Thinking About Architecture by Larry Speck

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    Building with High Thermal Mass in a Hot, Humid Climate

    lawrencewspeck Jul 16 '12 9

    It is hot and humid as hell in most of Texas at the moment.  The current conditions call into question whether our normal ways of dealing with summer heat (using primarily insulation and air conditioning for cooling) is the only economical and ecological approach to these climate extremes.

    I became interested in using high thermal mass as an alternative while traveling in Turkey with my son Sloan eight years ago. He and I visited remote Roman ruins on the south coast and the interior, where the sites are in raw states and are not much frequented by tourists.  The summer climate in Turkey is very hot and humid, not unlike Texas. But it was strikingly comfortable inside the stone ruins with their high thermal mass.

    I noted the same effect working beautifully in the all-masonry city of Ping Yao in western China, where homes have thick, stone walls and massive, stone beds that kept us amazingly cool on hot summer nights.

    This is a classic heating and cooling technique in climates with high diurnal swing where the thermal mass dampens large fluctuations between hot days and cool nights.  We have used rammed-earth walls effectively in places like Santa Fe to achieve this advantage.

    But when we used thick concrete walls for blast protection in a government office building in Houston, we also found that high mass could work to our thermal advantage.  That building was pleasantly cool under construction before the air conditioning was turned on, and it made me wonder—why aren’t we doing more of this in Texas? Why is high insulation and air conditioning the only method of cooling?

    Wiss, Janney, Elstner Associates, a renowned firm of building and forensic engineers, recently approached PageSoutherlandPage to design its one-story Austin office building, giving us a unique opportunity to thoroughly explore and analyze this question. WJE’s Austin office includes a bunch of the country’s best concrete experts.  When we proposed using high thermal mass concrete walls for their building, they saw an interesting test case. They used a WUFI model to demonstrate how temperature would move through the thick concrete walls at all hours of the day and all times of year.  They analyzed when the walls could produce thermal advantage as well as when dew point would be reached that might create condensation. In the end, the engineers convinced themselves and us it was worthwhile to proceed.

    This had to be a pretty inexpensive building—a small office for a small business. Our budget was equivalent to a stud wall building with brick or stone veneer. The structural loads on the walls were modest and, of course, greater thickness worked to our thermal advantage.  So we built unreinforced concrete walls—pure compression structures.  The absence of rebar along with the fact that all of the formwork was kept to simple rectangles meant labor costs became low enough to be affordable.  When we were pouring the walls, everyone said the finished pieces looked like Stonehenge.

    This project is very experimental, but we have the engineers’ analysis to tell us how the material will behave. Architecturally, the concrete has a beautiful look and feel, which we didn’t fuss up at all.  Though the air conditioning has not been activated and the temperature is approaching 100 degrees outside, the building interior is surprisingly cool.



      Jul 18, 12 3:34 pm

      This is a great idea. I enjoy hands on explorations of low-tech design solutions. Please post an update with more information about the project as it develops -- it would be great to know more about how these mass walls will read in the form and materials of the spaces.



      Ron AllenRon Allen
      Aug 14, 12 10:38 pm

      Would be nice to see results on other dense materials and configurations like the earth-filled 'earthship' tires, or Hemp, or even a mix of cellulose and concrete (like Pike-crete or similar)

      As beautiful and amazing as concrete is - it has a heck of a price tag when it comes to CO2.

      Sep 3, 15 11:51 pm


      I was wondering if you have any updates on how the material behaved long-term. I am currently planning to build a house out of aerated concrete blocks in Houston. I am originally from Germany, so building a house with a thick mass wall just seemed a lot more natural to me than stud. I am a littlebit concerned about the high outside humidity and the vapor pressure pointing inwards (in Germany it is usually the other way around). Did you install any kind of moisture barrier? Did you bave problems with the construction moisture? In this weather I could imagine the walls need a lot longer to dry. My other question is that in Germany we always install a moisture barrier on top of the foundation, to protect the walls and the inside living area from moisture coming from underneath. I understand that that is not a common practise here with the stud constructions. Though due to the poor drainage of the Houston clay soil, the underground is usually very wet, so I wonder why nobody seems to think that is a problem.

      I am very interested in how that concrete building performed. How thick were the walls? My father lives in a two hundred year old mediterranian house on the canary island build out of clay, mud and sandstone. The walls are over one meter thick and he still has not installed air conditioning because there is no need. 

      Here I could imagine it would be wise to install an AC with humidistad in those buildings to keep inside humidity comfortable and avoid mold problems. Between the high thermal mass and condensation, especially initially from construction moisture I would be concerned that the AC might not run enough otherwise.

      Well, this was a really long post, sorry for that and thank you for reading through it. Any advice will be highly appreciated. I have trouble finding people fond of mass walls around here.


      Inga Able

      Sep 6, 15 1:16 pm



      Why not use adobe?

      Sep 6, 15 4:01 pm


      I have thought about adobe, but as far as I know the bricks are not cured with fire, so in an area like Houston that has extremely high humidity levels over longer periods of time and is prone to flooding you run into the risk of it turning back into mud. You can build in wet climates with adobe, but it becomes a lot more tricky and in Houston you propably would not because of the flooding. If I lived somewhere more arid I would definately do adobe. 

      The other brick that I really like is Porotherm by Wienerberger. You get a high thermal mass, great insulation and it is all just nice natural clay. They even make them filled with Perlite for better insulation. And because they use thin bed mortar and the bricks themselves are dry you have very little construction moisture. I just have trouble finding a distributor in the U.S.

      Sep 8, 15 1:22 pm

      rammed earth!

      Sep 8, 15 2:34 pm

      Same problem. Too much water. Now I could build it elevated on a lot of concrete and build a wide overhang so there would be less erosion from rainwater and no flooding issues. The house would look like a giant mushroom. Not that I don't like mushrooms, but I wouldn't live in one. In Houston we have a lot of rain, and half the times it rains, it storms and the water comes down sideways. And if it doesn't rain the outside humidity is still very high. Everything I have read tells me rammed earth would erode here. Other than that I think it is great. Wish I lived in Austin. Or California. Houston isn't easy to build in due to the humidity. Everything molds away. We have a lot of days were you can hang up a wet shirt to dry outside, and it is still wet two days later, even if it didn't rain. My current back yard has been a swamp for the last two weeks where I sink in ancle deep with my rubber boots. Thats what happens if a lot of water comes down on solid clay soil with a bit of mud and grass on top of it. Zero drainage. 

      Oct 29, 15 1:05 am

      Hi Inga,

      concrete may be alright for thermal mass purpose, yet fired adobe brick is ace in regards of isothermal sorption and other properties. Although masonry work may be not cheap you would have an exterior / interior ( some people like facework ) finish which would last you a life time without maintenance.   Concrete would need formwork, and for most people an inside finish, maybe an clay render / Lehmputz. BUT brick would always outperform concrete. by the way you could use as foundation concrete pads and a ringbeam on top....this is the least intrusive foundation there is.....sach mal bescheid wie dein design sich weiter so macht.  Bjorn

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About this Blog

Although it may sound cliched, I live, eat and breathe architecture. I’m currently a principal in the architectural firm of PageSoutherlandPage and a professor, as well as the former dean, in the School of Architecture at the University of Texas at Austin. My teaching and my blog are aimed at educating people on the importance of great architecture in contemporary American culture.

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