Intro: Energy Efficient Tiny House on Wheels
Building your own house is quite an adventure. When my partner and I decided it was time for us to stop paying a rent and own our own house, we looked at the available options. One of them was to buy a house but the housing market is so high that we would have ended up with a 30 year mortgage. The other solution was to build our own house but land is also extremely expensive here in the Yukon. The solution we came up with was to build a tiny house on wheels, save money for a while and wait for a good opportunity to purchase a small piece of land.
Before building our home, I knew nothing about house construction. Thankfully, the internet is a great place to teach you pretty much anything. Throughout the design and construction process, I learned about woodworking, house design, building code, electrical code, local bylaws, efficiency, insulation and much more.
In this Instructable, I will explain what decisions we took and what problems we tried to solve. This guide will hopefully save you some time and show you some common mistakes to avoid.
Step 1: Preliminary Thoughts
This is the first step you should take before grabbing your power tools. It is important to try to foresee all the potential problems at this stage. There are a lot of factors that can influence the design of a tiny house such as:
- Number of occupants (1 person, 2 persons, kids, pets, etc)
- Climate (tropical, temperate, sub-arctic, etc)
- Need for transportation (how often do you want to move the house)
- Highways regulation (max width and height allowed)
- Access to water and electricity (water tank vs city water, grid vs off-grid)
- Toilet system (septic field vs sewer vs composting toilet)
Once these questions have been answered, you can start drawing a preliminary plan on a piece of paper. This will give you a sense of how much living space is available. From there, you can cut little pieces of paper that represents various items (oven, shower, toilet, bed, couch, fireplace, stairs, etc) and overlay them on your house plan.
To give you an idea, here's what we considered:
- We are 2 people so we decided to go over the regular 8.5 ft width. On Yukon highways, it is possible to drive trailers with a 10.5 ft width granted a special permit.
- In winter, the temperature can dip to -40C so we need thick walls, floor and ceiling.
- We will need to move the house once we find a piece of land so we are building on a trailer
- We don't have access to water so we need a water tank
- We have access to electricity (15 Amps for the whole house)
- To avoid black mold, we need a good ventilation
- We don't have access to a septic system so we'll use a composting toilet
Step 2: Visit Existing Tiny Houses
Visiting existing tiny houses is a great way of finding out what you like and what you don't. Sometimes concept can end up being not very practical. Every builder adds its own touch and you will be able to borrow ideas from them. This is how tiny house design evolves over time.
We have based our house after Andrew's design at https://tinyhousebuild.com/. His model is simple to build and provides lots of storage space as well as a large open space.
Step 3: Draw Your House Plans
You can start by drawing your own plans or purchasing existing plans online. The advantage of the latter option is that someone already went through the trouble of validating the building requirements or the space efficiency and you can generally get a bill of materials.
These software will let you arrange your furniture and you will be able to virtually visit your house before it's built. You will need Sweet Home 3D to open the attached plans.
Step 4: Materials
If you haven't purchased a plan, you will have to come up with your own estimation for wood and insulation materials.
To build the house described in this Instructable, you will need:
- 2x4 lumber for floor and walls
- 3/8" plywood for the outside walls
- 5/8" T&G plywood for the floor
- 1/2" plywood for the roof
- 1/2" drywall or 1/4" wood panels for the inside of the walls
- 4" mineral wool insulation for walls
- 3" expanded polystyrene (EPS)
- 8" closed cell foam insulation in the ceiling
- 2x10 for roof rafters
- Tin roof
- Triple pane windows
- Cedar channel boards for siding
- Corrugated metal for siding
- Tiles and flooring boards (hardwood or engineered flooring)
- Galvanised flashing under trailer
- Lots of screws, nails and other small hardware store items
The amount of each item depends on the size of your house. In order to estimate the number of 2x4, you will need to draw your walls on paper and put a stud every 2 feet. In addition to that, you will need to put a double stud (king stud) on each side of every windows for load bearing considerations. You will need a lot of them. For example, in our house (24ft x 10.5ft), we used about 120 2"x4"x12'.
The plywood boards are all 4ft x 8ft and are easier to estimate by measuring the overall surface of walls, floor and ceiling.
Step 5: The Trailer
The trailer is the foundation of your house. It needs to be sturdy and square. The axles need to be rated for a higher load than the total house weight. There are multiple options available:
- Purchase a second hand trailer (the kind to carry heavy equipment)
- Purchase a brand new trailer
- Purchase an old travel trailer and keep only the base
- Purchase a custom trailer and ask the builder to design it to your needs
- Build it yourself
We decided to go with the custom trailer option. It is more expensive but it saves time and simplifies the construction. Example of the customization we asked for:
- Low rider trailer (frame close to the axles) which gives more height inside the house
- Square wheel wells (simplifies insulation)
- No wooden deck
- Frame extended to the sides to a full 8.5 ft.
