Hello everyone. We are planning a slab on grade home in northwest Arkansas. 1300 sq ft, 2x6 exterior walls, 3.5” spray foam in the walls and ceiling. I’ve been trying to get feedback from local vendors for Mitsubishi and Daiken as they’re the only ones in my service area and that’s proving problematic. I’m being told 2 units, one head in the master and one head in the living and dining room is enough, the other two bedrooms don’t need a head unit. This set up, while affordable, seems problematic, especially if a door is closed. So I’m trying to find out what I would actually need in hopes of getting that installed. I know of Manual J calculations but am u sure if they apply to ductless and I don’t know how to use it anyways, how does a homeowner go about designing and/or verifying calculations for a build like this to ensure proper sizing, efficiency and comfort? Thank you for your assistance?

You didn't describe your overall envelop. Ceiling insulation? Quality of windows and doors? What measures are being taken to air seal? Exterior wall rigid foam / sheathing? Any insulation under the slab? What about the slab edge?

A tight well insulated home doesn't have a lot of room-to-room temperature variation and you can likely get by with just two heads. You might also have transfer grills installed above the extra bedroom doors to facilitate air movement.

Why build 2x6 walls and only install 3.5" of insulation in them? 2# density foam or .5# density foam? Fully filling that stud cavity with spray in cellulose would likely cost much less and give comparable or better performance.

Hi Arkie, thanks for the quick and detailed reply. The prices around me are, much to my surprise, not much more expensive for spray foam versus cellulose. Now this is for the netted and not the wet spray cellulose. Of the contractors I've called, cellulose is 75 cents a square foot and spray foam open OR closed cell is 1.10 -1.50 a square foot. Thankfully the 1.10 is from the contractor with the best reputation around here. So for not much more I can get spray foam. This was for spray foam in the walls and ceiling. I am still discussing the slab build with the contractor as we were contemplating radiant heat but it's proving to not be cost effective and not something we feel we must have in our climate. (It would be nice but we've lived this long without it jus fine) I do plan to insulate under the slab with foam panels. I do not know the poundage of the spray foam and have a call into the contractor to clarify. Which would you suggest? The home is a slab on grace home, stick built with metal roof and wall panels. A "pole barn house" for lack of a batter word. I had considered doing a insulation combo where I spray the metal shell with spray foam and then use Roxul or cellulose in the walls with spray foam around the edges and DIY it to seal it up. I do have a wood stove in this home as well. 2 exterior doors and one to the garage, all fiberglass door at this point. 8, Vinyl double hung, low E windows, 2 large ones out towards a covered porch. House will have a east to west orientation long ways, 60' long by 34' wide. I was always under the impression that spray foam was, for most residential purposes, the "best" and I do want to have it comfortable and energy efficient but also simple. It's all electric, marathon water heater, woodstock soapstone stove, ductless mini splits and spray foam made the short list of energy efficient "upgrades". The radiant heat and solar system will go away due to cost. Thank you.

Posted By arkie6 on 28 Feb 2018 12:53 PM
You didn't describe your overall envelop. Ceiling insulation? Quality of windows and doors? What measures are being taken to air seal? Exterior wall rigid foam / sheathing? Any insulation under the slab? What about the slab edge?

A tight well insulated home doesn't have a lot of room-to-room temperature variation and you can likely get by with just two heads. You might also have transfer grills installed above the extra bedroom doors to facilitate air movement.

Why build 2x6 walls and only install 3.5" of insulation in them? 2# density foam or .5# density foam? Fully filling that stud cavity with spray in cellulose would likely cost much less and give comparable or better performance.

You can't really get anywhere with this without first running a room by room, zone by zone complete Manual-J load calculation using aggressive assumptions (per the Manual-J instructions) a the 99% and 1% outside design temperatures. Don't leave this up to HVAC contractors- hire an engineer or RESNET rater who is competent to do the U-factor calculations on your non-standard wall design, somebody who makes their living on the accuracy of their calculations rather than the competency of installing and maintaining equipment.

