The aim is to design a sustainable tiny house on wheels intended for multi-week travels or short stays. As the word “tiny house” suggests, it’s a functional home equipped with all basic systems and spaces to enable a comfortable living. Time to get creative it seems.
To get a detailed and accurate insight into our available space, a 3D model of the stripped bus was created using high-precision laser scanning (more details in Chapter 2: 3D scan). This virtual model is now a very powerful source of information and allows for remote detailed design. As the design progresses, we hope to share some updates of the 3D model, a virtual preview of our future bus.
The detailed design phase starts with a basic floor plan. We opted for an L-shaped layout, making the front social area (living room + kitchen) feel as spacious as possible and create a somewhat hidden private area in the back of the bus for the bathroom and bedroom. As the original headroom is quite low (74” or 1.88m), it’s nice to have a kitchen section with maximal ceiling height and have the shower in a central location. From the outside we will try and keep the bus as authentic as possible. With the exception of a solar deck and rooftop terrace, nothing else will be modified or mounted on the exterior. The chassis (high above the ground) does however offer some great storage and hidden mounting opportunities underneath the bus.
In the section below you can find some more details on the different design tasks along with their status, general description and first ideas. Interested to get involved? Have a look at the ongoing topics and get in touch. Keep in mind our challenge is to focus on sustainability, which will guide the decisions we make during the design phase. Curious on your inputs :)
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Removing the original black vinyl flooring of the bus revealed some nasty and deteriorated coatings and glue. It appears that the steel subfloor sheets were originally coated from the inside with a blackish primer and a beige paint which has lost most of its adhesion to the primer. This beige paint along with the glue residues can be easily removed through soft grinding. The plan is to recoat the interior steel subfloor and ensure a proper (steel) protection for many more years. Question is, which new primer is suitable for the project and does the original black primer need to be grinded off as well?
Two new candidate primers were selected: waterbased (D5280) vs two component polyurethane (A29-75). A coating test was performed on both the old black primer and bare steel surfaces to assess and compare the adhesion quality of both primers. Note that a bare steel surface requires more intensive grinding which we would like to avoid if possible. The cross-cut tape test and scrape test revealed some interesting results (more details in the pictures below). In short, the two component primer (white) outperformed the waterbased primer (grey) on both surfaces. Its adhesion on the bare steel was perfect, on the old black primer a little variable which is possibly related to local surface impurities or insufficient coating thickness.
Final design: Only the beige (deteriorated) coating will be removed through soft grinding. Some local additional grinding will be performed to remove impurities and rust. Two layers of the two component polyurethane primer will be applied (datasheet).
Carbon compensation: In terms of ecological impact, the two component polyurethane primer scores somewhat worse than the waterbased primer. The coating process is somewhat unavoidable here and an appropriate compensation is still being assessed.
Acknowledgement: Geert - the selection of the new primers along with the careful guidance and detailed assessment of the coating tests would not have been possible without your help and expertise.
With the interior metal sheeting removed during the stripping process, there are a lot of possibilities for a new structure and finishing. To create a "cosy cocoon" effect and limit the amount of contact or exposure with the steel structure of the bus, a wooden structure was designed. There's however one ceiling section in the bus where the original metal sheeting will return and that's the cockpit. The idea here is to keep the driver's section as authentic as possible in order to maintain some original vibes of the schoolbus.
Final design: The subfloor structure consists of 25mm thick plywood straps (Ecoplex, Italy) assembled into a floating frame structure. This frame will be fixed along the right side to the lower strapping of the walls (to allow for expansion) and will contain the subfloor insulation. The frictional forces and fixation at one side should prevent the structure from sliding whilst driving. This design avoids gluing or screwing (which would make new holes in the steel subfloor) and can be easily disassembled for recycling purposes some day in the future.
For the walls, 2 layers of 12mm thick plywood straps (Ecoplex) will be mounted horizontally against the steel ribs of the bus. This is to minimize the contact surface with the steel structure. The first layer will be fixed with self-tapping screws to the ribs, whilst the second layer will be fixed with simple wooden screws to the first layer. Note that in this configuration the thermal bridges are avoided. An important aspect to consider is access to the windows (in case of damage). The design here only requires the vertical sections of the second layer to be removed. Note that a small cable duct was created just above the windows to guide and access the original and new wiring.
