Fiber cement ICFs were developed in Europe after World War II. This type of ICF consists of ground up post-consumer wood waste, portland cement and a non-compressible rot-proof insulation material such as mineral wool. This is a picture of a fiber cement ICF block:

durisol-ICF

Durisol is one brand of cement-fiber block, pictured above. It’s a natural product that’s easy to work with. Durisol blocks are also hygroscopic, meaning they absorb excess moisture and release it slowly, providing a more even moisture content in the air. But the best part is that the blocks bias the concrete to the inside of the building. That’s important, because it allows the building to take advantage of the large thermal mass of the concrete.

Most ICFs have the concrete in the middle. They make a great structure, but the polystyrene shell then releases as much stored energy to the outside of the structure as to the inside. That creates a good buffer against interior temperature swings, but it doesn’t capture the inherent energy of the structure.

By biasing the concrete to the inside, Durisol blocks store more of the energy used to heat the house. When paired with south-facing, low-energy windows, the house is heated by the sun during the day, and the excess energy is stored in the concrete blocks, extending the solar effect by many hours. This can be an effective technique for building a passive house.

Meadowlark Builders has developed a special technique to maximize the performance of Durisol Blocks. By wrapping the home with polyisocyanurate board insulation, we provide a thermal break from the outside elements. Then we install siding with a venting system called a Rain Screen.

This method creates a very tight exterior wall with an insulation value of R-34; it biases the concrete to the inside, and provides a great buffer for temperature and moisture content of the interior air. Even if the power goes out, the sun alone can keep the home reasonably comfortable in winter and naturally cool in summer. A drainage plane behind the siding and roof also helps cool the building.

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