I want some advice and help to come up with insulation retrofit ideas, which has stymied some pros.

My home is a 1960 split level, 2300 sq ft, built into a hillside so my lowest finished level is 7 ft below grade on one side (poured concrete foundation) and on grade (walk out) on the opposite side (either poured or cinderblock, don't know). I have had most of the house extensively airsealed and up insulated both DIY and by a few thousand dollar pro retrofit. Bottom line, we have reduced the energy required to heat the house from something like 11 BTU/sqft.degF.day to more like 5.

The Question: our energy rater concluded that the uninsulated concrete walls and slab of our finished basement level were a huge heat leak, but neither I nor my energy pros knew how to address it. There are really two parts:

Part 1) uninsulated (empty cavity) 2x4 framing inside a concrete wall, with finish drywall over. About 250 sq ft, varying from 3 to 7 ft below grade.We do get some water below the slab, but have a working french drain/sump that gets water and runs 0-5 times per year. We get light molding mustiness in closets set against this wall, but this is due IMO to coldness raising the local RH.

Part 2) uninsulated furring strips with drywall over, cavity depth about 1.5", inside a concrete/block wall. About 100 sq ft. Inspection of this space shows that it is filled with foot long shims at random locations providing a mechanical obstacles to filling with rigid products.

It is clear a lot of 'coolth' comes off these walls, which pools in a very cool lower level entryway. I think it could be 10 MMBTU/yr, or about 20% of my heating usage. As the upper part of the house was insulated, the finished basement got colder and colder....we maintain balance in our one zone house with a ceiling fan providing mixing 365 days per year.

Tearing off the drywall and rebuilding it is a no go for me. How can I cavity fill?

My ideas:

Part 1) fill with a pourable granular insulation product that is ok below grade. I.e. EPS beads, perlite or other?? Deeper cavity does not require huge R-value per inch.

Part 2) thinner cavity requires a higher performance product, like cavity fill foam of some sort. The fact that it is above grade (by about 1 ft) would seem to allow this, no?

Another question beyond what products to use is advice finding local professionals (in western Philly suburbs). I cannot find anyone that does cavity fill foam OR pourable granular insulation. I would be happy to tackle the granular DIY if needed, but would like to avoid doing a foam job DIY b/c of the risk of messing it up. Ideally I would love to have a pro handle both of these projects and write a check.

I wouldn't consider using any type of air permeable insulation. You don't want convection moving interior air to the cool concrete.

I'm in complete agreement with jonr. Also, you do not want to use an open cell foam here; you need closed cell due to it's ability to restrict moisture passage, and it needs to be solid across the wall without wood strapping interruptions. I'm also guessing, based a some experiences with newly insulated basements that your heat loss from this area is quite a bit larger than the 20% you estimate. I can't envision any way to do the project without ripping your walls apart, but think it is well worth doing it and doing right. You could install 2" (or 4") of sheet polyiso insulation, or spray 2-3" of closed cell on the block, then build a stud wall inside that. You should leave a gap of 1/4" below the sheet foam so it doesn't absorb the water. And foam the rim joist and sill.

i realize this becomes a major project, but think that the result will be well worth it.

Thanks guys. Sounds like I am boned on the below grade cavity.

For the above-grade 1.5" deep cavity, what do you think about some sort of injection foam between the furring strips? I found a local injection foam outfit.

It seems that they use a lot of injectable/pourable EPS beads in cavities in the UK, including up against (rain-driven, wet) masonry, and don't seem to have a problem. Anyone know how the US is different?

don't know why you'd treat the above ground area any differently. It will have larger heat loss, and whatever moisture is in the concrete blocks will migrate to the top of the blocks. Have no experience with EPS beads.

Is digging around foundation on outside out of the question? Its not as intense as it sounds with a mini unless you have intensive landscaping.

Much of the perimeter has no landscaping, so it might be ok. The above grade part of the wall is stuccoed. What do you propose...

A pic is worth a 1000 words. So if I understand right this 250 SF basement is in rear partially below grade 3' - 7' and there is a walk out pit 100 SF w/above grade walls both are sitting on slabs? The rest of the split level house has insulated floor joist over grade or a slab?

Feb/March ground temps are down to 42 F in PA. Wind driven rain out of the NE. Sound right? Is that the side that is getting the mold? What orientation is the building, need direction of Part 1-2 rooms. Again, pic would help.

I was just in landsdale doing another type of design last year and lived in Media for two years back in 1995. It can get nasty there.

Sorry. The finished basement is 750 sq ft floor area (uninsulated slab) with exterior walls on three sides. One side is buried, the opposite one is above grade, and the one between varies from being buried 6 to 3' below grade.

Given the floor plan and doors and windows, the sq footage provided is the wall area that needs to be insulated.The below grade walls are framed with 2x4s and drywall, the above grade wall has drywall on furring strips.

Above grade wall faces NW. Mold is not a problem anywhere.

Read my last post, need orientation. I thought that SF was low. In order to give good advice we need accurate info. It's easy to draw a pic and post it.

Above grade wall faces NW. Mold is not a problem anywhere..

Ok, got it......

" We get light molding mustiness in closets set against this wall" What direction is this wall facing?....Sounds like mold it is not always visable.

There are three built in storage closets tying into this wall....two on the completely buried wall, one on the above grade. All these closets get COLD when the doors are closed. I tend to keep the doors open to keep them warm in the winter, and no problems. This is of course a playroom and so they are filled with 'mold food', i.e. plush toys.

