Cob House Design: Tips for Maximizing Comfort and Efficiency

Two photographs of cob houses showing different designs. The left-hand photo shows the outside of a house with curved walls, a thatched roof, and stone foundations. The right-hand image shows an open-plan living area with sweeping curves and visible roof timbers. Across the bottom are the words "Cob House Design - Tips for Maximizing Comfort and Efficiency."

Images courtesy of Crazy Wisdom, Inc, and The Tiny Life.

Welcome to the world of cob house design, where beauty meets functionality.

For those who may not know, cob construction is a sustainable building technique that uses a mixture of clay, sand, silt, and straw. With these materials in mind, how can you design your cob house to maximize comfort and efficiency?

The comfort of any house comes down to thermal insulation, acoustics, moisture content, and indoor temperature. While cob can support most of these features, some require a few extra touches for optimum results. That’s why we’re here to guide you.

In the rest of this article, I’ll discuss design tips to make your cob house more comfortable and efficient. From insulation and ventilation to indoor temperatures and lighting, you’ll be living in absolute luxury before you know it. Let’s get started!

Insulate Your Cob House Walls

A photograph of a section of cob wall built in the laboratory comprises two layers: a stronger, denser layer for structural strength and a less dense layer with better thermal insulation. The section of wall sits on a pallet with wheels.
A section of cob wall was built in the laboratory comprising two layers: a stronger, denser layer for structural strength and a less dense layer with better thermal insulation. Image courtesy of BDAA.

Let’s get this out at the forefront – cob is not a good thermal insulator.

A material’s R-value plays an essential role in determining its insulation qualities.

R-value refers to a unit of thermal resistance; it measures the capacity of a material to resist heat flow. The higher the R-value, the better the insulation.

According to the Cob Code Appendix AU, cob has a low R-value of 0.22 per inch of thickness. To put this into perspective, a 24-inch (60.96-cm) thick cob wall will have an R-value of 5.28. This is relatively low, especially if you live in colder climates.

Cob’s low R-value means it has poor resistivity to heat flow and will lose heat faster when it becomes cold.

A house that loses heat much faster when it becomes cold is not comfortable to live in. Besides being cold, the home will not be energy-efficient as you must rely heavily on central heating or a similar system to maintain a comfortable temperature.

Designing your cob house walls to incorporate insulating materials enhances indoor comfort and energy efficiency.

An insulated cob wall will have a high R-value, making the house more comfortable and energy efficient.

Here are cob house design tips for effective insulation:

  • Use a dual wall system: As the name suggests, this approach entails installing double walls using a forming system. The cob wall should be on the interior, and another wall made from a high-insulation value fiber mix like straw bales, hempcrete, or straw-clay on the exterior part. Besides enhancing insulation, the dual wall system makes the wall wide enough for load-bearing purposes.
  • Sandwich insulation: You can sandwich an insulating material like fiberglass or sheep’s wool between two thin cob walls [preferably 11.5 inches (29.21 cm) thick each]. Once the insulation is sandwiched between the two cob walls, use rebar to tie the two sides together in the middle. This provides a high level of insulation and, in turn, more comfort and efficiency.
  • Create an interior stud frame siding: Have the cob wall built normally and then create a stud frame on the inside. Fill the frame cavities with insulation like fiberglass batts or sheep’s wool, and then use drywall or other suitable material to finish the look.
  • Install external cladding: This will provide an extra insulation layer for your cob wall. You can use a system incorporating fiberglass, foam board, or mineral wool as your cladding material.
  • Install windows with triple glazing: Replacing your single-glazed windows with triple-glazed ones helps keep the heat inside and reduce energy consumption.

Here is a demonstration video for cob wall insulation:

A screenshot of a video showing the different ways to improve the thermal insulation properties of cob walls. The image shows a CAD image taken from the software used to illustrate the different types of insulation.
The sandwich approach to cob insulation uses two layers of cob, one denser and stronger, the other lighter and better at keeping the heat in the building. Image courtesy of This Cob House on YouTube.

Incorporate Renewable Energy Sources

Renewable energy sources, like solar panels and wind turbines, increase your cob home’s efficiency by reducing your dependence on electricity.

Harnessing renewable energy reduces your electricity bill while lowering your carbon footprint.

Moreover, pairing these power sources with other energy-efficient systems, such as energy recovery ventilation and geothermal heat pumps, makes your home more sustainable.

These renewable energy sources must be part of your cob house design because they’ll likely be a permanent feature in your house.

Some design considerations for your renewable energy sources include:

  • Solar panel placement: Design the house to have solar panels erected in an unshaded area with maximum sun exposure. Besides placement, ensure the solar panels are mounted to the roof securely with appropriate bracing and support.
  • Wind turbine placement: Wind turbines must be located in an area exposed to unencumbered winds, away from trees, houses, or other obstructions. As such, you must select a site that meets these conditions.
  • Proper cob house orientation: North-south orientation increases winter solar exposure while reducing summer heat gain because the sun is lower in the sky. This design is ideal for maximizing passive solar gain.

