We recently built an addition. It's outside walls are 12" concrete block filled with concrete (overbuilt for heatmass, and holding a heavy slab/garage on top). The top of the building (other than garage) also houses an insulated sunroom. The top was finished with stone, and stone is sticking out ~4'inches on top of concrete. There is about 8-10" of flashing (it's bent inward). I am looking for options for external insulation. We do intend to put stone siding on top of it. Insulation would need to be dirt/moisture friendly, as the back of the basement is partially underground. We were a little worried about the looks of it, but I am more worried about picking the right product since we still want to take advantage of that heat mass (plan is to heat with radiant, and preheat it with solar) Currently the walls are only covered with Drylok on both sides.

I'd look at EPS foam board or Rockwool

I would suggest a higher density EPS foam (1.5# to 2.0# nominal density vs. the 1.0# density found at home centers) covered with a synthetic stucco over exposed portions of the insulation. Anything below grade I would coat with a rubberized waterproofing such as Black-Jack Rubr-Coat #57. This is not so much for the waterproofing, but to deter insects from burrowing into the foam.

https://www.lowes.com/pd/BLACK-JACK-Rubr-Coat-4-75-Gallon-Fibered-Roof-Sealant/3043257

It was mentioned that you intend to put stone siding on top of it. Real stone or thin stone? How exactly do you intend to attach and support that stone?

i was reading about EPS, and for under ground most articles recommend XPS (also seems to have higher R-value per inch)

As far as stone goes, on top they put a mesh on particle board, then created a scratch coat and attached stone.

I believe they would put the same mesh (via bolts) and put a scratch coat and attach stone veneer. http://www.fmsupply.net/prdq_product.php?profile=ledgestone

Does XPS have a higher initial R-value?

Yes!

HOWEVER, the product off-gasses over time. And, as it off-gasses, the R-value is reduced. Eventually it's no better than standard EPS.

So, why spend the extra money on a transient property? It's like throwing money away.
If you're trying to build to a certain spec, build with EPS to that spec and it'll STAY that way.

Also, if you're putting foam underground as anything other than a drainage layer, check your area for issues with termites and other boring insects. You may need to put on some form of Termi-mesh or similar product.

SO what about EPS being not very good for earth contact? Is there a special brand/type that should be considered?


Thanks.

EPS is widely used as sub-grade insulation, and is just fine in contact with the ground, with reasonable measured taken for waterproofing & drainage. The vast majority of insulated concrete forms (ICF) are made of 1.5lbs per cubic foot density (aka "Type-II") EPS, that performs at about R4.2/inch of thickness at a mean temp through the foam of 75F (the standard ASTM C518 test condition that the FTC allows for labeling purposes.)

There are a gazillion ways to waterproof sub-graded EPS a common topic in ICF industry discussions (and the ICF forum on this site.) Most of those methods would be directly appropriate for a CMU foundation wall as well. For a taste, see: https://www.icfmag.com/2017/09/effective-waterproofing-for-icf-structures/

Most XPS sheathing is also 1.5lbs density, and will also eventually drop to R4.2/inch as it's high global warming potential HFC blowing agents diffuse out over time. EPS is blown with comparatively low impact hydrocarbons (usually pentane), most of which escapes the foam and is recaptured at the factory, often burned for process heat.

EPS roofing foam is usually 1.25lb density "Type-VIII", which is still good enough for applying to the exterior of CMU walls & foundations, even though it isn't strong enough to use in insulated concrete forms. Roofing foam is commonly salvaged and traded for re-use, usually at less than 1/3 the price of virgin-stock goods, and well below the cost of box-store Type-I EPS (1lbs nominal density.) Finding local foam reclaimers isn't always easy, but it's worth searching the local craigslist materials section for rigid + insulation, eg:

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

Reclaimers also usually have stock in fiber faced polyisocyanurate roofing foam. While that's fine for above grade use and has a higher R/inch (between R5.5/inch - R6.0/inch) it will become waterlogged if in contact with soil. Unlike EPS polyiso can't be directly finished with a cementicious stucco-like material (eg QuiKrete Foam Coating), and would need a weather resistant barrier (Tyvek, etc) and siding. If you can't find a local source, Nationwide Foam will drop ship truckload quantities to your site from regional depots (for a price). http://www.nationwidefoam.com/

