Ok,

You're going to think I've lost my marbles, but I've become enamored with some of the historic stone homes in Colorado mining towns.

A little research reveals that some have walls as thick as 2.5', and stone typically has an R-Value of only 0.8/inch.  Since stone has little if any air entraped in it, there is little insulating value.  It's my understanding that stone actually acts as a heat conductor, not an insulator.  However, with proper joinery, it makes for an airtight wall.

We're in an alpine environment (summer = 75deg max; winter = -37 some nights), but we have incredible solar exposure do to our high altitude.

The question I'm trying to solve, without much luck is:  Will the stone work as a heat-sink and absorb and radiate back heat if properly oriented for solar gain?  Sort of like log homes do.

It seems like the major downside is the labor cost of building, but aside from that can anyone point me towards any good resources?!

Thanks in Advance!

Corey..
Crested Butte, CO

Hi Corey, You could put some Underfloor Heating pipes into the middle of the wall to create a heat-loss barrier and to make better use of the thermal mass. Low grade Solar Heat could then be pumped through the walls.

Corey; check out this website for a successful implementation of passive solar near you. www.thenaturalhome.com/passivesolar.html Logs don't absorb heat, but stone does. Stone needs to be insulated on the outside to do any good, so you probably end up with a stucco look, maybe not what you want. You may want to google the term slip form, a way to build what you are talking about.

You still need to fully insulate the house. I find the "stone laid in sand and then concrete poured over it and then tilt up the wall" technique interesting. Might even be possible to do some type of foam in the middle, stone on both sides variation.

Well if the walls are really in the 2 foot thickness range and your R value for stone is correct you are looking at a wall R value approaching 20. An ICF wall is usually R-22

The value given for stone's R/inch is off by an order of magnitude. I would expect it to be closer to that of concrete, nominally 0.08/inch. The total wall R value for ICF is due mostly to the foam on either side of the concrete.

cbryndal-

I am also in alpine Colorado, and the idea of thick stone walls sounds neat and fitting for the area. However, since the R-values quoted for stone run about 0.05 to 0.11 per inch, then the 24-inch wall would only give you about R-2, just as Dick Russell has stated. You would never meet any code with this, and it would be expensive to heat if you wanted it at something other than the outdoor temperature, moderated by the thermal inertia. You could insulate on the inside with a wood stud wall filled with insulation.

If you want stone on both sides, you could make a double stone wall, with the space between filled with rigid foam, in which case you could perhaps make the double walls at the same time with the foam in place. However, rigid foam is very expensive compared to cellulose or fiberglass. Those loose fill materials would require the the two walls be constructed without the insulation in place, with the insulation added after the walls were dry. There could be significant moisture issues with the loose-fill insulation that would need to be considered.

What they said- no amount of thermal mass is going to save you from the extreme loss of R2 walls.

With logs you're an order of magnitude higher in R-value, and order of magnitude lower in mass, but not necessarily an order of magnitude lower in thermal mass for walls of equivalent thickness/volume.

Wood is largely cellulose, hemicellulose, and lignin, which have a higher specific heat. In wood the specific heat is not a constant- it varies substantially with temperature over relevant temperature ranges, with some interesting non-linear heat-of-fusion things going on when near the melting/freezing points of the pitch, but between 0-70F it's ~0.3- 0.5 BTU/F-lb for most species used in construction, compared to concrete or most stone at a more steady ~0.20 BTU/F-lb. Per-pound wood has ~1.5-2.5x the thermal mass of stone.

As I understand it cellulose by itself, (not integrated into wood- basically paper) has a specific heat of ~ -0.37-0.40 over the relevant temperature range. It's the lignin & hemicellulose that give wood it's non-constant non-linear aspects.

Poured perlite or blown EPS beads can be used to insulate large cavity walls (but I'm not sure if anyone is using the latter in the US- it's a common retrofit in the UK.) When insulating heavy masonry walls in very cold climates you need to take care the the ends of structural timbers penetrating those walls don't absorb winter moisture and rot. There are no simple prescriptions for how to do this, but be forwarned...

I think you will find rigid foam inexpensive relative to the total cost for stone walls.

http://www.hollowtop.com/cls_html/tiltup.htm

Thanks to everyone who replied. The information is quite interesting. While I figured the R-Value would be low, I had hoped that the ability to absorb, store and re-emit heat would have made up for it, but it doesn't look that way. I'm not looking to build a refrigerated home! I spoke with a fellow up operates the local library - a historic building that is built of very thick stone walls, and he mentioned that the building is over-warm with very little heat in the winters, and that they did add cellulose to the roof structure a few years back. The inside is sheet-rocked, and I couldn't tell if it was cosmetic, or hiding some insulation cavity. I'm going to try to contact several other stone-home building owners and see what their experiences have been, and what the insulation approaches were. One that is inspiring is: http://rockhouseranchco.com/gallery2.html

This idea sort of grew out of my interest in Nudura ICF's and it seems like there's probably not a very reasonable way to pursue a 24" stone strategy. The double wall concept is interesting, but frankly, I think there would be issues there and even more cost. I may end up doing an ICF wall simply with 4"-6" external stone cladding in historic vernacular for the area.

Thanks again & please add any thoughts as you review the discussion.

Corey..

I don't believe there is a direct equivalent, but then I don't really know what your "stone house" wish means.
It would be useful if you would explain this a bit more.

I am an artist and designer. I also live in a stone 1856 historic home in the Texas Hill Country. The walls are about 20 inches thick inside and out.
Because of the mass of the stone, the temperature stays very constant except in extreme heat or cold.
We put in central AC/heating. The AC works very well. The heat is not efficient at all.
However, on sunny days in the winter the way the windows were aligned allows for a lot of free heat and absorption of heat. In our extreme summers the sun basically is overhead and as it is rising or setting our 300 year old oak trees keep the sun moderated.
The best help when we have the rare cold, wet spells is to keep the two downstairs fireplaces going. Once the walls heat up, the heat conducts and radiates. We have a lot of free firewood as there are always trees dying for one reason or another on the ranch.
And, we love the look and feel of our so much that we are willing to spend a bit more on heating to live in such a great place.
Pablo Solomon