Great Stuff vs. packed fiberglass


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Old 01-10-15, 05:27 PM
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Great Stuff vs. packed fiberglass

still in my basement...lol

So I noticed there are HVAC ducts running along the exterior edge in the cavity where basement wall meets the ceiling....I didn't think much of it as they appeared well insulated on the inside...but something made me feel that this job wasn't done right so I torn off the face paper and remove a bit of insulation to realize that whoever did it - he covered the duct from the basement side only....meaning that where insulation is most needed - facing the exterior wall - there is nothing.

Because the duct work runs very tight in that corner cavity I have one of two choices to insulate on that side:

1. Pack it with Great Stuff by simply inserting the little straw between the duct and the wall and blow it upwards

2. Tear fiberglass insulation into a very thin strips and pack them with a knife or such a tool little bit a time, hoping that it will all somehow nicely settle there on the other side.

I am thinking to go with Great Stuff as I understand that packing insulation is not really effective and I think this would take me A LOT of time.

What do you think ?

Thanks!

PS: if my description is not clear - let me know and I can post few pics
 
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Old 01-11-15, 05:33 AM
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Can you get rigid foam insulation into the space?
 
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Old 01-11-15, 06:11 AM
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Hi Paul,
Can you remove a section of the duct?

I had a window that needed air sealing around its perimeter, but there was only about 1/8" of a gap, too tight to even get the straw from the great stuff in there. So I took a long 1/4" drill bit and created a hole every couple of inches, big enough to get that straw all the way in. Took a few to get the rhythm but did allow me to seal all the way around. In your case, sealing is probably as important as the insulation and fiberglass insulation does little to stop air flow. Recognize that once you do this, that duct isn't coming out (easily).

Pictures as Pilot asked might provide better advice.

Bud

PS, I read somewhere that great stuff likes moisture. I can dig that info out, but it said to spritz all surfaces for better expansion. Also, the foam does not like the cold when applied.
 
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Old 01-11-15, 07:56 AM
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here are the pics.....I Really would NOT want to take the duct work apart...it is cold now in NJ and can't imagine turning off the heat even for a few hours.

To clarify; the pictures show the duct work from the basement, looking up....again, there is no insulation in the cavity behind the duct-work which is the most important area as that's where the exterior wall is

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Old 01-11-15, 08:20 AM
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Still hard for me to tell exactly what you are looking at. I'm guessing the duct is in the cavity parallel to the rim joist, but it looks to be near the bottom of the joist which means there is a considerable cavity above and to the outside. Great Stuff has its limitations for filling large cavities, in fact I believe they has a special large gap product. But if the space gets too large the product has trouble curing. Not a pro on this stuff so will hope others add their experience.

Now, my last big job I used one of the guns with larger cans and I extended the dispensing end with a piece of plastic tubing. I discovered I don't like the guns for anything other than very big jobs as the gun has to be thoroughly cleaned if left unused for a day, but I do like the extension idea. I have since used that approach with the cans, I just have to be careful the existing straw and the extension tube are secure so the pressure doesn't blow them off the can. But for a continuous job, no lunch breaks, less of a problem.

Bud
 
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Old 01-11-15, 09:27 AM
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Bud9051 - you are correct....it is in the cavity parallel to the rim joist and the duct runs closer to the basement side so for sure there is considerable cavity above and to the outside.

Hot air is getting cooled....bigger picture attached

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Old 01-11-15, 10:48 AM
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From the picture, the space looks sizeable enough to stuff batts up there. What does it actually measure? And is that duct round?
 
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Old 01-11-15, 11:20 AM
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duct is round...the top pic might be a bit misleading....if you look at the close-up, that's all the space there is in best of places.....I would say 1/4" to 1/2"
No way you can push even thinnest batts through.
 
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Old 01-11-15, 11:49 AM
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What is securing that duct in place?

Seeing wiring and given the size of the space to fill I would consider man-handling that duct. If you can release any brackets securing ir and wedge it away from the outside wall you should be able to push some reasonable pieces of insulation up into that space. I see you have Roxul, I'm doing some stuffing myself with Roxul around new windows. I'll cap the space with foam.

See how wide you can force that gap open. If some rigid will fit in places where there are no wires sneak some in.

