Another thought...

I have an 'USA insulation' franchise in my area (new since my last study of this project) and they offer an injection foam product that is appropriate for cavity fill retrofit.

It appears to be a clone of the latest for this class of products: phenolic based, similar to 'aminoplast', amino-foam or tripolymer foams. Sounds like it is R-5/in, closed cell, non-absorbant and would be vapor semi-permeable (1" is 15 perms, 3.5" is 4-5 perms).

Anyone familiar with this product/company? It seems that GBA thinks that this type of foam has some applications, and there are no/minimal formaldehyde offgas concerns. While I do worry about Formaldehyde and VOCs, and I might not want my whole house filled with this stuff, I figure 350 sq ft is prob ok.

I don't expect anyone here to approve any sprayfoam cavity fill in this application (at least for the below grade portion). I would suppose that the mold risk on the drywall paper would go down post foaming (since it would be warmer/dryer), but the wood in contact with the below grade concrete would be at elevated risk of rot.

For the record, I do not think there is ever surface water on that concrete, but I assume the concrete is saturated with moisture under many conditions.
Pls 'let me have it' regarding how dumb this plan is. Better or worse than loose fill? A case of perfect is the enemy of the good (i.e. leave as is if I have to demo to get perfect)??

Thanks in advance.

Thanks for the analysis....I think I get the model assumptions and the output data. MMBTU/yr match my own estimates for the entire house. 

Your welcome – I’m glad you get some of the assumptions I made since I don’t. Not having a drawing of your place was a challenge. I like challenges. If you ever do hire a pro make sure they ask lots of questions perhaps perform some test before answering. You need cavity temp/humidity levels to make a proper decision here, and a lot of other data.

For Case 1: does R-10 wall average mean for the finished basement walls, or for the rest of the structure? 

I did a “Zoned 850 SF DOE simulation” averaged the two room wall r-values studs/fur. I didn’t take a lot of time with it….3 walls fully exposed, one not, facing NW. The algorithm considers, r-assembly..thickness, density, framing factor, type, depths I did not know, and a lot of other factors.

I think that the above grade wall in the finished basement is maybe R-3 based upon skin temps measured by IR thermometry. That is, indoor drywall temps in cold (steady outdoor temp) weather are close to that of low-E double pane (~R-3 equivalent) windows in the same room/ventilation. This figure makes sense to me for a concrete wall, an empty cavity and two air films.

I didn’t take a lot of time with it….3 walls fully exposed, one not, facing NW. The algorithm considers, r-assembly thickness, density, framing factor, matl type, depths, I did not know and a lot of other factors had I had them you would have had a whole-house free accurate report.

Statically, a CMU ~U-.35-.54, perlite infill .15-.35, in window ranges. Dynamically that can drastically change.

Unfortunately, it’s not all about r-value like most people think in a dynamic building environment especially when mass and directional site specific environmental loads are involved. Without much consideration for hygric like this model, temps at interior surfaces can be misleading w/o other input data. EnergyPlus engine used NREL TMY3 weather tower @ PHL not far from you.

That said, I don't get your case 2, and its low projected savings. If I upped my assembly R-value from R-3 to R-10 (e.g. 3.5" of perlite less an R-1 cavity, with stud thermal bridges), it would seem that I would drop my heating load by UA*\Delta T = (200 sq ft / R-3 - 200 sqft / R- 10 )*40°F = 1867 BTU/h which is >10% of my heating load at that temp. So I would expect >5 MMBTU/yr rather than 1.2 MMBTU/yr savings for your Case 2. 

I would not expect a whole lot out of r-10 perlite insulation in this case. More out of outsulation combine exponentially as shown.

Is my reasoning wrong, or do I not understand the model fro Case 2? 

While perlite as a soil additive is absorbent, I thought that insulation perlite was treated to be hydrophobic, and non-absorbant. At any rate,I was leaning towards EPS beads for higher R-value and lower cost. I'd source larger beads (5-7 mm) to have less issue with spillage from wall openings (vs 2 mm beads). That said....I agree with the posters above that too permeable cavity fill is likely contra-indicated.

