Weighing the Value of Concrete Housing - Green Building Elements

Weighing the Value of Concrete Housing

A South African company called Moladi is promoting their system for quickly building homes. Using their system, the exterior walls for a single-family dwelling can be built in a matter of just a day or two, and it can be done using unskilled labor. But, while their goals are admirable, it’s a question whether or not this is a really green method of building.

The system uses lightweight formwork panels, much like those used for poured concrete walls. Once erected, the forms are filled with mortar (concrete without stone) which can be hand-mixed and hand-placed, or which can be mechanically mixed and pumped into place. Typically, the formwork can be removed the day after the mortar is poured. The result is a smooth finish material, little more than a roof is needed to complete the building.

On the downside, this material uses 250 kilograms of portland cement per cubic meter (about 420 pounds per cubic yard), making it fundamentally the same as a concrete building with an enormous carbon footprint stemming from the extensive use of cement in these buildings.


There are some benefits to a system such as this, however. For one, the construction is fast. Once the formwork is set up, it takes a day to pour the mortar, and the formwork can be stripped the next day. This allows for the rapid construction of multiple dwellings in a short period of time. The work is simpler in setting up, filling, and taking down the forms, so it can be carried out by unskilled laborers (though this falls into the give-a-man-a-fish/teach-a-man-to-fish question that may not be serving the greater needs of the community). The buildings which are monolithically cast are also stronger and more earthquake-resistant than structures built of brick or concrete block.

But, in addition to the enormous carbon footprint associated with extensive use of cement in these buildings, there are some other aspects of this building system that make it more problematic. Electrical conduit and plumbing piping as well as window and door openings are all cast into the walls. While this is touted as an advantage (and in some cases it would be) in comparison to the practice of cutting into masonry to recess piping and wiring into the wall, it is no more flexibility to repair or renovate.

The thermal performance of Moladi is also problematic. A 100mm (3.9 inches) Moladi wall has a comparable thermal performance to a 150mm (5.9 inches) masonry wall or to a 370mm (14.6 inches) concrete wall (nearly 4 times as thick). But, given concrete’s poor thermal properties, that’s not saying all that much. (This is about the same R-value as an uninsulated single-pane glass window provides.) For any sort of a climate where heating is a necessity, this material is obviously a poor choice.

Reducing the amount of material used in a house could help turn around some of the environmental negatives of this building method. Even using this system to build only the exterior walls of houses, and having the interiors built out by local workers would reduce the carbon footprint of these buildings substantially, as well as providing for more flexibility. It would also open up opportunities for local workers to contribute more, and potentially earn a higher wage for their work.

The tradeoffs are not an easy thing to dismiss, however. From a triple-bottom line perspective, rapid, low-cost home construction meets an important human need, and that weighs strongly in Moladi’s favor; it helps house people. But from an environmental perspective, the massive amounts of cement used in this process make it a poor choice; it’s bad for the planet. It is an example of how competing goals must be weighed, and some of the potential environmental costs in trying to do something good.

See also on Green Building Elements:
Insulated Concrete Forms
Shaver Green Building to Offer Sustainable Workforce Housing
Sustainable Architecture Benefits Chicago’s Underprivileged

image via Moladi


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  • Tim in Oxnard

    Must be way better than living in a mud hut wouldn’t you agree?What is with this “carbon footprint” BS anyway?

  • Tim in Oxnard

    Must be way better than living in a mud hut wouldn’t you agree?What is with this “carbon footprint” BS anyway?

  • I am hard pushed to find anything that is green in the building world. This one for instance attached to my user name. I mean, how green can building a new island be?

  • I am hard pushed to find anything that is green in the building world. This one for instance attached to my user name. I mean, how green can building a new island be?

  • Re: (This is about the same R-value as an uninsulated single-pane glass window provides.) Get your fact right Philip. The external wall is 150 mm and not 100 mm.
    From:http://www.coloradoenergy.org/procorner/stuff/r-values.htm
    Poured Concrete R/Inch=.08 per inch or .08X(560/25.4)=.08X22.05=1.764
    Single glass-.91
    The correct measurement for thermal conductivity moladi=0.54 W/m.K Glass=0.858 W/m.K

    For yor info read below

    Energy efficiency of building materials is determined by how it handles heat, how heat transfers through materials and how well materials hold or store heat. Remember, heat always moves from warm to cold, so during the summer, if the outside temperature is warmer than the inside temperature of a home, heat transfers through the walls from the outside in. Conversely during winter, if the inside air temperature is warmer than the outside, heat transfers from inside the home out.