arki6 is correct that with rare exceptions (say, buildings without sheathing located in flood zones) closed cell foam thermally bridged by framing is a waste of environmentally and financially expensive foam. A 5.5" thick R20 open cell foam fill outperforms a 3.5" thick R20 closed cell foam solution on thermal performances, since with open cell foam the framing fraction is ~ R6.5, whereas with the closed cell solution the framing fraction is ~ R4.2. With 16" on center framing the typical framing fraction is 25% of the total wall area- it's not a subtle difference. The "whole wall R" of the R20 closed cell is only about R10 after thermal bridging, the whole wall R of the R20 open cell solution is about R14. That's about a 29% reduction in heat flow through the wall. For the math on that see:

http://www.finehomebuilding.com/membership/pdf/184243/021269086NRGnerd.pdf

At 5.5" half pound open cell foam uses less than half the total amount of polymer that 3.5" of 2lb closed cell foam, and it's blown with water rather than the industry standard HFC245fa (an extremely powerful greenhouse gas.) There are a few closed cell foam vendors who have transitioned to much more benign HFO1234ze, but it's still more than twice the polymer at R20, with only ~70% the performance of a full cavity fill of open cell foam.

Hi Dana, thank you for your reply. First question is, do you have anyone you recommend I use (Engineer/RESNET wise) as it would appear this is more your wheelhouse than mine. If I can go with a more traditional insulation package then I can do it myself (or so I assume) and save a fair amount of money but again, I do want to do it correctly and be efficient. I'm glad I typed this up as I was under the impression spray foam was the end all be all and apparently it is not. To elaborate on something, if I am doing stick built, before the metal siding is up, what panel would you suggest I use to eliminate the thermal bridging from the framing? I assume I would want to tape the seams as well, correct?

Posted By Dana1 on 28 Feb 2018 04:21 PM
You can't really get anywhere with this without first running a room by room, zone by zone complete Manual-J load calculation using aggressive assumptions (per the Manual-J instructions) a the 99% and 1% outside design temperatures. Don't leave this up to HVAC contractors- hire an engineer or RESNET rater who is competent to do the U-factor calculations on your non-standard wall design, somebody who makes their living on the accuracy of their calculations rather than the competency of installing and maintaining equipment.

arki6 is correct that with rare exceptions (say, buildings without sheathing located in flood zones) closed cell foam thermally bridged by framing is a waste of environmentally and financially expensive foam. A 5.5" thick R20 open cell foam fill outperforms a 3.5" thick R20 closed cell foam solution on thermal performances, since with open cell foam the framing fraction is ~ R6.5, whereas with the closed cell solution the framing fraction is ~ R4.2. With 16" on center framing the typical framing fraction is 25% of the total wall area- it's not a subtle difference. The "whole wall R" of the R20 closed cell is only about R10 after thermal bridging, the whole wall R of the R20 open cell solution is about R14. That's about a 29% reduction in heat flow through the wall. For the math on that see:

http://www.finehomebuilding.com/membership/pdf/184243/021269086NRGnerd.pdf

At 5.5" half pound open cell foam uses less than half the total amount of polymer that 3.5" of 2lb closed cell foam, and it's blown with water rather than the industry standard HFC245fa (an extremely powerful greenhouse gas.) There are a few closed cell foam vendors who have transitioned to much more benign HFC1234ze, but it's still more than twice the polymer at R20, with only ~70% the performance of a full cavity fill of open cell foam.

BTW: As bad as rules of thumb are, most 1300' homes would have a cooling load less than 1.5 tons. The median load/ratio for homes that size would be about a ton per 1000' of conditioned space. But in new construction with higher performance envelope design (paying close attention to limiting the size and SHGC of west facing windows), that can easily grow to a ton per 2000' or more. A designer in the Atlanta GA area, Allison Bailes does dozens of careful Manual-Js per year, and compiled this graphic plotting square feet per ton vs. house size.

http://www.greenbuildingadvisor.com/sites/default/files/images/Bailes%20graph%20for%20Manual%20J%20blog.preview.png

http://www.greenbuildingadvisor.com/articles/dept/building-science/manual-j-load-calculations-vs-rules-thumb

Typical tight IRC 2015 code-min slab on grade houses with R14-ish whole-wall R values (the open cell solution) will have a design heat load of less than 10 BTU/hr per square footy @ 20F (a typical 99% outside design temp for Arkansas: https://articles.extension.org/sites/default/files/7.%20Outdoor_Design_Conditions_508.pdf ) That would make the heat load of a 1300 footer less than the output of 1-ton of better-class ductless.

