Case Study: Tiny House Trailer Design

A good foundation is important in any new venture, and, that is definitely true for a Tiny House!  For a Tiny House on wheels, the trailer IS the foundation – both literally and figuratively.  What is more important to the house than establishing a solid foundation?  So, let’s start by engineering the very best tiny house trailer, then make the plans available for sale.

Several of our customers who build tiny houses understand the importance of the foundation, and they come to Synthesis for engineering and design so their new “Tiny Homes” have that solid foundation.  They want something different, something more stable, and something stronger that other commercial options.

At Synthesis we’ve designed several Tiny House Trailer Foundations that include some pretty cool and unique features.  But, it’s not just the “cool” things that make the designs good.  It’s the integration of cool with the first and most important need for a solid foundation.

This is a “Case Study” for the design of our own tiny house trailer.  We will start with the thoughts and drivers in making a better trailer for Tiny Homes.  Come with us, and follow along with the process of thinking it all out.  This is how we design tiny house trailer plans.

What Makes A Tiny House Trailer Design Different?

The first step with any design is understanding requirements – especially unique ones.  You can see our emphasis by reading Product Requirements in the popular Product Development Process Article.

Here is a partial list of  things that are important for Tiny House Trailer Plans design comparing to other types of trailers:

1. For a Tiny House Trailer, the load is the house.  Once the house is built, it stays, but it’s not static.  (Utility trailers, car haulers and most flat beds have periodic loading – which is different.)
2. Loading is mostly at the edges where the walls attach.  Some loads are in the center, but most of the weight is at the perimeter, because the walls hold the loft, often storage, the roof, snow loads, and wind loads.  This all applies load at the deck edges.
3. While most trailers do sit for long times, the Tiny House is usually active even while it sits.
4. When the Tiny Home trailer sits, it remains loaded.  (Most trailers sit empty, and typically they store undisturbed.)
5. For most trailers, some flex is no problem rolling down the road.  As potholes and bumps, occur they flex slightly.  A little flex is fine for a car hauler or a utility flatbed, because the car (or hay, or whatever) doesn’t care.  However, in a Tiny Home, cracks appear in walls or ceilings, and windows can twist slightly and break.  For a tiny house trailer, stiffness is very important.
6. Every inch counts, so foundation trailers need maximum width – full size – within legal limits.  Of course, there are the wide trailers for homes also.
7. Maximum square footage and vertical space make long low trailers that need stiffness.  Thinking about tandem axles or sometimes triple axles is important.
8. A low bed height is good on many trailers, but the Tiny Home is unique as the bed is the start of the floor.  Tiny Houses often push legal limits for height as they include lofts and vertical expansion.  Gaining a few inches by making an even lower deck height is very desirable.
9. The house requires insulation in the floor, and the floor is atop the trailer.  Adding insulation is often contrary to the low deck height, because you don’t want the floor right on the steel beams.  So, creating a thermal envelope is a unique and important trailer feature.

Designing To The Requirements

In summary, the trailer must be super stiff, especially for edge loads.  It must be stiff for the always live loads with activity in the house; wind, snow and other environmental conditions.  The foundation built on a tiny house trailer must be strong to hold a full load all the time, and to travel flawlessly.  Finally, it must allow all sorts of varying loads like tanks, batteries and storage.

Oh, and a Tiny House trailer design must allow all sorts of floor plans and have a low deck height (with insulation and no thermal bridging) to allow customers a roomy loft, and a cozy home.  Most Tiny Homes are unique, not only in floor plan, but also in construction and in ways people live.  A great Tiny House Trailer must handle all of it – as well as the normal functions and towing chores.

Truly, designing well for a Tiny Home has an extra level of thought and greater need for attention to detail.

Conquering The Floor

In this discussion, we will tackle the floor first.  From the requirements above, we see 3 that potentially conflict.  Stiffness, Low Floor, and a proper thermal envelope.  In a nutshell, it is “How do you get the house floor as low as possible, while keeping it insulated?”

Let’s look at these items one at a time, and together.

A Low Floor

Why is a low floor important?  Trailers are typically height restricted.  Often in the USA, that is 13′ 9″.  That’s all you get.  If the floor is lower, it gives space within the interior volume for a loft, which is quite desirable in a tiny house.  The roominess feel of the loft is a function, in part, of the height of the house floor.  If we can reduce the deck height by 2″, that gives 2 more inches of head space in the loft.

Trailer Stiffness

As mentioned above, trailer frame stiffness is important so the house foundation does not flex.  We don’t want a flexy, breaking house.

To achieve stiffness, it usually means using stronger beams, which, for stiffness, means taller.  Taller beams for a stiffer trailer usually mean a higher floor.

Insulation

In a warm or cold climate, insulation in the floor becomes important if you don’t want a hot or cold floor.  How do we get it?  Typically, people build up the floor over the metal trailer framing so it gives the insulation they need.  That, of course, makes the floor higher.  Even if you put insulation between the metal beams, if the floor rests right on a beam, the metal will conduct the heat right to the floor, and you will end up with cold spots in the floor.