The amount of foam it takes to meet code varies by location, but if it's all on the exterior side it's dramatically less R than you'd need in a framed wall. This is because the foam is not thermally bridged by framing, and the thermal mass of the CMU moderates the peak and average loads, reducing the annual energy required to heat & cool the interior. See the "MASS WALL R-VALUE" column of TABLE N1102.1.2 in the IRC 2015:

https://up.codes/viewer/utah/irc-2015/chapter/11/re-energy-efficiency#N1102.1.2

Even in zone 5 (Boston, Chicago Denver, etc) it only takes a hair more than 3" of exterior EPS to meet code, with no insulation on the interior side of the CMU wall. In zone 6 (Minneapolis, Burlington VT, etc) it can be done with 3" of polyiso above grade, 4" of EPS below grade.

Where are you located?

Wow.. Thanks for that wealth of insulation. Will be plenty of reading for tonight.

I am in northern WV (aka eastern panhandle), where PA, MD, VA are all in <30m drive (25422)
I would like to get decent insulation to minimize heating expenses , as I am eyeing a relatively low capacity heating system (Sanden SanCO2) to supplement Solar panels during shady days.

Achieving high R value might be a bit challenging, as the wall is already 12" thick. R15-20 is my estimated requirement for this space (excluding windows)

Here's my quest for the heating system.
https://forum.heatinghelp.com/discussion/comment/1511676/#Comment_1511676

This outfit in PA seems to carry factory-seconds foam (probably for half retail, maybe less):

https://chambersburg.craigslist.org/mat/d/factory-seconds-of-foilback/6493723375.html

Running this search once/week or so might dig up other / closer / cheaper sources.

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

Morgan County WV is DOE climate zone 4A. (see the map: https://energycode.pnl.gov/EnergyCodeReqs/?state=West%20Virginia )

Under IRC 2015 a code-minimum in zone 4A would require only R8 (2" of EPS) on the exterior of a mass wall, but R10 for basements below grade or the slab edge (if slab-on grade.) See:

https://up.codes/viewer/utah/irc-2015/chapter/11/re-energy-efficiency#N1102.1.2

Using 1.5" of foil faced polyiso above grade would yield R9 (R10 with at least a 1/4" air gap to the siding), but 2" (R12) would be better. Using 3" of polyiso (any facer, any density) would get you to the R15-R20 range.

The Sanden SanCO2 is 1kw in, and at best 4kw-4.5kw out even at shoulder season outdoor temperatures. That's a fairly low ~14-15,000 BTU/hr of capacity. http://www.r744.com/files/57beefd3a94db1472131027rr47H.pdf

I suspect your 99% outside design temperture is under 15F (Martinsburg's is 14F). At +17F and cooler the capacity and efficiency of the Sanden will be lower, unless the output water temperature is WELL below domestic hot water temps. see: https://neea.org/docs/default-source/lab-test-reports/laboratory-assessment-of-sanden-gau-heat-pump-water-heater-lab.pdf?sfvrsn=6

The source recommends it as appropriate "For homes with a design temp of 23°F or higher, and a heat load of 8kbtu/hr or less... " : http://www.smallplanetsupply.com/sanden/

So, it'll probably need some auxillary heating to actually work on cloudy days.

Have you run the heat load numbers in this, or simulated the house using BeOpt?

Unit's capacity is 100% down to 5F based on other literature I have (due to CO2 based technology). It does lose efficiency (COP) from 4.5 to 2 down to those temps, but still 2x more efficient than coils/instant heater. I believe it starts reducing capacity and works at least down to -15F I plan to back it up with 11kW instant heater (can go higher if needed, but that's 35K BTU backup right there). During my research, I stumbled upon this paper, which talks about doing pretty much what I plan to do at this point... https://www.bpa.gov/EE/Technology/EE-emerging-technologies/Projects-Reports-Archives/Pages/Combined-Space-and-Water-CO2-Heat-Pump-System-Performance-Research-.aspx I agree it's small, but between this unit, + backup + remaining capacity on my 4 port mini-split (which I primarily plan to use for cooling) I should be OK. My design also allows for easy addition of solar later (or right away). I shared the link to heating forum above where i posted the design if you're interested. My rough heat load estimate with 0F outside temp is below 20K BTU for the space. I haven't done it properly though (e.g. infiltration, bridging are missing in my calc). However, if I insulate on the outside, and given these are either masonry or poured walls, both should be minimal. I haven't had a chance to assess all the information you provided fully, and will try to followup later with additional answers.