The very smallest 2-zone multi-splits may be oversized for your actual loads. A pair of half ton Mitsubishi FH06NA, (or may one will be 3/4 ton FH09NA) or a single 1-ton Fujitsu 12RLFCD mounted in the middle of the house with extremely short duct runs blowing both directions is probably going to be more appropriate for your loads, if you do any optimizing if the building envelope at all, and would modulate at high efficiency-high comfort most of the time, far better than oversized equipment.)

http://www.fujitsugeneral.com/us/resources/pdf/support/downloads/submittal-sheets/12RLFCD.pdf (<16,000 BTU/hr of capacity @ +17F, minimum modulation 3000 BTU/hr @ +47F)


http://meus1.mylinkdrive.com/files/MSZ-FH06NA_MUZ-FH06NA_ProductDataSheet.pdf (>10,000 BTU/hr capacity per unit @ +17F modulating to 1600 BTU/hr min @ +47F, 9000 BTU/hr cooling capacity per unit., modulating down to 1700 BTU/hr.)

[deleted double-post]

Posted By Dana1 on 28 Feb 2018 04:42 PM
BTW: As bad as rules of thumb are, most 1300' homes would have a cooling load less than 1.5 tons. The median load/ratio for homes that size would be about a ton per 1000' of conditioned space. But in new construction with higher performance envelope design (paying close attention to limiting the size and SHGC of west facing windows), that can easily grow to a ton per 2000' or more. A designer in the Atlanta GA area, Allison Bailes does dozens of careful Manual-Js per year, and compiled this graphic plotting square feet per ton vs. house size.

http://www.greenbuildingadvisor.com/sites/default/files/images/Bailes%20graph%20for%20Manual%20J%20blog.preview.png

http://www.greenbuildingadvisor.com/articles/dept/building-science/manual-j-load-calculations-vs-rules-thumb

Typical tight IRC 2015 code-min slab on grade houses with R14-ish whole-wall R values (the open cell solution) will have a design heat load of less than 10 BTU/hr per square footy @ 20F (a typical 99% outside design temp for Arkansas: https://articles.extension.org/sites/default/files/7.%20Outdoor_Design_Conditions_508.pdf ) That would make the heat load of a 1300 footer less than the output of 1-ton of better-class ductless.

The very smallest 2-zone multi-splits may be oversized for your actual loads. A pair of half ton Mitsubishi FH06NA, (or may one will be 3/4 ton FH09NA) or a single 1-ton Fujitsu 12RLFCD mounted in the middle of the house with extremely short duct runs blowing both directions is probably going to be more appropriate for your loads, if you do any optimizing if the building envelope at all, and would modulate at high efficiency-high comfort most of the time, far better than oversized equipment.)

http://www.fujitsugeneral.com/us/resources/pdf/support/downloads/submittal-sheets/12RLFCD.pdf (<16,000 BTU/hr of capacity @ +17F, minimum modulation 3000 BTU/hr @ +47F)


http://meus1.mylinkdrive.com/files/MSZ-FH06NA_MUZ-FH06NA_ProductDataSheet.pdf (>10,000 BTU/hr capacity per unit @ +17F modulating to 1600 BTU/hr min @ +47F, 9000 BTU/hr cooling capacity per unit., modulating down to 1700 BTU/hr.)

Back to the drawing board! lol This is great info And, thank you for taking the time to post this up. It's all a bit overwhelming contemplating hiring an engineer and all that when in the past, we just put in fiberglass and put up drywall and you had a house. lol I realize why it needs to be done differently because the newer way can be better, just a lot more complex for my simple mind to wrap around sometimes. Regarding the insulation, would I be better served using 2X4 construction, exterior rigid foam panels and spray foam inside on the walls and use 2X12 rafters to add blown in cellulose on the roof? Then i can cap it with plywood for attic storage? Or have a 1" stay foam used around walls and ceiling to seal things up and then follow up with rouxl or something on my own? I'm trying to find a happy medium here that is something I can accomplish in my small town neck of the woods with the almighty dollar.

A 2x4/R13 + R5 foam sheathing solution has about the same thermal performance of a 2x6/R20 (full-fill) approach. The rigid foam on the exterior helps protect the structural sheathing from direct wetting, and will be warmer (= drier) in winter if done right. But it also inhibits drying toward the exterior. If the contractor is familiar with how to do it right it can be somewhat more resilient than a 2x6/R20, and possibly less expensive, but the 2x6/R20 is also pretty resilient if the siding is back-ventilated, such as vinyl siding, or other siding installed with a gap/rainscreen between the siding and sheathing as a capillary break & drying channel.

