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texasprd 05-14-2011 12:13 PM

Ridge or Static Vents on Multi-level Hip Roof
 
3 Attachment(s)
Hello, all! Like many folks posting on here, my house does not have adequate attic ventilation. From county appraisal records, mortgage appraisal drawings, and my own measurements, I believe the total attic square-footage (including soffit area) is approx. 3013 sq. ft.

Current attic exhaust ventilation consists of 2 12" turbines. Using the 300 rule (50/50 split between intake/exhaust), and confirming by ventilation calculators on manufacturers website, this is inadequate. On a 100+ day, temps exceed 135 in the attic (and that wasn't even the hottest part of the day).

The roof is a series of hips, with the roof over the garage coming to a point ("smaller point") and the roof over the dining/master-bedroom/back-patio ("big point") making another point. Here's a satellite view from Google maps - the house is oriented slightly to the NE (the turbines are the two spots on the back side of the roof): Attachment 33085

Here are two more shots, showing the "smaller point" and the "big point" :
Attachment 33086 Attachment 33087
The "points" are not as apparent in the ground-level shots, so match those back up to the overhead shot.

Given this combination of level ridges and hip-points, am I better off going with ridge vents or low-profile static vents ("turtles")?

There is enough linear footage on the level ridges, and I know I can get hip-ridge vents for the "points", but on those hip-points above the garage and bedroom/eating/patio, how many of those ridges should be ventilated? Is there an issue with getting a short-circuit effect from "adjacent" ridges if (for example) both of the south-facing ridges on the "big point" are ventilated? Would it be okay to vent opposite ridges on the "points"?

From the low-profile perspective, I know I could spread "turtles" along the east & west sides and back-/south-side of the central section - but again, how to handle those "points"? The attic area covered by the "big point" is considerable, and I doubt one turtle is enough. So, where should turtles go on these "points"?

Many thanks for any input you can provide!!!!

texasprd 05-18-2011 02:44 AM

Any one? Please help me out with some advice and insight.

Thanks!

seeyou 05-18-2011 06:13 AM

What type/how much inlet do you currently have? If that house was built with such inadequate outlet, the inlet situation needs to be examined.

I'm not a fan of venting hips and it's not necessary in your situation. Assuming the inlet is adequate and unobstructed, I'd vent the ridges and add turtle vents on the least visible hip planes. I'd also consider decorative venting, such as dormer vents and/or cupolas.

texasprd 05-18-2011 12:17 PM

I don't recall the number with certainty, but it is either 32 or 36 8"x16" soffit vents. Judging by the NFA of the ones I see sold online or on mfgr sites, the inlet calculation seemed to be about adequate - fairly surprising given the exhaust situation.

When you say "venting hips", do you mean installing hip-ridge vents like these: http://www.airvent.com/professional/...hipridge.shtml If so, what is your objection?

Dormers/cupulos would be outside my budget (requiring an outside contractor - I wouldn't be comfortable doing that myself). What passive means, and location of same, would you recommend for venting the peaks/points over the garage (NE corner of house) and patio/bedroom (SE corner) ? I haven't worked out the area calculations for those two parts, but I suspect that I'd need more than one vent for each. If turtles, I was thinking about putting them on the east-facing and south-facing surfaces of those peaks, but I'm wondering about the dreaded "short circuit" effect - what do you think?

seeyou 05-18-2011 01:17 PM

Quote:

Originally Posted by texasprd (Post 650344)
I don't recall the number with certainty, but it is either 32 or 36 8"x16" soffit vents. Judging by the NFA of the ones I see sold online or on mfgr sites, the inlet calculation seemed to be about adequate - fairly surprising given the exhaust situation.

When you say "venting hips", do you mean installing hip-ridge vents like these: http://www.airvent.com/professional/...hipridge.shtml If so, what is your objection?

Dormers/cupulos would be outside my budget (requiring an outside contractor - I wouldn't be comfortable doing that myself). What passive means, and location of same, would you recommend for venting the peaks/points over the garage (NE corner of house) and patio/bedroom (SE corner) ? I haven't worked out the area calculations for those two parts, but I suspect that I'd need more than one vent for each. If turtles, I was thinking about putting them on the east-facing and south-facing surfaces of those peaks, but I'm wondering about the dreaded "short circuit" effect - what do you think?

Should be in the neighborhood of enough inlet if they are all functioning. Make sure there is no insulation blocking their flow and that they haven't been painted nearly shut.

Vented hips have potential to leak. Doesn't mean they will, but I envision added potential under extreme conditions. I have installed similar products when given limited options. I see them as a last option in your case.

edit: if one was going to be worried about short circuiting, the hip vent would be a potential short circuit creating device.

I'm not too concerned about short circuiting. Even if it really occurs, heated moist air is still exhausted from the attic, maybe just not at peak performance. Air passing through the attic, even if it is for just a couple of feet, will mix somewhat with the attic air and/or pick up some of the heat. I suspect the only time short circuiting actually occurs is during strong wind events. I seldom see 25mph or stronger winds on 90 degree sunny days in my neck of the woods.

On placing the turtle vents: you might want to install a pyramid of 3 or 6 units closely spaced at the top of the hip planes you intend to vent. Or, there are other options (larger off ridge vents with greater NFA ratings) to use instead.

texasprd 05-18-2011 02:49 PM

1 Attachment(s)
Thanks, SeeYou!

By "pyramid", do you suggest putting multiple turtles on the same hip plane? I was thinking about turtles at the same distance down from peak-point on adjacent/opposite planes.

