This 1,600 sq ft (interior), 2 bedroom, 1 bath home was completed in the spring of 2016 and features super-insulated straw bale walls, natural clay plasters, adobe mass accent walls, straw-clay partition walls, reclaimed wood, stained concrete floors, photovoltaics, hybrid heat pump water heater, efficient lighting, high fire-resistance, and an age-in-place layout.
The Fallgrens had dreamt of building a home here for over a decade. They envisioned an old adobe rancho from the turn of the last century that fit perfectly into the landscape but performed like a new, efficient building. When they met us (Rebecca and Mike of Simple Construct, a San Diego design/build construction company that specializes in straw bale building) they realized that straw bale building, with its high performance, thick walls, and “adobe” plaster, was a perfect match.
We worked closely with the Fallgrens to distill their vision for their home. We spent time refining their design, visiting other projects and even visiting local historic adobe homes together to capture ideas and details. As the general contractors for the construction and as hands-on builders of much of the home, we continued to work with closely as the home took shape.
Straw bale building is the most resource-efficient way to build a super-insulated home and results in superior indoor air quality and sound quality. Clay plasters use fewer resources than conventional plasters and are VOC free and nontoxic. By using natural, non-toxic, low and zero VOC products and finishes, fewer toxins were built into the building, contributing to better indoor air quality.
What makes this project exceptional is the priority placed on using lower tech, lower carbon, and lower cost systems and natural, non-toxic and low-embodied-energy materials.
Our philosophy is that simple is better than complicated, less is better than more, and that affordability matters. We also believe that sustainability counts at every step of the way, not just when the building is complete. Building smaller and more efficiently with materials that have a lower carbon footprint helps ensure that the building process, as well as the finished product, will be as low-impact as possible.
With good solar orientation for this climate, exceptional insulation and good air sealing details, this home performs well passively. Add to that a photovoltaic system and efficient heating and appliances, and the result is a healthy, efficient home that uses very little energy to keep its owners comfortable.
“When it was cold this winter, the house stayed at about 70° without any heat. When it got hot this summer, the house stayed at about 74° without air conditioning. It’s a very comfortable house.”
This home’s features include:
- Super-insulated straw bale walls (R-30) made of natural materials and greatly reduce heating and cooling needs. These walls use bales of wheat straw, an agricultural by-product of local food production. The bales replace conventional insulation and sheetrock, decrease the amount of framing lumber needed, and even sequester carbon in the wall.
- Natural clay plasters that are locally produced with non-toxic materials (clay, sand, straw, and water) with minimal embodied energy and zero VOCs. Clay plasters replace sheetrock and paint, and are vapor permeable and hydrophilic, helping to moderate indoor humidity.
- Passive solar orientation that focuses on shading rather than heating since high-thermal-mass homes like this need very little energy to heat but quite a bit to cool once they are overheated.
- Photovoltaic solar electric system supplies all of this home’s modest electrical needs and feeds extra electricity back into the power grid, making this a Net Zero Energy home.
- Hybrid electric heat pump water heater heats water efficiently using latent heat and electricity generated on-site.
- Resilience and passive survivability created by a home that functions well even when the power goes out.
- Concrete slab made with a percentage of fly ash to reduce Portland cement use. The slab, which was structurally necessary, was stained to become finish flooring so no additional flooring materials were needed. The slab also provides significant thermal mass, helping to stabilize the interior temperature.
- Cabinetry is low VOC and is made without melamine, utilizing sustainably-sourced plywood rather than chipboard.
- Native, water-wise plants will be planted in the disturbed area of the building site. They will require less watering even during the hottest months.
- Zero VOC paints and finishes used throughout the interior maintain good indoor air quality.
- Laundry-to-landscape greywater system sends the water used for clothes washing to trees in the landscape.
- R40+ blown cellulose attic insulation (made from recycled newspaper) and a radiant barrier prevent unwanted heat loss or gain through the roof, which can account for up to 40% of a home’s energy loses.
- Wood countertops are made from vintage, reclaimed oak timbers and are finished with non-toxic oils.
- Adobe block accent walls (made from adobe clay bricks made on site) contribute thermal mass and humidity stabilization.
- Trim and finishes made from wood recycled from old sheds on the building site.
- Efficient LED lighting and appliances throughout the house help keep the energy use low.
- A mini-split heat pump heater and wood stove are the only sources of heat for this house. The wood stove won’t pollute the indoor air because it is direct-vented and has dedicated make-up air.
- Modeled and tested at more than 21% better than the 2013 Title 24 minimums of the California Energy Code. It has an airtightness rating of 3 ACH50 meaning it won’t lose much heat or cool due to air leakage.
Why Straw Bale Walls: The plastered straw bale wall system creates a superior wall. It provides great heat and sound insulation, is fire safe, durable, and safe in an earthquake. It also offers unlimited aesthetic possibilities, such as deep window seats and graceful arches.
- Great insulation: Straw bale walls provide at least R30 insulation, which can greatly reduce energy used for heating and cooling. A typical 2×6 stud wall with maximum fiberglass insulation is rated R19.
- Good for the environment: Straw is an abundant agricultural waste product leftover from the production of grain. Straw bale building is not only an example of recycling, is a great example of upcycling.