Most of Arkansas is US climate zone 3, the rest is the very warm edge of zone 4. NW Arkansas is the transition between them-you could be in either:

http://www.greenbuildingadvisor.com/sites/default/files/images/DOE%20climate%20zone%20map.preview.jpg

In a zone 3 climate a whole-wall-R of R20 (=2x6/R20 + R6 insulation over the sheathing), is enough to hit Net Zero Energy with a PV array that fits on the roof. It's also generally going to be financially rational on a lifecycle basis. Going ahead with the 2x6/R20 of open cell foam and installing 1" foil faced polyisocyanurate (blown with hydrocarbons- usually pentane, which is fairly low impact) or 1.5" foil faced EPS (also pentane-blown) is going to be "worth it" over the long haul. See Table-2, p.10 of this document:

https://buildingscience.com/sites/default/files/migrate/pdf/BA-1005_High%20R-Value_Walls_Case_Study.pdf

Note, the recommended R50 (whole-assembly) roof or zone 3 in Table 2 can be done relatively cheaply with "energy heel" trusses sized to accommodate 15-16" of cellulose all the way out over the top-plates of the stud walls. A 2 x 12 joist is only 11.25" deep, which makes it hard to get 15" or more of insulation over the top plates while maintaining the code-required 1" ventilation space between the insulation and roof deck.

The R45 "compact roof could be R30 rock wool between the 2x8 rafters rafters, with 3.5" of roofing polyiso above the roof deck, HD38 fiberglass batts between 2x10s with 2" of polyiso above the roof deck, or R38 low-density fiberglass between 2x12s with 2" of roofing polyiso above the roof deck. The rigid foam starts to add up, but there may be a foam reclaimer near you to take some of the sting out of the wallet. Reclaimed roofing polyiso is typically only 25-35% the cost of virgin stock foam (often cheaper than batts, per R-foot!) Run this search on a few locations near you:

https://littlerock.craigslist.org/search/sss?query=rigid+insulation

This guy seems to have almost the right amount for your roof, along with deck screws long enough to hold the foam in place with a nailer deck, through-screwed to the structural roof deck:

https://littlerock.craigslist.org/mat/d/insulation-and-trusses/6475300278.html

Virgin stock 3" x 4' x 8' fiber faced roofing polyiso runs about $60/sheet & up at distributors near me, used goods about $15-20/sheet.

Dana1, I have a dumb question.

Why do you spec for polyiso in situations where it's got a strong likelihood of wetting?

I'm bouncing back and forth between a 2X6 and 2X4 exterior walls with 2' centers. I'm leaning towards 2X6 and using Roxul R23 interior batts with foam boards on the outside which should give me approx an R28. The difference in lumber is quite small (under $400 roughly) and I'm looking at transom windows to assist with the lack of actual HVAC vents/heads in the 2 bedrooms mentioned. I guess worse case scenario, I can add a 3rd ductless mini split for those rooms if it's unbearable in the summer. In winter we use the wood stove a lot and it will be well insulated, plus we want to sleep in the cooler part of the house so I don't anticipate issues there. Ceiling fans in each room as well so June, Jul and August SHOULD be ok. We shall see. Dana, is this an acceptable foam board for the wrap? https://www.lowes.com/pd/Common-0-5-in-x-8-ft-x-4-ft-Actual-0-437-in-x-7-937-ft-x-3-875-ft-R5-Unfaced-Polystyrene-Foam-Board-Insulation/3014183?cm_mmc=SCE_PLA-_-LumberAndBuildingMaterials-_-SheetInsulationAndAccessories-_-3014183:Dow&CAWELAID=&kpid=3014183&CAGPSPN=pla&store_code=422&k_clickID=7669eb3f-efab-459b-886d-48ab50e9f251&gclid=Cj0KCQiA5t7UBRDaARIsAOreQtj6bqbFNtPEsg_yuf0IDfXiOxGsmQaFpQIYECDtbvgHWkm56KYk5CIaAoH5EALw_wcB I've not even got my hands on this product yet but I assume it is rigid and would work fine sandwiched between the stands and the metal siding? Next I will focus on the under slab insulation and what specific product I would use there and how much. Seeing as how we will have concrete floors, wood heat, well insulated walls and attic, we all wear house slippers when inside, and our zone isn't that extreme, I don't think I will need to go overboard on the under slab insulation. Most of the builders in this area never do any unless you are doing a radiant heat system, which have decided to not do. Thank you again for your help, this is a great resource! (Sorry for the compacted view. When I submit my reply it removes the paragraphs layout and just makes everything one paragraph)

