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Old 02-13-2012, 11:40 AM   #16
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help! strange horizontal bubbles on new roof


Sorry, I thought the large vents were powered.

You have excessive moisture or excessive air pressure in the attic space forcing the builders paper up because of the gap between sheathing at the joints.

Is the HVAC system in the attic space, or the supply ducts?

A leaking duct could pressurize the attic or leaking plumbing holes from the crawlspace, especially if the exhaust vents are inadequate. Check your exhaust/intake NFVA: http://www.airvent.com/homeowner/pro...it-specs.shtml

One layer of felt/paper is 5-30 perms, depending on the moisture present. Two layers is 1/2 as much, still not a vapor retarder that would figure in the equation. (Unless something I may be missing- good possibility).
Any insulation changes or HVAC usages since the problem began?

Gary

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Old 02-13-2012, 12:45 PM   #17
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help! strange horizontal bubbles on new roof


I think I'm going to invest in a hygrometer to see about the moisture hypothesis. If I find that the attic humidity is mostly similar to the outdoors, would that rule that out?

The HVAC unit and a web of duct work is all in the attic. I had an AC guy out last summer to do a "check up" on my system but besides trying to sell me a condenser cleaning outside, he didn't find any issues.

I did notice last summer that on really hot days the AC struggled to maintain the temp set on the thermostat (74, but it was over 100 here for basically 3 months straight last summer). I suppose I could have a leaking duct.

No changes in insulation. I just have alot of that fuzzy pink stuff everywhere. The depth rulers seem to indicate that I haven't had any extreme settling or anything.

Would I call an AC guy to check into the leaking duct hypothesis? Or is there an easy for me to do it myself? (Do I just climb around the attic scouring all the ducts?)

Meanwhile, I'll run the numbers on my ridge to intake and see where that goes.

Thanks.
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Old 02-13-2012, 01:14 PM   #18
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If I'm doing the math right, we might be onto something.

Ok, so I have 10 8"x18" "undereave vents". 7 on the north side and 3 on the south side. According to that website, each one provides 56 square inches of net free area (I'm assuming mine aren't from that manufacturer, but are probably similar). That gives me 560 sq inches of net free area.

My home is about 2100 sq ft, and my attic spans all of it so I'm assuming I have 2100 sq ft of attic floor (maybe more for the garage?) Using the 1/300 rule, I need a minimum of 7 sq ft of net free area, right?

1 sq foot = 144 sq inches, so I need a minimum of 1008 sq inches of net free area?

If I use the more strict 1/150 rule (which apparently is more common for newer/tighter homes), then I'd actually need ~2000 sq inches of net free area.

I guess I'm supposed to then split the intake/exhaust 60/40? So I'd need somewhere between 600 and 1200 sq inches of net free area for intake and 400 to 800 sq inches of net free area for exhaust?

I have 5 large round vents and one slant back, which I estimate to provide about 700-800 sq inches of net free area using the values provided on the airvent.com site for similar materials). So that seems pretty good.

So the question is, am I significantly under ventilated for intake? Should a 6 year old home definitely be held to the 1/150 rule?

Last edited by dfwnewroof; 02-13-2012 at 02:11 PM. Reason: got more educated!
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Old 02-13-2012, 11:54 PM   #19
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help! strange horizontal bubbles on new roof


Use the 150 rule if no plastic vapor barrier in the attic above the ceiling drywall below. (Under the insulation).

Your intakes are lacking. 7 sq.ft of intake required, you have less than 4. I usually figure 18 sq.in. of ridge vent per foot that covers both sides of the house--- 9 sq.in. per ft. of soffit run. Anything less- as spaced out rectangular vents = 56" should vent 6' of soffit. But, soffit should vent every rafter bay or on will get the majority of the airflow, the rest get little. Continuous soffit ventinting is ideal, located as close as possible to the fascia board for best air pressure and draw. The wind follows the house, up the wall and around the top the wall, and somewhat back into itself - creating turbulence/negative pressure close to the house wall. You want the positive pressure, pp.616: http://books.google.com/books?id=Z8a...0vents&f=false

You could have a pressure test of the HVAC done to eliminate any doubt it may be the problem, though with it on- you should be able to see any insulation holes or gaps at any leak unless hidden from view. Since none of the things I said have much bearing, I feel the problem could be the lack of ventilation with the added moisture from :house below, HVAC, or ? - has wet the felts from the inside causing them to swell. All the bath fans exit outside.... Add the soffit vents to minimum code and watch....... Sorry I couldn't be of more help.

Gary
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Old 02-14-2012, 08:18 AM   #20
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Quote:
Originally Posted by GBR in WA View Post

One layer of felt/paper is 5-30 perms, depending on the moisture present. Two layers is 1/2 as much, still not a vapor retarder that would figure in the equation. (Unless something I may be missing- good possibility).