- Excellent fire resistance: Straw bale walls have a high fire rating: 1 hour for earth plastered walls, 2 hours for cement-lime plastered walls. A typical stick-built, drywalled wall has a 30-minute rating.
- Less materials: A plastered bale wall replaces the insulation, the drywall and the paint usually used in a conventional wall, and can reduce wood for framing.
- Better sound quality: Straw bale walls provide excellent sound insulation and improve interior acoustics.
- Healthier air quality: Straw is a natural, non-toxic building material, and when combined with zero VOC finishes (such as clay plaster), can create a healthier indoor environment.
- User-friendly: Building with bales can create opportunities to involve your friends and community through bale raisings and work parties.
- Beautiful: Straw bale walls are aesthetically versatile. They can be straight and flat or can be shaped to have sinuous, organic lines and accommodate built-in furniture or niches. Straw bale homes can be almost any style: from organic and ‘Hobbitty’ to clean and Contemporary; from straight and Modern to handmade and cottage-like.
Net Zero Energy Building
There are different ways of calculating (and even different names for) Net Zero Energy but the core concept is that the building does not use more energy than it produces. This home is all-electric (no gas) and has a 4.1 kWh solar/photovoltaic system that produces electricity whenever the sun is out. This relatively small PV system generates enough electricity to run everything in this home and sends quite a bit of extra energy back into the electric grid. This home has energy monitoring equipment that records how much energy is generated and how much is used every minute of every day. Our early data confirms that we will be eligible to receive the Net Zero Energy Building certification from one of the more rigorous green building certification programs, the Living Building Challenge. Update: this home received Zero Energy certification from the Internation Living Future Institue on Jan 3, 2018.
Net Zero Water Building
The idea of Net Zero Water is even newer and less familiar than Net Zero Energy, but the core concept is similar: to use no more water than is available on the site and to keep that water onsite. Most of the projects that seek to achieve Net Zero Water have small water budgets: they are often on smaller parcels of land and have city water instead of a well, which means that the amount of onsite water is limited to rainwater. They also have a small water battery: rainwater must be stored in tanks or cisterns which take up space and a smaller parcel might not have enough room for wastewater leeching. To work within this small water budget and battery, these projects must use very low-water-use appliances and, oftentimes, complex greywater or blackwater processing systems. If you are familiar with Net Zero Water, these are the technologies you’d expect.
Designing the water system for this home required stepping back and taking a fresh look at how Net Zero Water could work best for this particular site. This site has a larger budget and a larger battery: it’s a 10-acre parcel (that receives monsoon rains in the late summer) and it has a well. All of the water used in this home comes from the ground and is returned to the ground, filtering down to the aquifer that recharges the well.
Here is the full cycle: The rain falls on the ground and percolates down to the aquifer. The well pump draws water from the aquifer for use in the house. The water used to wash clothing is returned to the ground via a simple laundry-to-landscape greywater system, making some of the water available to plants on its way to the aquifer. The rest of the water used in the home goes to a septic tank that filters and settles out the solids and then sends the liquid to a leach field where it percolates down into the ground. When the solids left in the septic tank eventually build up and have to be removed, they will be taken to a plant that recycles biosolids into fertilizer.
It is important to keep pollutants out of the water since it will eventually return to the aquifer. The homeowners are committed to using bio-friendly cleaning products.
Some people may think this version of Net Zero Water is somehow “cheating” because it is so different from the systems we’ve come to expect but, for us, it was a fascinating challenge to rethink what we knew and design the most appropriate and lowest cost Net Zero Water system for this site. We are excited about this simple system and are exploring Net Zero Water certification through the Living Building Challenge as a third-party verification. Update: because we were not able to track the amount of water being drawn from the well, we were not able to pursue Net Zero Water certification for this project.
Our green building goal: Lower tech, lower carbon, and higher performance at a lower cost.
Frequently Asked Questions about Straw Bale Building
Won’t straw burn? – Like a page of the phone book, the surface of an unplastered straw bale is flammable, but the center is so dense that it does not burn easily. Once plastered, the surface is no longer flammable. Unlike stud construction which creates chimneys in the wall, the center of a bale wall is so dense that there is little oxygen available to feed a fire. Straw bale buildings have higher fire resistance than conventional buildings.
Won’t straw rot? – Most building materials, including wood, will rot if exposed to too much moisture. If kept dry, straw will not rot. Building any structure properly involves specific attention to keeping water out and making sure vapor doesn’t get trapped. Straw bale buildings are no different.
Won’t bugs eat it? – Straw is the stem of the plant with the seed head removed. There is very little food value in a straw bale. Straw is less attractive to most kinds of termites than wood, but normal termite precautions should be taken.
Won’t rodents live in it? – Although rodents will nest in a loose stack of bales in a barn, bales in a wall are stacked so tightly that there is no access for rodents and they do not try to nest there. Unlike hay, straw does not contain seeds to attract rodents. In fact, there is more room in a conventionally built wall for rodents to nest than in a straw bale wall.
Won’t the Big Bad Wolf blow it down? – With more than 730 straw bale buildings in the US, there have been no reported wolf-induced failures. There are even a few examples of straw bale buildings that have withstood the test of time (and wolves) for over 100 years.