- 10,000 pounds hydraulic jack in the front
- 2 additional supports in the back
- 2 axles rated 7,200 lbs each.
Step 6: Trailer Insulation
If you live in a cold climate, you will need to insulate the floor of your house. Since cold air can move freely under the trailer, a few layers of expanded polystyrene (EPS) need to be installed under the house.
This trailer has cross beams that are U shaped. The 3" thick EPS is cut in pieces and bevelled to fit between the metals beams. It is important to achieve a tight fit of the insulating material with the cross sections to avoid any heat loss.
Small gaps between metal and polystyrene can be filled with spray foam cans.
As you can see on the picture, the bottom part of the trailer is covered with galvanized flashing to minimise water and rocks projections while driving. It is also a good support for the EPS. The flashing is screwed onto the trailer using self tapping screws.
Step 7: The Floor
The trailer width is 8.5 feet wide. We decided that the house would be 2 feet larger than that so we will need to build an overhanging floor.
The structure of the floor is fairly simple. It is made of 2x4s aligned with the metal beams of the trailer underneath. That way, there is no flexion happening on the wood itself and we have a solid base to anchor our floor structure.
The 2x4 running on each side of the wheel well are doubled because there is more load applied to that spot (needs to support the weight of the wall above the wheels).
In order to attach the floor frame onto the trailer, we use long 3/8" galvanized hex bolts on the main trailer trusses. We also use countersunk self tapping screws on each 2x4s.
The space between the 2x4s is filled with another layer of 3" EPS.
Once the trailer structure is filled with insulation, we can add another layer of solid 1.5" thick EPS covered with 5/8" tongue and groove plywood (both glued with PL and screwed onto the 2x4s).
We now have a solid floor with 7.5" of expanded polystyrene insulation ready to receive 4 walls.
Step 8: The Walls
The walls are not really complicated to build but you will need to know the exact size of your windows and doors before hammering the first nail.
When ordering your windows, you will need to provide the company with the rough opening (R.O.) for each window. This is the size between the 2x4s.
Try to align upper and lower windows (and door) in order to minimise the amount of lumber required. This will reduce the overall weight of your house.
Start with the tallest wall, you can build it flat on the trailer and raise it to a vertical position when it's done. You need to place studs (vertical 2x4s) at regular intervals. This is important for 2 reasons:
- You will have to put screws and nails through plywood without seeing the studs.
- Insulation comes pre-cut to a certain width (16", 24", etc).
For each windows and doors, you will need a double stud that supports each side (king studs). You will also need a header above each windows to distribute the weight of the wall and ceiling above. The size of the header depends on the width of the window (4x4, 6x4, etc).
Once all the walls are built and raised, make sure they are square and vertical (make sure your trailer is levelled) and screw a temporary piece of lumber on each wall. This will keep them square while you attach the walls together.
Step 9: The Roof
The last big framing part is the roof. You will have to calculate the load it can support. For example, if you live in an area where snow is heavy, you will need larger roof rafters. The design of your roof will also influence the choice of lumber. A gable roof will be more complex than a flat roof but it will require thinner lumber.
After consulting a span calculator book, we decided to go with 2x10 lumber. These should be spaced evenly (same spacing as the wall studs) and anchored to the walls using hurricane ties.
The rafters are then covered with 1/2" plywood. the plywood should then be covered with a water repellent material. We stapled a thin membrane onto the plywood, screwed furring strips on it (1x4) and installed a metal roof. It is important to leave a bit of room between the plywood and the tin in order to minimise sound and increase air circulation.
Step 10: Electricity
Wires need to be installed before insulation so you will need to decide where your lights, switches, outlets and appliances will be located.
Read about the electrical code for your area. You may not have to pass an inspection because your house is not really considered a house but it's good practice to follow the rules when it comes to electricity.
Depending how you house receives electricity (extension cord for example) and what appliances you will use, you may want to install a breaker panel. You will also have to decide what size of cable to use. Lights are most of the time on 14 gauge (up to 15 amps) and outlets on 12 gauge (up to 20 amps). If you want to save money, you can wire your entire house on 14 gauge but remember that you won't be able to use any appliance rated higher than 15 amps (1800 watts).
