How Big Can I Make My Tiny House?

Size & Weight Limitations for Tiny Houses in Australia

One of the most important questions to ask at the beginning of your tiny house journey is ‘How big can I make my tiny house?’

While there are many examples of differently sized tiny house vehicles (tiny houses on wheels) out there on the internet and in people’s imaginations, if you’re planning on living in one you are probably thinking about how to make it as big as possible to increase its functionality to you, in your life, over many years.

So let’s just open the lid on this simple question because it reveals a lot of complexity when we look into it. We’ll thrash out the options here in this blog so that you can make an informed decision about how big to make your tiny house.

Tiny House Length:

How long can my tiny house trailer be?

The answer to this question in Australia is 12.5 meters long according to the Vehicle Standards Bulletin 1. The real issue with Tiny House Vehicles is weight, not length, but of course they are related issues, because long tiny houses are more likely to be heavy and go over their trailer’s weight limit.

Tiny House Weight:

How heavy can I make my tiny house?

This is the crucial question to ask yourself and the answer will impact how big you can make your tiny house.  Anticipating your ‘all up weight’ as your tiny house vehicle rolls down the road on it’s own wheels is a key task when planning a tiny house build.

Let’s break that down, while keeping in mind that tiny house trailers in the 6 – 9.5 meter range already weigh between 800-1000kg themselves (called the ‘tare weight’ of the trailer) and that is the very first part of your ‘all up weight’ estimate.

Let’s just nail this point and eliminate any confusion.  When someone says the trailer is rated to 3500kg, that does not mean you can go ahead and build 3500kg worth of house on that trailer, because you have to count (subtract) the weight of the trailer itself first.  

When doing your weight estimate there are 3 parts to keep track of: 

  1. The trailer itself (‘tare weight’ of the trailer itself);
  2. The “house” part you build on the trailer; 
  3. All your belongings that will travel inside the tiny house vehicle when moving down the road.

This “all up weight’ must be less than the weight rating of your trailer to be safely and legally towed on the roadway. 

“Making a comprehensive weight estimation is an essential part of any tiny house plan.” – Fred Schultz

How much weight is my trailer rated to carry?

The weight rating of your trailer is to be found on the trailer’s compliance plate.  You’re looking for the number of kilograms specified as the ATM or Aggregate Trailer Mass, which is what the trailer manufacture aimed for as the trailer’s  maximum capacity.

Tiny house trailers are often rated to meet standard weight ratings such as: 3500kgs, 4500kgs or more than 4500kgs. These are just the most common weight ratings, check your trailer’s complicate plate to find your ATM (Aggregate Trailer Mass.

Tiny House Trailers rated to 3500kgs:

If your tiny house trailer is rated to carry 3500kgs then it is reasonable to assume that you could build a six meter tiny house on it and get in under this 3500kg ATM. Trailers rated to carry 3500kg get a 50mm tow ball coupling and can be towed by a heavy duty towing family SUV like a Toyota Landcruiser 200 Series fitted with a brake controller (see Image 1: brake controller). Most family-friendly towing vehicles are rated to tow trailers in the range of 1800kg

Image 1: Note on towing vehicles for tiny houses on wheels: The towing vehicle (usually a truck) will be rated to tow two specified weight limits: One will be ‘braked’ and one will not be ‘un-braked’. When we say ‘braked’ we mean that the tow vehicle needs an extra piece of equipment installed called a bake controller. It activates the trailer’s own brakes when the driver puts their foot on the truck’s brakes. Without a brake controller, even a large tow vehicle like a Toyota Landcruiser will only tow about 750kgs.

to 3000kgs as an upper limit. Check your vehicle’s towing specifications in your owner’s manual and look for the “braked towing capacity” then verify that you have a brake controller fitted to that vehicle.

Tiny House Trailers rated to 4500kgs:

If your trailer is rated to 4500kg then it is reasonable to assume that you could build a 7.2 meter tiny house. And if you’re really confident in your weight calculations for your entire build and all your stuff, you might be able to stretch to building an 8 meter long tiny house. Anyone building a tiny house that is longer than 8 meters in length will probably have to make compromises on their design to make sure it fits within the weight rating, eg: building it with a lower roof height to reduce the overall weight of materials used.

