Tripolymer, Airkrete, Insulsmart?

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I built a new house with 2 x 6 walls. I was convinced that 2.5 inches of NCFI closed cell foam was enough. Now after one winter I don’t think it is.
I have 1.5 inches sprayed in the attic with an R-38 of cellulose on top. The doors and windows are all very tight. There are no drafts or cold areas anywhere in the house. I measure my need as to how fast the house would cool down with the heat off with it at 0 degrees outside. I don’t remember how fast it was but it got cold in a hurry.
So the question is, has anyone ever tried filling the wall cavity with an injection foam like Tripolymer, Airkrete, or Insulsmart after a closed cell foam has been used? One of my concerns is the same as a flash and batt. Will I have moisture concerns in my Northern Illinois climate?

With 2.5" of cc foam you're at ~ R15 and it's a class-II vapor retarder. Average January temps in Rockford<->Moline are 18-20F, so any R- you inject needs to be either air or vapor-tight, or at a level such that the average temp at the interface with the cc foam is at or above ~38F.

Airkrete is ~ R3.9/inch, but highly vapor permeable, and you'd be adding 3". That would be adding ~R12 to the stackup for a total of R27 (center-cavity). If the interior face of the wall is kept at 68F, assuming average outdoor temp of 18F, the average temp at the interior skin of the foam would be

18F + [(68F-18F) x R15/R27]=46F- you're good to go!

Insulsmart is R4.6/inch for an additional ~R14, rendering a total R of ~R29 It is also vapor permeable, so...

18F + [(68F-18F) x R15/R29]=44F, also fine.

Tripolymer is also highly vapor permeable, with an R value of 5.0/inch, for an additional R15, for R30 total.

18F + [(68F-18F) x R15/R30]=43F, just ducky!

With R25+ center cavity the heat loss is dominated by the thermal bridging at the studs (the 1.5" wide stripes of ~R5.5 in an R30 center-cavity 24" oc studwall reduces the clear-wall R to something like R24. It brings a R25-filled wall down to ~ R20.5) But considering the high cost of retro-fit cavity foam, from a $/performance point of view (not to mention the lower risk of wall blowout during installation) it's probably much more economic to go with cellulose at 2.5lb density for an additional R11, for an R26 total, and spend the rest of the money on plugging other heat leaks such as...

Are the band joist & foundation walls insulated?

Have you verified air-tightness with a blower door test and sealed all of the infiltration leaks?

Done any thermal imaging to find potential gaps that were missed? (Spot injecting foam or cellulose is a lot cheaper than 3" of retrofit foam x the total wall area.

Retrofit foam pours are easily 1.5-2x what it would have cost you to spray it in initially- this isn't a cheap approach by any means. While going higher than R15 center-cavity is advisable, the clear-wall difference in performance between Aircrete & cellulose will be under 3%, the performance difference between between Tripolymer & cellulose would be under 10% but the cost difference to get that extra performance will be very steep indeed.

Great response Dana1 we just need to fix the math a little.

18F + [(68F-18F) x R15/R27]=46F
18	50	0.555556	46	F     Aircrete
18F + [(68F-18F) x R15/R29]=44F
18	50	0.517241	44	F    Insulsmart
18F + [(68F-18F) x R15/R30]=43F
18	50	0.652174	51	F    Tripolymer
18F + [(68F-18F) x R15/R30]=43F
18	50	0.576923	47	F    Cellulose

I don't think it's fair to only use your calculation to try to determine performance differences between insulation materials. Results under ASTM guidelines show R values of these materials to be Aircrete @ R 3.9, Insulsmart R 4.6, Tripolymer R 5.1, and Cellulose R 3.4. So the real difference is that the R value of Tripolymer is 40%+ higher than Cellulose.
We find that installing injection foams is a little more expensive than Cellulose, but higher R values and the better air sealing qualities of foams like Tripolymer always pay dividends in doing it right the first time. 
Installing cellulose to 2.5lb density will do little to stop air infiltration. Installing "dense pack" Cellulose @ "3.5 to 4lb density per cubic ft" does a little better job stopping air infiltration but the R value drops to R 3.2 in. Professionals that actually "dense pack" cellulose don't do it cheap.

