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This question is most probably meaningful when there is a lot of area to build a single house. The main purpose is to keep the heat inside in winters, where it rarely drops below -5 degrees Celsius.

The concept house -with a living area of no more than 60m2- is designed in a way that its concrete walls are covered /surrounded by a sand barrier. The concrete walls are 5cm thick and 220cm high while the sand barrier is ~40cm thick and ~150cm tall. Several windows are planned to be placed between the sand barrier's top and the ceiling.

So, what should be taken into account before attempting to use sand as an insulation material in that way? For instance:

  1. What is the ideal grain size?
  2. When damp or wet, how effective would the sand barrier be?
  3. Is it easy to keep the sand dry, especially in rainy climates? Would the sand barrier absorb the moisture in the air -even when covered by a roof? What type of sand would be the best?
  4. What plants and other organisms would grow up in the sand?
  5. What constructional and functional complexities would be encountered?

The list may go on...

Considering all these and more, do you think a sand barrier is an effective, reliable and 'long term' solution for heat insulation? Thank you.

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    The thermal mass of the sand will dominate the insulation value. Also, because of its density it will be difficult to contain compared to just about anything else. Where sand is used as is in buildings they're usually buried in it to and the thermal mass works to cool the building, with the sand over the top helping heat it at night. Sand in the walls will not be an insulator in any meaningful sense, as @juhist points out in their answer
    – Móż
    Oct 10, 2021 at 8:48
  • Whatever keeps the water out of the sand should also stop plants growing in it, especially if you're in an area with termites. Otherwise you are likely to get roots or stems growing through it (rather than in it).
    – Móż
    Oct 10, 2021 at 8:49
  • @Móż By the sentence 'The thermal mass of the sand will dominate the insulation value' do you mean that I will spend too much energy to warm up the sand before it can act as a heat barrier?
    – Xfce4
    Oct 10, 2021 at 9:06
  • thermal mass: there are two numbers, the specific heat capacity and the speed of thermal transfer. If you get the depth right the heat wave in the sand will arrive at the inside just as the evening cools down (many hot climate buildings work this way). If you get it wrong it will just delay the point where the building gets uncomfortably hot and then when it cools down again in the evening. My brick house works this way - it gets hot inside mid-afternoon and stays hot until midnight.
    – Móż
    Oct 12, 2021 at 1:59
  • You would probably be better off looking at biocomposites, like mud/straw bricks, strawbale, hempcrete (which can be made using reeds or straw), or even concrete composites. "reverse brick veneer" is another way to mix concrete/brick and insulation, but only if you can get away from sand=insulation rather than sand=thermal mass.
    – Móż
    Oct 12, 2021 at 2:02

1 Answer 1

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Even though rock is a poor heat conductor for example in geothermal wells that slowly become cooler over time as heat is extracted, you cannot use sand as a general purpose heat insulator in houses. The coefficient of thermal conductivity isn't just small enough.

Sand has a coefficient of heat conductivity of about 1-2 W/mK.

A real insulator like expanded polystyrene has coefficient of heat conductivity of about 0.03 - 0.04 W/mK.

You need nearly 50 times more dimension in the walls for sand to work effectively. This means the exterior dimensions of your house could be several times bigger than the interior dimensions. Not practical.

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  • According to this link dry sand (sand with 0% water content) has thermal conductivity around 0.25 W/mK.
    – Xfce4
    Oct 9, 2021 at 8:42
  • So, for 25cm thick sand barrier, U-value is 1 W/m^2.K. That means 'each square-meter of the 25cm-thick-sand-barrier' will leak /conduct heat at the rate of 1W per Kelvin, right? Then, if the outside is 15 degrees colder than the inside in average, a 30m long and 1.5m high sand barrier will conduct heat at almost 0.7kW. This is around 17kWh daily and 500kWh monthly. Does not seem to be an economical solution.
    – Xfce4
    Oct 10, 2021 at 6:22
  • I don't know about sand, but rammed-earth walls get their insulating power not from heat conductivity, but from thermal mass: it takes several days to warm up a wall a half-meter thick, so the indoor temperature is the long-term average of the outdoor temperature.
    – Mark
    Oct 11, 2021 at 20:58
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    @Mark a properly designed mud brick wall will have a heat travel time of about 12 hours, so that successive waves of heat and cool reach the inside just as the day turns. Or alternatively the wall takes about 12 hours to heat up or cool down, depending on how you look at it. Sadly this is often not the case, and obviously not all walls can face the sun so in heating climates they just make it hard to heat the house. A friend has a house like this and it's really, really annoying in winter. You need actual insulation over most surfaces for the thermal mass to be useful.
    – Móż
    Oct 12, 2021 at 7:57

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