Tiny House Trailers Rated to More Than 4500kgs:

Section 6. GENERAL DESIGN REQUIREMENTS FOR TRAILERS OVER 4.5 TONNES ‘ATM’ (Vehicle Standard (Australian Design Rule 38:02 - Trailer Brake Systems) 2005)

Section 6. GENERAL DESIGN REQUIREMENTS FOR TRAILERS OVER 4.5 TONNES ‘ATM’ (Vehicle Standard (Australian Design Rule 38:02 – Trailer Brake Systems) 2005)

Trailer Braking systems for trailers over 4500kgs require a ‘stored energy’ type of braking system as found in air or hydraulic braking systems. If you are considering this option, the relevant document you will need to consult is: Australian Design Rule Vehicle Standard (Australian Design Rule 38:02 – Trailer Brake Systems) 2005 F2007C00493

Go to the Federal Register of Legislation for more information. 

Trailers rated to over 4500kgs also require an engineers certificate to be legal and can only be towed by someone holding a license that is of a higher rating than the common drivers license, ie MR (Medium Rigid) or HR (Heavy Rigid) licenses.

So in short, if you want a tiny house trailer to be rated to more than 4500kgs, the trailer will likely increase in price substantially.

These factors, combined with having fewer available towing vehicles that are suitable to move such a tiny house, leads most tiny house builders to choose a trailer ATM maximum of 4500kg and live with a more modest tiny house floor plan.

What if my tiny house is overweight?

For example: what if my trailer is rated to carry 4500kg and I accidentally create a tiny house where the overall weight comes to 4600kgs? If you make your tiny house on wheels and it’s overall weight is above the specified ATM, then your tiny house is not roadworthy.

This is a major problem for several reasons:

  • You will not be able to tow your tiny house on a road using its own wheels under any circumstances, even with an ‘Unregistered Vehicle Permit’ (UVP). This is because UVPs are only for roadworthy vehicles.
  • The only way of transporting your overweight tiny house on wheels would be loading it onto the back of a truck, or low-rider trailer (see image #2 below) using the truck’s tray, see below for a fuller explanation.
  • The trailer’s brakes will not be designed to adequately stop your tiny house vehicle while being transported. That means that because you cannot adequately brake the trailer while being transported it could push the towing vehicle out into traffic.
  • In the worst case scenario, if you knowingly took an unroadworthy tiny house vehicle on the road and then had an accident and someone was hurt you could be found to be criminally negligent.

What if I load the tiny house on wheels onto the back of a truck and transport it on the tray of the truck?

Yeah, you can do this. This will be your only option if your tiny house on wheels exceeds the trailer’s weight limit, because it cannot be transported using it’s own wheels and braking system. If your tiny house is built to the road vehicle height limit (4.3 meters tall) then loading the tiny house onto the back of a truck will mean that the overall load is higher than standard clearances, which may effect the route you can take or your chances of getting a willing driver or company to transport your tiny house.

Tiny house on back of low rider truck tray

Image 2: Tiny house on the back of a low-rider trailer.  Photo Credit: Fischer Spezialtransporte GmbH from YouTube video

Tiny House Width:

Can I make my tiny house 3 meters wide?

Yes you can, but let’s first talk about the consequences of that decision.
Making your tiny house 3 meters wide will mean that your tiny house vehicle cannot be registered as a caravan because the official vehicle limit is 2.5 meters wide. This might not seem like a problem, until this scenario arises:

If the council ever objects to your tiny house on the basis that it:

  • is an ‘unauthorised building’ or
  • ‘doesn’t have a planning permit’ or
  • requires a development application (DA).

Then your best defence is to demonstrate that your tiny house is not a building, requiring approvals, but rather a “caravan.”

The conversation with the council officer might go something like this:

Council Officer: “You have placed a building on this lot. You need a permit, but haven’t got one.”

Tiny House Owner: “Thank you for coming by, Officer. I agree that you may be right that placing a building here would have required planning approval and a building permit. However, what we have here is a caravan according to the Australian Vehicle Standard Bulletin One, which is the relevant standard and what I referenced to build it and what our state motor vehicle authority recognises as a registered caravan. Come with me and let me show you the license plate. I can also provide you with my registration paper if you like.”

Now, if you have the registration papers saying that your tiny house vehicle is a registered caravan and complies with road vehicle specifications according to the state and national road authorities, then you’re in a pretty strong position for avoiding further confusion about the status of your tiny house in the eyes of council.

If, on the other hand, you don’t have any paperwork to refer to because your tiny house does not comply to caravan standards and is not registered or able to be registered as a caravan (because it is 3 meters wide or fails in other ways to meet the VSB1 definition of ‘caravan’) then you may find yourself in an argument with council about the legal status of your tiny house. They might start to argue that its status as a dwelling/building is determined by the nature of its use since it does not meet the caravan standards.

