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Attic Venting strategy + PV panel layout + snow considerations

owen_p | Posted in General Questions on
I’m planning to replace my roof shingles (and 57 year old 3/8th decking) this spring.
We are also planning for a future solar PV installation.  Our roofline and orientation are not ideal and we anticipate a fully electrified home with 2 EVs within the next ~5 years.  We’ve planned for a maximum PV layout although we may never fully install it.
To that end I am struggling to come up with a plan as to where to place the attic vents so that they are effective year round once PV is instaleld and what type to select.
Most contractors use something like this:
The PV layout goal is to set them as high on the roof (i.e. near the ridge) to provide as much asphalt shingle space near the eavestroughs as possible to prevent big slides of snow in the winter.
I’ve always been skeptical of how well the continuous ridge vents function when covered in snow, but am prepared to be proven wrong.
Please see the attached diagram which will visually explain my conundrum.  You can assume a fairly well air sealed attic and SmartBaffles installed with a 2″ vent cavity (work that will get done when the roof decking is up).
Which option would you pick?  Or propose a new one.

Any thoughts, questions, opinions most welcome

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  1. sommerbros | | #1

    Ridge vents work very well, we use them regularly in CZ5. The fact that your house has a hip roof does reduce the amount of available horizontal ridge somewhat though. One option could be to keep your 3/8 in place but at the eaves cut it back in line with the exterior wall to create an opening to your soffit vents. You could then run 2x2 furring from eave to ridge on top of your trusses (pinching the 3/8 ply between truss and 2x2) to create a continuous ventilation path before installing your new sheathing and roofing material. You would need to discuss appropriate fasteners with your engineer to connect the the 2x2 to the trusses since you plan to eventually install PV.

    1. owen_p | | #3

      @sommerbros, thank you for the detailed post and diagram.

      A very similar approach had been recommended to me and I'm still giving it thought. The approach you proposed allows for more insulation especially since I don't have raised heels on my trusses.

      My current plan had been to install these SmartBaffles ( once the decking was up and to add GPS insulation to the top plates to maximise the r-value in the space I do have and create a backdam for the additional cellulose I'm planning.

      What's giving me pause with your idea are the following:
      1) Need to adjust the fascia, currently aluminum, (could be mitigated with custom extended vertical leg on the roofing drip-edge)

      2) Concern about the strength of the 2x4 (in my case vs 2x2) on the flat attached to the trusses (possibly harder to reliably hit with structural screws). But glued and screwed it could/should be fine. I don't have an engineer (yet)

      3) lack of easy visibility in the future to make sure that the venting is working well

      4) I still have the question about where best to place the vents with respect to the potential PV array to make sure they are effective in the winter and reduce shading onto the PV

      I will propose this approach with the roofing contractor who is also the PV contractor. They seem quite amenable to working with me.

      The primary reason to remove the 3/8ths is it is weak in spots and has had at least 3 previous roofs based on the # of now empty penetrations

    2. Expert Member
      MALCOLM TAYLOR | | #5


      I'm missing what advantage the new vent channel brings that leaving the attic open and just adding another layer of sheathing on top of the existing wouldn't? The advantage of an open attic with a hip roof is there are no dead end vent channels.

      1. sommerbros | | #6

        You’re right an open attic is key with a hip roof. The advantage of creating a vent channel by using the existing 3/8 provides a little more insulation at the heel and also saves some labour and waste by not completely stripping the existing sheathing. The top 4’ or so of 3/8 ply could be removed on the hip sections to allow the vent channels to communicate with the rest of the attic and exhaust through the ridge vent.

  2. Expert Member
    Akos | | #2

    How well ridge vents work depends on your local snow load.

    In my area with 25lb snow load ridge vents are pretty much the norm. Further north with 50lb snow load, those high vents seem to be standard.

    1. owen_p | | #4

      Thanks @Akos. I've read the claims that the ridge style vents work under snow but have always felt a bit skeptical of that claim.

      It did just occur to me though that the PV array having a gap under it may actually allow for more airflow to reach the ridge vents as they would in essence shelter the horizontal slot openings a bit.

      Any concern with adding too much ventilation options, i.e. one of the big boxy style maxi-vents and the ridge-vent? Does this create a short circuit type airflow system?

      1. Expert Member
        Akos | | #7

        Code min venting works, not need to add any more. Add up what you have and see where you are. You can reduce the amount of high vents by adding more soffit vent area. The general recommendation is to have 60% of the required vent area as soffit 40% as high vents which minimizes the chance of depressurizing the attic space.

        As for ridge vents, they are local climate related, if you see them on other houses in your area, than a good chance they work fine. Occasionally being covered by snow doesn't matter.

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