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Community and Q&A

Venting at “Soffit Area” in a Roof with No Soffit

Lindaloowho | Posted in General Questions on

Hi Everyone!

I am retrofitting a recently acquired summer cottage in Southern Ontario in order to make it more user friendly for year round use.

The roof has fibreglass insulation inside of degrading plastic covering haphazardly laid in the joists of the attic floor. (The plan is to remove them so I can see what air sealing needs to be done before re-insulating with blown-in cellulose.)

I am trying to find the best way to follow vented roof protocol, but there are no soffits. That is, the top of the exterior walls join the bottom of the roof. There is a large roof overhang (no eaves) but there is no return of this overhang to join back to the wall. Ridge vents are present at the top of the roof. 

In order to maintain the facade of the building, I would prefer not to do any alterations to the exterior trim in order to create a soffit. 

In the front of the cabin roof there is an aesthetic gable with a window. The bottom of the window lines up with the bottom of the gable and the bottom roof line. The window is about 2.5’ x 2.5’ in size. The roof base is about 1500 square feet. The pitch of the roof is “medium”, and is a square pyramid in shape (other than the gable). 

Is this window sufficient to vent the entire roof from below? That is, would it provide enough “soffit venting”? 

There are also scattered small, nominal gaps in the roofing where the exterior walls meet the bottom roof line, which would also provide some “soffit ventilation” too, I would imagine. 

The next challenge will be finding a way to baffle the ventilation at the bottom roof line to keep it from being obscured by the blown in insulation. 

Thanks for any input. 

 

 

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Replies

  1. Expert Member
    Malcolm Taylor | | #1

    Lindaloowho,

    In between each roof rafter you will have wood blocking which separates inside from out. On new construction the easiest way to vent the roof cavities is to make this blocking shorter than the rafters and install a strip vent between the top of it and the roof sheathing above. On existing roofs like yours it's often a lot easier to drill holes for circular vents in the blocking, and use something like this.
    https://www.homedepot.ca/product/gaf-master-flow-2-inch-resin-circular-mini-wall-louver-soffit-vent-in-white-6-pack-/1000169036

    1. Lindaloowho | | #3

      Hi Malcolm,
      Would this mean the vent would be oriented vertically? Thanks for the clarification.

  2. Expert Member
    Akos | | #2

    The OBC doesn't require soffit intake vents. You can vent the roof with a combination of gable and ridge vents as long as they meet the required area.

    Since the building won't be occupied all year around, getting the venting perfect is not really needed. If you are not seeing any signs of moisture issues under the roof deck and as long as the existing ridge vent meets the required free area for code, I would just leave it as is.

    Air sealing the ceiling will make a much bigger difference in the amount of moisture in the attic, focus on that instead.

    1. Lindaloowho | | #4

      Thanks Akos,
      We are moving toward occupying this cottage full-time. Would your suggestion be the same with this in mind? I‘ll have to check OBC for free area required.
      Thanks!

      1. Expert Member
        Akos | | #5

        After you seal up your ceiling, I would take a peak up there during a cold winter evening. If you don't see frost on the sheathing or shingle nails, than your existing roof ventilation is fine. A well sealed place needs very little roof venting plus you can always add a gable vent above the window down the road if needed.

        1. Lindaloowho | | #6

          Thanks so much for the suggestions.

          A few more questions Akos? After air sealing, would I take any precautions to maintain venting that I do have? Could I drape anything over the roof deck trusses so the insulation doesn’t cover the window and other spaces near the bottom edge of roof line?

          Oh, by the way, the window (which is just a screen) is currently boarded up tightly with plywood and caulk. Should I install a vent in the plywood?

          1. Expert Member
            Akos | | #7

            You should install baffles near the eaves to keep the insulation from touching the roof deck. That trim on top of the siding is generally never tight and you still get a fair bit of ventilation from there. These don't have to be anything fancy box store foam ones stapled to the roof deck are fine.

            A bit of extra gable venting doesn't hurt, just make sure you do it in a way to keep critters out.

          2. Lindaloowho | | #8

            Hi Akos,
            I was wondering if you would be able to advise me further on roof insulation in my attic (old 100 year old cottage). When we removed the existing attic bat insulation, so we could clean, seal, replace and add more batt insulation, I could see there is very little space between the roof deck and the top of the wall plate. How am I supposed to insulate over the wall without touching the roof deck? Can I fill that space with rigid and spray foam and allow it to touch the roof deck?

            But If I do that, I am sealing any ventilation at the soffit area that we discussed previously.

            Any other options??

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