Different councils and states address this situation differently. In Tasmania, for example, if a tiny house is registered as a vehicle (caravan) or is able to be registered (meets the standards and would pass the test upon application) then it will be deemed a vehicle and will be subject to caravan regulations. However, if the tiny house is not registered as a caravan and is not able to be registered as a caravan, then it may be classified as a building and may be subject to all the same building codes, standards and permit procedures as any other building.

Here is the source document for that information.

Tasmania is leading the nation in terms of making a state-wide policy that names tiny houses on wheels as a category of vehicle or building and naming their criteria for assessment (register-ability). If other states and territories decide to follow suit then it becomes all the more convincing to make your tiny house vehicle meet the caravan standards in order to maintain it’s convenient status as a caravan, and not be classified as a building, the standards of which would become hard to meet. Think of ceiling heights, stair clearance, ladders, etc.

Also, if you are wanting to build a tiny house that is 3 meters wide then it just automatically adds weight through building materials. So your length and height will be impacted to get the whole vehicle under the weight limit.

So just to reiterate, you can make tiny houses 3 meters wide, plenty of people do. We just need to let you know the likely consequences of going in that direction, so that you can make an informed decision.

But I’ve seen so many cool Tiny Houses on Wheels on the internet that must be un-roadworthy!

Yes. Roadworthy-ness is not often discussed on tiny house forums/videos etc. Ask the difficult questions about weight, adherence to caravan standards and durability before purchasing plans off the internet or getting your heart set on a design.

Also, the towing requirement in the United States are different from here in Australia. They seem to be able to tow much heavier weights without the kind of scrutiny we face here in Australia.

Gooseneck/5th Wheel Trailers for Tiny Houses:

Gooseneck trailers are designed to distribute the weight across a truck’s tray and over the truck’s axles. They are usually rated to over 4500kgs, so all the ‘Rated to higher than 4500kgs’ implications apply here, like the engineers certificate, hydraulic or air brakes, and a higher price.

Image 3: Tiny House on Gooseneck trailer, Photo credit Living Big in a Tiny House you tube video

Detachable Trailers:

In New Zealand there’s a company we often hear about that make tiny house trailers that are detachable from the tiny house.
Here in Australia, if you build a tiny house on wheels and then take the tiny house off the trailer, placing it on it’s own foundations, your tiny house will likely be considered a house/dwelling/building and be subject to all the permitting processes and council regulations that usually apply to buildings.

Image 4: This beautiful tiny house, called ‘Hazel’ in NZ uses a detachable trailer, which means the trailer travels separately from the tiny house.  Photo credit: Living Big in a Tiny House on YouTube.

Ornamental Wheels / “I’m never going to move my tiny house on wheels”:

If you’re in the situation where you:

  • own the land that you want to place your tiny house on;
  • you know that you will never move the tiny house on wheels; and
  • nobody will try to move it after you’ve finished with it;

then you may want to build a tiny house on wheels just to avoid the council regulations that apply to buildings.

If this is the case, then you might be considering what we call ‘ornamental’ wheels. Kevin McCloud the presenter of Grand Designs did this in his Man Made Home series, where he made a small building out of recycled materials, built on wheels to avoid planning permits, and nestled it into a ditch so that you couldn’t see the wheels. It looked like a building but he could argued that if council ever objected he could just dig out the dirt around the tyres and show them that it’s on wheels to avoid regulations. He did not attempt to make the building registrable as a caravan or vehicle, nor was it roadworthy.

Image 5: Kevin McCloud ‘Man Made Home’ using ornamental wheels. Photo credit: Wholewoods.co.uk

If you think that ornamental wheels is the way to go for you, then you can build the ‘trailer’ out of scrap metal and old parts. The trick will be to make it so obvious that the ‘trailer’ is not designed to roll on it’s own wheels on the road, that it is not capable of being towed any distance, so that if, after you’ve moved off the property, whomever ends up in possession of the tiny house on ornamental wheels does NOT try to move it – ever.

The danger is that if someone does take ownership of your property and sees value in your tiny house on ornamental wheels and wants to move it somewhere else, and tries to tow it, they could be facing an unsafe task and potentially a dangerous situation.

Summary:

We hope that this has answered some of your questions about how big you can make your tiny house on wheels. As you can see it’s not so much about tiny house size as it is about weight. And the weight question has to be explored considering all the consequences of all the decisions before it can be properly appreciated or answered. Making well-informed decisions is essential to having a successful tiny house project.

If you’d like to learn more about the nitty-gritty of tiny houses on wheels in Australia then this is the Online Course for you.

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