire a good roofer!
-Turtles, aka mushroom vents in each cavity. Would be an eyesore on a house, but probably ok on a utilitarian structure like a shop.
-Sleepers over the rafters to fir in a vent channel.
-Sprayfoam. I know it's generally frowned upon due to the global warming potential and cost, but it might be the easiest way out if the framing can't be changed.
-Over roof. Move the vent channel above the roof deck.