Solutions

Our answer?  Integrate floor supports right into the trailer frame.  That is not so unique, but we also combine it with making the frame both easier and faster to build.  And, we make it so there is no direct connection of metal to the floor, establishing a thermal envelope for the floor.  (Exception, the walls must be supported directly, so only wood layers are between the metal and the wall footers.)

Interestingly, our method also assures a better, straighter and flatter floor.  So, what’s the trade-off?  There are two:

1. First, since the frame of the trailer integrates with the house, it moves some of the “house” weight to the trailer.  It makes the trailer a little heavier, yet in the process, it makes the house lighter.
2. Second, the build process has an advanced technique for cutting for the main beams.  At Synthesis, we often use laser or waterjet cutting to build specialty manufacturing machines.  Since we know the value, we bring this technique to the Tiny House Trailer.  After getting the beams cut, construction is easier, more consistent, and gives a lower house floor.

Having floor supports built into the trailer frame reduces allows the taller, stiffer beams, yet keeps the floor height low.  (Effective a lower trailer deck height by approximately 6″.  Compared to an insulated floor of typical construction.)  Additionally, it gives superior stability, a flatter floor, and better wall anchoring.  This is part of our tiny house trailer plans.  Read more about walls below.

Addressing Space in the Tiny House Trailer Design

As a side note, if space is a concern, our plans have more than just a low floor.  The lower floor allows more vertical space, it’s true, but that’s not all.  Using the full legal width is another.  Our plans have frames that are 1″ less (each side) than the legal limit.  That allows outside finishing, like siding, to extend over and cover the frame edges within the limit.

Yes, it’s supposed to be tiny, but there is nothing wrong with using the full space for comfort.

The Right Support In The Right Places

Another big issue we tackle is perimeter support for the walls, and anchoring the house to the trailer.

Perimeter

Designs by Synthesis analyze the frame with loads primarily at the outer edges.  Our designs don’t leave perimeter loading as a side note, it’s part of the fundamentals.

In a house, the walls hold most of the total weight.  Certainly the roof, the loft, snow and wind loads, hanging storage, shelves and other forces come to the frame through the walls.  This is why we put a priority on strength for the trailer frame perimeter.  And, we anchor the walls securely for a truly strong foundation.

By using tools like FEA fueled by engineering experience, we use cross members designed to carry these loads.  This is a fundamental part of the design, not an afterthought like many of our competitor’s trailers.

Anchoring

A typical Tiny House trailer often has threaded studs welded to the frame as anchors for the walls, much like a standard stick built house.  It’ a great idea, but it has one rather important shortfall – wood changes over time, especially with weather and movement.  Yes, movement, and trailers introduce a lot of that.

I learned this lesson working for farmers where I grew up – bolting to wood often requires re-tightening.  While the big studs look like a great idea, and when they’re new, they feel like a great idea, there is no way to re-tighten over time.  (Maybe cutting holes in the walls to find the studs and tighten things?  I don’t want to punch holes in the walls to search for studs, do you?)

The solution is simple.  Set the anchors in the walls, solid to the footer board, and allow access to clamping bolts from underneath.  With anchors in place, you simply go around the trailer frame and tighten each bolt.  This way, the house is always solid to the trailer.  It’s simple, and the details are in the plans.

All The Way To The Ground

The frame is certainly a major component of the strong foundation.  So are the supports for the frame – like the axles and jacks and tongue and other supports.  The tiny house plans dictate square feet and the full size for your tiny house living.  From that we work out a tandem axle or a triple axle configuration.  It does depend on where and how big the loads are.

Finally, the corner jacks for trailer stabilization when parked.  By the way, don’t put the jacks right at the corners, rather bring them in a little from the ends for better load distribution.  It’s a mistake common with tiny home builders.   Oh, and don’t forget to put something wide and stout under the jacks so they don’t creep into the ground.

Tiny House Trailer Plans Available

The end goal of the exercise is an awesome Tiny House Trailer Plans Design – one that has a sturdy foundation for building a house to last a lifetime.  Secondly, get the plans into the hands of those building Tiny Homes.  With our engineering tools and expertise, we’ve created plans that are designed specifically for the Tiny Home market.

This case study ends with some really great Tiny House trailer plans are now available to everyone.

If you’re thinking about joining the Tiny House movement, we have something special for you.  At Synthesis we have awesome DIY plans, and now, and expanded line of Specialty Trailers with these tiny house trailer plans.  They are sold through  MechanicalElements.com, and plans are available now for immediate download.

Engineering is what we do, so these new plans are complete.  They include a balance for all the requirements.  The result is a heavy duty trailer ready to carry your new house.

Don’t settle for building your house on a car hauler or a large utility trailer.  Even a lot of trailers sold as “Tiny Home Trailers” are really just longer flat beds with a perimeter added.  Don’t settle for that.

At Synthesis, we don’t guess at loading while thinking it will be good enough – like some people on YouTube and around the internet.  Instead, we do the engineering.  When you invest in building the house, make sure to start on a solid foundation.

Good Luck with Your New Home Trailer Project.

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