Posted By Dana1 on 28 Feb 2018 06:29 PM
A 2x4/R13 + R5 foam sheathing solution has about the same thermal performance of a 2x6/R20 (full-fill) approach. The rigid foam on the exterior helps protect the structural sheathing from direct wetting, and will be warmer (= drier) in winter if done right. But it also inhibits drying toward the exterior. If the contractor is familiar with how to do it right it can be somewhat more resilient than a 2x6/R20, and possibly less expensive, but the 2x6/R20 is also pretty resilient if the siding is back-ventilated, such as vinyl siding, or other siding installed with a gap/rainscreen between the siding and sheathing as a capillary break & drying channel.

Most of Arkansas is US climate zone 3, the rest is the very warm edge of zone 4. NW Arkansas is the transition between them-you could be in either:

http://www.greenbuildingadvisor.com/sites/default/files/images/DOE%20climate%20zone%20map.preview.jpg

In a zone 3 climate a whole-wall-R of R20 (=2x6/R20 + R6 insulation over the sheathing), is enough to hit Net Zero Energy with a PV array that fits on the roof. It's also generally going to be financially rational on a lifecycle basis. Going ahead with the 2x6/R20 of open cell foam and installing 1" foil faced polyisocyanurate (blown with hydrocarbons- usually pentane, which is fairly low impact) or 1.5" foil faced EPS (also pentane-blown) is going to be "worth it" over the long haul. See Table-2, p.10 of this document:

https://buildingscience.com/sites/default/files/migrate/pdf/BA-1005_High%20R-Value_Walls_Case_Study.pdf

Note, the recommended R50 (whole-assembly) roof or zone 3 in Table 2 can be done relatively cheaply with "energy heel" trusses sized to accommodate 15-16" of cellulose all the way out over the top-plates of the stud walls. A 2 x 12 joist is only 11.25" deep, which makes it hard to get 15" or more of insulation over the top plates while maintaining the code-required 1" ventilation space between the insulation and roof deck.

The R45 "compact roof could be R30 rock wool between the 2x8 rafters rafters, with 3.5" of roofing polyiso above the roof deck, HD38 fiberglass batts between 2x10s with 2" of polyiso above the roof deck, or R38 low-density fiberglass between 2x12s with 2" of roofing polyiso above the roof deck. The rigid foam starts to add up, but there may be a foam reclaimer near you to take some of the sting out of the wallet. Reclaimed roofing polyiso is typically only 25-35% the cost of virgin stock foam (often cheaper than batts, per R-foot!) Run this search on a few locations near you:

https://littlerock.craigslist.org/search/sss?query=rigid+insulation

This guy seems to have almost the right amount for your roof, along with deck screws long enough to hold the foam in place with a nailer deck, through-screwed to the structural roof deck:

https://littlerock.craigslist.org/mat/d/insulation-and-trusses/6475300278.html

Virgin stock 3" x 4' x 8' fiber faced roofing polyiso runs about $60/sheet & up at distributors near me, used goods about $15-20/sheet.

Regarding the blown cellulose in the attic - I can, and have done that myself and intend to do so with this house. I am fine adding more than the R50 discussed in your earlier post, but at what point am I beyond any benefit and then wasting money? I'll blow that stuff in there until the cows come home if it will make a difference, but is an R100 a waste in my region? (at that point I would use my height as a guide for the proper insulation depth lol)

I still say your best bang for the buck is sprayed cellulose. Damp sprayed cellulose has an R value of ~3.7 per inch. That would be ~R20.5 for a 5.5" stud cavity. You should be able to get this sprayed in for <$1.00/sq ft in Arkansas (call some insulation contractors outside of your immediate area such as Ft. Smith - many will travel quite a ways for a job, I was quoted $0.75/sq ft for 2x6 walls). I checked on Roxul R23 and Lowes price was $47.97 for 39.8 sq ft for ~$1.20/sq ft. You should be able to beat that price easily with labor included with the cellulose and get better air sealing with the sprayed cellulose as it fills nooks and crannies better than pushed in batts.

