A Mobile Foundation

Posted May 4th, 2009 by Kevin Rose and filed in Issue 4: Do-It-Yourself

gypsy_rides_9Standing in front of a typical 2,500 square foot 21st century home, there may be few who would think to themselves, “I can build one of those.” But, if you were to put someone in front of a 150 square foot small home, the reaction might be quite different. Even though the large and small houses may be functionally equivalent (kitchen, bathroom, living, dining, and bedrooms), the scale of the small home project can dramatically alter the perception of what is possible in terms of building one’s own house.

That, in my view, is one of the beauties of the small house movement. At a time when so many are beginning to recognize the benefits of living in smaller spaces, they are also thinking, “Maybe I can build one of those myself.”

For two and a half years I have been writing a blog called “Building Gypsy Rose.” Like so many rookie bloggers, I began with the sole purpose of keeping family and friends apprised of my latest crazy ideas but the readership has grown and now includes many who have begun their own process of designing and building a tiny home. (Yes, you can!) Looking back over my blog entries (again, primarily aimed at family and friends), I’ve come to realize that for the do-it-yourselfer a bit more detail might be in order.

In this article I’d like to expand a bit on a component of my home that has prompted much interest and many questions in the blog – the foundation.

gypsy_rides_7Gypsy Rose is of the rolling variety. Her foundation has wheels. Certainly not a novel concept, but the design considerations involved with building a four-season, traditionally constructed house within the constraints of highway-legal dimensions on a roadworthy chassis have not been given the same treatment as the more common poured concrete platform. Needless to say, I couldn’t find a lot of literature on the topic and had to sort out the details on my own.

Back in the 60’s and 70’s the builders of “hippy trucks” used well-worn trucks or buses as a starting point, but many of today’s tiny home projects begin with a trailer that can be detached from the means of locomotion. Of those, the most commonly used is what is often referred to as a utility trailer. The larger trailers of this type may be rated at 7,000 or 10,000 pound gross weight capacity and can be purchased new for between $3,000 and $5,000. When I first started conceptualizing Gypsy Rose I envisioned using a utility trailer as a starting point. A closer look at my design parameters, however, led me to what I now believe is a more suitable alternative. Rather than adapting to a trailer that was meant for hauling landscaping equipment or automobiles, I decided on a custom-made, purpose built foundation for my tiny home.

frame_deliveredWe begin with the challenge of building within the dimensional restrictions of a vehicle that can be towed down the highway without needing a special wide-load permit. In Vermont, my tiny house is limited to an 8.5-foot width and a 13.5-foot height. The length (20 feet) was determined by the physical limits of the intended towing vehicle and the road I had to navigate to the land where Gypsy now rests. With those dimensions in mind, here are some of the considerations that were factored into the trailer’s design.

