Gents, Had to remove my batt insulation due to raccoon damage years ago from the previous owner. Got some quotes to apply 6-8in of open cell on the floor. Is that enough? Is that a recommend application of insulation. Lot of info for the roof deck not much for the floor. Please advise... Thanks

Where are you located?

Posted By Dllanzy on 23 Mar 2016 08:07 PM
...Got some quotes to apply 6-8in of open cell on the floor. Is that enough?

Generally, no.  Unless you live in a very mild climate.

Closed cell spray foam is approximately R3.6 per inch, so at 6-8 inches thick you are looking at R21.6 to R28.8.  In most areas of the country, R38 or higher is recommended/required.

So why didn't the spray foam company recommend spraying ~11 inches of closed cell foam to get R38?  I'm sure it is due to their concern that the high cost of spray foam would steer you away.  At an installed cost of ~$0.50 per board foot (1 sq ft x 1" thick) you would be looking at ~$5/sq ft for R38 spray foam.

Have you considered having stabilized cellulose installed rather than spray foam?  It is not quite as effective as an air barrier, but you could have the insulation company spot spray with foam or caulk areas prone to air leakage for a few hundred bucks then spray over that with ~11 inches of stabilized cellulose to get R38.  R38 damp sprayed stabilized cellulose insulation sprayed on the attic floor costs $0.60 per sq ft total in my area.  That is the total cost, labor and materials to get R38.  Spray foam costs at approximately 7 to 8 times as much as stabilized cellulose in my area to get the same R38 value.

Agree with that! Spray foam is great and has some areas where it really excels, like sealing and insulating the rim joice where it would be more difficult to use other material as effectively. But in some areas, and especially on top of a ceiling, another form of insulation will be far more cost effective...

So, the previous owner was a racoon? :-)

IRC 2012 & 2015 code-min for US climate zone 1 (southern Florida and Hawaii) is R30, so 8" would be "...enough..." to meet code minimums in those areas, but 6" would not. It would have to be installed in lifts of no more than 6" at a time, with a curing/cooling period between lifts for it to be fire safe during the curing period of the second.

In climate zones 3 & 4 code min is R38, which would take about 11" of open cell foam.

In zones 4 and higher it's R49 which is 13-14", installed in three lifts (unless the installer is insured for the fire damage, and you're just looking to replace the whole house and it's contents. :-) )

http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_11_sec002.htm

Many installers will push it and install 8-10" in a single pass, and they'll usually get away without burning the house down, but that also leads to uneven depths, shrinkage, and sometimes even cracking of the foam as it cures, which are all performance hits.

Many foam installers will say "_ _ inches are enough" at some sub-code level, but what that really means is "using this more expensive product the economics of going much higher isn't very good".

The best aspect of open cell foam is that it reliably air seals it. But it doesn't take more than 2" to get a decent air seal out of it, and in most houses it doesn't need to be a full layer, since 4x8 sheet goods are already an air barrier once you've meticulously air sealed all the seams and electrical / plumbing /flue penetrations. After that reasonably air-retardent & dense fiber insulation heaped on top is usually a much cheaper way to hit code min. A shot of 14" of open blown cellulose is about R50, and costs about $2 per square foot, installed. At 35 cents/ board foot that would buy you only 6" of open cell foam with than half the performance. Denser purpose designed blowing wools for attic floors such as AttiCat run only slightly more.

Low density fiberglass like R19 or R38 batts have performance issues unless covered by a top-side air barrier, or overtopped by 3" or more of cellulose, which is substantially more air retardent, and opaque to infra-red radiation.

11" of damp spray cellulose for less than $.06/board foot? thats a huge bargain, if it's correct. We see costs in the neighborhood of $.20 +/ bf for open spray cellulose and higher for dense packed. So while it is higher in cost, it's still good insulation and a fraction of the cost of foam.

The best bet for your attic would be a 1"- 2" layer of spray foam for air sealing, then a thick layer of cellulose for insulating. Cellulose containing borates might also help discourage creatures, although I'm unclear about raccoons.

Dry open-blown cellulose has recently going for about 15 cents per board foot (4 cents per R-foot) in my area, but never anything like 10 cents (even dry, let alone damp-sprayed.) R38 runs about 1.2 lbs per square foot. The material cost has been running between 30-40 cents/lb for dry blown, a bit higher for damp-sprayed, so the material alone is at least 35 cents per square foot. The remaining 25 cents to get to 60 cents/foot is not a lot of margin for buying & maintaining equipment, keeping the offis open, and paying employees.

Raccoons aren't much deterred by any insulation type, but it's usually possible to block them from gaining access to an vented attic. Squirrels can be a bit harder. I had a squirrel chew through cedar clapboard & solid 1x sheathing to gain access to my garage, and another decided to gain access to the space under my deck by widening out the gap between the foundation and the ipe decking by gnawing away at the ipe (one of the world's hardest species of wood.)

I just got a quote yesterday for R38 stabilized cellulose on the attic floor at $0.60/sq ft or R45 for $0.75/sq ft installed.

Thanks for the advice everyone.... I had a cellulose company come in also... 1036sq ft attic. With air sealing and r-49 $3500. 6-8 inches of open cell $2000. What does r value really mean any way without making it air sealed. I'm in Pittsburgh by the way

If an attic is living space and the open cell can only get about 5in open cell in a 2x6 rafter. are all room up there crazy hot/cold?

Code min is R49 (as quoted by the cellulose company), 8" of open cell foam is ~ R30, barely more than half the code requirement.

