This hyper-healthy home remodel features an air-sealed envelope with a whole house ERV for continuous ventilation. We also used natural clay plasters on all walls and ceilings, and sustainable cork flooring. With 4 bedrooms, 3 bathrooms, an office, and a fully featured basement bar, as well as two basement living areas, this new space allows an older home to take on a new life.
Healthy Basement Finish
We built out an unfinished basement using natural materials and systems that promote healthy indoor air quality and energy efficiency. Clay and lime plasters, a tadelakt shower, beetle-kill pine trim, barn door office partition, LED lighting, polished concrete floors and new fireplace and boiler round out the space.
Read about our process in the Case Study blog, over at our Learn page.
Hemp-clay Mountain Timber Frame
This beautiful timber frame home at the edge of the mountains has a fun twist: a hemp-clay infill between the timbers of the exterior walls. We installed a 4″ layer of hemp to the inside of the walls, using a clay binder instead of lime to keep embodied energy down. We then plastered over those walls with custom clay plasters.
Case Study: Healthy Basement
We were approached by a family that was hoping to have their currently unfinished basement built out to include a bedroom, bathroom, storage, living area, and home office/meditation space. This extra space will accommodate a family with up-and-coming teenagers.
Our clients already had a design for the new space and emptied the basement of most things, minus a piano which would be too difficult to move upstairs – so we built the basement around it! The bathroom design was tweaked a little by us and our plumber to make it easy to drain everything and provide required clearances and access for pipe clean-outs.
We also made some modifications to the office/meditation space, which ended up with a very cool and versatile corner of sliding barn doors.
Indoor Air Quality
Basements in older homes are notorious for being moldy, damp, and having stale air. Because we build healthy homes, breaking from the stereotype was necessary. This featured heavily in our materials selection and building method criteria.
This house has luckily not had any problems with bulk moisture in the basement (i.e. flooding). In order to create an air and vapor barrier inside the permeable concrete foundation walls, we used a polyiso foam board (a case of least-bad when it comes to foams). We foil taped all joints and caulked along the bottom. This barrier was completed using spray foam along the rim joist at the top of the wall to seal that area from air infiltration, both from outside and from the garage. Its very important to keep car fumes out of living spaces!
We also installed a small, two unit, balanced ERV, with one unit in the bedroom and the other in the living area, on the other side of the basement. These ceramic-core fans alternate drawing air in and pushing it out. The ceramic is a heat sink, designed to keep the air temperature inside the same and prevent energy loss.
A nearly silent, motion activated bathroom fan keeps excess moisture down. Clay plaster also plays a big role in managing humidity and keeping air quality high.
The existing wood-burning fireplace was replaced with a new gas insert. This is cleaner burning, and no more having to sweep dusty ashes.
Finally, we used a paperless drywall in all areas of the basement. This choice is mold resistant, since it’s actually the paper that provides the food for the mold spores. The only place that’s different is the shower, which we fully waterproofed using Schluter Kerdi products. Here, the longevity and mold resistance in the wet environment of a shower is valuable for a long lasting home. It will prevent unnecessary water damage and further remodeling work later on.
Insulation and Sound
Because of the possibility of moisture, we used mineral wool batts within the 2×4 framed walls to insulate the basement further. This insulation is rot-resistant, since it’s basically just rock, turned into fibers. Up in the ceiling, we used cellulose in mesh bags to insulate the top of the outside walls, between each joist, before the drywall went in.
Extra insulation batts went into the interior walls surrounding the bathroom and bedroom. This will allow the family to use the space in multiple ways without disturbing each other if someone is sleeping or showering.
As part of a healthy indoor environment, all the surfaces are treated with VOC-free finishes. Custom clay plasters cover all the walls and ceilings except the bathroom. The bathroom has a lime plaster on the walls and ceilings, and a groutless tadelakt shower, which will never have issues with mildew in grout lines.
All trim is custom milled beetle kill pine. Doors are from used building supply stores, and are all solid alder wood. All of the wood in the home is treated with a VOC-free and plant based oil finish.
The floor is the original slab of the basement, polished and tinted and then sealed. This is easy to keep clean, and will also keep air quality higher than if we’d used carpet. Area rugs can be used in places of high traffic or where you might be walking barefoot.
A Healthy, Natural Basement
This family was great to work with and be around, as we worked in their home. We’re excited to see how the space lives up to their needs. We are glad that this basement offers them some extra living space, without having to worry about the problems of unhealthy indoor air quality.
Check out finished photos of the job over at the projects page.
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?
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! 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.
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 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.
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.
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.
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.
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.
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!
Horsetooth Strawbale Residence
This beautiful contemporary southwest style home, built by Black Timber Builders, features straw bale insulated walls, interior clay plasters, and tadelakt showers, sink, and kitchen backsplash by Living Craft.
Urban Strawbale Addition
This straw bale addition features very high performing straw bale insulation with lath and slip straw above the windows. Warm interior clay wall plasters and smooth tadelakt windowsills give it a modern but cozy feel. Lime-washed tongue-and-groove beetle killed pine ceilings on the vaulted ceiling open up the space. Read the case study about our process to learn more about how it all went together.
Understanding Materials: Clay
We applied a lot of lime plaster in 2016. But we’re just as amped about clay and clay plasters. Curious about why?
