Basement Remodel Insulation

[Rossn]

I've read a number of posts here about basement insulation.

I have a 1964 split level near Denver, in which I'm remodeling the lower level. Current foundation and exterior walls have no insulation, other than batts in the bays.

Below is the cross section I'm thinking about. Today, only the foundation wall and 2x4 wall above exists. I was not thinking of filling the void with anything to promote breathing. There some moisture in the foundation, but nothing excessive and no bulk water. I am going to do some remediation of that through a sump pump, excavating and waterproofing in select areas, and whatever can be done on the exterior with compaction, clay top, and drainage away. I'm not overly concerned, but do want to ensure it could dry to the interior, given the sill plate sits directly on the foundation wall (no gasket).

Do you have recommendations to improve this approach?

If the building department requires me to fill the void, what is my best option?

Thanks in advance!
Ross

 

[Dana]

It's fine to use closed cell foam on the concrete, but it's not the most environmentally friendly approach, and it's expensive. Most closed cell foam in the US is blown with HFC245fa, an extremely powerful greenhouse gas, though there are some HFO1234ze versions coming out that run about R7/inch, with effectively no greenhouse gas potential. It's still a lot of polymer per R though.

At 2" all closed cell foam severely impedes drying rates, and would qualify as a vapor barrier under Canadian code definitions.

If there isn't much above-grade exposure on the concrete (which appears to be the case, as drawn) leave 6-12" at the bottom of the foundation wall uninsulated, otherwise moisture wicking up from the footing can rot out the foundation sill, assuming you don't have a good capillary break such as an EPDM sill gasket or metal flashing between the concrete & wood, which you clearly don't. You could jack up the house a section at at time and add one, which isn't as crazy a job as it might sound, but it's easier to just let the foundation dry toward the interior at the bottom of the foundation wall.

What sort of sheathing is there on the exterior side of the 2x4s? Is there at least a 1" air gap between the sheathing and brick? Are there unobstructed weep holes in the mortar on the bottom course every few bricks?

Current IRC code minimum for US climate zone 5B (that would be Denver) is R15 continuous insulation, which would take 2.5" of HFC blown closed cell foam, or just a hint over 2" for the HFO blown stuff. Putting it between R1.2/inch studs is a waste of good foam, since most of the heat moves through the wood. To hit code-min performance with insulation between the studs would take R19 or so. You can also get there with 1" of rigid polyiso (R5.5-R7 ) trapped to the concrete with a 2x4 studwall with unfaced (or kraft faced, but not foil faced) R13s, which provides sufficient exterior-R for dew point control at the foam/fiberglass boundary to prevent wintertime moisture accumulation.

The cheapest way to get there would be to find some 2.5" or 3" reclaimed fiber faced roofing polyiso, and strap it to the walls with 1x4 furring through screwed to the foundation with masonry screws on which to hang the wallboard. With polyiso the cut edges can't rest on a potentially damp slab, since it can wick moisture, but if you're stopping the foam 6-12" from the floor that's a moot point. There are multiple vendors of salvaged foam board in the Denver area. In my area 3" roofing iso runs about $15-25 for reclaimed 2lb density roofing polyiso (assume R5.5/inch.) This is what I did in my fairly humid basement that has a 1" rat-slab poured on clay, and 4 sump pumps to keep it dry during the spring thaw when the water table is above slab level. I stopped the foam above the high tide mark (there was a flooding history) and used 10" PVC trim boards at the bottom.

I'm not sure what "insulation thermal gap" refers to in the drawing(?)

 

[Sponsor]

 

[Rossn]

Dana,

Many thanks for taking the time to provide feedback. I actually stumbled across this site searching and finding some related threads that you had responded to, and learned a lot from your postings thus far.

I'm pretty environmentally minded, and sensitive to the impact of closed cell foams, but eventually came to the conclusion that for my situation with the moisture, etc, it may just be my practical best option. I did intend to ultimately seek out the blowing agents on the 'better' end of the spectrum, where possible. Definitely glad to have my eyes opened to other options.

To answer your question, the thermal gap as I labeled it was just a 1" gap between the existing foundation and stud wall and the new 2x3 stud wall, so as to allow 'wrapping' the closed cell foam around the exterior studs to at least give an R6.5 insulation to the studs.

My exterior wall situation is not very good. Grade is actually at or an inch or two *above* the sill around the house; one 20' section has the sill maybe 18" below grade. For that section I plan on excavating and sealing the exterior wall and possibly adding a drain, then re-filling. For the other sections, I think I can regrade a little bit, and one engineer suggested compaction of the area next to the house, slight grade for 4', and then topping it with clay. If the 20' excavation process goes easier than expected, then there is the potential to go around the house, but we're talking about another 140 linear feet, so that would be a big project. Grading options aren't great either.

