How to Build in the Face of Climate Change

Currently the conventional construction industry contributes heavily to climate change. That cannot be debated. What if it could be changed?

Welcome to the modern world of increasing carbon emissions.

No matter the exact numbers, we know that creating buildings from new materials that have been manufactured and then shipped long distances, using machinery that consumes fuel and electricity, and assembled by workers who travel to the site daily in gas burning vehicles cannot be the greatest thing for the planet right now. We are struggling with the real effects of climate change in the present day, while also hearing every day about the potential futures we and our children will face.

How can building actually help?

We are part of a small but growing class of builders who believe we can offer some solutions to the big problems of carbon emissions associated with construction. Some ways this can be done:

Use Local Materials

If you don’t have to ship pine boards from New Zealand, but can instead use wood harvested sustainably from the same region that you are building in, this will reduce the embodied energy of that material. Unless you live in New Zealand, and then go for it with your pine. If you live somewhere where forests aren’t abundant, then you could look into other options like straw bale, masonry, or stone.

Their local abundance is part of why we love to use natural plasters. Sand, clay, and lime are harvested and processed fairly locally, not shipped from across the sea. These materials can be used for floors, walls, and more.

Use Materials with Lower Embodied Energy

If you can choose build a home out of cement blocks or adobe blocks, you can drastically reduce your building’s carbon footprint by choosing the adobe. Cement is one of the biggest greenhouse gas emitters, but adobe blocks can provide as much structural support, increased thermal mass (means more comfortable home in the face of extreme temperature swings), and a much lower embodied energy.

Similarly to how single use to-go containers made of styrofoam can’t ever be considered “green,” a home insulated with lots of foam is also not very green, because of the amount of energy it requires to manufacture that foam. Materials like straw, hemp, and cellulose can perform just as well, at a lower embodied energy cost. There are many more examples of this, so feel free to ask us about low energy materials when designing your dream home!

Use Materials that Sequester Carbon

Straw is made of carbon, and when a home is insulated with carbon-rich materials like that, you’re locking that carbon out of the atmosphere for the life of the building, How cool is that?

In contrast, a fiberglass batt or mineral wool board (or foam of any kind) takes a ton of energy to create and doesn’t sequester carbon at all. Bummer.

Other materials that sequester carbon: wood studs, hemp, cross laminated timber, and fiber boards (some made from hemp are coming onto the market soon).

Practice Efficient Home Design

Paying attention to your climate and site conditions and using principles of passive solar design will keep your home comfortable throughout the seasons while reducing your energy bills. It also lowers your carbon emissions.

Another part of designing a wall system is preventing air and water leaks. A tightly air-sealed and well-insulated home will last longer, reduce issues of mold or rot, and be more energy efficient for both heating and cooling.

Start today

It’s a good start to begin thinking about some of the factors listed above when designing and building a home. We can’t change the industry overnight, but the broader acceptance of low carbon building methods today could go a long way.

The Hemp Clay Experience

We’re working in a home where we used a hemp and clay mixture between timbers to add insulation and thermal mass. Why did we choose this, and how is it different from the hemp-lime or hempcrete building processes?

Typical Hempcrete

Hempcrete, or hemp-lime, as you may know, is a popular form of wall infill that’s a mixture of hemp hurd, hydraulic lime, and water. As it cures, the lime in hempcrete chemically changes back into the same composition as limestone, making it rock solid. Frank has taught at a few hempcrete workshops around Colorado with John Patterson of Tiny Hemp Houses.

hemp building workshop
At a hempcrete workshop Frank co-taught at in Colorado.

The Good:

Hemp! It’s great. It grows fast, and needs less chemicals while growing: all reasons it may be more ecological than other building materials. Hemp is also better for soils than most other plants, with its deep roots that aerate soil. Additionally, the hemp stalk is composed of about 50% carbon by dry weight. This means that the carbon sequestered from the atmosphere during photosynthesis can be locked into our building like a carbon sink, not being released until the building is demolished much further down the line. This enables us the possibility to build a “carbon negative” wall system. If you’d like to learn more about carbon sequestering and building for climate change, we will be posting a blog soon.