An easy way to avoid tripping your breaker is to know how much power is available in your house. Let's say that your are on an extension cord plugged to a 15A outlet, that means you have 15 Amps x 120 Volts = 1800 Watts of power available in theory. In reality, there is a bit of resistance in all cables so if your extension cord is long, you will have a bit less than that. Let's say 1500W to be on the safe side. That's your limit and you should not go above. Every time you plug an electrical appliance (fridge, projector, computer, alarm clock, ventilation, heat trace, etc), you will have to add them up. That's also a good way to realise how much power you are using.
A Kill-A-Watt is a convenient device that lets you know in real time how much watt you are using. You can plug one on your extension cord and it will tell you how much current your house is drawing.
Step 11: Insulation
Insulation is a very important part of your house. It is true for both cold and warm climates. Since you can't really replace your insulation easily, you have to make sure to install it properly.
Thermal insulation is measured using the R value. It is a measure that describes how well an object will keep its heat over time. Make sure to look up the minimal R value to achieve for your walls, ceiling and floor. The U.S. department of energy has a page about climate zones and required insulation values.
A common option for walls is to use mineral wool bats. the standard 3.5" thick bats fit between the 2x4 structure of your walls. They come in various width so make sure to order the right one. For our house, we used the 24" wide. These bats provide us with R-14 thermal insulation and a good acoustical insulation as well. It is important not to squeeze the wool in tight spaces or it would decrease its insulating properties.
In order to further decrease the heat loss, we added an exterior insulation made of graphite polystyrene panels. These 1" thick panels provide an additional R-5 insulation.
In addition to that, we added interior insulation which provides an additional R-6.5 thermal insulation and acts as a vapour barrier.
To summarise, we have a wall structure that provides R-27.5:
- Drywall (R-0.5)
- Energy Shield (R-6.5)
- Roxul Bats (R-14)
- Plywood 3/8" (R-0.5)
- Exterra (R-5)
- Cedar Siding (R-1)
For the ceiling, we decided to shoot 8 inches of 2lbs medium density/closed cell foam between the roof rafters. This foam provides R-6 per inch giving us a total of R-48 for the ceiling.
For the floor, we have seen previously that the trailer is insulated with 7.5" of expansed polystyrene giving a R-37.5 value.
The wheel wells are covered with 3.5" of EPS and will later be covered by some furniture (stairs and kitchen cabinets).
Step 12: Windows and Doors
Windows have a trim that extends outwards with holes in them. That's where you will use fasteners (corrosion resistant screws or nails) to solidly anchor the window onto the wall. Please note that a tiny house on wheels is more subject to shear stress. This could put pressure on the glass if you place shims all around your windows. Therefore it is recommended to place shims only at the bottom.
Before installing the window, apply a water resistant membrane onto the bottom of the opening. This will provide an efficient vapour barrier and prevent water from seeping under your insulation of water repellent membrane (Tyvek).
Now apply some silicone onto the interior side of the plastic trims to make a tight fit between the windows and your exterior insulation.
After the window is installed, we will apply the same water resistant membrane to the sides and the top of the window, making sure to cover the window edge as well as the fasteners. That way, rain won't be able to get into your walls. In case some of it did, the bottom of the window is not taped so it would be able to flow outwards.
Step 13: Siding
For this step, you can let your imagination run wild. This is not as critical as wall structure or insulation. Just choose a material that you fits your personal taste and budget.
There are a few things you may want to consider:
- Try to use lumber coming from a sustainable source.
- Make sure the siding has a good resistance to water and the sun
- Use a lightweight material/wood to minimise load on the trailer axles
- Use galvanised nails or corrosion resistant screws
We decided to go with western red cedar because the wood weighs less than pine, is water resistant and comes from the west coast of Canada. We applied a mix of 3 oils to protect the wood from sun and rain.
We are also using galvanised corrugated metal sheets for the looks. It is a good option for the lower parts of tiny houses walls since this material doesn't get affected by snow, ice or water projections.
Step 14: Interior Walls
You have a few choices here.
A lot of people go with wood panels as they are somewhat flexible and they won't crack during transportation of the house. They can be painted and the can hold the weight of shelves and furniture.
Another option is pine or cedar tongue and groove boards. They are easy to install and quite decorative but they won't really work if you need to anchor heavy objects in the walls.
A third option is to use drywall. It is fairly easy to install and will give you the best seamless walls. The drawback is that it is more susceptible to cracks while moving the house. To decrease that risk, we re-enforced the 4 corners of the walls with L-shaped metal trims to give structural support to the drywall.
