Tiny House, Tiny Energy? Part II

This online-only article is a supplement to the Fall 2017 print edition of Home Energy Magazine.

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This is part 2 of a two-part series on Tiny Houses.

Another concern with building and living in a tiny house that could affect the health and safety of the occupants is the potential moisture generation and deficiency in indoor air quality because of the inherent "tighter" building envelope.

When constructing a Tiny House there are less junctures of walls, ceilings, and floors so there are less potential air leakage pathways thus making their shells inherently tighter. This is great for energy conservation but could also add some unseen dangers to the living environment. A smaller, tighter ‘box’, like a tiny house, should always be properly ventilated for moisture at the source such as the bathroom and above the cooking surfaces. Care should be taken to ensure these “moisture exhaust” ventilators run as long as there is excess moisture in the air. This is accomplished by installing ventilation fans with internal moisture sensors, or humidistats that delay the fan from shutting down until acceptable internal moisture levels are accomplished. Another option is to replace the switch that controls the fan with a humidistat switch. Now, any fan can be “moisture controlled” by simply replacing its on-off switch. Some of these replacement switches also have programmable delay-off functions that will keep these fans running for a set period long after you’ve left the room which is highly recommended.

For Brian and Siena’s tiny house design, they took great care in the assemblies, materials, and ventilation practices as it related to achieving and maintaining good indoor air quality (see Figure 1). They were conscientious in the selection of all their building products and opted to refrain from using petroleum-based foams and sealants for their build. They used Roxul Comfort board and Comfort batts for the interior wall insulation and outboard rigid insulation for the outer thermal boundary. Instead of caulks and foams that can breakdown and separate over time, Brian and Siena opted for SIGA tape and barrier products which has become the go-to supplier for Passive House enthusiasts. Brian knows from his building science training that the worst thing to do to any structure is pushing moisture into wall assemblies. By choosing the appropriate materials and products, the assemblies they have designed have good potential for drying IF moisture ever did sneak into the walls. This is always good practice. They have also added a set of Lunos E2 heat recovery through-the-wall vent systems. This allows for a very low-energy heat exchange and ventilation practice that is virtually silent.

Brian works on one of two through-the-wall Lunos E2 HRV exterior penetrations. He’s being careful with how the ducting travels through the wall, but he’s also careful with the fit of the external layer of rigid Roxul insulation. (Photo courtesy of Brian Rubin, RA, CPHD)

With the Roxul insulation fit and installed, sleepers are installed to receive the rain-screen layer.

The interior side of the HRV duct assembly prior to the finish layer.&nbsp (Photo courtesy of Brian Rubin, RA, CPHD)

Not only will internal moisture collect faster in a Tiny House, so can internal contaminants which often go unnoticed. There are unhealthy chemicals in a lot of building products that consumers may not realize. In larger homes with lots of volume this built-up contaminant concern is minimized somewhat due to the dilution affect in a home with large air exchange rates (measured as ACH, air changes per hour). There is enough air exchange in the structure (leaky shell) to dilute the “bad” stuff so it’s not so harmful for us. Now, if you placed all those bad products inside a Tiny House that is built “tighter”, you may start to feel the effects on your health. There are new products coming to market all the time and sometimes the research doesn’t come until much later as to the effects on human health. Tiny Home builders and dwellers should do what they can to only use organic building materials such as rock wool or cellulose for insulation, FSC rated lumber products, formaldehyde-free plywood and cabinets, rapidly renewable flooring such as wool, sisal, bamboo, and natural counter tops such as stone or granite. It’s hard to install plumbing and electrical work without using a lot of plastic products but occasionally there are alternatives. They may be more expensive, but you could use metal electrical boxes and conduit instead of plastic ones. You could run copper for your plumbing instead of PEX, just don’t forget to use “Lead-Free” solder if you do.

Andrew Morrison elected to install PEX tubing for his Tiny House plumbing work. Not only was it easier to work with having less connections (potential leakage points) it was less weight and had a proven track record for a healthier material choice. (Photo courtesy of tinyhousebuild.com)

Figure 1. Tiny House + Passive House design methodology for floor, wall, and roof assemblies. (Courtesy of Brian Rubin, RA, CPHD)

Brian Rubin works on the moisture barrier in his own Tiny House Build being meticulous about every joint and seam as he is striving for Passive House air tightness levels to help conserve energy and increase comfort. (Photo courtesy of Brian Rubin, RA, CPHD)

It all comes down to choices. The important thing to remember about indoor air quality in any building is that you won’t know how bad it is until construction is completed. There are horror stories of LEED buildings not having very good IAQ even though they received an award. If you can’t measure how bad things are you should really make sure the right materials are going in during construction. Tiny House builders have to be proactive about IAQ. Their family’s health depends upon it.

