I am in the process of securing bids for about 50,000 bd. ft. of open cell foam. I have one installer offering the Sealection Agribalance foam at 4.45 R-value per inch. There web site does support this claim via independent testening. It appears to be a 6 or 7 month aged value. There is a slight premium in cost (~.03 per bd. ft.), but the extra R-value seems to be worth it.

I have a couple of questions:
1) Why is it that most of the open cell installers push for only 5-6 inches max under the roof deck? Does it have to do with efficiency (they keep telling me that you get the most efficiency (what ever that means) with the first 3 inches), or does it have to do with the installers not being able to spray more than 5-6 inches at a pass and thus leading to a more labor intensive process to put in 10 inches?
2) In lines with question #1, they seem to be trying to convince me that R-49 is not needed on an attic floor or in the roof deck if the house is sealed. Something about the R-value of fiberglass having been determined during testing at 70 degrees, and thus not representing the true R-value at much colder temperatures.  They say that the actual R-value of R-49 fiberglass is really half and that is why 5-6 inches of open cell foam would be plenty in a roof deck.  Just hoping to get some clarification.
3) Is R-30 (or less if it is open cell spray foam) enough to insulate in the ceiling between a garage (with R-19/20 walls and R-14 garage doors) and the bonus room above? Thanks for the responses.

Fiberglass insulation isn't as good as most have us used to believe because it does not stop air infiltration. Also, you'll hear many people say that it over ... (insert whatever number) inches/R value the added insulation doesn't really help. This may have been true with standard fiberglass insulation and "standard (read crummy) installation, but many people including Building Science Corp, Passive House Institue and many others have proven that to be just plain wrong. The R value does matter and with the potential coming increase in the cost of fossil fuels, it will matter even more. BSC considers the "sweet spot" to be about R-30 walls, R-60 roof, but there are variations going to R-40/70 depending on climate. These also assume a very tight shell. I recently saw a blog of someone who had added a SIPS addition with R-30 SIPS floor on piers; he has noticed that the floor is colder than the rest of the house which is over the basement. I recently remodeled a "bonus" rooom over a garage. The 2x10 floor joists were R-30 fiberglass; we air sealed that and installed 2" of XPS (R10) above & 3/4" plywood over that. Much easier to heat now. Whatever your wall insulation, insulating outside of the framing is worth it.

#1 is partly a function of labor costs, the fact that half-pound foam can only be sprayed in lifts of 5-6 inches at a time, and it's harder to do an even job on the second lift over the now uneven surface.  There's also the cost-effectiveness issue- it costs more per unit R-value than fiber, and going high-R with spray foam gets expensive.  (You hear the same arguments for going with only 2" of closed cell foam.)  Going from R1 (the wooden roof deck) to R10 (2-3" open cell) cuts the conducted heat loss by ~90%, while going to 6" cuts it ~95%- only 5% more.  There are always diminishing returns with any insulation technology.


#2  They're misrepresenting how much fiberglass loses R with delta-T.   Did they specify at what temp it's been reduced by half? (I suspect not) Low density fiberglass does have convection issues.  While fiberglass does have internal convection issues and loses R-value, the thicker the layer, the lower this effect is, since the temperature gradient per inch is lower with thicker material. Most of the studies of the effect showing large losses were done with 5.5" thick R19 or low-density blown fiberglass at R19-R25.  R49 of fiberglass (batt or blown) is QUITE a bit more R-value than 6" of half-pound foam.  But sealing the attic does reduce convective losses, and is worth doing. You can also combine the R value of the sealed roof deck and attic floor insulation, but by how much depends on climate zone. (The average attic temp needs to stay above the dew point of the wintertime conditioned space air.)

#3:  How much is enough (or cost-effective) depends on your climate and heating/cooling system efficiency.  Got a zip code?

I was talking with a spray foam contractor at a builder show recently and he showed me some data stating Sealection Agrilbalance has a heat flow reduction of 82.5% for 1" thick, 2" is 90.4%, 3" is 93.4%, 4" is 95%. It also shows up to 10" thick and this is 97.9% He emailed me the sheet and I attached it... I hope this works.

And that's true of any insulation, not just spray foam. Going from nothing to something doesn't take much, but to then cut the remainder in half means doubling the amount of insulation, cutting it to 2% of the heat loss of an uninsulated roof or wall takes a lot. Mind you 2% of a gia-normous number is still a significant number.

