rasmichMay 3, 2012

We are framing stages now, so exciting... I was asked by the builder today if I'd like to upgrade my insulation from R21 with poly wrap vapor barrier for the sidewalls to blown cocoon spray. He is asking $1700 for this upgrade. The house is 2800 sq feet and in Upstate NY with cold winters. Is this upgrade with it. Is $1700 too much for this. Thanks for any with any experience or advice.

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Have you already addressed air infiltration? I would do that first before spending more on insulation.

    Bookmark   May 3, 2012 at 8:58PM
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the "r21" I assume you are meaning fiberglass batts. In the pure relation between batts and cacoon (cellulose) would nudge to the cellulose side due to several reasons. First it fills all of the wall space unlike batts ever can. It is greener and healthier, typically, compared to batts. It is also more dense so it has additional sound charactoristics to inscrease STC ratings. It also has some additional moisture properties that are better then batts.
However the big issue with either option is as dekeoboe states, air sealing should be the first option. r value means nothing if you have air going through it. Air moving through insulation, especially batts, greatly reduces the value of it. After air sealing is taken care of, do realize your r21 in a 2x6 framed wall will not perform anywhere near that. You are closer to an r15 after theraml bridging through the framing is taken into consideration. I would highly recommend considering adding exterior insulation, foam sheathing, to the home. Infact I would do this instead of changing the bay insulation. Cellulose in stud bays will perform slightly better then batts, but not much at all. Both have thermal bridging and both have the same framing loss factor. Adding exterior foam works to reduce thermal bridging and creates a tighter, more confortable home. By adding exterior foam sheathing it allows your stud bay insulation to be more useful.
Your home prorities with biggest bang for buck payoffs in heating dominate climates goes as follows:
1. air sealing- the cheapest possible way to make the biggest difference in the home performance.
2. exterior insulation or thermal bridging reduction- affects details and a lot of contractors still do not know how to build with it, but it is changing with energy code so all will have to learn sometime
3. overall wall insulation (r value)- without doing either of the 2 above, improvements in this area has minimal payback. Even going with spray foam in the walls still performs less then advertised due to thermal bridging of the wall.

    Bookmark   May 3, 2012 at 10:17PM
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So how do I go about air sealing?

    Bookmark   May 3, 2012 at 10:32PM
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It's almost certainly too late to add exterior insulation to reduce thermal bridging as any exterior insulation will overhang the sills and interfere with the siding or stone/brick veneer.

As for air sealing. It's a concept that has to be integrated with the build from the start; it's not just an add-on, though there are things that can be done to increase efficiency. For instance, instead of spray cellulose, you could consider "flash and batt", which combines spray foam and fg. And, if they're not included, sealed electrical boxes, insulated and caulked headers and caulking at built-up posts in the exterior wall will also improve air sealing.

The overriding difficulty is that at this point during the construction, most builders cannot or will not change their traditional approaches. And, to the extent they can change them, you might not be happy with the extra costs involved.

I wouldn't be in a rush to substitute cellulose for fg at this point unless I could be assured that documented moisture tests would be taken before the cellulose is enclosed. As well, despite claims of some cellulose enthusiasts, cellulose is not an air seal. I would be concerned that this common mis-perception might result in some short-cuts in air sealing.

Here is a link that might be useful: Air Leaks Rot Houses and Waste Energy

    Bookmark   May 3, 2012 at 11:22PM
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Adding exterior foam at this stage is certainly not too late. I have done a project where we added 5" of exterior foam to an exisitng shell. It just has to be detailed as such carefully. In many projects I have done, 1" of exterior insulation can be done without affecting siding attachment, trims, window flanges, etc. 1.5" is cutting it close and would need to check the windows as well as adding nail strips and a drainage plane. Anything over that would require special detailing that most contractors do not know how to do. However 1 or 1.5" of insulation is not enough for NY climate zone to be safely out of the dew point at your sheathing layer.

While air sealing is certainly easier at the framing stage (as the parts and pieces are going together) it can still be pulled off prior to the insulation stage, and actually fairly easily. Caulking top and bottom plates are a start. You can air seal the exterior sheathing plane as well by taping the joints of the sheathing (priming the seams would be required with typical osb). I perfer to detail the air barrier at the sheathing plane.
If this is not possible, the air barrier can be on the interior of the wall plane, at the drywall plane. Air tight drywall approaches would need to be done, including air tight boxes, caulking or gaskets at top and bottom plates, around windows, etc.
These above methods will give you the tightest options but do increase costs.
The other, cheaper option you can do is go around the house caulking all wood to wood joints in the exterior walls. Such as caulk the bottom plate to the floor sheathing, caulk and foam around windows, caulk around window sills and header to sheathing planes, etc.
Flash and batt is a good way to seal up the wall plane at a reduced cost (still higher then sealing at the sheathing layer or caulking) but it fails to address air leaks at sill and head plates in the wall and around openings.

Talk with your contractor and see if he is familiar with
any of the suggested options and go from there. As I tell everyone, improving the house shell is the only place in the house that will give you pay back on your investment (assuming you dont over invest, none of the suggestions would produce that however). Put the money here first in your home. It is not just about energy bills that will always continue to increase, but its about the overall comfort inside the home, the health, quieter, etc.

    Bookmark   May 4, 2012 at 12:26AM
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Exterior foam sheets for sure. The charge for 2 inches shouldn't be more than $3k or so. The problem that you will run into is that the foundation was not planned for that. I think the difficulty in changing has to do with whether you are doing brick or not.

In my area, the foundation would help support the brick and you would change all that by adding foam sheathing. Siding would not be a problem.

    Bookmark   May 4, 2012 at 5:39AM
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Your description of the upgrade is not clear.

Is the GC offering GreenFiber cellulose insulation that used to be called Cocoon? If so, there are several versions of it so you need to tell us which one is being offered.

"Blow In" is loose fill usually for attics.

"Dry dense pack" is used in walls for greater air infiltration resistance

"Stabilized" is wet spray applied with an adhesive and it can cause moisture problems during construction.

I would want to see a written description of the system being proposed and to discuss it with the original designer of the house and/or the insulation contractor.

Here is a link that might be useful: greenfiber cellulose products

    Bookmark   May 4, 2012 at 6:48AM
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