You mis-keyed the Tripolymer calc. (As the R-value of the of the new stuff goes up, the temp at the interface where it meets the old stuff goes down, not up.) It's a crude model, but good enough to tell where you're pushing the line on condensation and moisture buildup issues. Models like WUFI are more precise on the humidity front, but we don't know enough about the construction of this assembly to even begin there.

I wasn't using just my calc- I was using some educated guesstimates of the clear-wall R-values of the final assembly using the different products. If you were building a wall with no studs and no other insulation than the new stuff you could use their relative R-values to determine the overall performance difference. But when you're adding the insulation to something with studs, something that's already air-sealed and insulated with 2.5lb foam. The clear-wall wall (not center-cavity) R values after the retrofit will ANY of them will run ~R23 for cellulose, ~R25 forTripolymer.

And I wasn't recommending dense-packing the cellulose in this situation either, only ~2.5lb density (typical 2-hole method), since the assembly is already air-tight. The R-value of cellulose from most manufacturers tests out more like 3.5-3.8 at 3lbs density these days, but we won't quibble about a fractional-R here, eh? Assume R3.4/inch if you like, call the clear-wall R-value performance fo the cellulose retrofit more like R22 instead or R23- it doesn't change either the relative performance or the financial analysis much.

In my neighborhood retrofit injected foam is more like 2-3x the cost of retrofit low density cellulose, which doesn't feel exactly like "...a little more expensive..." than cellulose to my wallet.

And "...doing it right the first time..." would have meant starting with full cavity insulation and exterior foam as thermal breaks for the framing, in my book.

If this was an uninsulated air-leaky empty-cavity antique with 2x4 framing, where stripping the wall to spray foam wasn't in the cards, then foam injection vs. densepack cellulose would have to be weighed, and the benefits of going with the higher-performance goods may well be cost-effective. But in this case I'd be surprised if the performance delta would make the cost-delta NPV-positive even on a 25 year financial analysis.

Are you a Tripolymer installer? Got a typical per-board-foot (or other volumetric measure) installed cost you'd like to share? (Use a range, if you like.)

I did use a thermal camera on a zero degree day. No surprises. I took shots from both the inside and out. The big loser I saw from the outside was the bathroom vents even with them off. I am not at my home computer right now but I do remember the walls being cooler than the room temperature. I think it was 70 for the air temp and the wall contact was like 63.
The basement slab has 2" foam with radiant heat. The walls are Thermomass using 2" foam.
http://www.thermomass.com/downloads...ential.pdf

http://www.thermomass.com/construction/pouredinplace.htm

I also have insulated vinyl siding that is supposed to be an R-4. I think I remember the siding at about 10 degrees contact with the zero degree outside temp.
I have an average number of windows for a colonial style house other than a patio door and an 8’ x 8’ set of windows.
A blower door is in the future.
I think I was hoping for better. Like a $1 heat bill. I was at about $180 for my worst month on 2400 sqft. and 1700 sqft basement with a full exposure.
I think foam is great but the installers try to lead you to believe you don't need what you really need to keep the cost down so they get the job.

The mass of the thermomass system isn't buying you anything on days when it's 0F outside- it just averages out the heating load slightly, lowering the peak a bit, but the average heat loss & fuel use is the same as if you had the R10 foam on the interior instead of the middle. It does a bit more for you during the shoulder seasons when it's below 60F in the AM, over 75F in the PM, since it can moderate the interior temps to where the heating/cooling systems may not trip on at all, but not so much on full heat-load days. Consider it no more than an R10.5 wall- R10 for the foam, R0.5 for the concrete. R10.5 is less the whole-wall R value of an R11 batt insulated 2x4 wall with wood siding, and well UNDER your current studwall + insulating siding R values (barely more than half). The above-frostline portion of the wall is likely to be a significant fraction of your conducted heat loss, especially if you follow up with adding insulation to the stud cavities.

