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10-11-2009, 12:22 PM   #1
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## R-Value of solid stone wall

I can't seem to find reference values for solid stone R-values. I have a 20" basement wall- and I would like to calculate the heat loss. Unfortunately, I can't find R-values for stone, only concrete and brick. I'm not sure what kind of stone it is (or if that matters). The house is 100 years old and in the midwest.

Thanks!

10-11-2009, 12:34 PM   #2
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the heat loss factor is BBBBRRRRRRRRRRRRRRRRRRRRRR x 4 you'll find the wall temp is always the same as the soil directly touching it on the exterior of the wall multiplied by ( .85time factor ),,, nothing transmits energy slower than common stone/concrete/marble/etc,,, caution - if you're planning bsmt upgrades, plan NOW for moisture/water control,,, comparatively, its MUCH MORE EXPENSIVE later when you find wet floors

 10-11-2009, 12:42 PM #3 Civil Engineer   Join Date: Mar 2009 Location: Boston Posts: 5,688 Rewards Points: 4,956 Check out this link for R values for a wide variety of materials http://www.coloradoenergy.org/procor...f/r-values.htm As for stone, I would use the value for concrete, specifically .08 per inch. Most stone has a unit weight in the range of 150 to 180 lbs per cubic foot, which is very similar to concrete (150 lbs per cubic foot). Due to the lack of air in stone (except for certain highly unusual stones such as expanded shale or certain volcanic stones), the R value is very low. Without specific identification of the type of rock, you are going to be close enough using concrete values.

 10-11-2009, 01:37 PM #4 Member   Join Date: Jun 2009 Location: Somerset, England Posts: 721 Rewards Points: 582 I know what the U values for a 20inch stone wall are if thats any help. For sandstone it's about 2.3, but that doesn't allow for lime mortar and air voids which can bring it down to about 2.1. Limestone is similar. The walls on my cottage are 20 inch thick limestone and do lose a fair amount of heat compared to a modern house which has a U value of less than 0.30. The U value is the reciprocal of the R value, so there is a way of working it out from that.
 10-11-2009, 01:56 PM #5 Civil Engineer   Join Date: Mar 2009 Location: Boston Posts: 5,688 Rewards Points: 4,956 You are correct, the R value is simply the reciprocal of the U value, so for a 20 inch wall that has a U value of 2.3, the R value is 0.43, which works out to about .02 per inch, which is 1/4 the published value for concrete. This may be due to the fact that most concrete is air entrained at about 5 percent or so, which presumably adds some insulation value to concrete versus stone, which typically has almost no trapped air in it.
10-11-2009, 04:02 PM   #6
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If you are talking about R-values for a massive structure, you are just blowing in the wind. The R-value concept is for lightweight structures with no thermal inertia and geared for quick calculations and advertising. It is just a measure of the heat loss RATE and factors that affect it are the temperature difference and measuring time. To justify the values, the R-value is determined on a short term test in a lab with steady state conditions because the testing is cheap and fast. There are better methods such as a dynamic hot box with cyclical temperatures variation of a more realistic range.

Be aware that the R-value of a product is just for that material and not the wall. As an example, some pink R-19 stuff in a steel stud wall could give you a WALL R-value of as low as R-11 even in a short term case according to tests. The corners and double studs ar windows are also much worse than the plaininsulated stud wall.

Beware when insulating a basement wall because it is very easy to over-insulate and waste money. This is because the soil behind the wall is about 55F and not the 0F or -20F above grade. If you try to calculate the heat loss you would correctly use the temperature difference as about 15F (70F minus 55F) for the below grade portion and not the much higher 70F or more for that you see for and above grade wall. Dont forget about the floor area, since that is still quite cold and can have more area that the walls. - Also, no air infiltration for below grade walls, so attacking the crack between the wood and stone is the first thing to do.

For a real eye-opener, grab a laser thermometer and take some shots in your basement to measure the surface temperature of the different materials as they are now. Measuring the air infiltration is a bit more costly and only gives general, over-all information.

Dick

Last edited by concretemasonry; 10-11-2009 at 04:07 PM.

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