I need to install a ridge vent on my house. Simple. But, the main ridge has a shed dormer on one side, 2/12 pitch and a 8/12 pitch on the other side. The data on the ridge vents shows a minimum of 3/12 pitch so I wonder if I’m going to leak if we get a good storm from the 2/12 side.
One manufacturer has a wind activated flap that closes in a 10 mph wind. That seems like the answer.
Anybody have experience/advice? It’s 101 deg in the shade today so I can’t wait to get on the roof and drop a few pounds.
Thanks.
Replies
If there are no obstructions between the shed dormer and the 8/12 pitch (ie you have space below the ridge beam, wouldn't it be acceptable to only make your cut on the 8/12 side? Homes were built for years with no vents and then just with a couple of random metal vents so added even just a half of a ridge vent is going to be a massive improvement and it will avoid any issue at all with the low slope leaking.
One manufacturer has a wind activated flap that closes in a 10 mph wind. That seems like the answer.
If that deal really worked, the ridge vent wouldn't work half the time. The poster above answered correctly. Just cut the steep side of the sheathing out.
It's also possible that you won't end up with enough of an opening to do the job. I believe, the sq. ft. of the attic divided by 250 = the total sq. ft. of roof vent, and a matching sq. ft. of soffit/gable venting.
Dave
It's also possible that you won't end up with enough of an opening to do the job.
That's kind of correct. You need one sq ft of ventilation for every 300 sq ft of attic floor, divided equally between intake and outlet. But, some is often better than none and all we can do is generalize because we don't have any data except roof slope. And a ridge vent thats letting moisture in is kind of counter-productive.
Most better units have a baffle that prevents wind-driven water from running into the vent, and they should be reasonably effective even at a 2/12 pitfch. It's a question of how much risk you want to take. Partly it depends on your local weather and wind exposure situation.
Too simple
I never though of the simple solution of only opening the 8/12 side. The attic is on the 8/12 side anyway and I'll see what I can do to open the 2/12 from the inside. I may need to add some hip vents to get enough flow.
Thanks.
Jim
I'm not really getting up on the roof in the summer, I'll wait till Oct.
Most better units have a baffle that prevents wind-driven water from running into the vent, and they should be reasonably effective even at a 2/12 pitfch.
I guess you know more than the manufacturers. I've had to solve this problem before and I'm unaware of any ridge vent that's approved for less than 3/12. But I don't know everything.
I didn't say they were approved, I said they would be reasonably effective.
Life's a crapshoot.
I didn't say they were approved, I said they would be reasonably effective.
Oh, they'll work fine no matter what the pitch is. But the reason they're not approved for lower pitches is they'll leak. And the baffle doesn't matter. Water comes in under them. It's OK, Dan. You don't have to post in every thread. Wait 'til you know what you're talking about before you jump in there.
But the reason they're not approved for lower pitches is they'll leak.
They're more likely to leak, under a given set of circumstances -- no certainty, one way or the other. Any vent, of any design, will leak give the "right" wrong set of circumstances -- it's always a gamble based on the likelihood of those circumstances. "Approved" is just saying that the mfg has calculated the odds and decided to put its reputation/liability on the line.
Just admit you gave bad advice and move on.
I stand by my advice, which was that there's a risk, but the OP may want to weigh the risk.
What the heck is reasonably effective?
Would you want your mechanic to put on reasonably effective brakes?
Would you go to sea on a ship with a reasonably effective hull?
Want to go to war and bet your life on a reasonably effective gun?
Reasonably effective might be fine for car wax, poison ivy cream, bug spray, food, but you don't want it out of your heart surgeon or your roof.
I'd much rather have reasonably effective ventilation than a reasonably effective roof. Thats why I said cut just 1/2.
Funny that your a willing to dismiss manufacturers directions about minimum slope off hand and yet you want to follow chapter and verse for ventilation.
If a ridge vent meets your definiton of "totally effective" at 3/12, is it suddenly ineffective at 2.99/12?
I've never seen any sort of rooftop vent that doesn't let SOME rain in. The question is how much, & under what circumstances.
I HAD THE SAME CONCERN
Recently we did what you describe and I had the same concern; in fact, the dormer slope was so shallow it had to be a rubber roof. What we did was take a strip of EPDM and make a rubber flipper water guard on the shallow side and back under the ridge vent. We stapled it down with 1/2 x 1 1/2 staples. I think I have a picture.
I was thinking about this product:
http://www.cor-a-vent.com/in-vent.cfm
It's designed as a soffit vent though the roof deck instead of your soffit. Using this at the ridge would give you the vent only on the 8:12 side of the roof.
Jim,
I used this type of ridge vent when we kept the original R-panel roof intact and use the "Roofhugger" system to attach the Kynar paint new roof panels. There had to be a way to vent that 1-1/2" gap between the two metal roofs and be as sure as possible to keep out heavy moisture.
It seems that this type of venting would be one of the better ways to keep out both wind-driven fine grains of snow as well as rain. Maybe, consider the wider ridge vent, in that the wider it is, the less likely rain is going to travel up all those "straw like openings" and into the ridge opening itself.
http://www.cor-a-vent.com/metal-ridge-vents.cfm
That last rain storm , last Thursday afternoon, had winds to 35mph so some of the rain was sideways, and in less than two hours our rain gauge showed 2-1/2". All stayed dry. With the rain coming in perpendicular to the Armor Shield II shingles and ridge line, even with the garden shed's gambrel roof, the simple plastic GAF Cobra-3 ridge vent kept out wind driven rain...
Bill
I may need to add some hip vents to get enough flow.
It is never a good idea to attempt to provide venting through the hips. The reason: If there are ridge vents above the hips, air and water will be drawn into the "hip vents" to exhaust from the ridge vents. This makes for a leak originating from the hip vents. Not a good idea!
Attic/Roof venting.
If it is 101 degrees outside and it sounds like you have very little venting of the attic it is probably a lot hotter in there. I'm in Vermont and on a 80 degree day my attic was getting up to 130 degrees, that heat build up was getting to my rooms below. My 2nd story unbearable. I added 4 of these vents that go on the shingles and they lowered the temp in the attic down to 107 on the same type of day. My attic area was 600 square feet, you get 100 square inches of ventilation per attic vent. We noticed a big change right away, I also added a lot of insulation to the attic which also helped. If I had to do it over I would have 6 or more of these vents on my roof. More is better.
http://www.homedepot.com/h_d1/N-5yc1vZ1xqd/R-100090888/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053
i just reroofed my wifes office , and removed the ridge vent i was happy to see it never leeked , during the 16 yrs of use.
i did lay a bead of butyl flex calk down first for the vent to sit on .. was surprised it see the butyl flex was still soft even after 16 yrs ..
i'm in arkanasa with winter 20* and summer 95* extrems temps i do recomend stting the vent on a bead of calk ..