1

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.

enter image description here

6
  • What are the ground snow loads like where you're building this cabin at? Jul 7, 2023 at 4:00
  • Seems to me the easy button is to simply have an offset vent, if your OCD can hack it. If not, have two smaller vents. I don't think you need anything added to your birdsmouths. As to the overhang, I would extend the ridge beam a foot and add fascia boards in front, with a few pieces of blocking between the front rafter and fascia board. You are planning to have a fascia board on the rafter ends, right?
    – Huesmann
    Jul 7, 2023 at 12:58
  • @ThreePhaseEel 105 - 120 pounds per square foot Jul 7, 2023 at 17:26
  • @Huesmann yes I will add fascia board. I already have my ridge board purchased at 16', I'll need to find another way to extend it Jul 7, 2023 at 17:27
  • Plan first, then buy materials... If we assume your eave overhang is also one foot, you'll have up to 1,440 lbs of snow loading just on the overhang. You'll want some structure for that, yeah. If you design for the potential that it all drifts to one side (as the documents for my trusses suggest one should, as they did) all that could be on just one half of the overhang.
    – Ecnerwal
    Jul 7, 2023 at 17:36

2 Answers 2

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.

5
  • thanks for you answers. I follow #2 and #3 but I am being a bit dense on #1. Why am I wrapping the post? I am envisioning the post being in the way of the vent? Regarding ridge board vs beam you helped me out over here: diy.stackexchange.com/questions/270299/… Jul 10, 2023 at 22:56
  • The gable vent louver usually isn't weatherproof. You'd want to wrap any exposed lumber to protect it from rain.
    – isherwood
    Jul 11, 2023 at 12:51
  • won't the post block the vent and be in the way? I'm being dense. Nice bird pictures by the way. Jul 12, 2023 at 5:04
  • The post would only impede the vent a small amount it's narrow, and it's not necessarily in contact with the vent anyway.
    – isherwood
    Jul 12, 2023 at 12:39
  • Ended up running vents in the bird blocks between rafters (open eaves) and a ridge vent. Thanks for your help. Sep 27, 2023 at 3:32
1

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!

3
  • You had three questions to choose from and you avoided them all. :P Keep in mind that this is a tiny building. It wouldn't take much of a breeze to effectively scavenge the whole thing.
    – isherwood
    Jul 10, 2023 at 20:29
  • @isherwood meaning letting a breeze through the small space might be sufficient? Jul 10, 2023 at 23:43
  • Might. Depends on the insulation strategy, local climate, etc.
    – isherwood
    Jul 11, 2023 at 12:52

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.