Researching building material options has been an eye-opening process. We do not plan on ‘selecting’ a material as much as developing a portfolio of options for when we begin working with an architect. This of course applies to the other aspects of the house, such as utilities, safety, amenities etc.

As a point of clarity – I am defining ‘building materials’ as the material compromising the interior and exterior walls.

In this post I will discuss our current comparison criteria for building materials, associated costs, and functional attributes. This post does not discuss the foundation, roof, or reinforcing items (cross-beams etc.). We’ll look at the following topics for consideration:

Unit Based – Endurance – Feasibility – Efficiency – Design/Style – Affordability

Unit Based: The material is produced and sold in discreet and uniform increments, such as for example 40 cm x 20 cm x 20 cm blocks. This enables planners to estimate material requirements on a per square and cubic meter basis. This is important to us for cost control and predictability reasons. Using a material that is sold/made as a unit also allows us to purchase/make ‘spares’ for future construction and repairs.

Compressed earth blocks stabilized (CEB-S), adobe, cinder blocks, and to an extent Insulated Concrete Form (ICF) molds, meet this requirement. Rammed earth, poured concrete, and wood-based construction do not.

Endurance: The building material itself is capable retaining its structural and other attributes for 100 years. This endurance must derive from the innate qualities of the material along with normal internal and external treatments (such as render, lime plaster, etc.). This endurance must also include resistance to fire, insects, wind (tornados), ice, rain, and minor seismic disturbances. Resistance to mold and rot is another major requirement.

CEB-S, Cinder Blocks, and ICF meet almost all of these requirements. There are some articles stating the ICF foam is vulnerable to insects and must be treated during installation. I am not an engineer by any means, but from general reading it seems that bricks with a reinforcing web/net are better able to handle earthquakes than solid concrete. Wood, once again falls far short in this category. Adobe is able to endure, but only in specific climates. An adobe house would slowly dissolve in Oklahoma’s humidity, rain, and winter storms.

Feasibility: Does the product exist in our building area, and do local builders, engineers, and architects know how to work with it efficiently? I do not want my house to be the test-bed for a construction firm, unless they are paying for it, of course! Other aspects of feasibility include permitting and approval from the local government. Adobe and earth block homes are treated the same in most building codes, limiting height to 2-3 stories. Code requirements will play a big role if we decide to operate the home as a venue for weddings, parties, and fundraisers. Cost is also a part of feasibility, but I will discuss that separately.

Feasibility is the one category where wood reigns supreme. Every builder, designer, architect, engineer, and city code official know how to work with wood. CEB-S and adobe are not as prevalent outside of the Southwest, and Oklahoma is just on the edge of that knowledge and expertise reserve. ICF and cinder block are becoming more common, but from my research a lot of companies are hesitant to work outside of their normal material (wood) as they must completely redo their supply chains and work schedules, which in turn limits their economy of scale.

Efficiency: The ideal material delivers a 30% reduction in energy usage, while passively moderating the indoor moisture, temperature, and sound. We are planning on leveraging solar to further reduce energy costs and provide a measure of redundancy considering how often storms damage the power grid. The ideal material would provide sufficient thermal mass to buffer the temperature swings, work well with floor and ceramic heaters, and not trap moisture in rooms.

One of my big fears is creating a moisture-coffin that creates horrible humidity problems.

Regular wood construction is fairly inefficient and almost requires a forced air system to make the house livable. This is not that big of a deal if energy is cheap and constantly accessible. But, I predict that energy will increase in cost in the future, and that storms will continue to bring down power lines. Moisture control is more of a design issue with wood houses than a physical property issue. Mold remains a problem due to inadequate ventilation and placing bathrooms along interior walls with no windows.

Design/Style: Thick walls around 50 cm are an important design aspect for the house. This depth allows us to build very intricate nooks, built-in bookcases, and to create a really great transition effect among rooms, creating depth. Depth will give the house a layered quality, a sense of sturdiness, age, and durability that will add to its overall ‘spirit.’  Thicker walls also allow us to use conduits to route utilities, install flush speakers into rooms, and hide other functional elements that would otherwise detract from the overall design.

Any material can achieve this effect, however CEB-S, ICF, cinder blocks, and adobe offer functional benefits to depth, while thicker wood framed walls do not add much, outside of aesthetics.

Affordability: Cost and design drive each other which makes all of this somewhat frustrating. CEB-S, ICF, and cinder blocks all cost about 15-40% more than wood. This is due to materials cost, additional labor cost, and an increase in time required. Wood framed houses allow workers to traverse the house through unfinished walls and work on several levels at once. Brick and concrete do not allow that and force a more step-by-step construction process.

CEB-S costs can be partially mitigated by using the soil extracted from your building site – if it is the right type. I used homewyse.com  to calculate the rough per square foot cost of wood walls, which is $3 per square foot in Oklahoma. Each CEB-S cost $1.20, and 2.2 blocks are needed per square foot (using 17 x 35 x 10 cm blocks) plus labor. Various sources state CEB-S takes 30% less time to assemble and is easier to work with than bricks. My running estimate is $4-5 per square foot for CEB-S, $6-7 for ICF, and $7-8 for cinder block.

Final Notes on CEB-S

Based upon my research, my preferred material is the Compressed Earth Block – Stabilized. So, what are the downsides? CEB-S has a lot of thermal mass, but little insulation. This can be mitigated with passive solar design, heated floors, ceramic stoves, and gas heaters. An air gap can also be used, and if needed, this gap can be filled with an inorganic insulation. The risk of stuffing the gap is that it could absorb moisture and create corrosion or other water related issues between the walls. CEB-S walls will also be more expensive upfront, and if energy costs remain low, then the savings will not materialize. I am also unsure about the local building code and how tall I can build this riad. My last concern is the level of institutional knowledge in Oklahoma – are there builders and architects there who know how to work with CEB-S?

-Mike

The featured image for this post was taken from http://www.earthhomesnow.com/compressed-earth-block-homes.htm