Tiny house foundations are important! They can anchor your tiny home to the Earth, provide insulation and also help keep moisture out. There are a number of tiny house foundation options to choose from. And, there are a few environmental factors to think about when deciding on which foundation is the best for your build. In this post, we’ll dive into some of these considerations and also review tiny house foundation options.
The main purpose of a tiny house foundation is to support and distribute the building’s load. Furthermore, there are two different types of building loads: dead loads and live loads. Dead loads include anything that is permanent and immobile, like the weight of the tiny house itself. Live loads, on the other hand, include things that are temporary and move around, like people. When figuring out your tiny house foundation plans, you’ll need to know the total weight of your dead loads and live loads. This way, you can make sure to choose a foundation that will be able to support all of the weight. Wind loads and snow loads are also important to keep in mind. Your tiny house foundation will need to be able to withstand wind forces as well as the weight of snow on the roof, if you plan to live in a snowy area.
Observing the building site
After assessing your building loads, you’ll then want to spend some time observing your tiny house build site. In understanding environmental conditions, you’ll move one step closer to settling on the best tiny house foundation for your situation.
The soil found on-site is an important factor to consider when weighing your tiny house foundation options. Because soil carries the building load, soils with high bearing capacity (or strength) and good compaction are ideal to build on. Soils with high bearing capacity include gravel and sand. Soils with lower bearing capacity, like silt and clay, can be soft and trickier to build on. Therefore, you’ll want to conduct a soil test or review regional maps in order to learn what kind of soil you’re dealing with.
Another key environmental consideration is the build site’s frostline. Frostline is the depth at which the groundwater freezes, and this depth varies depending on location. Because groundwater expands as it freezes, it can cause upheaval of your foundation. So, be sure to check your regional frostline and make sure that your foundation can be constructed below that line. Tiny house foundations that are installed above the frostline can experience significant structural damage.
Notice the elevation, aspect, slope, and contour of your build site. The aspect is the orientation of the site in relation to the cardinal axis and the movement of the sun. The slope is the angle of steepness of change in elevation. And, the contour describes dips and bulges in the ground surface.
Check out the video below to hear more about the geographical features to consider at your build site.
Tiny house foundation options
Once you’ve assessed your building loads and site, you can hone in on which tiny house foundation is best for you.
Slab on grade
Slab on grade foundations are a shallow foundation used most commonly on a flat, level build site with good soil compaction. To construct a slab on grade foundation, a concrete slab is poured on top of prepared soil and gravel. This type of foundation integrates the floor with the foundation and allows for the floor to be close to the Earth. Slab on grade foundations are ideal in locations where there isn’t a deep frostline. However, they are labor intensive and require the use of concrete, which isn’t the most eco-friendly building material.
Post or pier foundation
Like the name implies, pier foundations are built on posts that carry the weight of your structure. These posts sit on a concrete footer and can be made of material including concrete blocks, poured concrete, and wood. Pier foundations are ideal for sloped sites, sites with unstable soil, and in areas prone to flooding. They don’t allow for basements, but they can offer access to the underside of your building. They also use less material, can be eco-friendly if built with wood, and may be faster to construct.
Check out the video below to review some more of the pros and cons of pier foundations.
Block wall foundation
A block wall foundation is built on top of a continuous concrete footer using concrete blocks, rebar and mortar. Block wall foundations offer continuous perimeter support, allowing for usable subterranean levels like a crawl space or basement. This allows you to take advantage of the consistent temperature of the Earth, which is around 50 degrees. Therefore, you can reduce how much you need to heat the home, keeping it moderated and comfortable. However, block wall foundations are expensive and are not well suited to sloping land. In fact, you’ll want to be sure to slope your grade away from block wall foundation structures. Otherwise, you could be dealing with a flooded basement whenever it rains.
Rubble trench foundation
Rubble trench foundations are perhaps the most ecologically friendly, as they don’t require the use of poured concrete or extensive earth moving. This type of foundation is a simple, ancient technique. In short, you dig a trench, fill it with stone or rubble, and then build your structure on top of it. It’s affordable, as less material is used, and it’s also efficient. That’s because it combines the structural functions of a foundation with drainage away from the building. Rubble trench foundations are not ideal for hillsides, unless you’re willing to do a lot of excavating. They also are best suited for soils with high bearing capacity.
Let’s not forget about mobile foundations! There are a few different types of foundations that you can choose from when building a mobile tiny house. One is a deckover trailer, a more expensive trailer in which the deck is built over top of the wheels. Another option is a dovetail trailer, where the deck is below the top of the wheels. Dovetail trailers offer less area to build on, but they’re less expensive than deckover trailers. Finally, there’s the option to skip the trailer altogether and build your tiny home on skids with a wheel kit. If you want to lower your tiny house foundation cost, then building on skids might be the best choice for you. When figuring out which mobile foundation to go with, you’ll want to consider the building’s weight, width and height limits. Also, be aware that connection of the structure to the trailer or skids is critical. This often requires welding or working with metal in some fashion. Finally, flat land is essential for hosting a tiny house on wheels.
Dig into the building process
Want to learn more about tiny house foundation options? In our online Tiny House Building Class, we address both mobile tiny homes and permanent tiny houses built on foundation. If you want to build on wheels now, but have a plan for a permanent tiny home in the future, we’ve got you covered for both! Learn more about the online class and sign up for the waitlist to be notified when class opens, plus receive special offers.