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I have a 1940s colonial with no eaves, no soffits, and soffits can't be added. I do have two gable vents (original) and a power fan that was added (but is broken). I have early stage mold. The diagram below shoes the attic space, which is small and insulated to R-49.

How do I solve this? I was on board with edge vents--until it appeared there are no baffles to get soffit to ridge airflow. Now my short list of contractors disagree on what to do: 1. Keep just gables 2.) Keep gables and add a ridge. WHAT DO I DO -- Please help me!

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  • Is cathedralizing (i.e. converting this to an unvented conditioned attic) an option for you? Jun 2 '21 at 11:40
  • One builder who builds houses with invented conditioned attics told me that conversion of a vented attic is not a good idea. H e cited the danger from leaky flues (water heater, furnace). Elsewhere I have seen references to enhanced mold formation in unvented attics. Jun 2 '21 at 13:02
  • If your'e not morally opposed to the idea, or constrained from doing so by odd local codes, an actual working vented cupola is one option.
    – Ecnerwal
    Jun 2 '21 at 14:06
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    Are you opposed to getting the fan repaired or replaced? Do you have reason to believe the fan won't help? Any other option is going to be significantly more expensive than taking care of the fan. Please explain why you have yet to get the fan fixed.
    – MonkeyZeus
    Jun 2 '21 at 15:06
  • @JimStewart -- yeah, that's a fair point, you'd want to ditch those atmospheric draft appliances for sealed combustion at that point, especially if they're living in the attic ;) Jun 3 '21 at 1:37
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I think the only way you're going to be able to achieve the needed airflow, or air exchange rate, is with a powered solution.

So I would 1) replace the non-working fan and 2) try to get as much vent area as possible along the lower part of the gables.

EDIT 1

On replacing the fan, you may be able to do that without removing the flashed in housing that's on the roof. I've done that in the past.

Buy a new roof vent fan, as close to the size of the one that's not working. Remove the motor and fan blade from the new fan's housing, and mount it into the existing housing on the roof. The one I replaced had a 3-point mount that attached to the side of the housing, and the new motor/blade assembly fit right in with a couple of shim washers.

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  • I agree with the overall strategy, but multiple unpowered turbines might do as well (or better than) one powered fan, which might tend to pull from just one gable most of the time.
    – isherwood
    Jun 2 '21 at 14:17
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    Good points. I was think "hey, he already has that hole in the roof from the old fan, and probably power available. Why not make use of it".
    – SteveSh
    Jun 2 '21 at 19:08
  • Is it possible to go with ridge and gables (ventilation lower down isn't possible, it seems)
    – GMoney
    Jun 7 '21 at 23:13
  • My personal opinion - I think standard gable vents (high in the gable) with a roof ridge isn't going to do squat. You're just not going to get much of a draft going to exhaust the warm air out of the ridge vent. The cupola idea is better because the chimney effect of the cupola enhances air flow.
    – SteveSh
    Jun 7 '21 at 23:32

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