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Old 07-24-2009, 12:15 PM   #1
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need some advice on best roof ventilation for this house


My wife and I are going to re-roof our house this summer, and we've been talking to various contractors about the best ventilation. Based on reading I've done, I've concluded that baffled ridge vents are probably best, but for some reason, all the contractors I've spoken with have suggest standard mushroom vents, which are present on most newer homes in our city in northern Canada. When pressed further, most of the contractors cited the additional cost of ridge vent as being the reason they recommended mushroom vents.

I've attached a drawing of our house for some further context. We've had an ice damming problem from a) skylights, and b) hot attic. The house only has soffit vents and gable vents at present. While there are clear paths between soffit vents and ridge for most of the house, the area I've circled around the skylights (a problem area) would not receive direct cold air wash due to the convergence of valleys.

Is there a better ventilation solution for this problem area? Should I stick with the contractor's advice and go with mushroom vents?

thanks for your help
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Old 07-24-2009, 04:25 PM   #2
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need some advice on best roof ventilation for this house


Each of those contractors would rather do a Cheap Job instead of the Right Job.

Your house is perfect for the type of ridge venting you described and would provide a great benefit to you, especially if you use the Shingle Vent II or one of the knock-offs.

Call some other contractors and one of the first questions that you ask them, is which brand of Roof Venting do they prefer and until one tells you the right answer, keep on calling.

Without knowing the exact lengths of your ridge lines, I would guess that you would need between 15-20 mushroom vents to equal the amount of exhaust provided by the ridge vents, run continuously from end to end.

Ed

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Old 07-25-2009, 07:33 AM   #3
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need some advice on best roof ventilation for this house


When doing a re-roof 'tear off' that currently has mushroom vents or no vents I always give three options.
1. Full ridge vent on all ridges.
2. Mushroom vents on rear of the home that will not be visible from the street and ridge vent on reverse gables on the front of the home that would be visible from the street.
3. Mushroom vents on both with the proper number of them installed.
(if you use a calculated method you would need twelve on your home to meet manufacturer specifications for warranty purposes)

I inform the home owners that all three methods have been time tested and proven to work, but the full ridge vent scenario is the best method hands down.

If your willing to spend the money to purchase the best, you should do like Ed said and keep calling contractors until you find one able/willing to provide you with the best.
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Old 07-25-2009, 10:49 AM   #4
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need some advice on best roof ventilation for this house


thanks for this feedback! I haven't yet found a roofer who has anything good to say about ridge vent. Comments such as 'looks ugly', 'too spendy', or 'not necessary' are what I'm hearing so far. I already know that we have some heat loss issues in this house, and the existing shingles have worn out prematurely, so I want to deal with it this round.

One question. I believe that we have around 80' of ridge total. Shinglevent's calculations for a 1900 sq. ft. attic (including garage) lead me to believe that I'd only need about 20' of shinglevent II. Is there any harm in doing the whole ridge, or does the ratio of soffit to ridge vents mean that I should stick with only 20'?

Based on the quotes (and opinions) I've received so far, I'm considering hiring a roofer to do the shingles while I figure out (and install) ridge vent once they have it 98% done. I have found a cheaper source for ridge vent than I've been quoted by the roofers so far too...

Last edited by longshanks; 07-25-2009 at 10:52 AM.
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Old 07-25-2009, 01:07 PM   #5
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need some advice on best roof ventilation for this house


Cheaper Ridge Vent does not equate to better.

In my opinion, only use a ridge vent that contains and external baffle, like the Shingle Vent II or one of the imitations, which each provide 18 square inches of NFVA per lineal foot.

Ed
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Old 07-25-2009, 02:45 PM   #6
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need some advice on best roof ventilation for this house


Ed, believe it or not, I've found shingle vent II for less $ than I've been quoted for other types of ridge vents. Not sure what they are worth in the US, but for 4' sections, $17 here in Canada.

Any thoughts on how much ridge vent I should be putting up there? Airvent's formula states that we need a minimum of 26'. We have about 80' of ridge. Is more ridge vent better?

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Old 07-25-2009, 03:22 PM   #7
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need some advice on best roof ventilation for this house


It costs a bit lower than that here in the States in the Midwest.

That is the best one in my opinion.

Ed
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Old 07-25-2009, 06:11 PM   #8
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need some advice on best roof ventilation for this house


I'm with Ed on this one. ShingleVent II is the best option. Full ridge vent will hurt nothing and keeping the vented profile the full length of the ridge will give the best appearance.

I really can't understand the bias against the ridge venting on the part of the contractors you've been talking to. It may be the challenge of hand nailing as the fastener spec for SV II is 2 1/2" nails. That means that the ridge vent and the cap shingles will need to be hand nailed. That's more time consuming, but as a contractor, if I'm getting paid for it, why not?

Check out www.airvent.com for some really great information on venting.

Andy

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Old 07-25-2009, 06:45 PM   #9
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Is more ridge vent better?------ http://books.google.com/books?id=Z8a...#PRA1-PA604,M1
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Old 07-26-2009, 06:49 AM   #10
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need some advice on best roof ventilation for this house


I noticed you talking about your shingles lasting this time around,
don't make the mistake in thinking that ridge vent will solve that problem.
Ventilation, proper placement and fastening of materials from the underlayment to the shingles, proper flashing details, proper gutter drainage and keeping the roof/gutters clean of debris yearly as the roof ages all play a part in rather or not your roof will last it's expected life span.

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