If the basement is currently unfinished, adding another R5-R8 to the above grade section, down to below the frost line will be a significant boost. The concrete has to be able to dry toward the interior, particularly below-grade, so use only permeable/semi-permeable foam board (without facers) or spray foam (up to 2" of closed cell, up to a foot of open-cell). EPS is usually the cheapest, but use only un-faced versions- poly or foil will drive moisture in the concrete higher, raising the rot-potential at the foundation sill. It can be glued in place with foam adhesive (walnut sized blobs on a 12-18" grid) and held permanently with furring strips through-screwed to the foundation to which you can mount the code-required thermal barrier against open flame (1/2" or thicker sheet rock will do.) 3" of EPS will add ~R12, bringing the assembly up to ~R22. Alternatively 3" of fiber faced iso (sold as roofing insulation in commercial construction) can add another ~ R20, bringing it to ~ R30 for a clear-wall value. ( I used 3" fiber faced iso in my place, which was previously uninsulated, now ~ R20, which cut my heating bill 15-20%. YMMV.)

The effectiveness of insulated vinyl siding depends a lot on the quality of installation and low wind levels. If it's a dead-calm 0F outside you can probably count on getting at least R3 out of it if it's reasonably tight, so you can add that directly to the exterior side R when guesstimating where in the wall the dew-point of the interior air occurs. You can also add ~R3-4 to the clear-wall R values as well.

You will not be the first to have fallen for the " two inches is all you need" line. What that really means is "two inches is all that is cost-effective using this premium product at a premium price", that, and 2-2.5" is the typical maximum lift for cc foam, so it takes more time/labor to do 3", 4", or more. What you get with 2.5" of cc foam and insulated siding at 0F is about the clear-wall R that you'd get with R19 batts with a half-inch of XPS installed with air-tight methods over the sheathing. At 32F a batt & XPS wall will likely outperform what you have. But with 3" of cavity to fill you can still boost the R considerably.

But first things first. From a raw economics point of view it's usually more cost effective to:

1. Start with finding & fixing all of the air leaks.

2. Then beef up the R of your lowest-R assemblies (the basement walls, at least upper half, or down to the frost line, if not the all the way to the floor.)

3. At which point filling the rest of wall cavity space is in order.

If you get both the basement & stud walls up to ~R25 clear-wall and tighten up the place it'll show clearly in the heating bills. At that point your glazing losses are likely to dominate. Price it out, but a simple 2-hole cellulose job is likely to be far cheaper than retro-foaming the cavities, and the money saved can be spent on bringing the basement walls up to par with the rest of the space.

To get it down to a $1 heating bill you'd have to get serious: R40-50+ clear-wall values everywhere,super-tight construction, shrinking some of those windows, and heat-recovery ventilation, but it's (theoretically, not economically, at least as a retrofit) possible.

I was considering using Airkrete in an upcoming project (6 inch blu wood framed walls). Any opinions on whether I could use Airkrete to air seal the bays and then fill the rest of the space with denim batts?

I don't want to use fiberglass or cellulose. I'm concerned that using 100% Airkrete would be too costly.

Posted By Atlplasma on 12 May 2010 04:08 PM
I was considering using Airkrete in an upcoming project (6 inch blu wood framed walls). Any opinions on whether I could use Airkrete to air seal the bays and then fill the rest of the space with denim batts?

I don't want to use fiberglass or cellulose. I'm concerned that using 100% Airkrete would be too costly.

Airkrete isn't likely to be sufficiently flexible to form a reliable air barrier in a wood-framed structure.  Even an all-airkrete cavity fill could have issues at the insulation/stud boundary, since the studs are hygroscopic and Airkrete is not.  Seasonal drying of the studs will create gaps.  Whatever virtues Airkrete may have, air-sealing stud bays isn't on the list.

It's also highly vapor permeable, and I'm not sure how it rates for capillary draw, so proper placement within the layup for the climate has to be taken into consideration.  The spec calls out using poly or other weather & vapor barriers to be used, to be installed only after it the Airkrete initially cured.  It's not a vapor retarder, or even an air-barrier in your application.

