Insulation options

[tc-vt]

I've built a 20x30 storey and a half in Northern VT (approx 8,500 - 12,999 heating degree days) and need to insulate it.  I have been reading quite a bit about the pros and cons of fiberglass, cellulose and sprayed foam.  And then as far as the foam goes there is the open cell vs closed cell debate.  Does anyone have opinions or experience with these?  Then there is also the vapor barrier debate and whether one is really needed at all regardless of the type of insulation installed.

From what I have read here is what I have gathered:

Fiberglass does sound like it is inferior and susceptible to being installed improperly.  Its actual r-value diminishes quite a bit when there is a great thermal difference, just when you need it the most.   Cellulose seems to be a step up, the major negative you here is settling - usually talked about by the fiberglass industry.  

Then there is foam.  As far as fire spread, all of the foams have lower ratings than the wood that the building is made of making any arguments there fairly unimportant.  Icynene is more environmentally  "green" and any outgassing of closed cell foams don't seem to be big issues either.
Closed cell foams act as a vapor barrier but it also seems to me that they may seal things up too tightly.  For example, I have a leak somewhere in the roof that needs to be fixed which got me thinking that the closed cell, with the metal roof and roofguard underlayment on the other side, would make a vapor tight sandwhich around the roof sheathing possibly holding moisture in the sheathing, especially in the event of a leak, making rot problems more severe.  The open cell icynene foam would let excessive water through (so they say) which seems better for the building materials, allowing things to dry out and not be locked up so much and allow water leaking problems to show themselves.  So, closed cell foam may trap moisture or worse, pool water, at the foam/plywood interface, where icynene may let moisture in, but may also be able to let it back out???  Moisture to me has a way of getting into places and not getting back out.  The icynene manufacturer recommends using a vapor barrier where the vapor pressure gradient may be high, like in areas where there are more than 7500 heating degree days.  They say a vapor barrier paint would be sufficient for this and a poly barrier would not be necessary, but some codes and inspectors may not recognize this.  (Where I am I don't have to have the building inspected.)  The icynene is about 30% cheaper I think, than the closed cell foam.

An interesting thing is that of the three foam estimates I have, some of these guys keep mentioning an r-value of 7 per inch, where after any thermal drift that may occur, a realistic value is supposed to be more like 6.6.  They give quotes to put approx r-19 in the walls and r-30 under the roof sheathing.  Code for this area would reuire r-49 in a ceiling insulation installation or r-38 under the roof deck.  Though going from r-30 to r-38 may be getting into the area of diminishing returns as one installer told me, it isn't to code.

Well, this is a start and I hope to see some thoughts on this or anecdotal information.  I think one of the confusing points underlying all of this is the vapor barrier debate.  I wish I had walls of stone or logs so none of this would be an issue.  The next one I build (if I do) will have solid walls.

Tom
 

[tc-vt]

Here is agood link on the vapor barrier/vapor retarder debate.  I remember reading something similar to this last year and just found it again.

http://www.buildingscience.com/resources/roofs/ceiling_vapor_barrier.htm

Tom

[John Raabe]

Tom:

Building a wall of stone (or logs) will not get away from the vapor pressure/ potential condensation issue and the insulation properties get even more complex. Think English castle in February.

For your climate I would suggest redundant insulation with any foam on the interior (warm in winter) side of the framing. I would use fiberglass in the cavities and then an interior foam sheathing under the the drywall or other interior finish. This will cause a bit of extra work for electrical boxes, etc. but will have the vapor barrier on the right side (tape the seams) and insulate the studs and any gaps missed in the batt installation.

In this installation you could use something like 1-2" of Thermax for a better R/per inch (use the aged value).

This will pump up your total values to where they should be for your cold climate.

Then make sure you have windows to match. And, a way to provide a fresh air wash through the house with an air exchanger. At 12K DD all this makes economic sense, especially with where fuel costs are headed.

[tc-vt]

Thanks for the suggestion, John.  That would work well and only double the cost of the fiberglass compared to the estimates for sprayed in foam that are 5 times the cost of fiberglass.

Tom

[John Raabe]

This is basically the "Poor Man's SIP" details I have in some of the plan sets. Superinsulation on the cheap.

Spray foam is great but very expensive.

[Lady_Novice]

I've been thinking about the same exact things and I'll probably choose a foam insulation rather than fiberglass, because I need to get a lot of R value in a small cavity. After reviewing the buildingscience.com website and purchasing their book for my climate, I realize how important it is to match the permeability of one's building materials to one's climate, or moisture can be trapped.

I believe the building science people would say Vermont is a "cold climate" but not a "very cold climate" (check their website to be sure?). In a cold climate, you want foam insulation that is somewhat permeable, not completely impermeable. In a very cold climate, less permeability is desired. Different foam insulations have different rates of permeability and you should be sure the foam insulation you choose has the permeability that's best for your climate. The permeability info is available from the foam manufacturers. I'm going to be researching this more.

Icynene sounded like a great option when I read about it, but expensive because it can't be self-installed. Is icynene a lot more expensive than self-installing the 4x8 sheets of foam? The typical 4x8 sheet of foam seems about twice the cost of fiberglass (per R value), but IIRC icynene would cost even more?
Lady Novice

[quil]

Most of the insulation in our house is foam insulation. There does not appear to be any moisture problems. We have walls in the basement that were fiberglass batts and a poly vaporbarrier type insulation. We ended up with lots of mold and dry rot. The only thing we could fiqure out was that condensation was forming on the nails from the siding. And soaking the batts. So we pulled off the wall and replaced the insulation with foam. This was on the north side of the house. The foam is easy to work with. And can be sealed tight with the spray foam in a can. I hope to build the next house with it.

[Okie_Bob]

I had Icyene sprayed in my apt/garage this past summer. Here in central/east Texas I used 2x4 stud walls 10' high. I have plywood sheeting on outside walls, then 30# felt and HardiBoard on top of it all. Then after running all elect and plumbing, I had the icyene sprayed in. Oh, roof is metal with 2x4 trusses. I had the entire roof of the garage and apartment sprayed to fill the 2x4 cavity in all exterior walls and the underside of the metal roofing. I did not sheetrock the ceiling in the apartment so the spray could be installed more easily and will have them back out once sheetrock is finisyhed.
Installed said common practice in our area is to go with no ventilation in the roof. Suprised me but he showed me many pictures of houses with no venting and also had pictues of electronic thermomters both above and below ceilings with only a 1/10 degee difference while outside about a 30 degree difference!
I am sold on Icynene and will use it on my house remodel if the price of lumber comes back down and I can get started.
Only problem with Icynene, my wife is upset because the apartment is so quiet now she can't hear the rain on the metal roof anymore!
Okie Bob
hope this helps