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Community and Q&A

Roof Ventilation for Cathedral Ceiling with no Eaves and 4×12 Ridgebeam

KimmyDesign | Posted in General Questions on

Hi there! I am building a studio in my backyard and am trying to find some information on the correct way to vent my roof.

I have a gabled roof with a 4/12 pitch. My ceilings will be cathedral with a ridge-beam that is 4×12 (so that the bottom is visible inside the finished structure). My rafters are 2×8 that currently join flush with the top of the ridge-beam.  Because of non-permitting codes in my area, we were only allowed to build 120 sqft roof structure, so to get the most square footage out of the interior, we have no eaves on the rakes or back gable, with a 18″ overhang on the front. To make things a bit more complex, I have 2 skylights that will be centered to the structure. Right now my rafters are 24″ oc with two smaller gaps flanking the skylights, approximately 6″. 

In order to properly ventilate, I know I need to use insulation baffles in the rafters, and that I need to vent each ‘shaft’. My issues are all the ridge vents I’m seeing are for 2x ridge-beams. Had I realized this issue before installing the rafters I probably would have just installed them to float over the top of the ridge-beam to create a gap for air circulation, but I didn’t so here we are. 

I know I can buy drip edge vents for the rakes, but I’m not sure how to ventilate at the ridge, or how I baffle the two small rafter shafts the flank the skylight. Should I cut notches out of the ridge beam so when the sheathing covers it there will still be a gap for the air to circulate? Or do I stop the sheathing short and try to find a ridge vent that fits? I suppose alternatively I could buy shingle roof vents for near the ridge. The woman at Owens Corning I spoke to said I only need 3 linear feet of intake vents per side, but how does the air get from one shaft to the other? Do I cut notches out of the 2×8 rafters? 

Thank you thank you for any advice here!!!


  1. andy_ | | #1

    Without soffits, you have a complicated air intake. Without clearance at the top, you'll have a complicated ridge vent. With a cathedral ceiling, you'll complicate things even further. You could put in turtles over each bay, but most people don't like the way they look. You could use shingle vents, but jury is out on how well they'd work. You could drop the ridge beam lower and use hangars, but that's a lot of work at this point.
    Sounds like you might be better off switching to an unvented assembly.

    1. KimmyDesign | | #3

      Unvented seems risky in Seattle, where we are basically living under Niagara Falls for 6 months a year. I know I've made things super complicate, erg. I'll look up turtles. Thank you!

      1. andy_ | | #18

        Hello neighbor! As a fellow Seattleite, I'd describe it as Niagra adjacent. We don't get the full deluge that often but are constantly in the mist from the falls.
        An unvented assembly isn't that risky if it's done correctly.
        This is a turtle:

  2. Expert Member


    I would suggest:

    - Frame you roof so the top of the rafters are flush with the top of your ridge beam.
    - Strap the top of the rafters with 2"x4"s at 24"oc. This will allow venting at the ridge, a bit more insulation, good airflow around the skylights, and support for your 18" front gable.
    - Fur out your fascia 1 1/2" at the eaves and ventilate behind it. (This means the fascia will only be 1 1/2" further out than the siding trim).
    - Install an appropriate continuous ridge vent for whatever type of roofing you are using.

    1. KimmyDesign | | #5

      Thanks Malcolm.

      - The top of the rafters are currently flush with the top of the ridge beam.

      - By 'strapping the top of the rafter with 2x4' do you mean attaching 2x4s on top of the existing 2x8s? Whole they be on the long short side? The issue here that we also have height limit for non-permitted structures in Seattle and we have reached that limit. I could probably go up an inch or two but I think that's it

      - I could fur out the fascia and vent behind but I don't have any issue install either shingle vents or drip edge vents to get air in at the base of the roof. It's the top that I'm struggling with

      1. Expert Member
        MALCOLM TAYLOR | | #7

        2"x4'" horizontal strapping (on the flat) only raises the roof 1 1/2", but by keeping the top one back from the ridge beam, allows ventilation at the peak - and all the other attributes I mentioned.
        Drip-edge vents are a lot easier to install and less prone to problems than shingle vents.

