Attic ventilation options - old house

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Old 12-02-18, 12:07 PM
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Attic ventilation options - old house

Hi all - looking for some opinions here. We're about to have a new roof put on our 1890 cottage-style house in RI. The roof currently has 4 turtle-back vents and I'm considering replacing those with a ridge vent in (a bit of snow comes in the turtle backs on heavy storms). However, I don't currently have any soffit venting that I can see. There is about 2 feet blown-in insulation in the attic and, for some reason, on one side of the attic there are 3 sections of soffit baffling in place all next to each other (but no visible vents). The attic is about 200 square feet (only about 3-1/2 feet high at the highest point) and there are gaps in several of the roof decking planks 1/4" or so (read: old house - unintentional ventilation?). Oh, and the roof is very steeply pitched.

My question is this: what are my options for proper venting of the attic space without pulling back all the blown-in insulation along the edge? Do I even need to worry about it with such gappy decking? Would trying to install vents where the current soffit baffling is be worthwhile (even though they're all clustered together)? What about putting 1-2 round "low gable" vents in the attic wall at opposite ends (basically just above the insulation level) to draw air in from lower in the attic?
 
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Old 12-02-18, 06:43 PM
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From what you described, it seems to me that a ridge vent and a couple gable vents would be easiest. Although I'm confused by what you said about the highest point being 3-1/2 ft high then said the roof pitch is very steep. With 2 ft of insulation and 3-1/2 ft peak, the majority of the attic would be stuffed with insulation.
 
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Old 12-03-18, 02:55 AM
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Thanks for the reply - I suppose my height estimates may be off a bit - the peak of the roof inside the attic is roughly 3-1/2 feet above the top layer of insulation, so probably 5-1/2 feet overall.

Would positioning gable-type vents lower on the wall be better for overall circulation (cool air in - warm air out)? Ultimately I'd like to do soffit vents, but I need to look more into pulling back / removing blown-in insulation.
 
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Old 12-03-18, 03:39 AM
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With a new roof the gaps in the decking should disappear, right?

There are basic guidelines for attic ventilation but in some cases they are not needed and other cases they are not enough, it becomes a judgment call. On the top of that list of guidelines is air sealing (between house and attic) and from your description of that attic floor is now buried with blown-in insulation which makes further sealing almost impossible. Off to a bad start.

Next on the guideline list is creating low intake vents (usually soffit vents) to compliment high exhaust vents (the proposed new ridge vents).The air pressure that pushes cold air in and warm air out is directly related to the difference in height between those two vents and yours will be minimal, read minimal natural ventilation.

But all is not lost, as mother nature may be providing a helping hand with the wind. When only gable vents are available, having sufficient vent area and being positioned so prevailing winds can push air in one side thus out the other, it works sometimes. Snow can be an issue so one must watch as with all vents.

Also on the list of guidelines is to avoid any insulation coming in contact with the bottom of the roof. Ideally that gap would have some air flow but when in direct contact that area becomes a potential condensation problem.

To the basic question, I would add both ridge and gable vents with the gable vents as low as reasonably possible. Hopefully you have some access to monitor any snow related issues.

Bud
 
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Old 12-03-18, 04:17 AM
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Thanks Bud - good info there. Yes, she’s an old leaky house and the PO seemed to do what they thought was right with the blown in insulation etc. obviously the roof has stood as it is now for many decades, but I’d like to improve the situation and prolong our new roof as much as possible (“new roof” is shingles and membrane only - most of the gaps in the decking will remain, I assume).

Im not terribly concerned about the attic pulling air from our 2nd story if there is a slight under-ventilation occurring - that space is easy to heat (low pitched ceiling etc) and that might actually be a plus in the summer.

Anyone have experience with shingle-over vents? I was thinking we could situate a line of those on the roof on each side at the height of the insulation on the inside (approx halfway up the roof). Might look funny though.
 
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Old 12-03-18, 05:00 AM
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I don't have any experience with shingle over low vents but do have a lot of experience with snow and ice and personally would avoid them. Air Vent advertises a ventilated drip edge but again no experience. Maybe a little better than an under shingle vent.

Ventilation is needed to remove moisture. Insulation is needed to reduce heat loss/gain. But ventilation has little effect on shingle life. Studies on attic temperatures resulting from sealed attics (no ventilation at all) show little concern for shingle life. These tests were done in much hotter climates, I can dig out the article if needed.

I did a quick search through my saved links and found this article, didn't re-read it but the author is the one I believe related to temp rise. Anyway, if you get through this one you will be ahead of me.
http://www.fsec.ucf.edu/en/publicati...CR-1496-05.pdf

Bud
 
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