The brick veneer seems to abut some (maybe 3/16") fiber board that is shiny on the inside abutting the stud wall. From what I can tell minimal to no gap between the brick and fiber board, though between some studs the fiber board has swelled inwards and has a slight cavity behind. Additionally, there are no weep holes in the brick (ugh!), and there is no gasket between the foundation wall and sill plate. Wood has clearly been wet over the years, but no signs of rot yet; one friend recommended using a wood preservative before insulating.

I'm actually 5a, and my county is on a pretty good energy kick. Basement wall is to e R 15(continuous)/20(cavity) or R13(cavity)+R5 continuous. Above grade wood frame wall is R19(cavity)+R5(continuous). By their definition, 'basement wall' is at least 50% below grade, and I'm 46% below grade, so who knows how they will treat it; that said, they told me if I took off the drywall "We wouldn’t require you to fur out the wall. What we would require is you to fill the cavity with the max R-value insulation possible." So, who knows what they'll require if I fur out the wall.

It would be great to be able to use reclaimed materials, though I need to submit for permit this week, and would need to make sure I had a supply that i could pick up, else risk having to buy new or change my plan with the county. I did look into Polyisocyanurate, and while seemingly better than other rigid options, the docs I had from buildinggreen.com seemed to indicate that it wasn't that great from a manufacturing or health perspective (chlorinated flame retardants). Additionally, it didn't sound good, given the need to vent moisture to my interior.

Let's assume I could find some 3" re-claimed polyisocyanurate - I have some questions on your proposed approach, which could save some real $ with 150' of wall. If you can shed some light on these, I'd really appreciate it:
- Is the face of the polyiso OK resting against the foundation wall if it needs to vent, or is there a furring strip on both sides of the polyiso? If there is a furring strip behind the poly iso, how is the air gap sealed at the bottom, since you're not going to the floor?
- So, a 6-12" gap at the bottom is enough to allow the wall to wick moisture out of it and keep the sill plate dry, even if grade tops out only an inch or so below the top of the foundation wall? This is probably my biggest concern.
- How do you run wall electrical with this approach?
- Do you fill the existing stud bays with fiberglass, or just skip and enhance breatheability? I guess there is not a condensation concern if the inner polyiso wall is continuous?
- Is there fireblocking at the top and/or bottom required, or does the drywall layer have you covered as far as IRC is concerned?
- With this continuous approach, what is the best approach air sealing of the existing cavity and rim? Unfortunately, some of the fiber board has rotted out in some places, near the sill plate.

Thanks again.
Ross

 

[Dana]

If the fiberboard has a shiny aluminium facer, that's a true vapor barrier, a class-I vapor retarder <<0.1 perms, so even the above grade assembly needs to dry toward the interior. With the fiberboard built tight to the brick, the wood preservative prior to indulation suggestion is prudent.

R5 on the exterior of R19 is not suffcient for dew point control in a Zone 5B climate (all of CO is on the "B" side of the DOE zone map.) it needs at minimum of R7.5 to meet code,. Ideally there would be more than 30% of the total center-cavity R value as air-impermeable foam, on the exterior side, but the IRC prescriptives ~28% for wall assemblies in a zone 5 climate. See Table R702.7.1. Given the facer on the fiberboard, despite the huge cut in thermal performance it's probably going to need closed cell foam (to a thickness that makes the foam ~30% or more of the total R in that section). If there is going to be polyiso on the interior of that section it MUST be fiberfaced, no foil facers, but from drying perspective it's better if it's fiber insulation on the interior side of the studwall, as long as there is sufficient closed cell foam in the stud bays for dew point control on the amount of fiber. (>30% foam-R, <70 fiber-R).

The facers of even fiber-faced polyiso are Class-II vapor retarders, and it's fine to have it in contact with the concrete. Take a look at the concrete near the slab, and note where there is any efflorescence- that's where the moisture is coming through the wall. In most cases where there is efflorescents it's heavier the closer it is to the slab, and there's none or almost none a foot above the slab. That's your indicator of where the polyiso needs to stop. If there is efflorescence higher than a foot it's an indication of bulk moisture coming from above, not mere wicking up from the footing. Digging in a French Drain down to a foot or two below grade (ideally sloped to where it can be daylighted, or worst case to a dry well more than 20' from the house) would be necessary to deal with it.

Half inch drywall is a sufficient thermal barrier against ignition of the foam board from a code point of view. Empty stud-bays behind the foam board would require fire-blocking, but as noted above, there are reasons to stop the foam board at the top of the foundation, and continue upward with only fiber insulation on the interior of that section, with sufficeint spray foam against the fiberboard sheathing for dew point control.

 

[Rossn]

Thanks, Dana!!

Let me see if I'm understanding correctly...