I like the challenges and quality control of my own insulation mixes. I could take all the above and come up with a mix once I understood the cavity more. I disagree w/the first two poster….. interior condition air is probably the only thing keeping your concrete walls dry other than the closets that have mold. Cavity convection most don’t understand, there are great simulation models out there for. Certain binders like lime need perform best when they see CO2 gas and small ACH. PCM need it for enthalpy. Moist convective cavity loops with loose fill batts can be problematic. I think your highest risk is at the concrete surface. Now you just have to figure out what interstitial core perm rating and chem reations will work with drywall/concrete. It cant be too high or low, and there are other properties you need to know besides perm/r-values.

Good luck with that……All I have time for hope it works out.

Ok. I have given this a little more thought.

Existing system is 10" thick concrete wall in good condition, with stucco applied to outside (above grade), with wood framing built out on the interior, which I assume is untreated conventional (but old, likely dense fir) dimensional lumber in contact with the concrete wall and slab at the bottom. I assume the slab gets periodically wet from below, and dries slowly if at all due to its impermeable surface treatment. The water table likely never gets much higher than the bottom of the slab, due to a working and well maintained french drain and sump system.

In my estimation, the assy to the outside air (above grade) is about R-3 to 4. I think the concrete is R-2, based upon IR measurements and modeling made in unfinished portions of the house. The balance of the R-value comes from the deep air cavity, drywall and inside air film. I would thus expect the inner surface of the concrete to never get colder than about 50°F under normal January weather (70°F inside, 30°F outside average temps), and maybe 35-40°F during extremely cold weather (that might last for a day or two every other year). Since my indoor RH is never above 30%, which is 37°F dewpoint, there is likely _never_ any significant condensation from indoor air in the current assy.

Previous to 2010, the house was heated hydronically by radiators at the base of this wall assy, fed by pipes in the slab, likely maintaining significantly higher slab and wall temps and promoting seasonal drying....explaining historical durability of this assy. Now the hydronics are abandoned and we have HP-based forced air heating.

A 10" dry concrete wall should have a permeance of 0.3 perms, while the (painted) drywall is more like 5 perms, allowing effective drying to the interior, even if the outer skin of the assy is in 100%RH vapor.

As the sill rim above this wall is unsealed or poorly sealed (its behind finish drywall) we likely have outside air infiltrating and mixing with the cavity air. This likely further assists winter drying.

There are really two hypothetical issues with retrofit: i) drywall paper growing mold and ii) wood getting wetter to the point that dry rot is possible, or termite/ant infestation becomes a possibility. Since insulation will make the drywall far warmer AND not impede its drying to the interior, I think the paper mold issue is improved by the retrofit. (ii) is another story...

Plan 1: granular, non-adsorbing, insulation blown or poured in. (e.g. perlite, EPS beads, non-adsorbing blown fiber products?)
It would seem that this would make the concrete wall far colder, allowing it to get well below indoor dewpoint temps, at least sometimes in the winter. My confusion, of course, is that my framed structure above the foundation looks like FG insulated wood framing with impermeable sheathing. I presumably have condensation on the sheathing in my framed construction, and my house is not rotting out. I seem to recall reading a GBA article about how this scenario....wet but frozen, and then drying out before it gets too warm outside, is a large part of the survival of existing US woodframe construction, especially after cellulose retrofit.

For the granular plan, the perm rating would be so high that the ability of the assy to dry to the interior would be unmodified, except for temperature. The above grade framing near the concrete would def be wetter in the winter due to this, but still able to dry just as well to the interior in other seasons as it can now. The retrofit assy might be **drier** near the base, as the ground and slab will likely be warmer in winter than before. So since we are most worried about the below grade portion and it staying dry (and being able to dry) how could this plan be worse than what I have now....the below grade will be warmer, if not almost up to ambient, while indoor RH is <30%.

Plan 2: Retrofit a non-adsorbing injection foam into cavity. (avoiding convection in assembly and associated water movement)
USA Premium Foam would have a perm rating of ~4 in a 3.5" thick block. Compared to above, the R-value would be higher, and assuming it didn't shrink and filled the cavity, all vapor motion would be diffusive. The permenance of the foam would allow drying about half as fast as before from the concrete to the interior. The perm rating of a 10" concrete (0.3) is still much less than the 2.5 perms for the foam+drywall+paint, so most water vapor is still coming and going from the interior. If this were true, the the foam is not a big deal; it slows vapor going to the concrete in the winter at the same rate it retards its drying in the spring. And the base/slab is even warmer in this scenario, due to its higher R_value. The thermal bridging by the studs will help to keep the studs drier, which is the concern.