I have some calls out to get prices but the vendors are far away so I'm not optimistic. That said, if it works and is an affordable option, I will of course consider it. One caveat, I've heard many a time that cellulose and fiberglass settle over time and leave a gap along the top in a wall scenario. I wonder how much of an issue this really is? spending a small fortune only to have a 5" gap or no insulation along the top perimeter of the wall after a few years would be irritating to put it mildly. That was one thing that had me looking at roxul as it apparently doesn't suffer from that issue. (if thats even an actual issue and not just competitor talk)

Posted By arkie6 on 01 Mar 2018 06:47 PM
I still say your best bang for the buck is sprayed cellulose. Damp sprayed cellulose has an R value of ~3.7 per inch. That would be ~R20.5 for a 5.5" stud cavity. You should be able to get this sprayed in for <$1.00/sq ft in Arkansas (call some insulation contractors outside of your immediate area such as Ft. Smith - many will travel quite a ways for a job, I was quoted $0.75/sq ft for 2x6 walls). I checked on Roxul R23 and Lowes price was $47.97 for 39.8 sq ft for ~$1.20/sq ft. You should be able to beat that price easily with labor included with the cellulose and get better air sealing with the sprayed cellulose as it fills nooks and crannies better than pushed in batts.

On an unrelated note, HOLY CRAP is the under slab insulation expensive. It rivals ALL the other insulation combined. Products like the formular 150 must have gold in it.

R100 attics don't isn't buy you very much in your climate. IRC 2015 code min is R49 between joists, or ~R40 "whole assembly) for zone 4, R38 or ~R33 whole-assembly for zone 3. At R50 whole-assembly the heat flow is next to nothing. Taking it to R100 cuts in in half, but half of "next to nothing", isn't worth much on either a financial or comfort basis.

The BSC paper suggests R60 (whole-assembly) as still financially rational for zone 4, R50 for zone 3. With a truss (rather than rafters) burying the bottom chords in the insulation R60-whole-assembly is pretty cheap-~21-22" initial blow for loose fill cellulose. Any higher-R than that is just for bragging rights- what's it worth to you? :-)

There is no reason to use extruded polystyrene under the slab (pink, blue, green whatever). It's blown with HFCs (primarilly HFC134a- automotive AC refrigerant), an extremely powerful greenhouse gas. As the gas diffuses out over a few decades it's performance drops toward EPS of similar density. If you install the same R-value using Type-II (1.5lbs per cubic foot nominal density) or Type-VIII (1.25lbs) under the slab it'll be 15% thicker, but substantially cheaper, and it's performance will still be the same in 50 years.

The same reclaimers that trade in used roofing polyiso also handle roofing EPS, which is usually either Type-II or Type-VIII, which can make it less than 1/4 the cost of using virgin stock XPS (and a heluva lot greener.)

Couldn't make the link work for the foam board you were looking at for behind the siding.

Dense packed to 3lbs per cubic foot density cellulose will not settle in your climate. Damp sprayed sometimes has a shrinkage separation where it meets the studs after a year (it sometimes shows up in infra-red imaging and diagonitic dissassembly) but won't settle.

Posted By rykertest on 02 Mar 2018 12:38 AM
I have some calls out to get prices but the vendors are far away so I'm not optimistic. That said, if it works and is an affordable option, I will of course consider it. One caveat, I've heard many a time that cellulose and fiberglass settle over time and leave a gap along the top in a wall scenario. I wonder how much of an issue this really is? spending a small fortune only to have a 5" gap or no insulation along the top perimeter of the wall after a few years would be irritating to put it mildly. That was one thing that had me looking at roxul as it apparently doesn't suffer from that issue. (if thats even an actual issue and not just competitor talk)

Posted By arkie6 on 01 Mar 2018 06:47 PM
I still say your best bang for the buck is sprayed cellulose. Damp sprayed cellulose has an R value of ~3.7 per inch. That would be ~R20.5 for a 5.5" stud cavity. You should be able to get this sprayed in for <$1.00/sq ft in Arkansas (call some insulation contractors outside of your immediate area such as Ft. Smith - many will travel quite a ways for a job, I was quoted $0.75/sq ft for 2x6 walls). I checked on Roxul R23 and Lowes price was $47.97 for 39.8 sq ft for ~$1.20/sq ft. You should be able to beat that price easily with labor included with the cellulose and get better air sealing with the sprayed cellulose as it fills nooks and crannies better than pushed in batts.