    There are a number of combinations of materials used in construction and their thermal mass and R-value efficiencies vary depending on how they are used in the region of the country (climate considerations). How efficient a system is and how much energy consumption is reduced depends on how fast heat transfers through materials, how well materials hold the heat and the fluctuation of outside temperature. High-heat capacity materials significantly reduce the time for the heat to pass or transfer through into the home. Often until late in the night, typically when systems are running more efficiently or consumers are being charged a lower rate for kilowatt usage from their utility company.

    Mass effect is real. High-mass walls really can significantly outperform low-mass walls of comparable steady-stated R-value. However, the mass-enhanced R-Value is only significant when the outdoor temperatures cycle above and below indoor temperatures within a 24-hour period. High mass walls are most beneficial in moderate climates that have high daily temperature swings and nearly all areas with significant cooling loads can benefit from thermal mass in EXTERIOR walls. This is especially true for the sunny Southwest areas of Arizona, New Mexico and Colorado.

    According to an article written by Jeffrey E. Christian and Jan Kosny titled “Wall R-Values that Tell It Like It Is,” wall systems with significant thermal mass have the potential, depending on climate, to reduce annual heating and cooling energy requirements below those required by standard wood frame construction with similar steady-state R-value.
    moladi=0.54 W/m.K Glass=0.858 W/m.K

  • Re: (This is about the same R-value as an uninsulated single-pane glass window provides.) Get your fact right Philip. The external wall is 150 mm and not 100 mm.
    From:http://www.coloradoenergy.org/procorner/stuff/r-values.htm
    Poured Concrete R/Inch=.08 per inch or .08X(560/25.4)=.08X22.05=1.764
    Single glass-.91
    The correct measurement for thermal conductivity moladi=0.54 W/m.K Glass=0.858 W/m.K

    For yor info read below

    Energy efficiency of building materials is determined by how it handles heat, how heat transfers through materials and how well materials hold or store heat. Remember, heat always moves from warm to cold, so during the summer, if the outside temperature is warmer than the inside temperature of a home, heat transfers through the walls from the outside in. Conversely during winter, if the inside air temperature is warmer than the outside, heat transfers from inside the home out.

    There are a number of combinations of materials used in construction and their thermal mass and R-value efficiencies vary depending on how they are used in the region of the country (climate considerations). How efficient a system is and how much energy consumption is reduced depends on how fast heat transfers through materials, how well materials hold the heat and the fluctuation of outside temperature. High-heat capacity materials significantly reduce the time for the heat to pass or transfer through into the home. Often until late in the night, typically when systems are running more efficiently or consumers are being charged a lower rate for kilowatt usage from their utility company.

    Mass effect is real. High-mass walls really can significantly outperform low-mass walls of comparable steady-stated R-value. However, the mass-enhanced R-Value is only significant when the outdoor temperatures cycle above and below indoor temperatures within a 24-hour period. High mass walls are most beneficial in moderate climates that have high daily temperature swings and nearly all areas with significant cooling loads can benefit from thermal mass in EXTERIOR walls. This is especially true for the sunny Southwest areas of Arizona, New Mexico and Colorado.

    According to an article written by Jeffrey E. Christian and Jan Kosny titled “Wall R-Values that Tell It Like It Is,” wall systems with significant thermal mass have the potential, depending on climate, to reduce annual heating and cooling energy requirements below those required by standard wood frame construction with similar steady-state R-value.
    moladi=0.54 W/m.K Glass=0.858 W/m.K

  • The comparison values I took were directly from the Moladi site, and, unless they’re factually incorrect, can be interpolated for a 150-mm wall. My comparison was approximate; I’m sorry if I upset you, but from a non-sunny southwest perspective (where a better wall would be R-20 or so, the value of the Moladi wall (your number of R-1.764) is about as good (not precisely, but about as good) as single pane glass R-0.91.

    Your quote about energy efficiency of building materials is very good, and talks about conditions where high mass walls can provide a positive benefit by delaying the infiltration of heat into a building. That is usually done with simple local materials such as adobe (the mud hut “Tim” referred to earlier, perhaps) and very thick walls. Do you have some performance data on how Moladi performs as a thermal mass wall (especially in comparison with a standard adobe wall) in delaying heat penetrating into a space?

  • The comparison values I took were directly from the Moladi site, and, unless they’re factually incorrect, can be interpolated for a 150-mm wall. My comparison was approximate; I’m sorry if I upset you, but from a non-sunny southwest perspective (where a better wall would be R-20 or so, the value of the Moladi wall (your number of R-1.764) is about as good (not precisely, but about as good) as single pane glass R-0.91.

    Your quote about energy efficiency of building materials is very good, and talks about conditions where high mass walls can provide a positive benefit by delaying the infiltration of heat into a building. That is usually done with simple local materials such as adobe (the mud hut “Tim” referred to earlier, perhaps) and very thick walls. Do you have some performance data on how Moladi performs as a thermal mass wall (especially in comparison with a standard adobe wall) in delaying heat penetrating into a space?

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