Clay is a fascinating material with many unique properties. Clay is made of very tiny particles of rock which have been broken down over millennia. Because of the small particle size of clay, it has a very large surface area. The surface area of the clay is important because it creates a lot of space for the clay to bond with minerals and hold water. The water holding, or hydrophilic property of clay means that water is drawn to clay and absorbed into its structure.
For building purposes, clay is used as a binder. Some clays are great for building, and others not so much. When you moisten clay, it becomes sticky and pliable. That’s why clay is so useful in making sculptures, pottery, tiles, and bricks. For our purposes, we use almost exclusively unfired clay instead of heating it to set its shape.
When you mix clay with sand and straw, everything gets held together by the sticky clay, but can still be molded into different shapes. Depending on the texture of the mix, it can be spread into a thin plaster, sculpted into a cob bench, or lightly coated onto straw to tamp into a wall cavity. As it dries and the water evaporates, the material hardens and holds its shape. The sand and straw ensure that the finished product is strong and that it won’t crack as it dries.
Benefits of Clay as a Building Material:
Clay is a time-tested building material, having been used in some of humanity’s earliest structures. When protected from direct rain and wicking moisture out of the ground, clay-sand-straw mixtures dry into a strong and durable material. Additives like wheat paste can be used in plasters to increase durability and hardness.
Clay can be found on-site or nearby almost anywhere that you are building, making it a low embodied energy material. Unlike many other modern building materials, if you have too much on hand, you don’t need to send the extra to a landfill because it is safe and simple to dispose of.
Again, unlike many building materials, clay is naturally free from volatile organic compounds (VOCs) and other unhealthy chemicals which can cause poor indoor air quality and adverse health effects. Clay’s ability to absorb and release humidity is also beneficial for improving the indoor air quality and comfort of a living space, particularly in high humidity areas like basements, kitchens, bathrooms, or laundry rooms.
Unfired clay can be easily rehydrated with water and then reworked. Most bricks and tiles are examples of fired clay, which has chemically changed from its original state due to the heating. But unfired clays can be moistened and will then bond again. This makes it easy to fix cracks, gouges, or other damages, or to replaster or add a layer of clay paint to walls to change color or texture.
Clay holds onto its temperature longer than the environment around it. This means that clay walls can hold the nighttime coolness in your home during the summer, even after the day begins to heat up. Conversely, a sunny earthen floor will continue to radiate heat into the room even after the sun has gone down in the winter.[divider]
Clay is easy to sculpt into curves or fun shapes to create a unique look. You can also tint clay to a variety of colors.
If this information has piqued your interest in clay or how we can incorporate clay building or clay finishes into your home remodel or backyard design, get in touch.
Case Study: A Straw-Cell Addition
Living Craft Design has been working on a straw bale addition to our friends’ home in Boulder. This family is already well-versed in the benefits of natural building, so their addition incorporates passive solar heating with large, south-facing windows and a concrete slab floor to hold all that sun-generated heat. The addition has the high insulation value (R-value) that is a great feature of straw bales as a building material. Additionally, the family chose to renovate the original rooms of their home and filled the walls and ceilings with densely-packed blown cellulose as part of that process. This home will be comfortable year-round and have low energy bills as well as a reduced need for running heating and cooling systems.
A Straw-Cell Design
We jumped into the project starting with straw bale installation. This house has what’s called a straw-cell wall, with an entire wall system behind the bales, complete with wood studs, recycled denim insulation, and exterior wood siding. The bales then are stacked on the inside of this wall, meaning that labor is reduced because you don’t have to cut or trim as many bales to fit within and around the walls’ wood frames. You also only need to apply plaster to the interior side of the bales.
A great thing about the insulation materials used in this home is that they are all carbon-based, and will now be locked away in the walls of this home for a very long time. This is actually a form of carbon sequestration, one technique to keep atmospheric carbon down and help mitigate climate change. This is in direct contrast to insulation materials like foam, fiberglass, and mineral wool, which consume a lot of energy to create. This means that the manufacture of those materials produces a lot of greenhouse gas emissions, upping their carbon footprint.
Healthy, Natural Plasters
Our next step was to start the plasters. A base coat of local red clay was applied to cover the bales first. At a fun summertime work party hosted by the family, we added a leveling coat which will provide the base and shape for the finish plasters. We introduced some folks to the techniques and tools for mixing and applying natural clay plasters and played in the mud with good friends. We also started to build out the windowsills into their final shape using a lime and clay mixture with lots of straw for strength.
The final wall finish was customized to get the exact color and texture that our clients wanted, and this last, thin layer of clay-based plaster went on like a dream. Thanks to additions like wheat paste, it dries into a hard and durable finish that will last for years, and also be easily reparable in case of accidental damages.
During the wall finish process, we were preparing for and creating the tadelakt windowsills that will become perfect benches for sitting on and reading in the natural light. This Moroccan finish plaster is created from lime, which is why the base coat for the sills incorporated lime with the clay. This results in a tight bond between the materials. The smooth layers of lime were applied, soaped, and burnished using stones to create a shiny finish. The sills were then waxed as the final step to create a long-lasting surface that can withstand some use.
The End Result: A Beyond Green Building
We’re departing this project with lots of hope for the future which will unfold in this family’s happy, healthy, non-toxic, and environmentally friendly home. Not only will it be a beautiful space to raise a family, but also a good model for other front range homeowners looking to sustainably add some space and renew their original home.