One approach you think would work would be to add 1.25" closed cell foam against the exterior wall of the stud bays (and maybe 2.5" on the rim), then put a layer of 2" polyiso continuous against the stud+stem wall from ceiling to about 6" off the floor, ensuring that the polyiso is fiber faced on both sides, then 1x4's attached through the foam to the concrete, and topped with 1/2" drywall?

If that's accurate, do I need to go any 'deeper' with the foam against the studs, and is there any manual air sealing that I should do of the rim before applying the polyiso?

Below are two pics of the wall. The first is a more typical wall on the South (yet shaded) side of the house. You can make out a little bit of efflorescence here and there. This section has soil about 3" above the mud sill currently, and would require re-grading and/or some form of drainage.

The second pic is the 20' section of wall that is about 18" below grade on the N side. On the N side of the house, there is a seasonal 6' deep irrigation ditch that runs about 6 weeks per year in the spring. It's top is probably about grade level, and about 100' slightly downhill from the house. Soil drains well here.

 

[Dana]

It's worth caulking the foundation sill to the foundation with a polyurethane caulk formulated for concrete, and caulking the seams & joints of the doubled-up framing. Closed cell foam in the cavites would not seal those gaps. The gap for the window framing seems big enough to seal with can-foam.

Don't leave the stud bays empty. A vertical channel is both a thermal bypass path for any air leakage, and a fire propagation path. If you installed 2" of closed cell foam in the stud bay you can fill the other 1.5" with split R15 rock wool batts or split R13 fiberglass or something, just make sure it has something dense enough to be air retardent, NOT split low density R11s.

If you put rigid foam board on the interor sides of the studs it risks trapping moisture in the studs, and it requires more closed cell foam in the stud bays for dew point control. A sheet of 3" roofing polyiso with paper facers has a vapor permeance of about 0.5 perms, sometimes as low as 0.2 perms, whereas a couple coats of interior latex paint on wall board runs 3-5 perms. That's 10x the drying capacity, and if there is moisture getting into the framing from the concrete (a big "if") it's drying capacity that you're going to need.

Extending the depth of the studs to where it matches the full depth of the foam board + furring on the foundation you could then fill it all with fiber insulation. eg:

Say you find a great deal on 3" foam board, and strap it to the walls with 1x4 furring. That's 3.75" from the concrete to the interior facing side of the furring. It should be possible to add on 2x4s onto the existing framing, shimmed out to the same plane as the furring, leaving a total cavity depth of 7.25". With 2" of closed cell foam (R12-R14) you'd then have 5.25" of space for fiber insulation. Compressing a fiberglass high density R21, or rock wool R23 would be the best, but cheaping out with R19s works too. The R21 would perform at about R20 when compressed to 5.25" the R23 would be R22, and the R19 would be about R17 . The worst-cast from a dew point control is R12 of spray foam and R23 of rock wool at full loft , which is R35 total. But R12/R35= 34%, which is plenty of dew point margin for walls in your climate.

When you mount the polyiso to the wall you can use foam-board construction adhesive both to hold it in place prior to putting up your furring, and to seal the top gap between the foundation (or foundation sill) and the top of the foam. Standard construction adhesives use solvents that would eat into the foam. Run the polyiso only up to the top of the doubled-up sill plate, and caulk it to the sill plate with foam board construction adhesive to prevent convection of room air in that micro-channel between the foam & concrete. Seal it at the bottom too, if you can (it's tough when trimmed at 6" off the slab. Tape the seams of the polyiso with housewrap tape, which sticks pretty well to most facer types.

Assuming the foam stops at the top of the foundation sill, cut in some horizontal 1x furring at the top to block air from convecting into & through the batts, which are sticking out 3/4" beyond the foam. Seal those seams with caulk as well.

 

[Rossn]

Thanks! I was thinking that one of the benefits of the polyiso would be that I wouldn't have to do as much wall construction. I think I've followed what you've mentioned and captured it in this drawing. Does this match what you're suggesting? I'm assuming 2.5" polyiso in this case, knowing I could always go thicker and the county wouldn't object.

Also, how is electrical run for the polyiso, or are above grade outlets the only option?

I am starting to wonder if there is a significant cost or construction/effort savings of this approach over using 2.5-3"closed cell throughout, and trying to find one with a blowing agent on the better end of the spectrum. I guess this option would allow the sill plate to dry better, though we did bring the polyiso up to the top of the top sill plate.

 

[Dana]

To run the power in the foam layer you have to route out a channel for the wires and electrical boxes. If you're thinking ahead you can route the channels on the foundation wall side of the foam as well as the electrical box cut-outs and run the wire as you install the foam board. Cut the box openings ~1/4" or more oversized, and once the box is installed, air seal behind it with a insulating non-expanding latex foam sealant (eg: DapTex Plus foam sealant, available at most box-stores). Low expansion window can foam can work too, but even those will sometimes push the electrical box out a bit.

