Last Updated: Jul 21, 2020
Tiny home construction usually brings to mind stick-frame 2 x 4s and plywood. Now, that’s a proven building strategy that’s lightweight and cost-effective. It’s also one of the reasons thousands of homeowners around the county are switching to smaller homes that consume less energy and require less building materials.
Homeowners are, however, building tiny homes from other materials. Tiny houses built from cob, shipping containers, and prefab kits are among the many methods being used. So why not Insulated concrete forms (ICFs)? Or structural insulated panels (SIPs)?
These two alternative building techniques might be appropriate in specific contexts for tiny house construction by offering several advantages.
Insulated concrete forms are prefab building components made from blocks of rigid insulation, most often from different types of polystyrene foam. The blocks are subsequently linked together and include an empty cavity in the middle for pouring a concrete filler.
ICFs were originally developed for use as foundation walls, as they incorporate water resistance and insulation properties. More recently, some builders have been using ICFs for above-ground walls as well, connecting foundation and walls into one solid structure.
A home with the walls and foundation built with poured concrete can’t, however, be towed or moved. Many people interested in the tiny home movement are young folks looking for an economical pathway to homeownership, but who aren’t ready to settle down long-term in a specific place.
A tiny home built with ICF, then, is probably best suited to people who are looking to downsize in a more permanent location. David Hill built a tiny home in the foothills of the Appalachian Mountains in Northeast Alabama as a retirement home. He decided to put the home on a foundation using multiple stabilizers buried six-feet-deep, which allowed him to raise the ceiling height to 15 feet.
Some other advantages associated with tiny homes built from ICFs include:
Durability: When constructed correctly, ICF construction can last hundreds of years. Poured concrete walls offer strength and robustness not usually associated with lightweight tiny homes on wheels. One manufacturer of ICF blocks states that its products “are disaster-resistant… (and) can withstand severe winds exceeding 200 MPH and projectile debris moving over 100 MPH.” Tiny homes located in areas prone to severe weather can, if built with ICFs, be more resilient. ICFs also offer an increased level of resistance to fire and earthquake damage.
Built-In Insulation: ICFs are incorporate insulation directly into the foundation and wall components. In most cases, ICFs are pre-manufactured to have an insulation rating between R-20 and R-22. This insulation rating might not be enough insulation for tiny homes located in areas with cold, long winters. Still, it will offer more than enough insulation for regions with more moderate climates. Additional insulation can be added to the outside of the walls to increase the thermal performance of the home.
Tight Building Envelope for Energy Efficiency: Because ICFs are prefabricated, they can efficiently be designed to create an airtight building envelope. Tiny homes that use ICFs, then, can often be built to passive house standards. Because of reduced interior space, many airtight, highly insulated ICF homes might be able to eliminate the need for mechanical heating and cooling.
Easy to Incorporate Sustainable Wall Alternatives: Most homeowners may not want polystyrene forms visible on the interior or exterior of their home. Fortunately, the foam blocks or “casing” of ICFs can easily be covered up with sustainable cladding or interior wall coverings. For interiors, natural earthen and mineral plasters work great with ICFs. For exteriors, wood cladding sourced from salvaged or reclaimed barn boards is an attractive option.
Quick Build: ICF homes are relatively quick to build. According to homeowner Luke Edwards, who is constructing a new, but not tiny, home for his family in Trinidad, “the speed of ICF construction was really a deciding factor for us as we considered how to build our new home.”
Insulated concrete forms also come with some sustainability drawbacks that homeowners should consider. Some studies suggest that the concrete industry might be responsible for upwards of 8 percent of total greenhouse gas emissions. The foam used in ICFs is often sourced from petrochemicals like polystyrene. Not only is this a non-renewable resource, but some of the foam options might also lead to VOCs leaching into a tiny home.
Considering ICF construction for your future tiny home? Consider using concrete with fly ash content, a recycled material that will lower the cement’s carbon footprint. Also, these green cement options would reduce the carbon footprint of an ICF home.
Structural Insulated Panels or SIPs are high-performance insulation materials inserted between two structural boards. The boards with SIPs are typically made from oriented strand board (OSB) or plywood. These pre-manufactured panels are significantly lighter than ICFs and are suitable for tiny homes on wheels.
SIPs offer several advantages over stick-frame tiny homes, namely:
Less Thermal Bridging: The studs in a stick-frame house often create thermal bridging that can drastically reduce the energy efficiency and thermal performance of a home. Even a small amount of thermal bridging can radically increase the mechanical heating and cooling load, even for a tiny house. SIPs have relatively few joints or connections, resulting in less heat loss.
Quick Construction: SIPs can be constructed quickly and might even be suitable for a DIY tiny home project. Once delivered to the building site, the pre-built walls need to be assembled onto an existing foundation and then filled in with insulation.
Compatible with Natural Insulation Options: The space in between the OSB or plywood form needs to be filled with insulation. The most common insulation options include expanded polystyrene (EPS), closed-cell polyurethane, and polyisocyanurate. Sustainability minded homeowners can opt for such natural insulation options as sheep wool, recycled cellulose, or even straw bales.
Strength and Customization Opportunities: Like ICFs, SIPs are significantly stronger than stick-frame construction. Homeowners thinking about building a SIP tiny house in a cold climate can find companies that manufacture thicker SIPs that would increase the R-Value of the home.
The downside of SIPs in tiny home construction is mostly associated with the type of insulation used. While foam insulation is energy- and cost-effective, it comes with a sizeable embodied energy footprint. The plywood used in the panels might also leach VOCs such as formaldehyde into the tiny home. Get around these drawbacks with sustainable and natural insulation options, and plywood made from durable and healthy bamboo.
One main advantage associated with tiny homes is the cost savings that help homeowners avoid the dreaded 30-year mortgage. Are ICFs and SIPs significantly more expensive than traditional stick frame tiny house construction?
According to one estimate, the average price for stick framing ranges from $10 to $20 per square foot for the materials and $5 to $10 per square foot for the labor. The U. S. Department of Housing and Urban Development (HUD) states that “the additional cost of ICF construction relative to wood-frame construction may typically range from $3 to $5 per square foot.” For SIPs, expect to pay $8 per square foot of panel, and installation costs can vary widely.
As a general rule of thumb, ICFs for small homes will generally cost a bit more than traditional stick-frame homes, while SIPs can cost less. ICFs, of course, do offer much more durability. This durability can factor into savings if you’re planning on building a tiny home you’ll live in for the rest of your life. Both SIPs and ICFs, when built sustainably and with a focus on energy efficiency, can help homeowners save money on their monthly heating and cooling expenses.
Know of anyone who’s building a tiny home with ICFs or SIPs? As Edwards told Rise about the construction of his ICF house, “Everyone who drives past the house is dumbfounded. They say things like, ‘You’re building a house out of Styrofoam? How does that work? It’s going to fall down.’ They’re really skeptical about it, but I’m an optimist.” So are we!
Tobias runs an agroecology farm and a natural building collective in the mountains of El Salvador. He specializes in earthen construction methods and uses permaculture design methods to integrate structures into the sustainability of the landscape.