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.

Design

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.

Finishes

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.

basement before
Before
basement after
After

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?

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!

What is “Building Science”?

We use the term building science a lot. For those who may have never heard the term, or fully explored it, here is a quick debrief.

Building Science

Taking into account experiences of architects, engineers, and builders, building science explores the way that a building responds over time to environmental factors and natural phenomena. Or, a detailed study of a building with the goal of increasing its life span, health, and/or performance, and applying those lessons to new buildings.

Big Topics

Indoor Air Quality/Indoor Environmental Quality

This covers things like sound/acoustics, lighting, indoor air pollutants and how to control them. Ever heard of “sick building syndrome”? In those cases, actually being inside a building will negatively affect a person’s health, whether from stale or toxic air, lack of good ventilation, noise levels, or a number of other factors.

Mechanical Systems

Air conditioning, heating, and ventilation are some of the important mechanical systems. Without proper systems, filtration, and flow, a building will not function well and keep its inhabitants comfortable. We prefer balanced ventilation, like an energy recovery ventilation system that is continuously alternating between bringing fresh air in and venting stale air out, while maintaining the temperature indoors to prevent energy loss.

ENCLOSURES and Air/Moisture Barriers

An enclosure is simply the surfaces of a building that separate indoors and outdoors. Walls, ceilings, windows, and soffits. Not surprisingly, better methods for keeping moisture out of building materials will prolong their life and reduce problems like mold and rot. So, things like air and vapor barriers are very important. They also increase the energy efficiency of buildings, and reduce operating costs from heating and cooling. However, its all connected. Since a home with a “tight envelope” or a continuous air or moisture barrier doesn’t allow air to flow through cracks, it will also need to be closely monitored and have a good, balanced ventilation system in place to circulate fresh air and reduce indoor air pollutants.

Building Sustainability

With the increasing awareness of the pressures that humans are placing on the global environment, we recognize the role that the construction industry needs to take on in reducing our impact. Big changes can be made with a choice of materials that have a low carbon footprint, or by building using carbon rich materials like wood, hemp, and straw that sequester the carbon out of the atmosphere. Things like passive solar design and an integrated landscape and water management plan also help to greatly reduce a building’s need for external energy inputs.

Modern Building Science, Traditional Materials

Hopefully it’s all coming together for you. At Living Craft, we are always trying to educate ourselves on the latest innovations in building science. We are doing the work of researching and picking out the best solutions which honor the traditions of building and respect the environment on all levels. If you have questions, we would love to hear them!

Understanding Materials: Clay

clay plaster

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:

Durable
adobe house
A traditional adobe home with proper roof and foundation detailing is a durable and affordable home in a warm climate, with a long and rich history.

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.
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Ecological
cob clay balls
Cob is just clay, sand, and straw and could be used in the yard if you have leftover material.

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.
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Healthy
clay plaster window
Clay finish plaster drying around the laundry room window.

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.
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Repairable
cob oven
A cob oven during a repair process, ready for the final plaster over a recently finished intermediate clay layer.

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.
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Thermal Mass
earth floor clay
An earthen floor being installed. The earth will absorb heat on sunny days and regulate the temperature of the home.

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]

Beautiful
clay plaster kitchen
Clay plaster in a kitchen adds some texture and shine to the walls.

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.
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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.

clay samples
Cheryl labeling clay plaster samples.

Reusing Concrete

Concrete is everywhere in the urban environment.  It is the building block of the 21st century and does not appear to be going anywhere anytime soon. As a natural builder, it is hard to be a fan of a material that has such an enormous level of embodied energy. That being said there is definitely a place in natural building for concrete, particularly in dense urban areas. It is hard to find a better material for foundations and as the saying goes all buildings need a good hat and good boots. When properly thought through and designed, the use of concrete can be minimized and go a long way in ensuring an earthen structure is here for a long time.

What is quite exciting about concrete for me though is being able to use it again and giving it a second life. You may have heard of recycled concrete referred to as urbanite. Urbanite often comes in 3-4″ slabs that are harvested from old driveways, sidewalks, or porches. You can use it for foundation work, retaining walls, patios, or even just “filler” in structures. There are quite a lot of options and a quick look around the internet will certainly get you inspired on the many possibilities of urbanite.

I’ve primarily used urbanite for foundations and retaining walls. In some cases, the client has wanted to disguise or hide the urbanite all together. That is fairly easy to achieve by using another material like cob or a veneer stone such as Colorado Red Flag Stone. By using the urbanite as essentially “structural fill” you save money and can feel good about using a material that would otherwise would be a waste product or destined for another high embodied energy processing facility.

Yet, there is certainly something beautiful about a well laid, dry-stacked urbanite retaining wall.

Hidden Urbanite Foundation
A foundation for a cob bench. Local granite stone was used for the front of the bench. Urbanite was used for the less visible backside of the bench.
Urbanite Foundation
Urbanite foundation that would later be hidden with cob and Colorado red flag stone.