Case Study: A Straw-Cell Addition

straw wallsLiving 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.

Low Carbon

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

Applying a base layer of clay plaster at the work party.
Applying a base layer of clay plaster at the work party.

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.

Ben talks building with some volunteers while others work on shaping the windowsills.
Ben talks building with some volunteers while others work on shaping the windowsills.
The finish plaster drying around the laundry room window.
The finish plaster drying around the laundry room window.

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 burnished and waxed tadelakt windowsills have an amazing shine and reflection, as well as feeling silky smooth.
The burnished and waxed tadelakt windowsills have an amazing shine and reflection, as well as feeling silky smooth.

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.

finished window and wall plaster

Controlling Humidity in Your Home

We live in an incredibly dry climate along the Colorado Front Range.  The lack of humidity has both positive and negative benefits for the comfort of your home throughout the year. One advantage to our dry climate is that homeowners need to worry much less about rotting framing members and mold growth. The dry heat is also much more comfortable during the summer than a humid, wet heat that folks experience in the U.S southeast.

During the winter though, maintaining an appropriate level of humidity in interior spaces will help your home’s heating system work more efficently and create more warming, comfortable spaces. Since you typically keep the windows and doors to your home closed throughout the winter though too much humidity is a common occurrence. Humidity is added to our indoor spaces though quite a few activities including humans exhaling, cooking, and showering to name a few. Too much humidity can cause condensation to form on your windows, particularly if you have single pane windows. Conventional, building practices will lead you to use expensive, high maintenance, energy-intensive humidifier / dehumidifier systems.

A better, natural alternative exists.

Earthen plasters (clay plasters) can help balance the levels of humidity in your home very efficiently with little to no maintenance. Clay is hydrophilic meaning that it is attracted to water and naturally wants to dissolve in water. As humidity levels build up in your home, earthen plasters on your home’s walls will naturally absorb this moisture and then release the vapor overtime as the humidity levels in your home begin to drop. A very simple, hands-off way to let nature take care of a problem for us. But it wouldn’t be a great, ecological alternative if earthen plasters didn’t also have other benefits. Besides offering stunningly gorgeous finishes, clay is completely non-toxic and VOC free meaning that your walls will not pollute your indoor air quality. Earthen plasters are fire-resistant, produce very little to no waste from installation, resist grime and dirt, won’t fade over time, eliminate the need to repaint, extremely easy to repair, and have a lower carbon footprint than any other interior finish.

Check out the demonstration video below from American Clay, a New Mexico based earthen plaster manufacturer, for a helpful visual of how earthen plasters and humidity interact. You can also download a handout from American Clay that explains these principles as well. To read more in depth about earthen plasters and their benefits, visit American Clay on the web.

With trained and certified applicators, Living Craft can offer professional, custom installations of earthen plasters that are guaranteed to help create a more temperate indoor space and captivate you for years to come. Contact us today for more information about earthen plasters in your home.

Thumbnail photo by Jenny Downing under CC License.

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