So, to summarize, I don't think either plan is the kiss of death. I have a 'fragile' assy that (like the rest of house) precludec over humidification in the winter. It relies upon being able to dry to the interior in all seasons. I don't see how either retrofit plan really affects that equilibirium, so long as we assume the surface of the concrete is dry.

Unknowns...
1) Wall is cracked, admitting liquid water
2) Wall is saturated with liquid water on its exterior by contact with wet earth, so perms do not apply.
3) capillary rise of water from (assumed wet) slab up wall some distance.
4) Reduced heat leak to earth causes the slab and below grade wall to run colder post retroft than they do currently.

Just saw @parahomes reply after posting the above....seems that we agree about cavity convection, drying to the interior and the inner surface of the concrete being important. Thanks for the modeling and advice!

You might look at some more "worse case" situations. For example, the upper part of the wall when it's 15F outside. Or the upper midpoint of the wall in spring when the soil is still cool but it's warm and humid outside and the interior %RH is being held at ~50% by the dehumidifier. Also consider that mold only needs high %RH, not condensation. Combined with a little air movement, it can be a problem.

I think that shrinking of injected foam fill could be a concern.

Any chance you could fill a single cavity with EPS beads and monitor it?

Good points.

I get the no condensation not being enough...I worked out this AM that dry rot takes 22% wood moisture content, which occurs without condensation at 95% RH.

The complexity of the convection in the current open cavity is throwing me a little, but I think tends to probably even out temps and dry the whole assembly.

I guess I am still thinking that the permable, non adsorbant insulation like EPS is the 'safest' for the below grade, because it has the highest drying potential, and ironically, the poorest performance (R-3/in or less). This assumes I am 'ok' now, so it is the smallest perturbation.

Since I think I would have to do the EPS DIY, I can always do a little and monitor. I would prob do all a couple adjacent cavities, since the concrete and ground would conduct laterally by an amount comparable to 16".

Speaking of, with eps beads I could just do the whole job, monitor (with T and RH probes and nose), and then I could always vacuum it all out in the case it was a fiasco. If the foam has a problem, its a complete demo job.

For the above grade segment with the 1.5" cavity, I will probably just have a guy foam it, since I will want the higher R-value performance.

?

Some data.... We have had a decent cold spell for several days, and I have taken some measurements and done some more, um, thinking.

Humidity readings in closed closets are consistent with the same dewpoint as air in the house (which is 70°F, 25%RH), so no apparent water sources in winter, everything appears to be in equilibrium with interior air.

Temps were interesting, measured with a (calibrated) IR ±1°F.

Outdoor surface temps of the concrete foundation were 9-13°F warmer than the air temp (21°F), the sheathing on my stick construction was 3-4°F warmer. Overall, I think this is consistent with R-10 assy walls in the stick construction and R-3-4 in the foundation, as previously believed.

Indoors, the surface of my concrete slab (in a closed closet) was 54°F. Bare bedrock in a nearby sump pit was 50°F. AFAIK, the house was built on a ledge blasted out of the bedrock underlaying a hill. I **hope** there is a bed of gravel between the concrete and the rock.

In my location (Delaware county), deep ground temps are supposed to be about 54°F, and 6' deep in midwinter we might expect temps to be 6-10°F colder than this, or 44-48°F. So, the bedrock in my sump pit is a little warmer than might be expected, presumably from space heat. The vertical gradient is confirmed by scanning along the slab's indoor perimeter....points closer to the outdoor ground surface are consistently colder. There is one wall section that may have been filled with cellulose (by mistake) a few years ago. It seems that slab temps there are indistinguishable from elsewhere.

What to make of all this? Temp gradients are all actually quite small and temps are quite reproducible and stable over time. I think that insulating the cavities are unlikely to lead to a much cooler slab or concrete wall near the base. I think the deep empty cavity is actually carrying coolth down the assembly, and might be cooling the slab edge by more than it would be in the insulated case.

I think cavity insulation will make the bottom of the assembly stay the same temps, or even get slightly warmer. The wall above grade will likely get 10°F colder, but again, I am less worried about condensation or rot above grade. And again, drywall paper, carpet near wall, stuff in closets will all get warmer, and less mold susceptible.

One concern....if there is a curtain drain installed to french drain, how do I prevent foam from draining into and plugging the french drain network?

Sounds like you have given this alot of thought, good for you! I hope you have researched the hazards of SPF especially if you don't have an experience installer.