PS

The link you provide to CL seems to be for polyisocyanurate insulation.
I thought it was a "no no" to use this on exterior, but I certailnly would appreciate the extra R-vallue per inch.
Is there a particular thickness one would be looking for?

Thanks,

Polyiso is fine for above-grade applications, but should never be in contact with soil.

Reclaimers trading in used roofing polyiso almost always have roofing EPS too.

Assume any fiber faced roofing polyiso to be at least R5.5/inch. Most of it is more than R5.8/inch. Type-VIII roofing EPS is typically R4.0/inch. So code- mass-wall of R8 insulation on the exterior would only need 1.5" of roofing polyiso, or 2" of EPS. But you're probably going to need better than code min on the above grade walls.

Code-min for below grade is R10. If it's on the exterior that would need to be a minimum of 2.5" of Type-VIII EPS, but 3" or 3.5" would not be insane. If you made it 3"-3.5" EPS below grade (up to 6-12" above grade), installed EPDM flashing tape as Z-flashing between the EPS and polyiso of the same thickness above that it would be nice and co-planar. The above grade stub of EPS can be finished/protected with a cementicious stucco-like purpose made material such as Quikrete Foam Coating. The polyiso can be mounted to the wall with 1x4 furring through-screwed to the CMU with masonry screws, and the siding can be mounted to the furring. The 3/4" gap between the siding and polyiso is an excellent capillary break, and allows both the polyiso & siding to dry into the cavity without any problem- both will stay dry.

With 3-3.5" of roofing polyiso you'll be looking at R16.5- R20, more than twice the code minimum for a mass wall, and a higher steady-state whole-wall value than a code-min 2x6/R20 type framed wall. Going with 2 layers of 2" (with staggered taped seams) works too, but any thicker than that gets more awkward to build, and the longer masonry screws starts to add cost too. Spending the money on better-tuned higher-performance glass becomes a bigger bang/buck at that point. (But I assume that ship has already sailed?)

Even though the discussion is primarily about framed walls, installing 1x4 furring 16" o.c. with fastener spacing in Table 1 on this page would be about right for your stone veneer wall:

http://www.greenbuildingadvisor.com/blogs/dept/musings/fastening-furring-strips-foam-sheathed-wall

Note, the fastener spacing gets to be really tight with 4" of foam and stone veneer siding, 50% more (and longer, fatter) masonry screws than with 3" foam, which may be a good reason to hold the line at 3".

Thank you. You may have missed that there is below grade installation involved
from my original post:

Insulation would need to be dirt/moisture friendly, as the back of the basement is partially underground

Nonetheless, i found articles talking about polyiso can be installed under grade with proper care.

Thanks again for your feedback, will continue reviewing..

Posted By Dana1 on 21 Mar 2018 07:01 PM
The above grade stub of EPS can be finished/protected with a cementicious stucco-like purpose made material such as Quikrete Foam Coating. The polyiso can be mounted to the wall with 1x4 furring through-screwed to the CMU with masonry screws, and the siding can be mounted to the furring. The 3/4" gap between the siding and polyiso is an excellent capillary break, and allows both the polyiso & siding to dry into the cavity without any problem- both will stay dry.

Dana1,

1.) Is it necessary to coat the polyiso with stucco if it is going to be covered with siding?

2.) Is it a good idea (or not) to cover everything with a house wrap?

3.) Also, I understand how you can attach siding to the furring strips, but how could you attach cedar shingles instead?

Hanging plywood through the foam and into the concrete walls or even to the furring strips and then attaching the shingles to it would take a pretty beefy screw attachment system I'd think. How can it be done?