The ceiling structure will only consist of 1 layer of 12mm thick plywood straps (Ecoplex), this is to maximize the final headroom.
Carbon compensation: The plywood purchased for the project is known as Ecoplex from Panguaneta (Tutto-Pioppo), made of 100% Italian poplar veneer. The short production chain (biomass powered) and local (European) certified forest management were decisive in the selection of the final wood supplier. The gluing process of this plywood has a low formaldehyde release (class E1). For info, the company also manufactures NAF plywood (no-added formaldehyde), but unfortunately the project budget did not allow for this extra sustainable option.
Acknowledgement: The Ecoplex plywood was purchased from Groene Bouwmaterialen, which provided splendid support in the selection process.
Originally only the roof of the bus was insulated with glass wool, which was removed during the stripping process. To minimize the heat losses in the bus, an overall upgrade of the insulation is planned for the roof, walls, floor and windows. We'll further aim to minimize unwanted air leakages by sealing off small gaps and holes. Pure natural insulation materials were selected for the project, being a sustainable and recyclable alternative for the more traditional spray foaming or PU insulation.
Final design: The floor will be insulated with 25mm of expanded cork (ref. Amorim, Portugal) and has a thermal conductivity of 0,039 W/(m.K). Some advantages: the cork is moisture resistant (important in case of accidental water ingress), provides decent structural support and has acoustic and vibration damping properties. Given the limited headroom in the bus (1.88m), the final floor insulation thickness was a trade-off between additional insulation and reduced headroom or space.
The walls and ceiling will be insulated with 60mm of sheep wool (ref. Isolena, Austria) and has a thermal conductivity of 0,033 W/(m.K). This natural waste stream product has some unique additional properties: acoustic damping, humidity regulation (can absorb and release moisture up to 33% of its own weight without losing its thermal properties) and neutralizes harmful substances in the air such as formaldehyde which is present in most wood-based sheet material.
Although the sheep wool is capable of absorbing some moisture, we do want to limit the moisture transfer between the (hot) interior of the bus and the (cold) outer structures. This is to avoid possible condensation in or behind the insulation which will damage the steel structure of the bus or insulation materials over time. Hence, a vapor barrier (Pro Clima Intello) will be installed as well.
Carbon compensation: The expanded cork is claimed to be carbon negative (i.e. more carbon was absorbed during its growing process than released during production). We will however compensate for its transport from Portugal. Although the sheep wool is a natural waste product, it does have a global warming potential (GWP) linked to it. The Isolena (page 17) indicates a GWP of 0.83 kg CO2eq / kg Isolena sheep wool and also includes a comparison with glass wool and rock wool. An additional compensation will be considered for the transport from Austria. The only non-natural material is the vapor barrier, which is unfortunately difficult to avoid and an appropriate compensation is still being assessed.
Acknowledgement: Above natural insulation materials were purchased from Groene Bouwmaterialen, which provided splendid support in the selection process.
The original sliding windows are a key design feature of the bus giving its authentic and unique look. A lot of design efforts were spent so far finding different solutions to upgrade the insulation and air tightness of these windows. A long considered solution was installing a second row of windows from the inside of the bus, integrated into the wooden shell structure. A tricky aspect and challenge was however accessing the interior windows for cleaning, which meant the glass had to be easily accessible and removable. In addition, the fixation of the glass had to persist the vibrations and shocks whilst driving. It's probably clear by now this solution was not straightforward.
Final solution: Although not yet 100% confirmed, the idea is to keep the original aluminium window frames and replace the 2 smaller panes by a single vacuum glass (Fineo, AGC). This vacuum glass is double-paned (2x 3mm) and is separated by 0.1mm of vacuum through small 3D printed dots. The insulation properties of this very thin glass are identical to triple-paned standard windows (U =0.7 W/(m2.K). The original frame has a 14x13mm U-shaped profile on both vertical edges. Critical question, is this sufficient to fix the new vacuum glass? We're currently in contact with some specialized glass suppliers to assess the feasibility of the final solution.
Note that we won't be able to open the individual windows any longer, but the design foresees sufficient active ventilation and we can still open the front door, emergency side door, back door, driver's window and 2 emergency windows for extra ventilation. The horizontal mid-window aluminium profile can remain, so that visually the window looks nearly identical to its original state.
