How to frame gable ends above top plate?

Question

10'x16' insulated off grid "cabin" build. I want to use gable vents for my ventilation because it seems way simpler than a ride beam and soffit vents. I have a post centered on each 10" wall to support the ridge board.

1. how would I install a centered gable vent around this post?
2. what other framing do I need in these triangles on the gable ends above the top wall plate?
3. if I want a foot overhang can I accomplish that by just overhanging my sheathing on the gable end or do I need to build a "ladder"?

I have my walls framed and stood up with some bracing. I am stuck overthinking and over researching roof venting, soffits, rafters, etc.

Answer 1

How would I install a centered gable vent around a ridge post?

Gable vents are little more than penetrations in the sheathing, and if you're using a commercial grille they pretty much just lay over the surface as a trim and pest prevention component. Wrap your post in something weatherproof and dark colored (so it isn't so conspicuous) and carry on.

FYI, a ridge board doesn't require posts. Its sole purpose is to make holding rafters in position a bit easier, and once the sheathing is on it's rather superfluous. However, a ridge beam would require posts, but it needs to be substantial enough to carry much of the roof's load. You may not need either if you have adequate rafter ties.

What other framing do I need in these triangles on the gable ends above the top wall plate?

Put studs in there at 16" or 24" centers to support your sheathing. You might only need two aside from the post. Once the gap height is below 24" you're good unless you want siding backing.

If I want a foot overhang can I accomplish that by just overhanging my sheathing?

Yes. 12" overhangs are adequately supported by the sheathing and by the fly rafters, which are in turn supported by the subfascia at the bottom of the slope.

Answer 2

Bad news: your gable vents will not cut it

The primary point of venting attics in cold, snowy places (like where you're building this cabin at) is to keep the roof deck below freezing when there's a giant pile of snow on the roof that'd otherwise insulate the roof deck to the point where it's above freezing, causing the snow to melt and form ice dams. However, washing the underside of the deck with somewhat-colder-than-freezing air is not a very efficient way of chilling said roof deck, especially if there are ceiling penetrations or worse yet, ducts that are leaking hot air from the house into the attic.

As a result, gable vents are not even close to sufficient for a vented attic to work, as you need to provide cold air to every part of every rafter bay, which means you need a fully vented soffit, and likely ridge venting to match so that you have enough exit area to correspond to the entrance area at the soffits. See the (admittedly limited) discussion in BSI-046 and the more comprehensive work of Tobiasson et al. if you want more information on this topic.

Of course, if you want to go with a vented over-roof over a compact structural roof, that's an option as well. BSI-046 has more details on this as well if you want to know more.

P.S. if you do go with the vented attic, make sure your ceiling detailing is as airtight (literally!) as you can make it, and please, for the love of all that is good, don't put your ducts up there!