Tiny House Trailer Design

Case Study: Tiny House Trailer Design

A good foundation is important in any venture, and so very true for a Tiny Home Trailer!  Yes, for a Tiny House on wheels, the trailer IS the foundation - both literally and figuratively.  What is more important to a house than a solid foundation?

So, we set out for a better tiny house trailer design - to engineer one, then make the plans available for you.

Plans PageSeveral of our customers who build tiny houses understand the importance of the foundation, and they come to Synthesis for engineering and design so their Tiny Homes have a solid foundation.

But what about plans for you?  Can we take the knowledge and make something even better?

At Synthesis we have designed many Tiny House Trailer Foundations that include some pretty cool and unique features.  But, it is not just the "cool" things that make a design good.  It is the integration of cool with the first and most important need for a solid foundation.

This is a "Case Study" for engineering an excellent tiny house trailer design.  We start with the thoughts that drive a better trailer for Tiny Homes.

Come with us, and follow the process of thinking it all out.  This is how we design tiny house trailer plans.

What Makes A Tiny House Trailer Design Better?

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

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

  1. For a Tiny House Trailer, the load is the house, and the people, and the "stuff".  Once the house is built, it stays on the trailer, but it is not static.  (Utility trailers, car haulers and most flat beds have periodic loading - instead of a constant load.)
  2. While most trailers do sit for long times, the Tiny House is usually active even while it sits - with people and things moving around.  (Most trailers sit empty, and typically they store undisturbed.)
  3. 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.
  4. 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, for a Tiny Home, trailer flex can cause cracks in walls or ceilings, and windows can break.  For a tiny house trailer, stiffness is very important.
  5. Every inch counts, so trailers need maximum width - full size - within legal limits.  Of course, there are the wide trailers for homes also.
  6. Maximum square footage and vertical space make a need for long low trailers.  The lower the better for ingress, and for interior space.
  7. 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 having a lower deck height is very desirable.
  8. 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 tiny house trailer feature.

Designing To Tiny Home Trailer Requirements

Tiny House Foundation TrailerIn summary, the trailer must be super stiff, and especially strong for edge loads.  It must be stiff for the 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 space for extras like in-frame tanks, storage, and batteries.

Oh, and a good Tiny House trailer design must allow all sorts of floor plans with a low deck height (with insulation and no thermal bridging) to allow customers a roomy loft, and a cozy home.  Tiny Homes are unique, not only in floor plan, but also in construction and in ways people live.  A great Tiny House Trailer design must handle it all - as well as the normal trailer 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 potential conflicts.  Stiffness, Low Floor, and a proper Thermal Envelope.  In a nutshell, "How do you get the house floor as low as possible, while keeping it stiff and insulated?"

Let's look at these items one at a time, then the solutions altogether.

A Low Floor

Why is a low floor important?  Tiny homes are typically height restricted.  Often in the USA, that is 13' 9".  That's all you get.  If the floor is lower, it gives more 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.  While it is not huge, it will make a big difference.  It is also that much less of a step up into the house.

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 is important so you don't have a hot or cold floor.  How do we get it?  Typically, people build the floor over the metal trailer frame so it has the insulation they need.  That makes the floor quite a bit higher.

Even if you put insulation between the metal beams, if the wood decking of the floor rests on a beam, the metal will conduct heat right up to the floor, and you will end up with cold spots.  We call this thermal bridging when the metal "bypasses" the insulation.

Our Solutions

Our answer?  Integrate the floor supports within 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, so it is easy for you to establish a thermal envelope for the floor.  (Exception, the walls must be supported directly, so at the perimeter, only wood layers are between the metal and the wall footers.)

Another advantage of this method is the allowance for plumbing and wiring to route easily in the floor with natural channels both cross-wise and length-wise.  That makes it so much easier than drilling a bunch of holes for your routing.  And it is all in the insulated envelope.  Perfect.

Interestingly, this method also assures a better, straighter and flatter floor.  So, what is 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.  This is not really a problem, except that people often judge a trailer by the weight, which makes this design appear heavier.  Don't be fooled by the trade-off.
  2. Second, the build process requires 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 of these techniques, we bring it to the Tiny House Trailer design.  After getting the beams cut, construction is much easier, more consistent, stronger, and gives a lower house floor.  Plus it takes a lot less cutting, measuring, and welding.