Carbon compensation:
Acknowledgement: Bart (2B GlasTechnieken) - without your help and expertise we would not have been familiar with this unique glass and its unique solutions.
With the insulation tucked behind or inside the wooden strapping and the windows replaced, it's time to cover and finish the interior of our cosy cocoon.
Final design: The floor will be covered with 6mm thick plywood sheets (Ecoplex, Italy) to even out any bumps or irregularities. The living area (front part of the bus) and passway to the back will be finished with a linoleum floor (Forbo, Marmoleum Click) which provides a natural, durable and easy to maintain flooring solution.
The walls will be finished with 12mm thick plywood sheets (Ecoplex) whereas for the roof we will use 6mm thick flexible plywood sheets (Ecoplex) to preserve the curvature of the roof structure.
All visible or exposed woodwork will be protected with an invisible, waterbased and natural wood wax from Horsemen. This company has a very interesting background and vision which is reflected in all of their products.
Carbon compensation: The plywood purchased for the project is known as Ecoplex from Panguaneta (Tutto-Pioppo), made of 100% Italian poplar veneer. The short production chain (biomass powered) and local (European) certified forest management were decisive in the selection of the final wood supplier. The gluing process of this plywood has a low formaldehyde release (class E1). For info, the company also manufactures NAF plywood (no-added formaldehyde), but unfortunately the project budget did not allow for this extra sustainable option.
Acknowledgement: The Ecoplex plywood and natural wood wax was purchased from Groene Bouwmaterialen, which provided splendid support in the selection process.
With the exception of the engine and back-up heating system, everything else in the bus will be electrified. This means that we’ll need an advanced and robust system allowing to connect and integrate all subsystems (solar panels, solar controller, battery storage, inverter, battery charger, shore power, etc). To build this central system, we’ll be using Victron Energy products, a well-known and high-quality supplier of off-grid electrical solutions.
Final design: A technical area or wall is foreseen in the back of the toilet. This is a central and easy accessible location but at the same time somewhat hidden away. Any audible noise from the inverter should thus be limited in the living or sleeping areas. Based on an initial assessment of the AC and DC loads in the bus, following products from Victron Energy were selected and purchased from Dobbelaere-AE (an official and local dealer of Victron Energy):
- Victron MultiPlus-II 48V 5kVA 230V
- Victron Cerbo GX
- Victron Lynx Distributor (2x)
- Victron Lynx Shunt VE.Can
- Victron SmartSolar MPPT 150/35
- Victron Orion-Tr 48/12-30 (360 W)
- Victron GX Tank
The final fuses, switches, cables, clamps, etc. will be selected and purchased at a later stage.
Carbon compensation: These are all new products, an appropriate compensation for its production and transportation is being assessed.
Acknowledgement: As this electrical system is the core of the bus (no electricity, no fun), it's been very reassuring to have Donald from Dobbelaere-AE follow up on the design together and provide very valuable expertise and user experience.
PS: EXPLORIST.life has some great youtube content on DIY camper electrical system installs.
As electricity is our main energy demand, we will definitely need a sustainable and off-grid power supply source. The front roof section of the bus (up until the emergency hatch) is an ideal location for a solar deck. We initially had in mind to design an adjustable tilt structure, but were advised it's not worth the time, efforts and risk.
Final design: Three large bifacial solar modules will be installed (ref. Meyer Burger Glass). Some key specs: 380 Wp (rated power), 120 half-cells, monocrystalline n-Si, HJT (heterojunction) cells, 1722 x 1041 x 35 mm (dimensions), 24.4 kg (weight). Given the solar modules will be permanently fixed in horizontal position, we hope to gain some additional output through the reflection on the roof of the bus (hence the choice for bifacials). The overall installed capacity as such is 1.140 Wp.
As the installed (permanent) capacity might be insufficient for an all-electric living, we will foresee an additional connection for a ground deployed solar array. This gives us quite some flexibility depending on the time of the year, intended travel duration or location.
Carbon compensation: The solar modules from Meyer Burger are manufactured in Germany (and designed in Switzerland). It's not yet clear what amount of carbon compensation is required to offset its initial production. We will however compensate the transport from the manufacturing plant in Germany (Freiberg or Bitterfeld-Wolfen).