Case Study—Living off the Grid

Some tiny houses are designed to be “off the grid” and have self-contained systems and equipment. They have to produce their own power, heat their own water (typically with propane), and deal with waste water management. Each of these systems use power so each kWh and Therm in an off-grid Tiny House has to be carefully monitored by the occupants. Andrew Morrison, along with his family, live off-grid in their tiny home in Oregon. “We have hot summers and cold winters here and since we are off grid monitoring our energy use is a daily activity,” says Morrison.

So, how much energy does a tiny house actually use? For the Morrison’s tiny house up in Oregon, the electrical use is about 100kWh/month on average. The U.S. national average for electrical use is ~901 kWh/month. That’s about 1/10th the energy used. Tiny houses are also about 1/10th the size, so isn’t it all relative? The Morrison’s energy consumption number covers their tiny house and their kids’ sleeping cabins (120sf and 160sf). As such, the total square footage for their “compound” is 487 square feet. This was the basis for the 100kWh per month measurement.

Andrew, and his equally passionate wife Gabriella, designed their Tiny House with all LED lighting to conserve electrical use. For appliances, they had originally planned to use a propane refrigerator but opted for a conventional one due to costs. They figured the money saved by not buying the propane one could be used to install more PV which also helps with other uses. With two teenage kids there are now four laptops plus one desktop that also need energy. The Morrisons try to conserve where they can, even charging their cell phones whenever they’re out driving in lieu of charging them at home. One of the big energy users on their property is a water pump that pushes water from a well 75 feet up a hill to a 1500-gallon water storage tank once a month. This allows them to create the needed head pressure to serve their home’s plumbing fixtures. According to Andrew, this once a month pumping activity uses a lot of energy and they need to plan ahead for it. “We either make sure there’s plenty of solar production on the day we’ll be pumping or, if it’s in winter and our water storage is running low, we may need to use our gas-powered generator.”

Andrew Morrison standing in front of his dynamic solar PV array. He can turn it for optimum production. (Photo courtesy of tinyhousebuild.com) 

What about the gas usage in a Tiny House? “This is one of the challenges facing the Tiny House movement” Irwin shares. “They may be able to conserve on space conditioning due to their smaller size, but people generally use the same amount of hot water regardless of the size of home they’re living in for bathing, and washing clothes.” Graham may be correct but there are a lot of Tiny Home enthusiasts that a very resource conscious. Most tiny house designs do not include a dishwasher so people wash by hand. Additionally, off-grid tiny house dwellers have fresh water tanks or systems where there is a closer relationship with monitoring usage.

For their own tiny house, the Morrisons opted for a tankless water heater and a propane space heater. Their propane usage is about 21-gallons per month at $80. Andrew adds, “The kids are pretty conscientious of our energy use, but they’re 17 and 20 and ‘just living’. My daughter will go into her cabin and crank up the heat to 250 degrees (exaggerated), she loves warm winters. So we placed her gas connection to her own smaller 20 lb. propane tank. This allows us to take the tank into town for refilling in winter when the propane distributors can’t get to us because of snowy conditions. It’s also a great physical connection for her. Once she’s out, she’s out, so she gets to experience her usage in real time.”

The Morrison’s Tiny Home is designed to provide comfort in summer and winter. (Photo courtesy of tinyhousebuild.com)

Another consideration that effects the energy usage of any home is siting, or where a home is oriented on the site its being placed. Passive solar design (not to be confused with Passive House design) is very important when siting a tiny house on a property. One should consider; wind direction and speed for cross ventilation and air flow, solar exposure for passive heating in the winter, and shading to reduce cooling demands in the summer.

The Morrison’s tiny house was going to be temporary until they found the perfect spot on their property to build a new straw bale home. Their plan was to start with a tiny house and shift it about the property in an effort to find the “sweet spot” on the land that made best use of the surroundings, exposure, and aesthetic appeal and that’s where they would build their permanent residence. It turned out that the location they built the tiny house on was the ideal spot on their property. There were oak trees that would shade them against the hot summer sun and then shed their leaves for good solar gain in the winter. “Ironically, where we built our tiny house was the perfect spot” says Andrew “and we loved living in it so much we never felt the need to build anything larger.”

