Site selection is crucial for thermal efficiency, structural integrity, and aesthetic appeal when building an adobe house.
Getting these factors right ensures the construction of a house that meets the International Building Code standards for an adobe house. Therefore, knowing how to choose the right site for an adobe house should be a priority.
Although adobe is a sustainable building material, without proper maintenance, it’s susceptible to destruction by the elements. This is because it’s made from unfired earthen bricks, usually held together with mud or a mixture of mud and straw.
Therefore, the wrong site for your adobe house can shorten the life of the structure.
In this article, I’ll discuss the top tips on choosing the right site for an adobe house. From solar orientation and drainage to wind protection, this guide will help ensure your adobe house survives the test of time.
Let’s get started!
“Choosing a site that satisfies most of the prerequisites means almost half of the work is done,” is an age-old saying that demonstrates how important site selection is.
The following are the benefits of choosing the right site for an adobe house:
According to the U.S. Department of the Interior National Park Service Cultural Resources, deterioration due to moisture is the most common form of damage caused to adobe buildings. How is this so?
Well, it stems from the nature of the unfired adobe bricks.
Firing bricks at about 1,000℃ (1,832℉) makes them stronger and more waterproof. Moreover, firing plays an important role in preventing salt crystallization in the walls and ceilings.
Unlike conventional bricks, adobe bricks are usually unfired, making them much more susceptible to moisture damage.
When exposed to moisture, adobe bricks can start eroding, crumbling, and weakening. The weakening is because moisture trapped within the bricks reduces their tensile and compressive strength and weakens the mud mortar.
Therefore, choosing the right site helps to prevent moisture buildup within the adobe bricks and increases the house’s longevity.
Temperature variations due to seasonal changes like summer and winter can make the indoor environment uncomfortable. However, clever site selection can help mitigate this menace based on the orientation of the house towards the sun.
Adobe bricks have high thermal mass, thanks to their thickness.
The wall thickness of around 300 mm (11.81 inches) created by adobe bricks increases the house’s thermal mass.
Thermal mass refers to the ability of a material to absorb and store heat due to rising temperatures and releases it gradually when temperatures start dropping. Thus, the higher the thermal mass, the better for evening out large diurnal variations in temperature.
Coupled with its high specific heat capacity of 1,260 J/kg K, adobe is excellent at absorbing the sun’s heat to keep the house cool in the heat of the summer day and warmer when the temperature drops at night.
According to the University of Florida, some consequences of wind on houses include breaking the load path and creating holes in the building’s envelope due to the erosion of the walls.
These consequences are more pronounced in adobe houses because the bricks are made from unfired earth.
It’s easy for wind to erode unfired earthen bricks because of the poor bonding between their aggregates.
Firing joins the alkali, silica, and alumina in the clay with oxides in the iron through a chemical union that creates a dense and durable mass resistant to wind erosion.
That said, the right site for an adobe house will protect against wind damage to ensure longevity.
Another way to guard against this type of erosion is to use Portland cement as a stabilizer when making adobe bricks.
The quality of the soil from which adobe bricks are made is essential. The soil must have the right clay, sand, and silt proportions for the best results.
Because the soil for adobe bricks commonly comes from the construction site itself, having the right soil quality for your adobe bricks starts from good site selection, unless you import the soil from elsewhere.
Since determining the right soil composition can be hard, it’s advisable to consult a local soil expert.
You can use soil composition tests like the mason jar test to ascertain the soil composition before choosing the site.
Poor-quality soil with inappropriate sand, clay, and silt proportions will lead to issues like:
- Cracking of the adobe bricks.
- Water seepage through the walls and ceilings.
- Low durability of the bricks.
Now that you know the importance of selecting the right site for an adobe house, let’s look at the top tips for choosing one.
How to Assess the Soil and Water Drainage on a Potential Site
Soil quality and water drainage are essential considerations for the right adobe house site. Assessing these site characteristics will help you make the right decision.
Let’s discuss how to assess each component below:
Soil composition varies from place to place. As such, it’s vital to assess your site soil to determine its composition to see if it meets the requirements for making adobe bricks.
Subsoil is required for adobe bricks because it contains little organic matter and microorganisms that can alter the brick’s structural integrity.
Moreover, subsoil is more likely to have the right amount of clay.
Loamy soils are the most preferred option. These soils should contain sand, clay, and silt in the proportions shown in the table below:
|Soil Textural Name||Percent Sand||Percent Clay||Percent Silt|
|Loamy sand||70 to 85||0 to 15||0 to 30|
|Sandy loam||50 to 70||15 to 20||0 to 30|
|Sandy clay loam||50 to 70||20 to 30||0 to 30|
Table 1: Soil compositions for good adobe bricks. Source: ABCs of Making Adobe Bricks
Therefore, if you don’t intend to import soil, you must choose a site with the right soil proportions, as shown in the above table.