To get nearly the same thermal performance as continuous foam you COULD rip some 2" wide strips of foam and glue or cap-nail them to the studs, then run the furring at each stud all the way down, long-screwing the furring to the studs through the foam every 12-16". You would aslo cut'n' cobble foam for all of the lateral framing too. The result would put an R15+ thermal break on the framing fraction (compared to about R4 -R4.5 for the added on stud. If going that route use sheet of housewrap (or better yet Certainteed MemBrain "smart" vapor retarder) detailed as a continuous air barrier over the entire studwall area, caulked & taped at the edges & seams prior to installing the furring.

If installing electrical runs in the studwall section, use air-tight electrical boxes and take care to seal the air barrier well to the electrical boxes. I've seen some air-tight installations where they cut the bottom off a milk carton stapled to the side of a stud, taping the air barrier folded over to the inside of the carton, then installing the electrical box in that space, filling the gap between the carton and electrical box with latex foam. That approach has been commercialized with a pre-made apporiately sized box, but I don't remember the name of the product.

With foil-faced polyiso it's pretty easy to cut stud-edge strips using a 6" steel drywall taping knife that has been sharpened on the sides but with fiber faced goods that doesn't work so well. A table saw or band saw works, but it's a bit messier. Unlike polystyrene, hot-knife solutions don't work very well for cutting polyisocyanurate foam.

 

[Rossn]

Hi Dana --- that's good information. I got all of that except for the lateral framing and cut 'n cobble part. Maybe a track saw with a shop vac attached would work well on cutting strips of the fiber faced polyiso.

Would the vapor retarder prohibit the wall from venting to the interior?

My friend, who is a GC and is helping me through the process, took the plans down to the county to do a review. It all went as well as could be expected, except for the insulation part. Apparently, they think I do need to treat it as an above grade wood framed wall, with a minimum or R19+5. Ouch. I'm guessing they also don't like the venting gap at the bottom of the wall, but haven't been able to get details.

Would doing 1" continuous EPS or another highly permeable sheet foam on the upper half of the wall be an option, then 4" polyiso on the bottom? I think we were already there from an R19 on the upper part.

Alternatively, I don't know if they would allow the continuous to be counted as the sprayed closed-cell foam if I lined the sides of the studs with it, put strips of foam on the edge of the stud (as you outlined above), and overlapped the sill plates. At that point I wouldn't be letting it breathe much.

Any thoughts on that?

 

[Dana]

Studs are vertical framing. Top plates and window headers etc are horizontal framing. If you add 3" foam extenders to the studs the horizontal framing will be set back 3", and filling it with cut-to-fit foam board gives the thermally-conductive horizontal framing the samethermal break as the vertical framing.

R19+ 5 is actually a somewhat risky assembly in your climate zone, since R5 is well under the 28%+ needed for dew point control. The "whole-wall-R" of R19 + 5 is about R19-R20, depending on the actual % framing faction and siding options. The whole-wall R of your framed pony walls will be more than R20 even for the framing fraction, assuming 3" x R5.5/inch roofing polyiso (= R16.5) and 3.5" x R1.2/inch (= R4.2) hemlock for a total of R20.7 for the framing fraction.

An R19 +5's framing fraction is only R5 + R4.2 = R9, more than twice as thermally conductive.

At center cavity you'll have 2" of closed cell polyurethane (R12+), and ~R16+ fiber (R19s compressed to 5.25"), which is R28+, whereas an R19+ 5 is really only R5+ R18 (R19s compressed to 5.5") for R23.

I the inspectors aren't comfortable with skipping interior side vapor barriers, point them TABLE R702.7.1 in the IRC, (print it out, submit it with the other drawings, circling the relevant line) and note that the cavity will no more than a 2x6 cavity, and that 2" of closed cell polyurethane exceeds the R7.5 minimum required for dew point control on 2x6 framing.

The 3" of polyiso on the foundation exceeds the IRC 2015 code, and at R16.5=R17 would meet or beat the R19 +5 wall on a U-factor basis in TABLE N1102.1.4 . You could also argue that the roofing foam is R5.7/inch (pretty typical, actually, R5.5 /inch is lowballing it) and R17.1, treating it as a "Mass wall" in TABLE N1102.1.2 .

As examples of published R-values of 3" roofing polyiso, Hunter calls out R17.4 @ 3" (R5.8/inch), as do Atlas, and Johns Manville. Some of the older foam blown with CFHCs (pre- Montreal Protocol) are north of R6/inch, but you can't assume anything other than typical valuves for current product when going with used foam.

What is the "venting gap" that they are objecting to? If it's the 3/4" between the polyiso and wallboard, horizontal strapping would serve as a fire stop, and you COULD fill that gap with split batts, adding another ~R2.5-R3 to the R-value.

