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It’s Not Rocket Science #1: Thermal Mass

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This is part of the village of Kandovan, on the Iran side of the border with Azerbaijan. Dating from the 13th century, the original inhabitants allegedly escaped to these strange mountains of volcanic ash, to get away from invading Mongols – as one does. You can find more pictures of Kandovan here.


Local residents say that the homes are not only strong but also unusually energy efficient – the homes require minimal supplemental heat during the long cold season and remain cool in the summer.  [Thanks environmentalgraffiti.]  

Something very similar happened in Cappadocia, in Anatolia in what is now Turkey. There are several towns like this one, Goreme. Their main purpose, allegedly, was to provide a place where the (very) early Christians could be secure against Romans out to get them. It goes back that far, apparently – although, to me, carving houses out of rock doesn’t convey any sense of urgency as far as finding safe refuge goes. I doubt those insecure Cappadocians gave much thought to the benefits of thermal mass, but I suppose the less time spent gathering firewood when the hills are alive with Romans, the better.


No account of the history of thermal mass would be complete without a mention of The Pyramids. The temperature of what little inside there is, is a cool 68°F (20°C) and does not change – ever. This is interesting  but not very useful. Of more practical use to people actually alive, is the town of Coober Pedy in South Australia. Opals are mined here.


Why people choose to carve their dwellings instead of construct them above ground seems to attract myth and speculation whatever the century.

Supposedly, many soldiers returning from the First World War moved onto the opal fields and easily adapted to living in the dug-outs they had made looking for opal. They found the temperature in their dug-outs was consistently in the low 20s; cooler than outside in hot weather and warmer than outside in the cold weather. (Thanks travellingaustralia.)

As you might expect, these houses aren’t much to look at on the outside but their construction cost is comparable to that of a ‘surface house’. Running costs are, of course, much less. Most countries have had some form of semi underground or cave house. Here’s some in Germany.

Rotswoningen in Geulhem, gemeente Valkenburg aan de Geul
Foto door Cicero, 23 april 2005

Here’s two views of a nice one in Tunisia. Some people may recognise it as the Tatoonie home of Luke Skywalker who was a character in a movie called Star Wars.

Bernard Gagnon
Bernard Gagnon

The cave dwelling is now the hotel Hotel Sidi Driss and you can stay there for just $12 a night. Nearby is the Dune Sea where R2-D2 and C-3PO crashed in Episode IV.


Traditional Berber pit-houses show a perfect solution to the difficult problem of adapting the zone’s extremely warm climate – the best defence against summer heat.  According to the historians, the Matmata Berbers built their underground homes to escape the notice of their enemies and to protect themselves from Arab incursions. Underground houses were also very practical from construction point of view. It was easier to dig into the mountains’ soft cohesive sandstone rather then use it as a building material.

The pits are circular and around 30 feet (9 metres) in both depth and diameter. An open air entrance starts some distance away to allow gentle slope through the side of the hill. Above the entrance you may find painted blue symbols of fish, star and a hand of Fatima which may protect inhabitants from bad luck. The fish is a good luck charm and the hand and five fingers represent the five pillars of Islam. Houses have an open air courtyard (haush) which is surrounded by the 20 feet long rooms. In summer, the temperature inside the house can be around 30 degrees cooler than in the midday heat above the ground level. [Thanks for that geographicaladventures – the Star Wars stuff was interesting, but it was the temperature thing I was interested in.] 

Sooner or later, Architecture was going to come along and mess with what is basically a nice idea. The problem of course, with building inside a mountain or underground is that you need to own a mountain or some ground to go under. Building in mountains or underground will never be mainstream. Ever. Most people don’t own land, let along mountains. dezeen_Wadi-Rum-by-Oppenheim-Architecture-16

Florida-based practice Oppenheim Architecture + Design have released these images of their proposals for 47 desert lodges at a resort in Wadi Rum, Jordan. [Thank you Dezeen, thank you Oppenheim Architecture + Design.]

If you think that’s scary …

wadi rum

… it won in WAF’s Future Commercial and Future Experimental categories. Thinking about it, where would an architectural competition be without those categories eh? There was and still is no green or sustainable category btw. If there had been, then Oppenheimer A+D would surely have won that as well because of this compelling justification you can see on their website.


If I was any of those critters, I’d be very worried about their Construction Waste Management Plan. Anyway. The climate in Wadi Rum, Jordan isn’t really that extreme – I think it looks rather pleasant. I suppose a bit of fancy glass would stop any thermal advantage from being totally wasted.


What we are seeing here is an architectural statement of course, the unnecessary proof that anything can be used to justify anything. The most recent example of architecture not driven by thermal mass is Villa Vals – you know the one, by SeARCH [!].

1260367826-villa-vals-search-7923The planners were pleased that the proposal did not appear ‘residential’ or impose on the adjacent baths building. The scheme was not perceived as a typical structure but rather an example of pragmatic unobtrusive development in a sensitive location. [Thanks ArchDaily.]1260367236-section-01-1000x707The villa is thermally insulated and features ground source heat pump, radiant floors, heat exchanger and uses only hydroelectric power generated by the nearby reservoir. [From the architects’ website.]

Once again, thermal mass is not mentioned. The only reason this house is underground is so that people in Zumthor’s famous baths nearby don’t have to look at it – as you can see from the following two images. The house lies between the baths and the building you can see in the background in the second photograph.


The desert people seem to get it right. Thermal mass works best when there are large day-night temperature variations.

The wall predominantly acts to retard heat transfer from the exterior to the interior during the day. The high volumetric heat capacity and thickness prevents thermal energy from reaching the inner surface. When temperatures fall at night, the walls re-radiate the thermal energy back into the night sky. In this application it is important for such walls to be massive to prevent heat transfer into the interior. [Thanks W.]

Skyscrapers, City of Shibam,Yemen

Plus, you don’t need to mess with your mountains. In the thousand-year old city of Shibham in Yemen, the walls are mud brick and thick. Many of them are shaded by other walls. The narrow streets channel what breeze there is and, importantly, helps dissipate heat stored in the walls. The uneven rooftops disturb the smooth flow of that breeze, extracting maximum value from it. I’m not saying that the old ways were better but only that people did extract quite a lot of performance from what they had, and with only observation and acquired experience to go on. Today we pay consultants.

A high-density artificial city such as Shibam with its various passive (read, cheap) ways of doing things is always going to be a winning prototype for modern commercial development so it’s no surprise to find these lessons applied in Transsolar’s conceptual guidelines for Masdar.