A mason jar test comes in handy to determine these soil constituents when choosing a building site.
Tools and Materials
- Subsoil from your preferred site (dig until you see a darker to lighter soil color change).
- Clear, straight-edged jar.
- Permanent marker.
- Powdered dishwashing detergent.
- Mesh sieve.
- Sift the soil sample with a mesh sieve to remove rocks and debris.
- Pour the sieved soil into the jar (fill up to ⅓ of the jar).
- Fill the remaining jar space with clean water (leave a small space at the top).
- Add a tablespoon of the dishwashing detergent.
- Place the jar with its components on a level surface and time it for one minute.
- Mark the coarse sand layer at the bottom of the jar and leave the jar for about two hours.
- Mark the second layer that forms (this is silt). Leave the jar for another 48 hours.
- Mark the top of the final layer, which comprises clay soil.
- Measure and record the height of each layer using a ruler.
- Measure the total height of the three layers and record.
Once you have the measurements, determine the percentage of each soil component based on the calculations below:
- Sand percentage: (Height of sand/total height)✕100%.
- Silt percentage: (Height of silt/total height)✕100%.
- Clay percentage: (Height of clay/total height)✕100%.
A good rule of thumb is to aim for at most 30% clay, 70 to 85% sand, and 0 to 15% silt.
Efficient drainage is vital for protecting your adobe home against water accumulation.
The best site for an adobe house must be well-drained to prevent surface runoff.
Here’s how to assess the site for water drainage using a percolation soil test:
- Dig a hole at least 12 inches (305 mm) deep and 4 to 12 inches (102 to 305 mm) wide into the soil and fill it with water.
- Refill the hole with water and immediately measure its depth using a ruler.
- After 15 minutes, measure the drop in water depth in inches and multiply it by 4 to get hourly water drainage.
A site whose soil drains 1 to 3 inches (25 to 76 mm) per hour is well-drained and suitable for adobe houses. Otherwise, select a different site or consider amending the soil by adding more sand to enhance drainage.
Alternatively, consider building a rubble trench below the perimeter of your adobe house to facilitate drainage.
Due to adobe’s high thermal mass, you need a site that facilitates passive heating (in the winter) and passive cooling (in the summer) based on your climate zone. Such a site contributes towards a self-sustaining home since it increases a home’s energy efficiency.
The first step to choosing an appropriate adobe house site with adequate sunlight and wind protection is by considering your climate zone and ensure the site permits orienting the house based on the design and climate sample shown below:
A site with a north-facing aspect is ideal for adobe houses in temperate or cold locations in the southern hemishphere as it facilitates adequate sunlight exposure.
North-facing walls receive sufficient solar radiation that’s then absorbed by the adobe’s high thermal mass. The material releases the absorbed heat energy when temperatures drop, warming the house.
A site situated up to 25° east of north and 15° west of north is still viable for excellent passive sun access.
Remember that these recommendations are reversed for houses in the northern hemisphere because the sun’s path is to the south there. Also, if your site is in a hot location, you’ll want to protect your home from solar gain rather than seek to maximize it.
As for wind protection, consider a site sheltered from prevailing winds and with natural barriers like hills, trees, and vegetation.
Because they’re unfired, adobe bricks swell and shrink with the weather.
For instance, an extremely wet climate with excessive flooding can turn the bricks into mud.
Moreover, thawing and freezing can crumble adobe bricks. Therefore, adobe houses perform the best in dry and primarily warm climates.
Here’s how to consider the local climate for your adobe house:
- Humidity: Adobe bricks are suited for peak relative humidity of about 60%.
- Rainfall: The site should receive moderate rainfall throughout the year. Heavy rainfall and surface runoff can cause brick erosion.
- Snowfall: The area should receive moderate to no snowfall. Otherwise, consider a roof pitch of at least 40° if the climate experiences heavy snowfall. This will prevent the roof from collapsing due to accumulated snow.
Final Thoughts On How To Choose the Right Site for an Adobe House
Choosing the right site for an adobe house is essential to its longevity and performance. As daunting as the process seems, it’s not rocket science, and getting some advice from knowledgeable experts simplifies and speeds things up.
The above tips provide an excellent starting point when scouting the perfect site for your adobe house.
Remember to consider local building codes, zoning laws, and other regulations before settling on a site.
Before you leave, check out these awesome examples of using sustainable construction.