If it's the gap with no insulation between the bottom of the slab and the polyiso you can fill that with R15 rock wool or a compressed R19 batt, but put an EPDM capillary break (EPDM flashing tape) between the cut bottom edge of the polyiso and the rock wool to keep moisture from wicking into the polyiso.

 

[Rossn]

Thanks, Dana -- I'm going to digest this for a bit.

 

[Rossn]

Dana, based on our conversations, there are a few things discovered during the remodel process that are requiring me to change the design of the insulated wall.

> If the fiberboard has a shiny aluminium facer, that's a true vapor barrier, a class-I vapor retarder <<0.1 perms, so even the above grade assembly needs to dry toward the interior. With the fiberboard built tight to the brick, the wood preservative prior to indulation suggestion is prudent.

After closer inspection, the shiny aluminum facer actually seems to have microperforations... I'm guessing this means it is vapor permeable, to some greater extent.

Additionally, the reality is that the walls have a lot of unevenness in multiple dimensions and in different areas... it was not very well constructed.

Furthermore, I'm having difficulty finding any reclaimed polyiso that is 3", which is needed to some extent required to make the whole wall u-factor of 0.045. I can find paper-faced 2.5" and 2", and it would be possible to contruct the wall with multiple layers... but, the wall construction is starting to get highly complex.

I'll also note that in any design of the wall, there will be a lot of sections that are not standard 14.5" spacing, and where there is going to be a lot of cutting, layer separation/etc of any rigid or pre-cut insulation (versus something blown-in or foamed in-place).

So, my questions are this:

1) does the surface having micro perforations change the approach or available options?
2) given I'll do actual framing (either conventional flat framed or mooney wall), is there a simplified insulation approach that could be used with only 1-2 materials, versus using 4+ materials?
3) other ideas?

Given the microperforations, I am wondering if using the R4 Icynene insulation would be an alternate approach without a heavy environmental impact. If it was possible to use cellulose, I'd certainly prefer that, but it would not serve as an air barrier, and thus would have condensation issues and require additional air sealing.

Of course, with anything like Icynene, blown fiberglass, blown rock wool, etc I'm concerned from a health perspective, too. There doesn't seem to be a great answer, though I know there will be so many cavities of odd proportion that manually cutting insulation will either be time consuming and/or poorly completed.

Note, we still need to have the stem wall dry-able, due to the non-treated lumber mud sill without a sill gasket between the stem wall and the sill plate, as well as venting the stem wall to the interior.

 

[Dana]

The micro perforations allow the assembly some capacity to dry toward the exterior, but doesn't really affect the stack up in your climate.

Using 0.7lb open cell (such as the R4/inch Icynene Classic Plus) is fine in the framed wall cavities (even if framed as a Mooney wall). Since it's 20 perms @ 2" it would need to be 10" deep to drop under 1 perm to qualify as a Class-II vapor retarder. Thinner than that you'll want to add a smart vapor retarder under the interior gypsum if not installing the layer of rigid foam. Certainteed MemBrain is good enough, Intello Plus is also fine, and quite a bit more rugged (not that it necessarily needs to be rugged here.) Since the open cell foam is already an adequate air barrier, the installation of the smart vapor retarder doesn't need detailing as an air barrier, just 100% coverage.

 

[Rossn]

Thanks, Dana. Based on your comment, are you are suggesting the vapor retarder on the interior, with the moisture flowing from interior to exterior, and exiting through the open cell foam, and out the micro perforations on the sheathing? If not, what is the advantage of the vapor retarder, knowing I'm in arid CO, and that my humidity in the basement (no vapor retarder) has been mild to dry, at most.

I'm taking from your comment that you feel the icynene classic plus would allow enough vapor permeability to amply vent moisture from the stem wall and sill plate, even at 100% coverage ceiling to floor. I'm guessing moisture also wouldn't run down the stem wall and collect at the bottom, versus diffusing more evenly.

What is your take on the icynene from an environmental perspective, and do you see any alternate wall composition options which would allow form-fitting insulation (lots of irregularities) without a high labor factor, while offering the needed moisture ventilation? I'm concerned that doing a lot of fiberglass cutting can lead to less than ideal installation, lots of airborne fibers, and a more difficult sale to the inspector. I'd love to use cellulose for health and environmental reasons, but it seems I'd still need 3" of the open cell before doing that, and then on the lower part of the wall, it may trap moisture. I'd also be open to using 2.5" reclaimed polyiso on the lower half and then adding an inch of OC foam or cellulose over that, but not sure that buys me much. Any thoughts or alternatives to offer?