        1. KimmyDesign | | #8

          great, thank you for the suggestion.

        2. KimmyDesign | | #9

          Could I install a drip -edge vent at the bottom and then a shingle vent toward the ridge line ( on each side of course) if I didn't have enough room for the 2x4's ?

          1. Expert Member
            MALCOLM TAYLOR | | #11

            My problem with shingle vents are:

            - You have to cut the sheathing - usually near the top or bottom, leaving a narrow unsupported strip.
            - With low-sloped roofs the shingles immediately above the vent are pitched even lower.
            - In areas with coniferous trees (most of the PNW) they are very prone to getting blocked by needles.

            How are you planning to vent the roof at the skylights?

          2. Expert Member
            Michael Maines | | #16

            Kimmy, this article explains how to design an unvented roof: What climate zone are you in? The ratio of open cell to closed cell foam varies with location.

        3. KimmyDesign | | #12

          Malcolm, for some reason it won't let me reply to you bottom response. I spoke with a local architect who said I could drill 1/2" holes every 12" or so through all the rafters to get the moving from one rafter shaft to another. Due to the small footprint of the roof I only need 50 sq in of air on each side, so as long as I allow air to move between rafters I should only have to install a small intake and exhaust vent at the bottom and top (respectively) of each side of the roof.


          1. Expert Member
            MALCOLM TAYLOR | | #13

            That simply won't work. You won't get any meaningful drying or air movement horizontally through the holes.

            In many climates, with good air-sealing and low indoor humidity, you might get away with it, but in the PNW we also experience roof moisture problems even with well ventilated roofs due to night sky radiance. I don't see a roof vented at the sides and linked by such small holes as practically being any different than not venting the roof cavities at all.

            Unfortunately venting is an all or nothing strategy. You need to provide adequate ventilation, or go with an unvented roof. Either works fine if done properly.

          2. Deleted | | #14


          3. KimmyDesign | | #15

            Malcolm, so now I am looking at doing 2" of closed cell spray insulation and then the rest of the 8" rafter with open cell spray insulation. Would that be sufficient for a non-vented roof?

          4. Expert Member
            MALCOLM TAYLOR | | #17

            If you decide to go that route, Michael has given you good advice in post #16. I think using two types of spray foam on such a small project is like using a framing hammer to kill an ant. Strap the rafters, fill the bays with 6" of batt insulation, make sure you air-seal diligently, and you are done.

  3. Expert Member
    Michael Maines | | #4

    Kimmy, standard practice when you have a fat ridge beam is to drop it 1-2" below the top of the rafters. It's technically a code violation but not one that I've ever had called out because it doesn't reduce the strength of the assembly enough to matter. Then you extend the roof sheathing beyond the highest point of the rafter, leaving just a 2-3" gap for air to exit. If you're worried about supporting the sheathing you can make little pentagonal spacers out of 2x that sit on top of the ridge. But with just a 4" beam that shouldn't be necessary.

    1. KimmyDesign | | #6

      I am very well aware of this now, ha! I'm doing all this for the first time and am (clearly) learning from my mistakes. We are going step by step and didn't really think about roof venting when we were figuring out our rafter framing.

      1. Expert Member
        Michael Maines | | #10

        In that case I'd go with Malcolm's suggestion to add furring on top of the rafters. I agree that drip-edge venting is better than shingle venting. I learned this lesson the hard way, along with a lot of others--just try not to make the same mistake twice!

  4. KimmyDesign | | #19

    Just wanted to put this out there for anyone looking at this post for advice in the future. I ended up strapping 2x4s to the top of the raters and that worked great. I am now able to use a ridge vent. I brought the 2x4s out with an inch overhand and will install 1" soffit vents behind the fascia.

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