Whether it's cost-effective depends on your heating & cooling loads, the price of energy, the efficiency of the equipment, and (no surprise) the incremental cost of goods for the insulating material. Spray foam is good stuff, great for forming a perfect air seal, but expensive when going for high R-values. Flash + batt, or flash + blown is commonly done, using the spray for the air-tighness, and the lower cost goods for boosting the R.

52722 is the Zip. I would like to make a decision... my mind is going to explode ;o) I am thinking of going with some sort of attic seal followed by blown fiberglass/cellulose on the attic floor to make up the differenct.  Any suggestions would be greatly appreciated.  Would a house plan help? Also, what do you think about the ceiling of the garage below the bonus room?

I would spray foam the underside of the subfloor for the bonus room to air seal and keep fumes from coming into the bonus room from the garage... at least an 1" or so, then you could blow in cellulose the balance of the garage ceiling. I would also continue the spray foam up the knee wall (is the bonus room an attic truss?) and spray foam the sloped ceiling.

Thats what I was thinking! Could I block the air in the sloped portion (at the knee wall, roof junction) with some rigid foam or OSB,  and then just air seal the sloped portion with 1" of closed cell foam or 3-4 inches of open cell, followed by batts to an R of about 28?

I would naturally seal around the air block with the foam!

Posted By dolphin on 03 Mar 2010 03:14 PM
52722 is the Zip. I would like to make a decision... my mind is going to explode ;o) I am thinking of going with some sort of attic seal followed by blown fiberglass/cellulose on the attic floor to make up the differenct.  Any suggestions would be greatly appreciated.  Would a house plan help? Also, what do you think about the ceiling of the garage below the bonus room?

Bettendorf has about a 6500 heating degree-day climate with Dec/Jan/Feb average temps of ~25F/20F/25F respectively. (Climate info for the quad-cities lives here.) You definitely need more than ~R20 (5-6" of half-pound foam) in the attic to keep heating bills bounded.  The Oak Ridge Nat'l Labs zip code recommendations for your zip calls for R49 in the attic, but you can safely split it between foamed rafters & fiber-insulated floor if you follow this rough guideline:

Don't go more than ~R40 on the floor portion- not the full R49.  Keep the fiber to 2/3 of the total R-value or less, or you run a risk of wintertime condensation/mildew issues in the attic.  Monitor the relative humidity in the attic during the first winter season- if it stays at 70% or higher for weeks on end, put a dehumidifier up there to keep it at 60% or less.  The duty cycle will be low- the heating savings will more than offset a few kwh/month in dehumidification costs.

But if you seal it well at the ceiling below you probably won't need mechanical dehumidifation if you keep it to 1/3-2/3 in your location.  The less warm air from conditioned space infiltrates into the now-sealed attic, the lower the humidity issue.  Foam sealing all plumbing & electrical penetrations into that area is best.  If you have a bunch of recessed lights it's a real PITA though.  Blown cellulose passes significantly less air than batts or blown fiberglass, and will wick any condensation that DOES occur away from structural materials.  This hygric buffering effect makes the attic more moisture-tolerant and moderates the humidity.  (The only down side to insulating attics with cellulose is when roof leaks occur it doesn't dry quickly, and it's better to scoop out any wet stuff and replace it with fresh stuff. ) Use weather stripping or other air-sealing methods on the attic access as well.  Applying vapor-retardent paints on the ceilings below the attic floor is also a good idea, but not nearly as important as air-sealing.  Air transported moisture will usually greater than vapor-diffusion through wall surfaces.  If you use cellulose to buffer it and reasonable air sealing you'll be in good shape.  During the spring/summer/fall the cellulose will dry sufficiently to buffer the following heating season's humidity load.

If you already have R49 batts up there, leave them, but plan on monitoring the RH and dehumidifying as-necessary.  The risk is low, but not as low as if you had less air-permeable insulation and more hygric buffer.

Under the bonus room applying a 2" lift of 2lb (closed cell) foam on the sub-floor from below both air seals it an puts a class-II vapor retarder on the correct (warmer in winter) side of the assembly.  Rather than batts, again blown insulation is your friend, as it leaves no gaps.  With a warm-side up configuration with a perfect air seal (the foam) there's less convection loss (= performance reduction) that you'd otherwise get with fiberglass, but blown fiberglass is far preferable to batts. Cellulose weighs more, but may be preferable here too (again, for hygric buffering reasons, though it's less critical here.)

Try lower R value spray foam.I have applied high R value Ultimate linings polyurethane foam  for closed cell .It's result amazing.