The Not-So-Good:

Lime, while a natural and healthy building material, requires a lot of energy input to be created. Also, we import a lot of the natural hydraulic limes from overseas, increasing the embodied energy of the material. Alternately, a mix with cement is used, which also has very high embodied energy and accounts for an absurd amount of greenhouse gas emissions. There are other additives that can be mixed with lime to make it hydraulic, such as different types of pozzolans and geopolymers. These have their own benefits and drawbacks, but it comes down to manufacturing processes, local availability, and toxicity.

What about Hemp-Clay?

Colorado is blessed with beautiful and strong clay, an alternative binder to lime or cement. The best part of this is that the energy required to dig up and screen local clay is minuscule compared to burning lime.

We made a test brick with hemp hurd and clay slip, and the result was strong and lightweight – a perfect combination of insulation and thermal mass (especially once clay plaster is added).

The Installation

The hemp clay installation process went very similarly to hemp-lime. Forms were packed with wet material and then moved up. It goes pretty quickly if you can make your mix dry enough, but still sticky and workable. That way, forms are moved up and the packed in hemp-clay sticks in place without slumping.

hemp building process
Forms and the tamped hemp-clay mixture.

Drying

Since clay does not set chemically, like lime or cement, it has to dry naturally, with time. With several fans and dehumidifiers placed around the home, it still took a while to fully dry. We used a moisture meter to check deep within the walls, and later patched those spots where we had to put the probe in.

hemp wall drying
Hemp wall drying in the basement. Some forms had to stay up a little longer for extra reinforcement of thinner areas.

This step is very important because if you seal the hemp up with plasters before it’s dry, although it can still breathe through the plasters, there is a greater chance that some moisture will get stuck deep in the wall. Over time, this could lead to mold.

Another thing to note is the clay tends to shrink as it dries. This led to some cracking and pulling away from timbers. We took an extra half day to come back and fill those cracks in to prevent thermal bridges and loss of insulation in those places.

hemp clay dried
The dried hemp-clay infill shrunk and pulled away slightly from the timbers. Nothing plaster can’t cover.

Plaster Prep and Plastering

This step is again just about the same as with hemp-lime or hempcrete. We had a few places where the mix was too dry or didn’t have enough clay, as well as fragile corners around windows where we used an expanded metal lath to shore up the hemp clay. Landscape staples were used to attach the lath to the hemp, where needed.

We used clay plaster and our sprayer to get a base coat up first. The texture is perfect for plaster to stick to. Although clay plaster is the safest bet for a strong bond, a lime plaster or lime stabilized clay mix would also key in well to the rough surface.

hemp clay wall
Before
hemp plastered wall timber frame
After

We’re pretty happy with the results and process. It’s not too dissimilar to a woodchip-clay infill wall. The fact that it’s a low embodied energy and carbon sequestering solution is exciting, but the amount of time it takes to dry is a challenge. However, working in the summer could speed that up easily. We would also consider adding a small amount of cement or lime to the mix in order to create that chemical set and allow us to fill higher and faster.

We used a mortar mixer for mixing, which only allows a certain amount of minimum moisture. If you wanted the mix dryer, a horizontal drum mixer would be a better option.

Unsurprisingly, we’re not the first to try this. Check out Chris Magwood and the Endeavour Centre Blog below for their experience.  Scroll to the bottom if you just want to read the hemp-clay part. I think that the hemp-clay block shows the most promise. Because they are small, that minimizes the risks of cracking and pulling away that can happen during the drying of a large wall.

Hempcrete developments

Thanks for reading, and let us know your latest hemp building experience, or if you are interested in trying it out for yourself, or in your home, backyard studio, or shed!