 

[Dana]

A 5" of thickness Icynene Classic Plus isn't quite a class-III vapor retarder- it's as vapor permeable as some housewraps. A smart vapor retarder on the interior will allow the assembly to dry toward the interior if/when it needs to, but will still impede moisture drives from the interior when the sheathing is colder than the dew point of the indoor air in winter. This is a moisture diffusion process, not bulk water or liquid moisture wicking.

Blown fiberglass at 1.8lbs density has about the same R/inch of rock wool or Type-2 EPS, and would wick and redistribute at least some of the adsorb moisture out of the framing. It's possible to use Intello Plus as both a blowing mesh for fiberglass (any vendor) at that density as well as the interior side vapor retarder. If you use damp-sprayed JM Spider it's water activated adhesives are good enough that it can hit 1.8lbs without mesh (making it a somewhat easier 1 step process) and leveled flush with the framing with a "stud scrubber" (see picture) prior to putting up the vapor retarder, and much cheaper MemBrain could be used. With fiberglass it will be more important to detail the vapor retarder as an air barrier.

^^flattening 1.8lb Spider with a stud scrubber^^

As foam insulation goes reclaimed foam is by far the greenest (no new polymer, no new blowing agent) f0llowed by 0.5lb open cell polyurethane (~R3.7/inch) which has the least amount of polymer per R, followed closely by 0.7lb polyurethane (~R4/inch). Open cell foam is blown with water, and releases some C02 during installation, but those are extremely low impact gases compared to HFC245fa or HFC134a use in the manufactureing of different closed cell foams.

If the installer screws up the chemical mix and temperature there can be ongoing releases of polyols into the living space and there is a long history of lawsuits over the lingering smell and outgassing. The fire retardents used are also not healthy for humans, but don't generally get out once the foam has cured. Both the polyol and fire retardent issues are primarily an occupational health risk factor for installers, not the homeowner. They wear protective clothing and respirators during the intallation, and you need to ventilate the space well for several days post-installation to purge the bulk of any outgassing as it cures.

 

[Rossn]

Thanks for all the information, and for turning me on to spider. I am definitely concerned about the health effects/risks of any foam in place solution - it seems easy to make a mistake and not get proper polymerization/foaming, yielding reacted components.

The spider does sound like a pretty good product; I was concerned about using any blown-in fiberglass, imagining it may be next to impossible to get all the fibers out of the place and not wanting to inhale them. It's not clear if the spider is drastically better, but it does seem like it has the potential with wet application. That said, if using just spider, I think I'd have to go up to 8" deep on the upper half of the wall, and it wounds like wet application may not be an option at that thickness.

On the referenced article (good read), you commented with some hesitation to believe they could get to 1.8lbs without a netting... have your thoughts changed on this in recent years?

In my situation, with no external continuous sheet of insulation, would I need to be concerned about the temperature gradient and condensate forming within the insulation (due to not being an air barrier)? Or, are you saying that a well-detailed smart membrane effectively prevents that?

In terms of air barrier... I have a lot of leaking in the wall - holes abound. Is it safe to assume that I'd need to manually seal those with caulking before applying any Spider? I definitely want to tighten up the house.

Lastly on spider, are you thinking it is OK to use it directly on the stem wall, where there is *some* evidence of efflorescence over it's 55 year history? Or, are you thinking I would still need to use the PolyIso layer (which may be a good option).

Are there any other materials you think I should consider? I did see Owens Corning Thermafiber Insul-fill product, but at R3.7, I would be pushing it to meet local energy code. Cellulose seems like it is practically out of the mix, due to potential moisture content.

Thanks for clarifying on the smart membrane, too.

As of now, it seems the below are my options (possibly withstanding direct fill with thermafiber). Do any stand our as the winner to you, or are there other materials to consider that may work without an exterior continuous layer of insulation and with some potential moisture in the wall

Stud Wall Options (top half):
a) 2" Closed cell foam in bays and rim/sill plate + spider fill (may have to be netted, not wet sprayed)
b) Polyiso 2.5" (minus bottom 6" for stem wall drying) + fill void with Open Cell .7lb foam. Very bottom - Open Cell .7 lb foam
c) Manually air seal wall. Fill with spider (may have to be netted, not wet sprayed)
d) Fill all with open cell .7lb foam
e) Manually air seal wall. Fill with Thermafiber Insul-Fill

Stem Wall Options (bottom half):
f) Polyiso 2.5" (minus bottom 6" for stem wall drying) + fill void with spider. Very bottom, below polyiso - Open Cell or Thermafiber Insul-fill
g) Polyiso 2.5" (minus bottom 6" for stem wall drying) + fill void with Open Cell .7lb foam. Very bottom - Open Cell .7 lb foam
h) Fill with spider, possibly using moisture sealant on stem wall
i) Fill all with open cell .7lb foam
j) Fill all with Thermafiber Insul-fill

Use membrane, as appropriate.