Having floor supports built into the trailer frame allows  the desired taller, stiffer beams, yet it keeps the floor height low.  (Effectively lowering the trailer deck height by approximately 6" compared to an insulated floor of a more typical construction.)  Additionally, it gives superior stability, a flatter floor, and better wall anchoring.

This manufacturing technique is part of our tiny home trailer plans.  Read more about walls below.

Addressing Space in the Tiny House Trailer Design

As a side note, if the house interior space is a concern, our plans have more than just a low floor.  Of course the lower floor allows more vertical space, 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.

Or, if you want more allowance for things on the exterior, shorten the cross members a little to make the trailer slightly narrower.  See the plans for prescribed construction techniques before making changes to the trailer.

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

Then again, if you want more space, why not?  On our plans site, MechanicalElements.com, you can read about our wide versions at 10' width, and also 12' width.  Permits will be required to move them, but you can build your awesome new tiny home with a little more space using the same fundamentals in these better tiny home trailer design.

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
5th Wheel Engineering

Finite Element Analysis (FEA) on a custom Tiny House Trailer Design. A sure foundation design by Synthesis Engineering Services.

Designs by Synthesis analyze the frame with loads primarily at the outer edges.  Our designs don't leave perimeter loading as a side note, because it is part of the tiny home trailer fundamentals.

In a house, the walls hold most of the total weight.  Certainly wall weight, 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 competitive trailers.

Anchoring

A typical Tiny House trailer has threaded studs welded to the frame as anchors for the walls, much like a standard stick built house.  It is a good 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 threaded studs look like a great idea, and when they are new, they feel like a good idea, yet, 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 walls to search for studs, do you?)

- Or maybe you like some squeak and creak when the wind blows?

The solution is simple.  Set anchors in the walls, solid to the footer members, then allow access to the 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 is simple.  Anchoring details are in the plans.

All The Way To The Ground

The frame is certainly a major component of the strong foundation.  So are supports for the frame - like the axles, jacks, the tongue and other supports.  The tiny house plans dictate square feet and the full size of 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 jacks right at the corners of your tiny home trailer.  Rather, bring them in from the ends for better load distribution.  This is a mistake common with tiny home builders, because jacks at the corners will effectively cause the trailer frame to bow the opposite direction of how it does when rolling on the wheels.  You want the house stable on the trailer with the loads in the same general direction.

Oh, and don't forget to put something nice and wide, and stout under the jacks so they don't creep into the ground.  Also, this is something you should check, along with the jacks occasionally.

Tiny House Trailer Plans Are Available

Trailer Plans Drawing PageThe end goal of this design exercise is awesome Tiny House Trailer Plans.  A foundation that is sturdy for building your house to last a lifetime.  Second, get the plans into the hands of those building Tiny Homes.  With our engineering tools and expertise, we now have trailer plans specifically for the Tiny Home market.

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

If you are thinking about joining the Tiny House movement, we have something special for you.  These awesome DIY plans, are available now, along with an expanded line of Specialty Trailers including several sizes of tiny home trailer plans.  20' Trailers, 24' Trailers, 30' Trailers, and 32' Trailers.  They are all sold through  MechanicalElements.com, and plans are ready for immediate download.

Engineering is what we do, so these new plans are complete.  They include a complete List of both Materials and Components.  The result is a heavy duty trailer design ready to build to carry your new house.  We may have a bias, but after doing all the research, we highly recommend this trailer design direction over any others we have seen.

Don't settle for building your house on a car hauler or large utility trailer.  Unfortunately, a lot of trailers sold as "Tiny Home Trailers" are really just long flat beds with a perimeter added.  Don't settle for that.

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

Good Luck with Your New Home Trailer Project.

Next to Read:  A Case Study on the design and engineering of a  Twin Torsion Walking Beam Suspension for Smaller Trailers - Part 1, then the follow-up to finish the discussion with words on the Engineering Design Analysis - Part 2.

Among other  Engineering Services,  Synthesis does specialty trailer design.  Please feel free to  Contact Us  if you need a custom tiny house trailer design to meet your specific needs.  We are happy to help.

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