To achieve good air-tightness without SPF foam, use a primer-paint at the seams in the sheathing to apply a seam-sealing tape (like the Huber Zip tape, etc) onto, and caulk all of the edges & plumbing/electrical penetrations on the exterior prior to applying houswrap or felt drain-plane/air-barrier.  Install all of the doors & windows, then alternately pressurize & depressurize the shell with a large window fan or blower door, running around with a smoke pencil caulking all leaks as you find them.  After the interior walls are in and all electrical & plumbing penetrations caulked, repeat the pressurization/depressurization exercise before interior paint or wallpapers go up- it'll be pretty good when you're done.

Blown/sprayed denim insulation will function better than batts, and can fill any size/shape cavity, and will have about the same R value as Airkrete or cellulose, with wicking & hygric buffering characteristics similar to those of cellulose (and the same borate fire retardents are used.)

I'm not sure in the end what the fascination with denim insulation is as compared to other organic-fibers (cellulose, hemp, etc.)- cotton has a nice feel to it in the hand, but it's has a bigger environmental footprint than other fibers in terms of pesticides, fertilizers, water use, etc. Yes, it's most-often made from clothes manufacturing scrap, but I'm not sure it's worth paying  premium for.  (The batts are sure a lot nicer to handle than rock wool or fiberglass batts though.)

Posted By Dana1 on 12 May 2010 05:24 PM

Posted By Atlplasma on 12 May 2010 04:08 PM
I was considering using Airkrete in an upcoming project (6 inch blu wood framed walls). Any opinions on whether I could use Airkrete to air seal the bays and then fill the rest of the space with denim batts?

I don't want to use fiberglass or cellulose. I'm concerned that using 100% Airkrete would be too costly.

Airkrete isn't likely to be sufficiently flexible to form a reliable air barrier in a wood-framed structure.  Even an all-airkrete cavity fill could have issues at the insulation/stud boundary, since the studs are hygroscopic and Airkrete is not.  Seasonal drying of the studs will create gaps.  Whatever virtues Airkrete may have, air-sealing stud bays isn't on the list.

It's also highly vapor permeable, and I'm not sure how it rates for capillary draw, so proper placement within the layup for the climate has to be taken into consideration.  The spec calls out using poly or other weather & vapor barriers to be used, to be installed only after it the Airkrete initially cured.  It's not a vapor retarder, or even an air-barrier in your application.

To achieve good air-tightness without SPF foam, use a primer-paint at the seams in the sheathing to apply a seam-sealing tape (like the Huber Zip tape, etc) onto, and caulk all of the edges & plumbing/electrical penetrations on the exterior prior to applying houswrap or felt drain-plane/air-barrier.  Install all of the doors & windows, then alternately pressurize & depressurize the shell with a large window fan or blower door, running around with a smoke pencil caulking all leaks as you find them.  After the interior walls are in and all electrical & plumbing penetrations caulked, repeat the pressurization/depressurization exercise before interior paint or wallpapers go up- it'll be pretty good when you're done.

Blown/sprayed denim insulation will function better than batts, and can fill any size/shape cavity, and will have about the same R value as Airkrete or cellulose, with wicking & hygric buffering characteristics similar to those of cellulose (and the same borate fire retardents are used.)

I'm not sure in the end what the fascination with denim insulation is as compared to other organic-fibers (cellulose, hemp, etc.)- cotton has a nice feel to it in the hand, but it's has a bigger environmental footprint than other fibers in terms of pesticides, fertilizers, water use, etc. Yes, it's most-often made from clothes manufacturing scrap, but I'm not sure it's worth paying  premium for.  (The batts are sure a lot nicer to handle than rock wool or fiberglass batts though.)

Are you certain that Airkrete is not hygroscopic? My understanding is it is an MgO product with considerable hygroscopic characteristics.

On the denim, I'm considering it as an alternative since it is hygroscopic, and there are no issues with airborne fibers or dust. I have some issues with environmental pollutants and want the new house to be as "benign" as possible.