Open cell foam on the underside of the roof deck in US climate zone 5 can work (from a moisture issue point of view, not R-value if it's only 5.5"), but it requires a class-II vapor retarder on the interior to protect the unvented roof deck from interior moisture drives. If you can spare come interior head room, you can fatten up the rafter edges with 1-2" of rigid polyisocyanurate foam board cut into 2-3" wide strips as a thermal break on the rafters (which will reduce the ice-damming potential), and fatten up the amount of open cell foam to suit.

Overfill the rafter bays slightly, and trim flush with the rafter edges (or edge strips), then apply a layer of 2-mil nylon (eg Certainteed MemBrain) with seams lapped & taped before hanging the gypsum board. Sheet nylon is a variable vapor retarder, that responds to humidity that will be come vapor open if the moisture content of the open cell foam becomes high enough to support rot, but during the winter when the roof deck is cold, the moisture from the foam is drawn into the wood, making it a class-II vapor retarder, and it won't continue to draw moisture from the conditioned space air (or at least not at a rate high enough to matter. On the warmer days of winter or the early spring when the roof deck temperatures rise, driving the moisture back into the open cell foam, the sheet nylon opens up a bit, allowing that moisture to dry toward the interior. This characteristic has been expoited by the food wrap industry for decades, but it's only been 10-15 years in the construction industry. You can sometimes find MemBrain in box stores in my area, but worst-case you can buy it online. In sheets of 8' x 100' or 10' x 100' it's about 12 cents per square foot though distributors, somewhat more expensive in the smaller rolls found in box stores.

Do NOT use 4 or 6 mil polyethylene in place of 2-mil nylon! Polyethylene would be too vapor tight, 100% of the time. That would create a moisture trap for the roof deck & rafters between the ~0.1 perm roofing felt & shingles, and the 0.05 perm plastic. MemBrain is about 0.5 perms when the proximate air is under 30% relative humidity, but over 10 perms when it's over 75% RH (which is where the rot risk begins to soar.) Latex paint is about 3-5 perms, and will be the limiting factor on the drying rate, but isn't sufficiently vapor tight to be protective from winter moisture drives in your climate. You could also use 0.5 perm "vapor barrier latex primer" on the ceiling gypsum, but that's not necessarily going to be cheaper in small amounts than the far-superior variable "smart" vapor retarder such as 2-mil nylon.

When it's time to re-roof, installing 4" of polyiso above the roof deck (or 2" polyiso + 2.5" or 3" polyiso nailbase panel) will bring the performance up nearer to code, and be even more protective of the roof deck by keeping it's average wintertime temperature above the average dew point of the interior space air. In zone 5 a minimum of 40% of the total R has to be on the exterior to be protective, but with MemBrain in place you could cheat that. With only 5.5" of ocSPF in the rafter bays it'll be about R20, and with 4" of polyiso on the exterior you'd have another R20 (derated to R5/inch for mid-winter performance), a bit more than R20 at the full seasonal average, and since it would be thermally breaking the rafters it would just squeak into code compliance on a U-factor basis, if not quite on an R-value basis. If you added 2" deep polyiso edge strips on the interior (and long-screwed or long-nailed the gypsum in place), you'd have about R28 in the rafter bays, and the labeled R of the 4" polyiso would be about R24, which would meet code, and even at the derated ~R20 mid-winter performance it would still be over 40% of the total R, and thus moisture safe.

http://www.lowes.com/pd_750463-27-902018_0__?productId=999958593

http://www.homedepot.com/p/CertainTeed-MemBrain-100-in-x-50-ft-Air-Barrier-with-Smart-Vapor-Retarder-902018/205920791

http://www.certainteed.com/products/insulation/mold-prevention/317391

http://www.naturalspacesdomes.com/dome_store/dome_insulation_systems/images/Membrain3.jpg

If going with more than 5.5", the open cell foam has to be installed in two lifts to be fire-safe as it cures.

BTW: The $3500 for 1036 square feet of cellulose works out to nearly 7 cents per R per square foot which is on the high to VERY-high side. I'm more accustomed to seeing open blow cellulose quotes come in at ~4 cents/R-ft^2 in my area. It's worth getting competitive quotes- should be able to get 1036 square feet of R49 for $2000-$2500, maybe less.

Assuming a 7" average depth on the o.c. foam that's about R26. At $2000 that's about 7.5 cents per R-foot, which is slightly lower than I'm accustomed to seeing it in my area (I usually budget 8 cents per R-ft^2) but in the right ball park.

Is there a floor in the attic?

The $3500 is probably that high because of the air sealing. It might be $2000 for the cellulose (4 cents/sq ft R), plus $1500 for sealing. You might ask the spray foam company if they'll do 2" of foam for $1k. That plus the R49 cellulose at $2000 would be cheaper and better than the $3500 sealing and insulating job.

Or do the air sealing yourself and have the cellulose company do just the cellulose.

Or do 2" of spray foam and do the cellulose yourself with a blower from the big box store.

Posted By chrs on 27 Mar 2016 09:22 PM
The $3500 is probably that high because of the air sealing. It might be $2000 for the cellulose (4 cents/sq ft R), plus $1500 for sealing. You might ask the spray foam company if they'll do 2" of foam for $1k. That plus the R49 cellulose at $2000 would be cheaper and better than the $3500 sealing and insulating job.

Or do the air sealing yourself and have the cellulose company do just the cellulose.

Or do 2" of spray foam and do the cellulose yourself with a blower from the big box store.

$1500 for air sealing 1036' of attic?

It would have to be a very complicated attic (say multiple flue penetrations with clearance issues, and maybe a bunch of duct penetrations to boot) for it to run that much!