Some Challenges Ahead

Like Brian and Siena’s tiny house design, some tiny houses on wheels are designed for utility hook-ups like you’d find in an RV park. Upon arrival at a “full facility” RV park (one that will accept Tiny Houses), they would need to "connect" to services in the park such as; water, power, and waste water disposal. This all seems conducive to a harmonious relationship between the tiny house owners and RV parks. However, this isn’t always the case. Many RV parks are refusing inclusion of tiny houses in their parks for one reason or another, so finding that ‘next spot’ may be challenging. As the Tiny House network grows more locations, RV Parks, and amenable locations are being identified and shared through blog posts and websites geared towards the tiny house community.

The same building techniques for building a conventional home are utilized when building a tiny house as well. If you’re building a THOW, there are many other considerations to contend with such as a balanced load, trailer capacity, transportability, and dimensions. If you’ve ever pulled a trailer of significant size, you’ll understand the importance of balancing the weight front to back and side to side. Think about that for a minute. If I’m designing a conventional home on a foundation, I could have 90% of its weight on the west side and only 10% on the east and the house would be fine. If I did that in my THOW, my trailer would be wobbling back and forth on the highway when being towed creating an unsafe scenario. This affects the design of a tiny house. Even if I wanted the fridge, the washing machine and the bath tub all on one side of my THOW, I wouldn’t be able to simply because I’m going to be towing it out on public highways.

Above the trailer, the construction of a tiny house is basically the same as conventional, it’s just smaller. Most opt for conventional stick-framed construction (wood) 2x4 walls because they will take up less of the valuable square footage inside. Harsher climates utilize 2x6 framing or go with SIPS panels instead for added thermal performance. Windows and doors often serve double duty in tiny house construction. They not only let in natural light (reducing lighting needs), they also often serve as the cooling system. Strategically placed windows high and low in the structure can promote cross ventilation. There is a wide variety of exterior finish materials being utilized in tiny house construction. The main emphasis is on making sure your exterior finish products aren’t going to strip off when you hit the highway. The mechanical systems are the same as conventional construction. There is still electrical to run in the walls, plumbing fixtures to install, and ventilation and heating systems to put in. If you’re building your own it is strongly recommended that you hire out these specialty trades if you’re not qualified. Unlike other aspects of the build, screwing up your electrical system or plumbing could have disastrous effects.

In addition to a few Tiny House manufactures building Tiny Houses there are Community Colleges and Universities jumping on the band wagon. Joe Giampietro, an architect in the state of Washington, joined forces with a local Community College’s construction program to construct a 300 square foot Tiny House that, on paper, also met the Passive House design criteria. Joe’s goal was to inspire these future builders and to demonstrate to local builders that Tiny House + Passive House makes a good marriage. “We went through the Passive House pre-certification process and had the design certified. Our Tiny House passed the blower door testing requirements but never went all the way to final certification because at that point it was sold,” says Joe. “The original intent was to have a design that could be factory built, put on a carrier, and delivered to a site for use as a small cottage or auxiliary structure. In that effort, the floor is designed with two large glulam beams and 2x10s. This allowed the structure to be moved by a modular home transport company that picked it up and set it on posts set on footings at the site.”

This Tiny House, built by students at Seattle Central College’s Wood Technology Center also meets Passive House standards. (Photo courtesy of Joe Giampietro)

At the Wood Technology Center, the Open House for their first Tiny House project drew big crowds of folks curious about Tiny House and Passive House benefits and value. (Photo courtesy of Steve Allwine) 

It will be state by state how Tiny House is received. Joe and the construction students in Washington had a fairly straight forward process to get through. In Washington, they have a process where factory-built modular home plans can be pre-approved by the state Modular Home Inspector. The construction of the modular home is monitored by an inspector at the factory. In Joe’s case the ‘factory’ was the school’s warehouse where the Tiny House was being built. The Modular Home Inspector would come and inspect construction right at the school site, following the IRC codes applicable there. The only job the local building official had to do was to inspect the installation to the foundation at the site. This resulted in a manufactured home that met the local building code.

So, are tiny house a legitimate alternative for future homeowners? I think they could be. For someone like me they fit my lifestyle. I’m single and not too caught up in material things. I don’t need much, especially a lot of extra square footage that I’d have to: pay for, condition, light, maintain, and insure. If I don’t need all that, why should I be forced to live that way. I am hopeful that Andrew Morrison and his cohorts will work out the THOW issues with the IRC and that the tiny house approach can be the third option for those of us eager to tread a little lighter on the planet.

Kevin Beck is a senior energy analyst for the Association of Energy Affordability.

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