Airkrete is hygroscopic, but like all cementicious products it's mechanically rigid, with low inherent adhesion to wood. Wood changes dimensions slightly with humidity, Airkrete does not. They advertise it's zero shrinkage aspect as an asset, but that's a double-edged sword. Zero shrinkage=zero expansion, and the air-tightness of the interface at the stud changes with the overall humidity of the assembly. Urethane polymer foams are much more flexible, and have very good adhesion to wood- it's essentially foamed-glue, which gives it excellent air-sealing characteristics.

Denim insulation uses the same fire retardents as cellulose, and neither outgases environmental pollutants to the home, both are made from recycled product, but the chemical, land, & water use footprint of cotton is many times that of cellulose fiber production. I don't see how denim is more benign than cellulose, but maybe you can point me to some relevant information on that? (I understand the differences surrounding those issues with fiberglass.)

But whatever the fiber, the performance of blown or sprayed insulation is measurably better than batts. From an ongoing footprint point of view you'll do better with blown cotton than batt cotton. Batts never fit perfectly- there is ALWAYS compressions & voids. If the goal is to make it as air-tight as possible without using SPF, caulked-taped seams & edges at the sheathing, and dense-packing the cavity with blown cellulose makes a near perfect air-barrier- any air leaks in to the cavity are severely impeded with the dense-pack, but not so much with batts.

Posted By Dana1 on 20 May 2010 10:30 AM
Airkrete is hygroscopic, but like all cementicious products it's mechanically rigid, with low inherent adhesion to wood. Wood changes dimensions slightly with humidity, Airkrete does not. They advertise it's zero shrinkage aspect as an asset, but that's a double-edged sword. Zero shrinkage=zero expansion, and the air-tightness of the interface at the stud changes with the overall humidity of the assembly. Urethane polymer foams are much more flexible, and have very good adhesion to wood- it's essentially foamed-glue, which gives it excellent air-sealing characteristics.

Denim insulation uses the same fire retardents as cellulose, and neither outgases environmental pollutants to the home, both are made from recycled product, but the chemical, land, & water use footprint of cotton is many times that of cellulose fiber production. I don't see how denim is more benign than cellulose, but maybe you can point me to some relevant information on that? (I understand the differences surrounding those issues with fiberglass.)

But whatever the fiber, the performance of blown or sprayed insulation is measurably better than batts. From an ongoing footprint point of view you'll do better with blown cotton than batt cotton. Batts never fit perfectly- there is ALWAYS compressions & voids. If the goal is to make it as air-tight as possible without using SPF, caulked-taped seams & edges at the sheathing, and dense-packing the cavity with blown cellulose makes a near perfect air-barrier- any air leaks in to the cavity are severely impeded with the dense-pack, but not so much with batts.

You raise some good points, and I'm reconsidering trying to combine wood framing with Airkrete and/or denim insulation. My concern about using wet-blown cellulose has more to do with airborne dust over the long term. Unless it is completely encapsulated, I understand it has a tendency to release particulars into the air. My goal with my new house is to maximize indoor air quality. Some type of open cell foam might be the best alternative (and probably less expensive than mgo foam).

If you use air-tight construction methods on both the sheathing & interior wallboard, there simply isn't a path for cellulose to release particles into air.  The cellulose itself is in fairly long fibers, and wet-sprayed they're even glued together when dry(!).  The only particulates would be the fire-retardent borates (the same borates used in denim insulation), and even those are glued in place with wet-sprayed cellulose.

Whether cellulose-only would require an interior vapor retarder varies with climate.  Air sealing cavities with 1" of closed cell SPF (a thickness where it's still semi-permeable) on the sheathing and filling the rest with cellulose or batts works in many places.  What's your zip code (to look up climate info)? 

Posted By Dana1 on 20 May 2010 06:16 PM
If you use air-tight construction methods on both the sheathing & interior wallboard, there simply isn't a path for cellulose to release particles into air.  The cellulose itself is in fairly long fibers, and wet-sprayed they're even glued together when dry(!).  The only particulates would be the fire-retardent borates (the same borates used in denim insulation), and even those are glued in place with wet-sprayed cellulose.

Whether cellulose-only would require an interior vapor retarder varies with climate.  Air sealing cavities with 1" of closed cell SPF (a thickness where it's still semi-permeable) on the sheathing and filling the rest with cellulose or batts works in many places.  What's your zip code (to look up climate info)? 