 

[Dana]

Consult with the installers, but since that blog piece I've read claims that damp-sprayed Spider is regularly installed without netting even at R49. (11+ inches.) If the local installer insists on mesh to hit that mark it'll be a cost adder, but worth it. There may be strength limitations to the thin sheathing to worry about with dense packing too, since the application pressures can be high, especially when blown behind mesh. If need be it can be reinforced with 3/4" asphalted fiberboard (about R2, 20 perms, water tolerant) cut to fit between the studs. (That would be a real PITA compared to open cell foam, to be sure.)

A smart vapor retarder detailed as an air barrier would block both moisture transport by convection (the biggest transport mechanism) as well as by vapor diffusion (still an important factor.) The fact that your exterior sheathing it at least somewhat vapor permeable helps too. The air leakage of all of those perforations is still very small, and inconsequential from a thermal performance perspective.

Spider would offer much greater drying capacity than polyiso or closed cell foam. The only reason to use closed cell foam in the cavity would be to establish a condensing surface that's much warmer than the sheathing, to limit the wintertime moisture accumulation from the indoor air, which has a dew point higher than the temperature of the sheathing. As long as there is no air convection from the interior and the vapor diffusion is impeded with sub 1-perm smart vapor retarder that moisture source is well controlled. With Spider during the winter the dew of the entrained air in the fiber will track the temperature of the sheathing, which is lower than that of the indoor air. But the low dew point lowers the relative humidity of the air next to the smart vapor retarder, which lowers it's vapor permenance. In spring or whenever moisture wicking through the foundation raises the moisture content of the entrained air, the RH rises which makes the smart vapor retarder more vapor open, allowing the moisture to dry toward the interior. A layer of polyiso on the interior would block that interior drying.

At the same R/inch cellulose would be superior to Owens Corning Thermafiber Insul-fill in the studwall cavities, due to it's higher wicking and moisture buffering capacity. That keeps the structural wood drier, and minimized the risk of condensation events that could lead to liquid moisture running down the face of the sheathing. The moisture is stored as adsorb (a 1-molecule thick layer of water) on the interior and exterior surfaces of the (hollow) cellulose fibers. The capacity of adsorbed water storage of cellulose is several times that of rock wool or fiberglass fibers.

A key thing with any fiber insulation is to avoid direct contact with the concrete, since it can wick moisture much faster than the concrete would move due to normal drying to the air, increasing the moisture flow through the concrete, and potentially wetting susceptible wood surfaces. So at the stemwall you'd still need to use the sheet foam of sufficient R for dew point control. Where it MUST contact the concrete to estabish the drying path at the bottom of the stemwall and slab, use a lower wicking fiber such as rock wool.

Open cell foam in contact with humid/damp concrete has a bad track record, so keep it off the slab and foundation wall. As long as there's sufficient rigid foam for dew point control between the foundation and the open cell it's fine to use as cavity fill, but spraying it directly onto the foundation would be risky.

 

[Rossn]

Dana, I feel like every time I have a handle on some aspect of the insulation, you school me You should probably earn a nick name that has guru in it!

Ok, so let me see if I understand the cellulose and spider options:

1) air-seal tape, hand-foam, caulk all seams, holes, leaks to the home exterior (I'm assuming this must be done)
2) 1.5"+ polyiso on stem wall (no fiberous contact), except bottom 6-8"(?) to allow for venting. Top of polyiso up to the bottom of the sill plate.
3) Fill beneath polyiso with loose fill rock-wool (Insul-fill), and possibly up a foot or so for the cavity between the polyiso and stud face
4a) Cellulose option
- attach and finely detail intello plus as a Cellulose retainer and vapor retarder to preventing moisture driving from house to interior of the wall, and it will allow the wall to dry to the interior of the house. Finely detailing prevents forced convection an air exchange between inside-of-house and inside-of-wall. Would need to seal electrical receptacles, etc very well.
- blow in cellulose remainder of the cavity (including between the polyiso and stud face)
4b) Spider option
- wet-blow in spider for remainder of cavity (including between the polyiso and stud face)
- attach and finely detail certainteed membrain as a vapor retarder to preventing moisture driving from house to interior of the wall, and it will allow the wall to dry to the interior of the house. Finely detailing prevents forced convection an air exchange between inside-of-house and inside-of-wall. Would need to seal electrical receptacles, etc very well.

I guess the top of the wall cavity needs to be solid, double 2x4's which are air sealed, to prevent any air from leaking into the wall from the top side. Or, I guess I need to use 3+" OC spray foam above the double 2x4's to seal the rim area and top of those back to back 2x4's? Perhaps there is a better way.

I'm not clear... will condensate actually occur in the above walls, but it's assumed the studs/sill plates and both of these insulations can handle it and it will dry to the interior?