NetComrade: Point me to those articles! Polyiso is somewhat hygroscopic, and will wick & retain moisture when buried. (Polystyrene is not hyrgroscopic and even if it takes on moisture in saturated soil, the moisture will leave when the tide goes out.)

Roger: Stucco-type foam finishes can't be applied to the facers on foam, and almost all polyiso comes with paper, fiberglass or foil facers. Those finishes only work with unfaced EPS and XPS. [edited to add] Actually those finishes will stick to the facers, but it's more prone to flaking off when applied in thin layers than when applied to unfaced EPS. [end edit]

If the EPS is going to be covered with siding it doesn't need cementicious or other coatings for protection. But if it's going to exposed to direct sunlight (even reflected sunlight) it will degrade over time.

To hang cedar shingles you'd have to run some lateral girts at the intended spacing for the shingles: http://forestryforum.com/gallery/albums/userpics/26833/Rainscreen_Wall_Design.jpg

For a CMU or concrete wall it's best to use a spray applied water/weatherproofing between the foam & structural wall. If installing the windows & window flashing "outie" style, with the glass roughly co-planar with the siding rather than with the strucutural wall ("innie" mount) it'll still need a layer of housewrap on the exterior side of the foam, lapped properly with the window flashing.

http://www.greenbuildingadvisor.com/articles/dept/musings/installing-windows-foam-sheathed-wall

http://www.greenbuildingadvisor.com/blogs/dept/musings/innie-windows-or-outie-windows

Posted By NetComrade on 21 Mar 2018 08:08 PM
Thank you. You may have missed that there is below grade installation involved
from my original post:

Insulation would need to be dirt/moisture friendly, as the back of the basement is partially underground

I didn't miss that at all, which is why I discussed transitioning from EPS to polyiso a few inches to a foot above-grade, with EPDM Z-flashing at the transition.

Dana1, Good info thanks. Regarding: To hang cedar shingles you'd have to run some lateral girts at the intended spacing for the shingles: http://forestryforum.com/gallery/albums/userpics/26833/Rainscreen_Wall_Design.jpg Do you think it is necessary to add the venting and spacing as shown in the drawing since a lot of air infiltrates within and between the cedar shakes anyway - especially with the webbing they are attached to?

I apologize, unlike my claim that you may have missed some is going underground, it looks like I was doing the 'missing'. I understand now the part where you recommended transitioning from EPS to Polyiso.

Links

https://www.jm.com/content/dam/jm/global/en/building-insulation/Files/BI%20Toolbox/BID-0149_AP_Foil_Residential_Installation_Instructions_Below_Grade_Exterior_Walls.pdf

Protect foam insulation that is exposed above grade
and 6 inches below grade. Options include fiber
cement board, pressure-treated wood, or stucco
parging

This one is talks mostly about exterior (but above grade).. Talks how well Polyiso performs when wet, btw . I think I stand corrected again (blushing) looks like most of the reading I did was for exterior use, not necessarily below grade (except for JM link above)
https://www.carlisleccw.com/download.aspx?fileID=2861

I found this to be a good read on exterior insulation (discourages polyiso)
http://www.greenbuildingadvisor.com/blogs/dept/musings/how-insulate-basement-wall

The windows are Andersen double-pane Low-E.. It's too snowy to go take a look now, but I recorded their R value as 2.5 in my spreadsheet (total area estimated at 96sqft)

JM's sheet notwithstanding, I wouldn't use it in soil contact (but on the interior side of a basement wall, sure!)

The SHGC (solar heat gain coefficient) is at least as important as the U-factor. An R-value of R2.5 is a U-factor of (1/2.5-)= 0.4, which would not meet code minimum performance. A U-factor of U0.25 is an R-valuve of (1/0.2.5=) 4.

Thank you.. I didn't realize R value can even be this high on windows w/o focusing on that (which I probably should have done, as these were no minor investment).. The snow receded and I went to check, the U is 0.28 on the bigger ones (it's close on the other two.. .27 and .29).. SHGC is 0.32..

These are south facing, although no sun until about noon (east wall/trees)

That would make it R-value of slightly above 3.