  • Weight capacity: This was a tough one. When I started building Gypsy I didn’t have any idea how much she’d weigh when all was done. I ended up selecting axles rated at 3,500 pounds apiece. Using two axles, I have a capacity of 7,000 pounds for my home. (If I had to do it again, I’d have gone with a pair of 5,000 pound axles for a 10,000 pound capacity.)
  • bolt_nailersFrame material: For strength and rigidity, as well as ease of attaching the floor joists, I went with 2” x 6” box steel (as opposed to angle iron or I-beam cross-sections).
  • Hitch size: The minimum for a tiny house of Gypsy’s size is two and five-sixteenths inches.
  • Wheel size: I used 16” wheels capable of handling (the still unknown) weight of my home.
  • Brakes: Surge brakes are commonly used on trailers. (The requirement for brakes varies by state.)
  • Tongue weight (the amount of weight that rests on the hitch of the towing vehicle): This should be about 10% of the gross weight. For a tiny house that tips the scales at 5000 pounds, the tongue weight should be 500 pounds. Tongue weight is altered by how the weight of the house is distributed over its length and by the positioning of the axles along the frame. If the axles are placed too far back you’ll end up with too much weight on the hitch. If they are placed too far forward you will have less weight on the hitch but it will cause the towed trailer to handle poorly (dangerous!). Gypsy Rose’s configuration ended up with a tad too much weight on the hitch due to the fact that the heavier rooms (kitchen and bathroom) plus the tool shed (an afterthought) brought more weight forward.
  • Ground clearance: If you’re trying to squeeze two levels of living space into the 13.5 foot overall height, the lower the trailer frame can ride while still negotiating the obstacles on the highway, the better.
  • joists_nearly_completeFloor joist attachment: This was the consideration that more than any other led to a custom-built trailer. Most utility trailers come with a frame that is designed to accommodate a thick plank bed. Small house builders often construct their floor joist systems on top of that bed – quite commonly out of 2×4’s. Well, here in Vermont where wintertime temperatures get darned cold, I knew that I’d need more insulating space than what is offered by a 2×4 cavity. At a minimum, I needed the room provided by 2×6 floor joists, but if I’d built it on the bed of a utility trailer I’d be subtracting more precious inches from the space I needed to accommodate the combined height of the first floor and the sleeping loft above. I ended up having the trailer built with 2” x 6” box steel in a configuration that allowed me to bolt the joists alongside the steel frame members without losing any interior space to the floor joists. As you can see in the accompanying photos, my trailer frame is completely integral to the floor joist system. The plywood sub-flooring rests cleanly on both the steel and wooden surfaces.
  • subfloorFender wells: I didn’t want my trailer to come with any. I preferred the ability to integrate the fender wells into the interior of my home – again to avoid any unnecessary loss of interior space. On Gypsy Rose, the surface of the exterior siding is on the same plane as the outside edge of the trailer tires and the wooden fender wells were constructed as part of the wall/floor framing.
  • Taillights, etc.: I didn’t want my home to sport taillights and a license plate holder so I opted for fixtures that can be temporarily screwed to the underside of the trailer’s aft end for use only during transport.

With all of the above in mind, where does one find such a one-of-a-kind specialty rolling frame on which to build a tiny house? I ended up hiring a friend who is in the business of manufacturing custom boat trailers, but there are many custom trailer manufacturers that one can choose from. (Although I would not recommend it to the inexperienced, one could buy all of the components I’ve listed above from readily available sources and, with welder in hand, assemble a trailer in true do-it-yourself fashion.)

What about cost? I paid $2,600 for my custom-made trailer but that might be somewhat lower than average due to the fact that it was a long-time friend who did the work for me.

Foundations aren’t glamorous. In the end they are mostly hidden from view, but beginning with a well-designed trailer frame was an essential first step in my Gypsy Rose project.

gypsy_rides_4

To read more of Kevin’s small home adventures, visit his blog, “Building Gypsy Rose .”

6 Responses to “A Mobile Foundation”

  1. [...] Kevin Rose created an interesting post today on A Mobile Foundation | Small Living JournalHere’s a short outlineOf those, the most commonly used is what is often referred to as a utility trailer. The larger trailers of this type may be rated at 7000 or 10000 pound gross weight capacity and can be purchased new for between $3000 and $5000. … [...]

  2. bucket trucksNo Gravatar says:

    When it comes to landscaping and labor intensive work I always bring out the bad boy toys. After destroying two back ends in my truck I finally decided to purchase some heavy duty equipment to help me on my way. I have found my dump truck and bucket truck to be very helpful with trimming tall trees and removing the debris from my yard.

  3. Digger DerrickNo Gravatar says:

    Interesting Article. The first step to building a home is investing in some heavy equipment. Thanks for sharing.

  4. KyleNo Gravatar says:

    Hey Kevin, just about to start buying materials for my own similar project. What box steel thickness did you choose for your trailer?

  5. Einar MikkelsenNo Gravatar says:

    I was wondering what the deck height ended up being for you on your custom trailer. Love the idea!