Gary
That was my thought. That 30 lb. got that Perm rating close to 0 and the moisture in the attic condensed between the sheets and created a bump. Seen it a few times, but usually it shows up with just 15 lb. My guess was like the OP said, it was the tipping point and the 30lb on top of 15 lb made it show up.

Either way, it's a ventilation problem.

I'm guessing the other "wavy roof" thread is the same deal. Inadequate insulation and ventilation, and no vapor barrier(just kraft paper).
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Old 02-14-2012, 08:43 AM   #21
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help! strange horizontal bubbles on new roof


Definitely bad ventilation in this case.

No need for a vapor barrier in Texas but the venting still has to be right.
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Old 02-14-2012, 09:47 AM   #22
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Thanks guys!

Ok, so if no vapor barrier is needed here, does that mean I should still expect the 1/150 formula to apply when calculating net free area needs?

In my "exploration", I've definitely noticed that the soffit vents are not evenly spaced and I've even spotted a baffle in the attic that doesn't even have a vent on the exterior.

I've got a call in to the builder. We'll see how they stand behind their work after 6 years. Wish me luck.

P.S. My soffits are hardi plank. What are my odds of cutting new vent holes (if I can figure out how to push back the existing insulation without disturbing everything in the process).
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Old 02-14-2012, 10:16 AM   #23
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help! strange horizontal bubbles on new roof


Your drywall ceiling is your vapor retarder layer, but not a true vapor barrier.

You don't need one in any part of Texas.

I would get into that attic and make sure the soffits are not blocked in any capacity. Hardie soffit is not real friendly to work with and not re-useable in most cases (i.e. able to be removed easily and put back easily).
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Old 02-14-2012, 10:42 AM   #24
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if intake is lacking wouldn't that tend to depressurize the attic?
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Old 02-14-2012, 11:11 AM   #25
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if intake is lacking wouldn't that tend to depressurize the attic?
Yes.

And drive stack pressures which would accelerate the loss of conditioned air and moisture from the living space.

Intake should always be more than exhaust (shoot for 2:1 ratio).

I am not a fan of Hardie soffit as it does not seem to flow that much air in my opinion.
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Old 02-14-2012, 12:09 PM   #26
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but isn't over pressurization being blamed for this?..or am i not following?
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Old 02-14-2012, 12:20 PM   #27
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but isn't over pressurization being blamed for this?..or am i not following?
Heck if I know Tom. Seems to be a few of these running around lately.
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Old 02-14-2012, 01:11 PM   #28
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Ok, y'all please tell me if I'm reading all this correctly:
  1. My house is underventilated, especially on intake. For 2500 sq ft of attic space [now including the garage foot print] I should have well over 1000 sq in of net free area for intake, probably closer to 1500 - right? And I sadly only have ~560.
  2. This is likely causing air to be pulled in from the house which only has drywall and blown insulation betwen indoors and attic space (which might help explain why I've had trouble cooling in the summers)
  3. My problem has gotten worse due to the addition of 30lb felt on top of the original 15lb felt (the gaps in my roof decking can no longer serve as part of the ventilation system)
  4. This is also likely causing air from outside to get "stuck" in the attic, possibly causing it to dampen the plywood decking and the 15lb+30lb felt on top of it
  5. The moisture is causing the felt to bubble, which makes my roof look terrible (and long term will cause it to fail prematurely?)
  6. My existing soffit vents (though baffled) may be blocked so I should clear any obstructions (I'll probably just rip off the old ones and put up new ones with screws since the builder used nails...)
  7. Hardi plank is a beast to cut in place and adding soffits is gonna be a beating due to the existing insulation
Anything I missed?

Is there a way to get more intake performance out of existing, baffled soffit vents. Like a solar fan driven intake?

Thanks for all y'alls help. I have the builder coming out tomorrow to take a look and I want to be ready to share what I've learned.
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Old 02-14-2012, 01:18 PM   #29
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help! strange horizontal bubbles on new roof


Leave the fan off because it will only exacerbate the issue until you fix the intake issues.

Ditch the Hardie soffit and get to opening those eaves up.

You needn't really factor the garage into the calculations because it is not conditioned space but while you are doing all the other venting, go for broke and make sure it is done once and right.
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Old 02-14-2012, 10:27 PM   #30
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Definitely not planning to use any exhaust fans. Was more wondering if I could increase my intake somehow with a fan since I assume it's going to be really hard for me to get more vents without dropping some $$$...

If I yank down the soffit, am I likely going to have to reinsulate the sides of the attic to replace the fill that falls/settles? Is that expensive?

Or, once the eave is open, do you think I would be able to push baffles up (without it all falling to the ground) to displace some of the existing insulation before replacing the soffit (one with more vented openings)?

Also, do you think doing this will cause the roof to return to normal or do I also have to then take some remedial actions there as well? I'm obviously hoping you'll say that improved ventilation and some Texas sunshine will flatten things back out...

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