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Old 02-15-2015, 02:30 PM   #1
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Old attic insulation, facing, and ventilation


Hi all,

I recently purchased a home built in 1969 near Seattle and am planning to update the insulation. I'm not planning to do this work myself due to attic access issues and rebates, but the 4 companies I've gotten estimates from conflict with each other and with my research, so I'm hoping I can get some advice here.

Current insulation/ventilation:
a few inches of rock wool (probably original) with faced R-19 fiberglass batts rolled over the top (probably 15 or so years old). Facing is downwards for the most part, but some areas overlap - looks like it was not amazingly well installed but not horribly. It is above the old rock wool though. We have about 22 4" x ~2 feet soffit vents (technically not soffit since we have exposed rafter tails) scattered around the perimeter of the house as well as sufficient box vents.

Planned: Air seal as much as possible and blow in cellulose to R-49

There are two specific questions I have.
  1. Is removing the old insulation necessary? It's in good shape, but old. The only issue is that the facing is above the old rock wool. We've had three companies say it's fine to leave it this way and one company want to remove everything before blowing in all new insulation. My understanding is that having insulation under facing is bad, but the question is how bad? I've also read that if everything is air sealed then the facing doesn't do that much. If we had unlimited money, completely replacing the insulation might be the best thing, but it doesn't sound like its worth the expense.
  2. Some of the sheathing in the very northeast corner has a thin white something on it - almost like paint. But it is at least 4 feet or so away from any of the soffit vents and that corner is not ventilated itself. Two of the companies have said that it's mold, two have said it's just dirt. Any thoughts on how to figure out if this is mold, and if so, would adding more venting specifically in that corner be worthwhile?
Thanks for your help!
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Old 02-15-2015, 04:28 PM   #2
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1. Not really but depending on the age and any contamination, sometimes it is easier to just remove it and have a nice blank canvas to work with. The vapor retarder level should be facing the warm side of the assembly so that would be towards the conditioned space in this case. Once the attic is properly air sealed, the amount of moisture is minimal so it is usually overkill.

http://www.buildingscience.com/docum...doctypes/diges

2. Most older homes are undervented at the end of the day. Use the 1:150 NFA guidelines and add additional venting as necessary. If you don't have a mold plume in the home now, the likelihood that you will after thorough and proper air sealing is even less likely.

That being said, there was a poster that just mentioned how he was getting sweating now as result of properly insulating his attic. His problem...not enough NFA and ventilation.

Post up a picture of the vent and understand that ideal ventilation is balanced, continuous, and sufficient. Most homes are undervented at the intake.
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Old 02-15-2015, 05:19 PM   #3
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Thanks for the reply! I've attached a photo of that corner (this is a hip roof). I actually realized there are two vents in the very corner, but you'll notice there is something there. The two bays on the left have no vent, and the next vent is just to the left of what is in the photograph.

It may be worthwhile for us to have the batts pulled out, since some of them are just draped over wires or similar. If we leave the rock wool (which is in good shape and loose fill). I'm guessing that that'll be cheaper than actually having to vacuum everything out. If the batts were properly installed it would probably be worthwhile to keep them. Since they were installed somewhat weirdly, it may not be.

Total attic area is 1250 sq ft or so. The one thing everyone has agreed on is that the amount of venting is fine. We have around 22 vents covered by wire netting that are 2 feet by 4" - even if each of them has ~48 sq in. NFA (assuming half the area is blocked) I think we're good for the square footage of the attic. I believe we also have 6 box vents for exhaust and that's also fine (in fact, we may have too much intake ventilation).
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Old attic insulation, facing, and ventilation-dsc_6359.jpg  
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Old 02-15-2015, 05:43 PM   #4
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Looks like a bit of mold. Hips don't tend to have good exhaust and maybe the air was stagnate there.

Is that area above a bathroom? How are the bathrooms vented?
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Old 02-15-2015, 05:54 PM   #5
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That area is just above the master bedroom. The bathroom attached to the master is just to the left of there, with another bathroom just to the left of that one. Both are vented through fans that are attached via ducts to roof jacks. I doubt they're sealed, but they're probably 10 feet away from the area with the mold and the sheathing around them looks fine. Moisture from there was my first guess as well, and I looked to see if I could spot any substantial air leaks but the ducting looks fine and any minor leaks I expect would be more noticeable near the ducts.

In any case, sealing them as well as the rest of the attic is one of my priorities, so hopefully that will remove that problem. Worst case we can always open another vent there.
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Old 02-15-2015, 07:44 PM   #6
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Being tight in those locations, the venting from the eave might be a bit obstructed with the batts.

Make sure the baffles are intact and go all the way down the the soffit.

Seal up all the plates and you should be good.
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Old 02-16-2015, 11:51 PM   #7
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Every rafter bay should be vented. A hip roof is worse in that the top of the cavity is not vented stagnating the air-flow at the hip rafter (diagonal one). Yes, add venting at every bay or you could easily get mold, the airflow follows the rafters upwards; not sideways (laterally) with your individual bays vented. http://www.buildingscience.com/docum...on?full_view=1

The faced insulation is fine if you add more insulation on top (though air-seal attic first) to have 2/3 of total insulation on attic side of VB- with 1/3 under it; it doesn't need to be right next to drywall to be effective.

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Old 02-17-2015, 05:43 PM   #8
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Good info above.
I'd agree that the old insulation can stay, although air sealing can be much easier and less likely to miss areas if it is removed. If the costs are not much more to remove it, I'd probably go that way. I'd also get that mold treated prior to getting the work completed.
Definitely add the baffles in every bay and you should be good going forward.
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