If I were to calculate the heat loss after you do a (example) poor job and then compare it to a good job, I doubt you would find a $5 yearly difference. Filling that gap as best you can will be perfect. Take the extra effort and do some air sealing on the rest of the ducts (assuming they are not now sealed) and save $100 per year.

Stuff away,
Bud
 
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Old 01-11-15, 12:12 PM
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There will be more space above the sill for insulation. I would take the duct down and place some batts or rigid foam. Trying to fill that space with great stuff is going to be futile.
 
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Old 01-11-15, 01:37 PM
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thanks guys...though I was hoping that Great Stuff (at least that new super expending) would do the trick....but if you all say to get the duct down then I guess I will add that to my TO DO list.

By the way... for rectangular duct that runs in the middle of the basement (no contact with any walls) what value Rigid foam would you use?
I am thinking 1 inch for R5.0??
 
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Old 01-11-15, 01:49 PM
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I saw the Roxul, so why is the ceiling/floor insulated?
Is your furnace down there with all the ducts?
Are the foundation walls insulated?
If this what we refer to as a conditioned basement, even though it may be unintentionally heated, but the foundation is insulated, then there is less need for the insulation layer at the basement ceiling. If so, any heat lost from the furnace and ducts to the basement is still part of the home heating.

If it is a cold basement with no heat and no insulation on the walls, then 1" would be a good start, but technically it also needs to have a fire rated covering, like drywall.

I vote for a conditioned basement with insulated walls, makes the floors above nice and warm.

Bud
 
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Old 01-11-15, 02:28 PM
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thank you again.
It is a cold basement in the process of being finished.
The furnace and all the ducts are running down here.
The concrete foundation walls of the basement will get treatment after I paint them with Drylok
But I do not want to apply more than 1inch total to the walls...so would probably use half inch rigid insulation and then drywall.

Putting Roxul up was the the first step only
 
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Old 01-12-15, 03:13 PM
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Bud,
Going back to your comment about "sealing the ducts"...did you mean making sure that the air is not leaking anywhere along the runs ?

What would you recommend for that?
Would those special duct tapes be enough to seal around the seams ?
 
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Old 01-12-15, 04:46 PM
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LOL, the "duct tape curse". Unfortunately, about the only place you should not use duct tape is on ducts, it does not age well. I find the foil tape easy to use and it has a good reputation and when I have to tape around the diameter of a duct where I cannot reach I feed the tape over the duct with a tail of the backing peeled back so I can grab it and pull it over the top. It is one of those things that is easy to do but hard to describe. But sure beats the other method of brushing on duct mastic. There are places where the duct mastic is easier, like covering an entire flex elbow.

The objective is to seal all ducts from source to destination so the sir comes and goes where it should. It becomes especially important when avoiding and leaks outside the conditioned space, like an attic or vented crawlspace.

As for where to seal, big leaks are more important, but every seal and joint.

Bud
 
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Old 01-12-15, 05:52 PM
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you are right...I wasn't thinking of the duct tape as in common tape that most people use to seal boxes and fix things around the house....I meant the foil tape for ducts that looks like Aluminium..

Would you say this is better than the duct mastic.... I never heard of this special paint but I just checked it out and it seems very cheap 1/2 gal for $13....I could probably paint every connection, every flex elbow and every bend.
 
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Old 01-12-15, 06:23 PM
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The duct mastic looks like vinyl floor adhesive and is just as messy. Brushing in onto round ducts tucked up into joist cavities will turn the air blue. My trick with the foil tape is to peel back a starter section and fold the backing onto the end with its backing still in place. Sometimes have to waste a little of the tape to get enough excess backing. But then you can feed the excess and the remaining end over the top of a duct and after sealing the exposed end, pull the backing off and seal the rest.

Although the foil tape probably doesn't meet government standards i have yet to see any falling off or hear complaints about such. It can also be removed if repairs or renovations are needed. i would sure hate to make changes with the mastic. BTW, the pro method with the mastic is one layer of mastic covered with a fiber mesh and then a second layer of mastic. Bet that cost a bundle.

Bud where the mastic can be easily applied and no changes are on the drawing board, it works fine.

Bud
 
 

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