Leverage Cob’s High Thermal Energy Storage Capacity

Thermal energy storage (TES) refers to the ability of a material to store and release heat energy based on temperature variations. In this case, the cob material gains and stores heat energy due to increasing temperature and then releases it gradually once the temperature drops.

Cob has high thermal energy storage capacity thanks to its high thermal mass.

Cob’s high thermal mass is responsible for its high heat capacity of 1205 Jkg−1K−1. Its high heat capacity allows the material to absorb and store heat during the day and release it at night when temperatures drop. This makes the indoor environment more even and comfortable throughout the day and night.

Moreover, it reduces energy consumption when using central heating.

Here are cob house design tips for leveraging cob’s high TES:

  • Solarize your cob house: Solarization ensures the house receives full sunlight throughout the day. Situate the house in such a way that the walls receive maximum sunlight.
  • Insulate the roof: Install a high-insulation roof to reduce heat transmission during extremely cold days.
  • Install thermal collectors: Thermal collectors are devices that absorb, store, and release energy. You can install or embed them on your cob walls.
  • Create south-facing windows: Maximize sunlight penetration into your house during the day with big south-facing windows. This ensures maximum solar gain and helps maintain a comfortable temperature indoors.

Regulate Indoor Humidity

A photograph of a cob wall with pieces of straw visible at the surface. Overlain is an icon of a water droplet with a percentage symbol and a thermometer to indicate humidity and temperature.
Cob walls can regulate humidity and temperature thanks to their ability to absorb heat and moisture from the air, releasing it later when conditions are drier and cooler.

Your home’s indoor humidity is crucial for your comfort and well-being.

Too much humidity and you’ll be sweating all day; too low, and your home will become dry, stuffy, and uncomfortable for living.

Excessive humidity is also a recipe for mold and fungus growth, which can cause allergies and other health issues.

Before proceeding, it’s necessary to make clear the impact of excessive moisture and humidity on earth-building materials like cob.

While water swells, weakening earthen building materials, water vapor in the form of humidity absorbs into the walls, leaving the structure intact.

Luckily, cob walls act as a natural indoor humidity regulator due to their porous nature. Therefore, when indoor air humidity gets high, the walls absorb the extra vapor, and vice versa.

However, since most cob walls are sealed with linseed oil or lime plasters for waterproofing, their ability to regulate indoor humidity is reduced. As such, here are design tips to help regulate indoor humidity:

  • Install vapor barriers: Vapor barriers block the passage of water vapor through your walls, reducing the chances of mold and fungus growth.
  • Ventilation and air exchange: The more air there is circulating through a house, the less likely it is to build up moisture. You can leverage cross ventilation by installing windows on opposite walls to maximize air exchange. Moreover, consider using exhaust fans in bathrooms and other moisture-prone areas.
  • Use dehumidifiers: Dehumidifiers help reduce indoor humidity levels by absorbing water vapor from the air. Place your dehumidifier where you can monitor it easily and keep a close eye on your home’s indoor relative humidity.

Incorporate Water Collection and Management

Although freshwater exists in rivers and lakes, it’s a limited resource that makes up only three percent of the earth’s water.

Therefore, designing your cob house with water collection and management in mind will increase its efficiency by reducing water wastage and preserving this precious resource.

You can collect and reuse rainwater by incorporating the right design elements, like rainwater catchment and greywater recycling systems.

Moreover, you can use solar energy to power pumps that draw stored rainwater for gardening and other outdoor activities.

Finally, consider installing drainage systems around your house’s perimeter to keep the area dry and prevent water building up in the wrong places.

Incorporate Sustainable Landscaping

Sustainable landscaping is an integral part of cob house design for many reasons. It not only enhances the overall aesthetic value of your home but also reduces water consumption, conserves energy, and prevents soil erosion.

To achieve sustainable landscaping in your cob home, select the right plants for your climate and consider incorporating native species.

Additionally, use mulching to conserve moisture and reduce weeds.

Install Energy-Efficient Appliances and Lighting

A cob wall with a light hanging down and a person's hand switching it on at the cord.
Using energy-efficient lighting is a good way to reduce your home’s energy usage.

Energy conservation should be a priority to make the house more efficient.

Your cob house design should make it possible to install energy-efficient devices like LED bulbs, refrigerators, air conditioners, and dehumidifiers.

The best way to ensure you buy energy-efficient appliances is by looking for an ENERGY STAR label. The label means the appliance is among the most energy-efficient options in the market.

Alternatively, you can opt for low-wattage appliances to reduce power consumption.

Finally, consider installing motion sensors in outdoor lighting and other areas to minimize light pollution and conserve energy.

Final Thoughts

Your cob house design should incorporate various elements to maximize efficiency and comfort.

The above tips will help you incorporate elements that maximize comfort and efficiency without compromising on style.

Overall, prioritize sustainability and efficiency by incorporating the right strategies and designs.

If you feel overwhelmed by the process, consider consulting an experienced architect or designer. These professionals are knowledgeable and experienced enough to guide you through.

Before leaving, check out this guide on how to use reclaimed wood as a building material and where to find it.

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