Step 15: Ceiling
To keep the house on the light side, we decided to use 1/4" tongue and groove lumber for the ceiling. With this option, you only need small brad nails to attach your ceiling to the roof rafters.
If your roof insulation is a fibrous material, you'll want to staple a plastic film on the rafters before nailing your ceiling boards. This will keep dust from falling through the cracks over time.
Step 16: Lofts and Upstairs Access
Having a loft is a great way to optimise space in your tiny house. In our design, we opted for 2 lofts, one is 8.5 ft long and the other is 5 ft long.
The largest loft is the bedroom. It can be accessed using the 28" wide stairs. These stairs double up as storage underneath. They are built on top of the wheel well and are made of 3/4 shop grade plywood covered with 1/8" Baltic birch veneer and maple hardwood steps.
Both lofts have multiple 4x4 supporting them. The floor is made of 1x6 tongue and groove pine lumber.
To access the second loft, we decided to go with a mobile ladder. This one is built out of 1x4 and 1x6 maple lumber. The vertical sides are made of two 1x4 glued together. The angle of the ladder is 20 degrees; the top has a cut out to prevent slipping and the feet are covered with cork.
Step 17: Flooring
The flooring boards were damaged by flooding and were donated to us by family. We managed to keep the best boards and install them in our house. In the entrance area and the bathroom, we used tiles because these are areas that are more likely to get covered by water.
The maple hardwood floor is attached to the floor using flooring nails and a pneumatic hammer. You can rent this kind of tool for a couple of days instead of buying a brand new one.
The tiles are installed using a thin-set mortar. A grouting mix is later applied between the tiles.
Step 18: Windows Sills
It took a long time for us to decide what to use for window sills. Our window return is 3/4" thick. This usually means that you slide a 3/4" board inside the groove. However, this board would look quite thin and we wanted to have a thicker piece of wood at the bottom of the windows.
The solution we came up with was to use 2x6 lumber. We went with red cedar because it is light and water resistant. In order to keep that thick 1.5" appearance despite the 3/4" return, we had to cut a slice underneath the boards. This is best done on a table saw. Once installed, the boards appear to have a full thickness.
You can finish the window sills with some wipe-on polyurethane or linseed oil to protect it from condensation.
Step 19: Lighting
The choice is yours but keep your power consumption in mind. Go for L.E.D. light bulbs. They cost a bit more than incandescent ones but you'll save money in the end and you'll have more watts available for other appliances.
Our main light fixture has 12 light bulbs drawing 5W of power each. The advantage of such a design is that it doesn't cast any hard shadow.
Above the sink and kitchen range, we are using Ikea light pucks. They each use 3.5W of power.
The lofts are equipped with 9W recessed led wide angle spotlights.
When choosing your light bulbs, pay attention to the color temperature and try to go with the lower values (3000K, 2700K or 2200K) as these are more natural and have less impact on night vision, sleep and health than the cold white ones.
Step 20: Shelves
When your house is small, you need a lot of storage. Shelves are great for books and items in the kitchen.
The ideal solution is to anchor your supports in the 2x4 studs of your walls. However, if this is not an option (foam insulation under drywall, support not aligned with stud, etc), you will need drywall anchors. They are usually made of plastic and expand inside the wall while your put a screw in.
If you don't like visible supports, you can install floating shelves by using special brackets with a keyhole shape. These are great for vertical boards. The good thing with these is that you can remove your shelf by simply lifting it.
Recessed storage is a great option for interior walls since you don't need insulation in them.
Step 21: Storage Bench
There was some unused space on the left side of our wood stove so I decided to build a shelf/bench combo from leftovers. The structure is made of plywood and 1x3. The surface is corrugated metal sheets left overs from the siding. They reflect the heat and it is therefore possible to build a big enough shelf without risk of over heating.
The seat of the bench is made of hardwood strips from various past projects. The strips are glued together, planned down and sanded to a fine grit. The board was then cut and a piano hinge was added to create storage underneath.
Step 22: Coat Hanger
Hardwood left overs can also be used to make various items in the house such as cutting boards. In my case, I made a coat hanger to match the bench seat below.
Step 23: Bathroom Door
The only interior room in the house is the bathroom door. It is build from off cuts from the lofts flooring. We decided to glue the tongue and groove boards together at an angle and hang it to a barn door system.
The sliding hardware is made from 1/4" steel bars and patio door bearings. The steel can be bent on an anvil. Use a hammer and a large screwdriver to create the right bend.