Do you feel that either the cellulose wall or the spider wall is a less risky proposition from a mold and wood rot perspective?

 

[Dana]

I think you've got it. I'd personally use rock wool batts for your bottom of the wall "foundation breather" section rather than blown rock wool. The total amount of insulation volume is miniscule, and if you ever needed to remove it due to some moisture problem blown goods would be a real PITA.

The top plates of the added studwall do not need to be doubled-up, since it's not a load bearing wall. The rim joist can be sealed with either open cell or closed cell.

With open cell on the rim joist there is a small risk of wintertime moisture accumulation but in practice those problems are very rare. At just 3" open cell foam not sufficient total R to meet code either. With 1.5-2" of closed cell plus 3.5"-5.5" of carefully fitted rock wool batting is safer, and meets/beats Boulder's code in TABLE N1102.1.2 for wall-R minimums (defined as R19+ R5 in the local code, with caveats about needing R7.5 for 5.5" of fiber insulation depth) .

Condensate (=liquid water) only occurs with the high levels of air leakage from the interior. With reasonable air tightness these walls will end up accumulating water as adsorb on the sheathing, in the structural wood, and the cooler portion of the fiber insulation, but will not raise the moisture content of the wood high enough to be a problem.

Dry rot can can get going at a moisture content of 15%, but really takes off at chronic moisture content above 20%. Other things can get going above 25%, but even 30% moisture content isn't a problem if it's only that high for week out of the year, and drops quickly to below 20%, and isn't above 15% for more than couple of months out of the year. (Most of the wood in your conditioned space stays below 10% moisture content.)

Your proposed wall is most similar to wall #2 in this test study, which was unvented stucco (which retains as much moisture as brick), OSB sheathing, 5.5" of fiberglass, and MemBrain, but also an unusually high interior relative humidity. Take a look at the graph for Wall #2 on page 16 (pdf pagination) You can ignore the moisture content tracking of the OSB sheathing locations and the outdoor RH stuff, but pay attention to the framing member moisture content tracking, MC_1 (top plate- the red line) MC_5 (stud- the black line) and MC_6 (bottom plate- the yellow line.)

You can see the top plate rose to the 15% mark on day 37 (early February) peaked at about 19% moisture content on about day 50 (end of winter), but dropped to 15% by day 90 (end of April). So it was above 15% for 7-8 weeks tops, and never broke above 20% where the risk really begins. The stud and bottom plates stayed below 15% all year long. And this was a pretty sever test- the drier winter outdoor air of your location relative to Puyallup WA (where the test facility is located) and your lower indoor relative humidity which probably average well under 40%, well below the 50-55% used in the test would result in even lower peak & average moisture content in the framing. Intello is also more vapor tight than MemBrain, which would be at over 1-perm most of the time at the RH_4 moving average (the heavy dark blue line) measured at the vapor retarder. Intello would let even less moisture diffusion into the cavity than MemBrain.

So you're pretty much good to go with Intello + Spider (or cellulose), assuming the sheathing can take the blowing pressures.

 

[Rossn]

I probably need a little more time to absorb and think through the moisture aspects of this and how it's possible to manage the condensation, but trust you're very comfortable with this. I'll take the weekend review/digest the referenced data and to chew on that. One thing I'm really focused on is if that stem wall, leaching moisture, will affect my situation more dramatically than in the study, and then leave me at risk for mold.

Sounds like closed cell is best on the rim, and I wasn't sure if it would bridge a gap between the two top plates (due to wall thickness), but sounds like for the .5" to 1.5" gap, the foam could just spray over without 'dripping down'. I also wasn't sure of any fire blocking requirements where those top plates meet the floor joists.

I'm planning on putting insulation (likely cellulose or cotton) in the ceiling joists, since I will be adding radiant ceiling, so I am thinking I won't need to put the rock wool behind the CC at the rim.

I may try to pick up the polyiso this weekend. Can you remind me the acceptable facers in this situation? I am thinking you had said paper or fiberglass, but not the poly/shiny faced stuff.

My hesitation about doing the more rigid rock wool insulation at the base is that 1) I don't know how easy it will be to remove it later, with 16" OC framing 2) I don't know how easy it is to get around here, but can check into that 3) it seems you need to have a good means to cut that square and precisely fitted, but maybe it compresses OK. I'm thinking of it not just being a standard extruded rectangle, but having other shape to accommodate the bottom plate of the interior wall, etc. 4) I was also thinking about the moisture wicking and exiting issue and possibly wanting to have the same insulation extend up, between the drywall and polyiso for maybe a foot or so. My thinking was that if I have a 2" or greater gap between the polyiso and the back of the drywall, that instead of having to do some specialty breathable baseboard, I could just allow it to vent up the interior of the polyiso and out the drywall (assume I have a 6-8" baseboard). Is that sound?