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Old 04-01-2012, 10:57 PM   #1
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Reworking attic insulation


My home was built in 1978 and has a 26' * 40' attic with about 4' of clearance at the peak of the roof. I don't think the attic was originally insulated, but at some point about 6 inches of blown in pink fiberglass was added (to the tops of the joists) blocking every soffit in the process. Additionally there is a ridge vent that runs nearly the length of the roof, a gable vent at either end, and a gable fan, which is temperature and humidity controlled, blowing outward. Obviously air flow is poor, way under insulated for PA, and I'm starting to get a little mold speckling in the middle of the attic.

My plan at this point is to get the soffits unblocked, slide fiberglass batting in to keep the loose stuff out, and install vent baffles. At the same time I'll be putting 3/4 plywood down to have something to crawl on. Once that is done I'll add at least another R-30 worth of batting. Should I keep both gable vents at that point, or can I close up the one without the fan and let the fan draw air in through the soffit and ridge when it runs?

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Old 04-01-2012, 11:03 PM   #2
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Reworking attic insulation


With working soffit vents and a ridge vent there is no need to the gable or a power vent. In fact it will mess up the air flow across the rafter bays.
I also would just use some 1/2 OSB to lay on and not screw it down. Your going to need all the room you can get for insulation.
You do know you need to air seal the attic before insulating right.
http://www.energystar.gov/index.cfm?...sulation_table


Last edited by joecaption; 04-01-2012 at 11:07 PM.
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Old 04-01-2012, 11:41 PM   #3
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Reworking attic insulation


So I could do away with the gable vents and fan once the soffits are functional? I think I like that idea. You're not kidding about lack of room! And the worst part is all the ductwork that is up there, crawling over that is a real pain. Fortunately it's metal duct, so it can hold my weight briefly as I shimmy over it. By air sealing you mean sealing up all the ceiling penetrations in the attic, right? I hadn't thought about it until now, but I'll take care of it while I'm up there. I've got a few ceiling fan boxes to install in place of old fixture boxes anyway. Oh, did I mention that I need to run some lighting up there too?
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Old 04-19-2012, 01:42 PM   #4
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Reworking attic insulation


chenman your house sounds exactly like mine. low pitched roof, gable vents and soffit vents. Getting around in that attic with the 4 inches of insulation that is up there and crawling over ducts sucksssss. I'm thinking about taking out all the crappy used to be rodent infested fiberglass blown insulation out and replacing it with spray foam. I also need to redo my ducts but that's another thread. Subbed to see what you end up doing with yours!
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Old 04-19-2012, 09:51 PM   #5
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Reworking attic insulation


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chenman your house sounds exactly like mine. low pitched roof, gable vents and soffit vents. Getting around in that attic with the 4 inches of insulation that is up there and crawling over ducts sucksssss. I'm thinking about taking out all the crappy used to be rodent infested fiberglass blown insulation out and replacing it with spray foam. I also need to redo my ducts but that's another thread. Subbed to see what you end up doing with yours!
Spray foam is a complete waste of money if you are using it as an insulation for the attic floor.

It is expensive and its effectiveness as and insulator can easily be duplicated by cellulose at a fraction of the cost.

You would use spray foam as and air sealant across top plates, recessed fixtures (after boxing them in) and other penetrations to properly air seal the envelope layer at the attic floor......

or

You can use spray foam to covert the attic into a conditioned space and make the roof a "hot" roof deck design.

Using it as merely and insulation in a normal vented attic design is going to be a huge waste of money.
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Old 04-19-2012, 10:28 PM   #6
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Reworking attic insulation


No spray foam here. And no blown-in either. My attic is currently a perfect example of how blown-in insulation can go bad; level is inconsistent, soffits full of insulation. I'm putting R-19 batts in the 2*6 joists, soffit baffles in the rafters, and air sealing as I go. The ends of the batts are enclosed plastic so air won't filter through, and the loose stuff I've got now is going on top and getting tucked around the duct work. Once that's done I'll put R-38 or greater across the top of that and perhaps a perforated radiant barrier too. I'll close up the gable vents and ditch the gable power fan as well. That's my plan right now anyway.
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Old 04-19-2012, 10:43 PM   #7
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Reworking attic insulation


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No spray foam here. And no blown-in either. My attic is currently a perfect example of how blown-in insulation can go bad; level is inconsistent, soffits full of insulation. I'm putting R-19 batts in the 2*6 joists, soffit baffles in the rafters, and air sealing as I go. The ends of the batts are enclosed plastic so air won't filter through, and the loose stuff I've got now is going on top and getting tucked around the duct work. Once that's done I'll put R-38 or greater across the top of that and perhaps a perforated radiant barrier too. I'll close up the gable vents and ditch the gable power fan as well. That's my plan right now anyway.
Not to be argumentative, however, blown in insulation does not go bad.

It can be done poorly as it was in your attic's case, but that is certainly a function of installation error and not the insulation's fault.

The amount of time required to properly prep the attic (i.e. soffit baffles, walls around AC units and the hatch, etc) can easily be made up in the speed of the blown in work vs. putting in batts.

Blown in insulation will also more completely insulate the floor as compared to batts in about 99% of the cases because it will get into all the crevices and settle in the gaps vs. the incomplete contact usually resulted in batt installations.
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Old 04-19-2012, 11:38 PM   #8
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Reworking attic insulation


In your location, you want the winter warmth from solar gain, insulation is more effective, and r.b. gain is less with more insulation: http://www.homeenergy.org/show/article/year/2000/id/37

Don't use the fan, but try an experiment with the gable vents; measure the attic temperature before and shortly after closing them off--- in the exact same location, and let us know the outcome; http://en.allexperts.com/q/Roofing-1...able-Vents.htm

http://www.finehomebuilding.com/desi...ble-vents.aspx

I'd use a higher density batt than R-19 (0.55 density per cubic ft.) over the top of the first layer to stop any convective loops, OR just cover it all with a housewrap.

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Old 04-20-2012, 10:02 AM   #9
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Reworking attic insulation


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Not to be argumentative, however, blown in insulation does not go bad.

It can be done poorly as it was in your attic's case, but that is certainly a function of installation error and not the insulation's fault.
Yes, of course I meant the installation. They didn't blow in cheese up there. As cramped and difficult to negotiate as my attic is, I would expect more blown-in insulation to be either prohibitively expensive or another crappy "it sucks up here, just get it done" job. I shouldn't have a problem with the gaps and cracks, I've got a fair amount of blown-in already up there to work with. Like you said, it'll just take time.

GBA, good read on the ridge vent and radiant barrier. I wasn't sure about the RB yet, I'm still reading up on the subject. I haven't called around about the HD batts yet, but thats what I'm planning on for the second layer.
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Old 07-08-2012, 10:05 PM   #10
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Reworking attic insulation


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Originally Posted by Windows on Wash View Post
Spray foam is a complete waste of money if you are using it as an insulation for the attic floor.

It is expensive and its effectiveness as and insulator can easily be duplicated by cellulose at a fraction of the cost.

You would use spray foam as and air sealant across top plates, recessed fixtures (after boxing them in) and other penetrations to properly air seal the envelope layer at the attic floor......

or

You can use spray foam to covert the attic into a conditioned space and make the roof a "hot" roof deck design.

Using it as merely and insulation in a normal vented attic design is going to be a huge waste of money.
Thanks for the heads up. Just trying to get the most insulation in the smallest area. I figured R7 per inch was the best I could get.

If i put the recommended R30-R60 in my attic I might as well just stick the insulation hose in the gable vent and let it blow till the whole thing fills up. That's the ONLY way I'll get that much in there

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