Step 24: Trims
Remember the window sills step? We had to take a piece of wood off in order to fit the 2x6 in a 3/4" groove. Well, we can use these off cuts to make door trims and base boards. It is a good idea to bevel the upper edge to make the trims smoother.
Step 25: Ventillation
We are using a system called Lunos e2 neo. This is a heat recovery ventilation (HRV) system that works without ducts or a central unit. You need to install one on each side of your house and they will work together to recycle your air. The air goes through a ceramic core which traps the heat and redistributes it in your house when the fans change direction.
It is important to have a ventilation system in a tiny house, especially if you have a wood stove. Carbon monoxide can accumulate if you don't have enough oxygen in the room.
Also, the ventilation gets rid of high humidity that can potentially cause black mold.
In the winter, we found that humidity can cause the outside vents to ice up. This will stop your flow of air. If you are burning wood, it will trigger your carbon monoxide detector. We are now only using the plastic cover in spring summer and fall (prevents insects, seeds, birds, etc).
Step 26: Heating
If you live in a cold climate, you will need heat. Fortunately, this house is highly energy efficient because of its thick insulation and heat recovery ventilation system. In addition to that, the volume of air to warm up is small so you don't need a full size heating device.
We chose a small wood stove from Cubic Mini Wood Stoves which outputs up to 18,000 BTU. This is enough to heat the whole house even when the temperature outside reaches -40C.
The flue is a 3" Pellet stove pipe with double walls. Since the stove is so small, the gas produced are colder than a traditional wood stove and we can use pellet stove pipes.
For the fuel source, we are using compressed hardwood bricks cut in half. They last 2 to 3 hours, have a steady burn rate and produce hardly any creosote.
During the day, when no one is at home, a 1,000W convection heater maintains the heat to around 15C.
Step 27: Cooking
In order to cook, you need a heating source. There are usually 2 types: electric or propane.
We opted for a 24" propane range in order to be more independent from the electrical grid. Since the propane line hasn't been installed yet, we are using electric appliances in the meantime.
Surprisingly, we have found that a 1,000W table top stove and a 1,200W induction plate are enough to cook most meals.
Step 28: Water
In most cases, you tiny house on wheels won't have a direct access to city water. A solution to that is to have a water tank and a pump to deliver water to the kitchen and bathroom faucets.
For this house, we are using a rectangular tank with a capacity of 65 gallons. If you don't have a shower and you are reasonable about your water consumption, this is enough to last weeks in a row. For example, we use less than 10 gallons per week between drinking, cooking and washing the dishes.
Faucets are getting water from the tank using PEX tubing. In between the tank and the PEX line, we installed a 12V water pump, a filter and pressure accumulator. With this setup, you don't trigger the pump every time you pour a glass of water.
For hot water, we have a propane on-demand water heater that will be plugged in once the propane line is installed.
If you live in a cold climate area, do not install your water lines in exterior walls as they would freeze in winter.
All the water collects into a single 1.5" ABS pipe to a grey water pit. Make sure to check your bylaws to know the regulations around waste water in your area. A heat trace needs to be installed along the waste water pipe to prevent freezing in winter.
Step 29: Composting Toilet
The toilet is one of the points I wasn't quite sure about when we decided to build a tiny house. I have to admit that a composting toilet is really easy to use and maintain. First, let's mention that it doesn't smell anything. There is a small 12V fan that pushes the air outside. The concept is quite simple, solids go in a bucket and urine goes through a rubber pipe that you can connect to your grey water drain. There is no need for a septic field since urine is sterile and the rest is composted. Add some wood chips or saw dust from time to time to decrease humidity, increase aerobic reactions and fasten the composting process.
Step 30: Entertainment
Having a small house doesn't mean you can't have a large screen. A projector is ideal since you can fold the screen to save space.
Our projector is located on the storage loft and the screen is on the first bean of the bedroom loft. You have to make sure the angle produced by the projector fits the size of your screen (you don't want to have to move the projector back too much).
For sound, we are using a Bluetooth speaker. The Anker is simply amazing. We watch shows every night and we probably only charge it once every 2 months.
Step 31: Conclusion
While it may not fit everyone's need, a tiny house is a great way to start owning your own house at a fraction of the cost of standard home. The small footprint allows to spend more money on good insulating materials which in turns makes you save money on heating and electricity.
The furnished house cost us about CAD $45,000 which roughly breaks down into the custom made trailer ($10k), building materials ($25k) and appliances ($10k).
This house costs about $30 electricity per month to run ($5 per month in summer and $60 in winter).
The overall environmental footprint of this house is minimal compared to a standard house.
Grand Prize in the
Tiny Home Contest