Attachment 33232

I could replace the existing turbine vent between locations 1 & 2 with a turtle (costing some NFA), and add turtles in one or both adjacent locations (1 & 2) to take care of the larger peak. Locations 3-5 could take care of the smaller peak (though #5 would be used only if really needed since it would be visible from the front - I wouldn't use it if calculations show that locations 3 & 4 would provide enough area).

seeyou 05-18-2011 02:57 PM

1 Attachment(s)
Quote:

Originally Posted by texasprd (Post 650418)
Thanks, SeeYou!

By "pyramid", do you suggest putting multiple turtles on the same hip plane? I was thinking about turtles at the same distance down from peak-point on adjacent/opposite planes.

Attachment 33232

I could replace the existing turbine vent between locations 1 & 2 with a turtle (costing some NFA), and add turtles in one or both adjacent locations (1 & 2) to take care of the larger peak. Locations 3-5 could take care of the smaller peak (though #5 would be used only if really needed since it would be visible from the front - I wouldn't use it if calculations show that locations 3 & 4 would provide enough area).


Yes - like this:

Ed the Roofer 05-18-2011 08:02 PM

I would like to give this some deeper thought when I have more time tomorrow, but at first insight, I "Think" that I would recommend using multiple Solar Activated Power Vents.

Each different level of attic space must be closed off from the adjoining level per instructions though, so that each individual attic cavity could haver it's own Intake and Exhaust Ventilation.

Therefor, although you counted the amount of Total Soffit Intake Vents, you would need to individually calculate the NFVA per each level of attic space on it's own merits and make sure there are enough.

You can not go too much in regards to the Intake Ventilation Supply. I would rather have more than eenough, than Not Enough.

Ed

texasprd 05-19-2011 05:39 PM

Thanks, Ed - I'll be interested to see what you come up with at "second glance". With solar-powered roof vents, how much of an issue would there be with residual heat/temps (either from heat absorbed in the roofing or ambient air/attic temps) after sun-down, when the fans stop? is it safe to assume that, if the fans are doing the job during the day, that there wouldn't be much heat stored in the shingles/decking? I'm thinking about the 100+ degree days we get here...

SeeYou, would you please list some names or links to the "larger off-ridge" vents you mentioned? I've come across one or two, but could use more instances.

Thanks, both of you!

seeyou 05-20-2011 08:12 AM

Quote:

Originally Posted by texasprd (Post 651120)
Thanks, Ed - I'll be interested to see what you come up with at "second glance". With solar-powered roof vents, how much of an issue would there be with residual heat/temps (either from heat absorbed in the roofing or ambient air/attic temps) after sun-down, when the fans stop? is it safe to assume that, if the fans are doing the job during the day, that there wouldn't be much heat stored in the shingles/decking? I'm thinking about the 100+ degree days we get here...

SeeYou, would you please list some names or links to the "larger off-ridge" vents you mentioned? I've come across one or two, but could use more instances.

Thanks, both of you!


My experience consists of one personal home with power vents I could hear. After a sunny, 90 degree day, the fans usually ran 'til after midnight, at which time they would start turning on and off until they finally stayed off. All houses are not equal, but there was quite a bit of stored heat in that structure.

http://www.grantlogancopper.com/roof-vents

texasprd 05-20-2011 12:51 PM

I've been up in my attic in the evening after a hot day - it's still quite warm in there. Since the fans (being solar powered) would stop running around sundown, wouldn't that greatly reduce the NFA of the fan openings - resulting in greatly reduced ventilation?

I understand it wouldn't be an issue with the fans running, but seems like it could be an issue after sundown. What about cloudy days, also?

Thanks for input!

texasprd 05-23-2011 11:46 AM

I haven't decided for certain, but I'm leaning in the ridge vent/static vent direction. The original owners allowed the builder to get away with 3/8" roof sheathing - it might be 7/16, but I don't think so (since the builder used edge/joining clips, this appears to marginally within code according to my research). Since the sheathing is so thin, would I be wise to use screws to attach ridge vents? If so, what head-style? Triangular deck-/wood-style, or flat-head?

ratherbefishing 05-23-2011 01:11 PM

I'm not a roofer, and don't play one on TV. But I just went through this on my house. I had lost a couple soffit inlets due to additions on the house. I had turtle vents on a hip roof, but the last roofer had punched 3" holes under 10" turtles. I had totally inadequate venting. In fact, when I cut off the rafter tails and soffit for my current addition project, heat poured down, out of the attic. That's gotta be a bad sign.

With my new roof, I installed 4 of these: http://roofvents.com/roof-vent.html. I also installed 6 more 8x16 soffit vents. We haven't had a 100 degree day yet, but so far I'm impressed with the drop in temp in the attic. And no more hot air coming out of the soffit.

texasprd 05-27-2011 09:43 AM

Quote:

Originally Posted by texasprd (Post 653184)
Since the sheathing is so thin, would I be wise to use screws to attach ridge vents? If so, what head-style? Triangular deck-/wood-style, or flat-head?

Hi, all - any thoughts on this question?

Thanks!

seeyou 05-27-2011 11:32 AM

Quote:

Originally Posted by texasprd (Post 653184)
I haven't decided for certain, but I'm leaning in the ridge vent/static vent direction. The original owners allowed the builder to get away with 3/8" roof sheathing - it might be 7/16, but I don't think so (since the builder used edge/joining clips, this appears to marginally within code according to my research). Since the sheathing is so thin, would I be wise to use screws to attach ridge vents? If so, what head-style? Triangular deck-/wood-style, or flat-head?

If you use "shingle over" type ridge vent, then you'll still have to nail the ridge caps down. I wouldn't advise using the exposed aluminum ridge vent, if they even still sell that stuff.

7/16" and 1/2" plywood or OSB should be H clipped.


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