The Romans figured it out a long time ago, but it took a company in Iowa to
revolutionize this classic construction material.
For most people in our part of New England, the term "concrete house" conjures dank Colonial basements, small cinderblock homes or apartment complexes. Wood has always been the favored family home construction material here, mostly because we have access to lots of it, but also because of our long woodworking heritage. Since the 1600's, shipbuilders, carpenters and cabinetmakers from England and Europe thrived in this new land of virgin forest, and some of the grander homes built over the centuries are still around.
Travel back some 8,500 years, to the treeless terrain of what is now Syria and Jordan. The ancient Nabataeans (Bedouins) were using another material to build with — a waterproof concrete with which they lined underground water cisterns and mortared rough stone buildings. The Greeks elevated the process and the recipes for cement and concrete, and the Romans perfected them in roads, aqueducts, bridges, huts, houses and monumental buildings like the 1,890-year-old Pantheon, which is crowned with what is still the world's largest unsupported concrete dome. Concrete in various forms was also employed by the Chinese and Egyptians from about 3,000 BC.
The Pantheon in Rome
Concrete was born in places that have natural resources of Lime (calcium oxide,) Limestone, sand and rock. A versatile material, it reached its modern form in the mid 1800's with the development of Portland Cement in England. Cement is the glue that holds concrete — a variable recipe of stone, sand, minerals — together. Portland's main ingredient is hydraulic calcium oxide or Lime, which has the unique ability to harden when exposed to water and create a waterproof product. Continuous experimentation with the processes and mixes over the decades gave us concrete as we know it today — the most versatile, widely used construction material on the planet.
Modern concrete has been called "catnip for architects" because there's hardly a limit to the shapes and forms it can take. It's fun to design with. It's also immensely strong, does not warp, shrink or expand, is impervious to water, rot, insects and fire, and properly engineered can last for thousands of years. Yet there is one huge benefit to concrete that sometimes gets overlooked, even by architects and builders — its thermal mass.
Thermal mass is essentially the ability of a material to absorb and store heat energy. Dense materials like concrete have a higher thermal mass than less dense ones like wood. Concrete can slowly warm in the sun and radiate that stored heat after the sun's gone. This is part of the essence of Passive House design, and getting these thermodynamics to work in harmony with a home heating and cooling system is a major part of the realsmarthouse project. It is also where a company named Thermomass™ comes in.
Thermomass wall in progress by Purinton Builders
Thermomass is a closed cell insulation system placed between two layers of concrete, connected by structurally designed composite fiber connectors that do not create heat-losing thermal bridges between the concrete layers. The system utilizes the thermal mass of concrete: inside heating and cooling is absorbed into the inner layer of concrete, kept from escaping by the closed cell insulation and returned to the inside of the structure. Outside heat and cold are kept out the same way; once the heat or cold reaches the closed cell insulation it is blocked from entering the structure. The closed cell insulation for realsmarthouse #1 is extruded polystyrene foam, or XPS, that also has an extremely high resistance to vapor transmission, which is good because moist air is harder to heat and cool. So, with a Thermomass structure, the bottom line is what's inside stays inside and what's outside stays outside. Structures built utilizing Thermomass Systems are extremely energy efficient.
CM John O'Keefe reviews Thermomass plans with Dennis Purinton
Thermomass was founded in 1980 by Robert T. Long in Cedar Rapids, Iowa. Widely employed in large scale commercial and industrial construction, Thermomass insulation systems are also an ideal solution for the residential construction market. In fact, one contractor in Connecticut, Dennis Purinton, saw the benefits of Thermomass in 2002 and realized that the product and the process had a good deal to offer home builders. Fourteen years later, Purinton Builders is one of five Connecticut Thermomass contractors, and through sister company New England Concrete Supply delivers Thermomass components throughout the region.
Our first interview with Dennis back in July was an educational experience, not to mention a long one. Dennis walked us through an impressive portfolio of projects and detailed reviews of the Thermomass process and system, asking all the right questions about realsmarthouse, and even improving the wall design plans on the spot. While I tried to trip him up with questions like "Who built the first concrete house in America?" (Thomas Edison,) Dennis was always a step ahead. Wrapping up the meeting outside with plans and drawing pads on the hood of his truck, I learned he was also president of the national Concrete Foundations Association in Iowa, a big supporter of Habitat for Humanity, and ran both businesses with his wife Gayl and son Mike. Plus he loved his job.
That became apparent when he and Mike showed up at the site and got to work. Peter O'Keefe had just finished the site prep and dug out for the footings when they started, and in the space of five days the footings and frost walls were done and ready for stone and drains. That would have been fast for a crew of four, but Dennis and Mike did it alone with tightly coordinated six truck deliveries from Tilcon Connecticut. Now entering the third week of October, the race is on to get the walls up and roof in. As they say on Game of Thrones, winter is coming... but with Thermomass walls, we'll be ready for it.
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Good reads: The Rise of the Hybrid Home | What's a Real Smart House? | Location: Daylight | Process: Design | Virtual Reality, Wabi-Sabi