I'm in 30080. I don't believe interior vapor barriers are used in this area.

I understand what you are saying about making the envelope airtight, but I'm not sure there is anyone in this area who would be able to do the work correctly. Is there a certification for this type of work that would help to identify someone?

atlplasma.... I travel the world and could certainly work on your air sealing.

Farthest away build... Curacao... google two thirds up the Southwestern shore on Google Earth... zoom in to homes built on a small bay... and look for the 6 sided cedar Lincoln Log home...

aj

Your climate is a mixed heating/cooling, but still heating dominated, ~3000HDD/1500CDD. Vapor retarders aren't necessary, but placing the most vapor-retardent layer on the interior side will be better for most wall stackups than putting it on the exterior. Highly-retardent Class-I vapor retarders (like foil or poly) are best avoided. But an all-cellulose or cotton dense-packed cavity fill would work fine here no matter which side was more vapor retardent, as long as it's somewhat vapor permeable.

If the siding is masonry, stucco, or fiber-cement it'll need at least a semi-permeable or semi-impermeable layer between the siding and the structural framing, as well as a cavity/ rainscreen air-gap. These materials can soak up a lot of rain or dew, and have very high vapor-drives as they heat up. When back-vented that vapor can escape to somewhere other than the interior wall, and should it condense later, will fall harmlessly to the bottom of the cavity & drain toward the exterior, if properly designed. An exterior layer of an inch o unfaced EPS bead-board or XPS foam can provide the vapor retardency, and will dramatically increase the R-value of the structure by providing an insulating thermal break over the low-R framing structures. A cellulose-filled 2x6 wall with cellulose fill goes from ~R18-R19 clear-wall to ~R24-R25 with that inch of rigid foam. Taping & caulking the seams & edges of the foam makes it a pretty good air-barrier too.

Though less critical when using other types of siding, exterior foam board and something like a 3/8'' rainscreen-gap between the siding & houswrap/felt is still a good idea in a place as rainy (well, USUALLY rainy, recent droughts notwithstanding) and humid as GA. Even morning dew on the siding can result in a substantial humidity drive when the sun hits it. Rainscreen gaps also reduce air-infiltration forces from wind etc.

If you do an internet search on [air sealing contractors atlanta ga] you get lots of hits- get references, find somebody you can work with. Many insulation contractors and some HVAC contractors will do calibrated testing & remediation of air leakage. If done two passes during construction, air-sealing the unfinished shell with just sheathing, windows & doors installed (and the attic floor gypsum, if that's the pressure boundary) using a blower door to pressurize/depressurize to find all the leaks, then again after the electrical & plumbing and interior gypsum is up and the wall insulation is in you can get it REMARKABLY tight. Using air-tight methods on the interior wall, any particulates that are in the wall stay in the wall.

On a house built air-tight active ventilation will be required- budget for an ERV (Energy Recovery Ventilation) system, which can usually be incorporated into the AC. During the warm-hot seasons the ventilation rates should be dialed back to the minimum, to limit the amount of humidity you're drawing into the house, but it doesn't take huge ventilation rates to keep indoor air healthy.

Hi,

You mention using 3" of fiber faced polyiso. What tape did you use to seal the seams? We have quite a bit of used fiber faced polyisocyanurate and we are trying to figure out the best way to seal the seams. I assume tape would have a hard time sticking to the fiber facing, but maybe I'm wrong.

Thanks,

Claudia

Posted By camyers2 on 01 Dec 2010 10:20 PM

Hi,

You mention using 3" of fiber faced polyiso. What tape did you use to seal the seams? We have quite a bit of used fiber faced polyisocyanurate and we are trying to figure out the best way to seal the seams. I assume tape would have a hard time sticking to the fiber facing, but maybe I'm wrong.

Thanks,

Claudia

A bead of low expansion foam worked for me, applied as the new sheet is going in, with the excess trimmed after the fact.  (I'll rip it apart in 20 years and let you know how well that held up! )

Thanks for the idea of using foam to seal the seams with the fiber faced polyiso. It is a creative idea. Thanks.