If you're doing damp-spray, I wouldn't worry.
Dampening it down helps pack it VERY tight and gives good adhesion to the entire cavity.  Settling shouldn't be an issue.

Basically, take a look at your options.
Figure out which makes the best sense for/to you.

Settling isn't the issue with damp- sprayed cellulose- shrinkage is the problem.

See Armando Cobo's post-mortem diagnositic dissection pictures in response #4 of this thread:

http://www.greenbuildingadvisor.com/patrick

http://www.greenbuildingadvisor.com/sites/default/files/Wet%20Cellulose%20and%20Stud%202.jpg

http://www.greenbuildingadvisor.com/sites/default/files/Wet%20Cellulose%20and%20Stud%201.jpg

Cobo isn't an armchair hack with an opinion making stuff up for the sake of argument- he's VERY experienced high performance home designer:

https://cobodesigner.com/

If he's thrown in the towel on damp sprayed cellulose for walls, I'm paying attention.

If you use too much water while spraying cellulose, you will get more shrinkage when it dries. As with most things in life, details matter. The quality of the material matters also.

I had a friend that had his house sprayed and the guy (not a reputable insulation installer) used the dry blow cellulose without the dry moisture activated adhesive. Large blocks of cellulose were falling out of the walls when the guys were nailing siding on the outside.

On my new home I had to run some additional wiring after the cellulose was sprayed in my house and it was difficult to cut the cellulose away from the studs to run the wires. There were no gaps in the insulation prior to drywall installation. But I talked to the installer and made sure he knew what he was doing and was using the correct material. I asked specifically what cellulose was being used prior to the guy bringing his equipment on site and he provided me with the manufacturer's product datasheet to review.

Posted By Dilettante on 02 Mar 2018 09:40 PM

Posted By rykertest on 02 Mar 2018 12:38 AM


I have some calls out to get prices but the vendors are far away so I'm not optimistic. That said, if it works and is an affordable option, I will of course consider it. One caveat, I've heard many a time that cellulose and fiberglass settle over time and leave a gap along the top in a wall scenario. I wonder how much of an issue this really is? spending a small fortune only to have a 5" gap or no insulation along the top perimeter of the wall after a few years would be irritating to put it mildly. That was one thing that had me looking at roxul as it apparently doesn't suffer from that issue. (if thats even an actual issue and not just competitor talk)

Posted By arkie6 on 01 Mar 2018 06:47 PM


I still say your best bang for the buck is sprayed cellulose. Damp sprayed cellulose has an R value of ~3.7 per inch. That would be ~R20.5 for a 5.5" stud cavity. You should be able to get this sprayed in for <$1.00/sq ft in Arkansas (call some insulation contractors outside of your immediate area such as Ft. Smith - many will travel quite a ways for a job, I was quoted $0.75/sq ft for 2x6 walls). I checked on Roxul R23 and Lowes price was $47.97 for 39.8 sq ft for ~$1.20/sq ft. You should be able to beat that price easily with labor included with the cellulose and get better air sealing with the sprayed cellulose as it fills nooks and crannies better than pushed in batts.

If you're doing damp-spray, I wouldn't worry.
Dampening it down helps pack it VERY tight and gives good adhesion to the entire cavity.  Settling shouldn't be an issue.

Basically, take a look at your options.
Figure out which makes the best sense for/to you.

Thats some interesting stuff, Dana. Your subsequent post with the images of shrinking cellulose was enlightening as well.

The last few days have been fruitful with our build and also have a new player in the game, ICF. I was speaking with a Nudura friend of mine and he's going to given me a bid for our house so we'll see where that comes into play. I don't expect much settling with a 6" ICF wall. lol

The bids for the ductless mini splits are all over the map and it is brand dependent as expected. Mitsubishi is of course the most expensive. Now a lower end Haier dealer/installer with good reputation gave me a very reasonable bid. Whats unknown now is if that reasonable bid will result in a replacement needed long before a top tier brand would, resulting in no real savings over the long haul.

Regarding the attic insulation, I'd shoot for the zone 3 blown cellulose guidelines of R60, maybe 65 for bragging rights. lol

Moving to ICF would almost ensure the need for an HRV or ERV working with the mini splits. I'm considering installing that myself but will need to figure out what CFM needs my 1300 sq ft home would need. The panasonic whisper comfort seems to receive high marks for air exchange, but April air also is a common recommendation I'm seeing online. I may need to do my research and install that myself to save some costs.