You may consider some others like blown in mineral wool. See the graph below taken out of Wufiwiki and excellent source of info.

While the heat conductivity of mineral materials, such as the cellular concrete shown here, increases linearly with moisture content, the heat conductivity of polystyrene foam shows a slightly progressive increase. Surprisingly, it takes only a very low moisture content to increase the heat conductivity of mineral wool markedly. This is due to the pronounced moisture redistribution by vapor diffusion in the mineral wool when a temperature gradient is applied across the sample. These are so-called non-steady latent heat effects, due to phase changes of the moisture in the material during the measurement in the guarded hot plate apparatus. These latent heat effects are usually of short duration only and have nothing to do with the true heat conductivity of the insulation material. Since their effect depends strongly on the materials adjacent to the insulation layer, they are not a characteristic of the insulation material itself [2]. Therefore the heat conductivity of mineral wool determined in this way and shown in Fig. 1 is not well suited as a material property function for non-steady calculations or for determining the steady-state U-factor. The true heat conductivity of mineral wool can be determined in the guarded hot plate apparatus if appropriate precautions are employed. Results of such measurements demonstrate that if latent heat effects are excluded, the heat conductivity of mineral wool shows a moisture dependence very similar to that of the polystyrene foam in Fig. 1. Similar remarks apply to other permeable insulation materials.

Just goes to show how misleading lab tested steady state r-values used by these "building scientist" & "green advisors" is, even some "non-steady state" properties can be misleading. Chew on that a while, let me know what you think. I have not got into some other properties that will completely change your thermal analysis like moisture transports, or below ground hygrothermal, etc. The best way to obtain data to make design decisions are hourly simulations for at least 1 year, some 10 Wufi Plus performs well as opposed to static lab mfg data and the measurements you are taking.

I have thought about blown in mineral wool as being a nice choice, but could not find any installers in the area.

I get the whole water vapor driven transport, but I have convinced myself that in the winter the assy is pretty dry.

I am somewhat concerned about the rare (<1 per year) weather event that wets the structure, and the subsequent drying time, but it is not clear how well WUFI would model that.

Posted By woodgeek68 on 14 Jan 2017 07:05 AM

I have thought about blown in mineral wool as being a nice choice, but could not find any installers in the area.

I get the whole water vapor driven transport, but I have convinced myself that in the winter the assy is pretty dry.

I am somewhat concerned about the rare (<1 per year) weather event that wets the structure, and the subsequent drying time, but it is not clear how well WUFI would model that.

I don't know of anyone making blown in MW. Last I talked to Roxul Engineers couple years ago it was once made but too costly so they dropped it. I'm pretty sure nobody out here gets the liquid & water transport w/o WUFI it's next to impossible. WUFI is most accurate with "measured" user input data you don't have enough. As I said, one year including wind driven rain, etc, with your north facing facades will have the biggest impacts. Once the model is set-up a qualified user determines what time cycle to look at.

And no, it's not entirely dependent on  RH/cold condensation driving potentials , more on the four phases: vapor, liquid, solid and adsorbate & how they interact with one another to cause certain interstitial mold spore growths seen in WUFI BIO it can accurately model. BIO is new I'm still on the learning curve but, from test reports I read and my experience in a hot box lab, you have about 24 hours to dry before mold is a potential, not until the next season like you stated above. A mineral fill is going to affect the boundary conditions much differently than SPF in the physical states.

It's complicated and there is no way it can be determined by a bunch of talk on forums. I don't recommend for a DIY one-off retro you take on the expensive of PLUS & the long learning curve.  One thing you would get out of it's education is how off most are out here in GBA are. It's VERY entertaining!  :)  All the answers/bad advice to questions, most often there is just one right answer for had a qualified pro been involved. Then again, what do ppl expect for free?

Here's some entertainment, sad but the reality these days: https://www.youtube.com/watch?v=0Hh5MYv7lWc

Little outdated, not much has changed plenty of warnings all over EPA and internet ppl ignore. Oh well, I'll be looking forward to the business of fixing them along w/other IAQ pros. :)

Other add-ons coming soon I'm looking fwd too,

• Corrosion of metals exposed to concrete, stucco, and other natural, mineral-based building materials
• Assessing risk of wood rot as a function of moisture and temperature conditions
• Evaluating interior insulation recommendations given by the WTA (International Association for Science and Technology of Building Maintenance and the Preservation of Monuments)