Ok, think I'm getting a better idea whats going on. In a cold year more like now to April worse case most of the cold wind and driving snow/rain is coming out of the NE, some the NW, N, so having these uninsulated walls common to those directions not good. Some of those directional loads/temps can be well below zero. The exterior vapour barrier from 1960 has probably failed and the above grades are hygro - thermally bridging causing dew on interior wall hence the "musty smell" is probably from a fungi food in the wall or on it's surface not toys in a room.

I take it these rooms are not conditioned w/ducts or any heat to them or humidity control? Some temp and humidity levels would be good in those rooms so you can use an online dew calculator to verify this. You can buy one at Walmart cheap you'll want anyway. Humidity needs to be no higher than 35% relative.

The walls we can deal with as the bulk of the issue but the last thing you want to do is add fungi food to fungi like a SPF. You should spray those walls with borax and boric acid before you do anything or higher a IAQ consultant or get a test kit at the big box stores send it to a lab especially if young ones are playing in it. There there are plenty of other choices, absorbents like per-lite, other natural rock resources there in PA.....EPS bead aggregate is one in the right binder. I can help you come up with a mix and design that won't burst your lower walls. Also, your short wave winter ground reflectance is pretty high there so, if the ground is not shaded you can add a light build surface to help heat the walls by radiation.

Before we get to that, the under slab & edges needs at least R-10, R-15 better to resist the 40 F ground temps to 2' footing depths min or there will be a conductive path to the rooms. The only way out of that is to fur the basement floor if your moldings/thresholds can take the height? 1.5" rigid mineral wool @ R-6, 3" R-12 better or again we design a mix thats not all about r-value.

https://energycode.pnl.gov/EnergyCodeReqs/?state=Pennsylvania

Its a finished basement and so we do have adequate forced air heating into these rooms, and they are maintained at setpoint, ~70°F. The exception is the closets when closed. We usually run ~30% max RH in the winter, but that prob goes higher in the cold closets and even higher in the even colder wall cavities.

The slab edges on the walkout side of the house have decorative stonework and associated hardscaping, so I think I will eat the associated heat losses from that, roughly 30' section of the perimeter.

Didn't follow the radiation discussion....but do you think a pourable cavity fill is appropriate without demo?

I see. These puzzles are challenging. Whomever did not put insulation in these walls did not know what they were doing. It's not just the slab edges you'll eat it's the entire slab floor seeing 40F on the other side a set point of 70F. What is the slab floor finish? What about the floor in the split area is it over a crawl and insulated floor joist? Is there a rim joist to the basement wall?

Is the furnace keeping the humidity to 30% max or are you using a dehumidifier? Did you air seal the basement walls?

How are you planning to gain access to fill the wall cavities?

Yes, but we are going to need humidity levels in the cavities at least one location by corners will be highest in each wall, two, at each corner per wall be best. 

"Didn't follow the radiation discussion"

Two types of counterradiation on external building matls are terrestrial and atmospheric. Where your at the totals are decent so your vertical walls could see ~ 300 BTUs/SF by a light reflective ground cover if they are not shaded . I didn't realize your landscape was done so forget it.

The slab has 1960 asphalt asbestos linoleum tiles covering it (in excellent condition), with a modern carpet pad and wall to wall over that. The pad seems to stay dry, i suppose the old linoleum is a decent vapor barrier.

I was under the impression that uninsulated slabs charge a layer of soil underneath them to close to house setpoint temps, and that most of the slab losses are around the perimeter (in slab on grade). I doubt I have a vapor barrier under the 1960 slab, but I probably have a deep bed of gravel, which is a decent insulator, at least when dry.

The indoor humidity cruises around 30% in the winter without added humidification (we don't run the bath fans during showering in the winter, but do the other 3 seasons). In the summer we run central AC to keep RH <50% or so.

For the cavities, I was hoping for a solution that could be poured or blown through 1.5 or 2" drywall holes from the interior, which would then be patched.

It be interesting to see what’s growing under those tiles. We don’t want to heat the soil most of it probably ends up out the wings so today we put insulation under it. Complex building physics under slabs for another thread. I think your northern exposed walls are the bigger issue.  

Assuming no windows, leaky door, no penetrations, and some others I made.I think you’d be wise to keep RH below 35% at all times in basement even if that means a dehumidifier for interior drying.

Zoned 850 SF DOE simulations show,

<!--[if gte mso 9]> W/R-10 under-edge slab vs none no wall insulation ~ $35/yr utility bill saving. Not much. 

1. No slab insul, interior wall average R-10 ~ Perlite fill no humidity set point.

Following no slab insulation,

2. R-10 Perlite filled.

Following 35% RH set points,

3. R-10 Perlite filled w/R-6 rigid sheathing + medium dark absorptive fiber cement (use light reflective ground cover if not shaded for best results). I’d add some Mule borax you can get at most Wallmart ~10% by volume antifungal/antiseptic. Perlite is absorbent incase or if you can find scoria, pumice, lava, or other similar rock aggregates locals suggest cheaper use it. You could increase the sorption ratios by using a Type SA (better, aerated, lighter) or S lime but it will get messy and you’ll need more info let me know.  Be about the same for cellulose if you can find a mfg to warrantee this installation. GreenFiber makes a stabilized or loose Borate .

4.CC Foam + R-6 sheathing (make sure foam is inert, non-reactive, chemically stable).

Delivered energy shows latent heat benefits, size for dehumidifier cooling load reductions, utility bills.

Any questions let me know.

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.

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

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.

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.

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.