Acknowledgement: Brecht - without your procurement and logistic support we would not have been able to select these specific solar modules for the project.
It's anticipated that the bus will be stationed mostly off-grid. To ensure electrical power supply, even in days with limited to no sun, an adequate battery pack will be installed. This particular design is one of the key examples of our focus on sustainability in this project. Considering the significant ecological and carbon footprint of newly produced batteries, we instead opted for second-life EV batteries (EV = electric vehicle). These “end-of-life” battery packs (for transport purposes) usually still have a capacity of over 80%, making them ideal for stationary energy storage applications where weight/volume vs capacity is less critical.
Final design: The initial battery pack design consists of 6 second-life Porsche Taycan battery modules. Some quick module specs: 2.86 kWh (capacity), 22.2 V (nominal voltage), 12 kg (weight), 390 x 150 x 110 mm (L x W x H). These modules will be arranged in a 48 V configuration. A custom BMS was developed by wdrautomatisering to control and monitor the battery pack. The BMS is capable of communicating with the Victron Energy system. Further extension of the battery pack is possible should this be desired in the future.
The modules itself will be mounted indoor underneath the bed and near the central electrical system of Victron Energy. The advantage of indoor installation is better protection against environmental conditions (incl. freezing temperatures) and monitoring of the battery conditions. The modules have a mounting hole in every corner (very practical at first sight), the idea would be to stack the modules per two, install some rubber dampers and fix the structure with the aluminium 40x40 framing.
Carbon compensation: As these are second-life components, no compensation is accounted for its original production. We do however take into consideration the transportation from its storage warehouse to the bus and back, roughly 572 km or 42 kg CO2. An emission factor of 1.326 kg CO2/ton/km was applied (source).
Acknowledgement: This somewhat showcase design using second-life EV batteries would not have been possible without the support and expertise of Walter from WDRAutomatisering.
The thought of having breakfast or dinner on top of the bus, or stargazing at night seems incredible.
First ideas: Towards the rear of the bus we have some space left for a rooftop terrace, accessible via a little stairs on the back. The idea would be to design a minimalistic terrace with some removable safety guides to keep the total height of the bus as limited as possible.
Carbon compensation:
As the available storage area is limited in the bus, we'll need to optimize and use every little corner or space.
First ideas: There was this initial idea of creating additional sub-floor storage. This however requires making additional openings in the steel floor, which we want to avoid. At a later stage during the build, it might be worthwhile to investigate left-over and convenient spaces which we might use for extra storage. (to be continued)
Carbon compensation:
With the wooden and insulated inner shell in place (on paper at least :D), the interior framing and subdivision of the bus can be designed. A common and lightweight choice is wooden framing. A likely risk and issue with wooden studs (usually young spruce wood) is deformation and twisting over time. This can be avoided by using (tropical) hardwoods or extensive gluing but doesn't feel like the most sustainable and circular option.
Final design: The primary structure of the bedroom, dressing, bathroom, shower, and wheel well platforms will be constructed from 40x40 mm extruded aluminium ISB profiles (ref. Easy Systems). This aluminium framing creates a very rigid and strong structure which does not deform over time and is not susceptible to vibrations or loosening bolts when properly assembled with blue loctite. This single-piece aluminium structure (when assembled) will be fixed to the steel structure of the bus at some specific locations (not too many as these connections create cold thermal bridges).
Carbon compensation: The aluminium framing design allows for easy disassembly and segregation of the raw building materials in the (far) future. This circular, sustainable and recyclable aspect was an additional trigger to choose for the aluminium framing. The aluminium profiles do have a non-negligible carbon footprint linked to their initial production, hence we're also looking into secondhand profiles for the project and a suitable carbon compensation.
Acknowledgement: Jan - brilliant in the design and construction of large machinery, was so kind to review and assess this (relatively simple) aluminium framing design and provide some very valuable suggestions along with mounting techniques.
Waking up surrounded by nature and having windows pretty much all around you to enjoy the magical views is a must :) The rear two sections (or windows) of the bus are an ideal space for the bedroom and in principle large enough to fit a queen's bed (160 x 200 cm).
Final design: The primary structure of the bed and bedroom is constructed from 40x40 mm extruded aluminium ISB profiles (ref. Easy Systems), which forms part of the larger aluminium framing design. The bed platform is lifted 68 cm from the ground as to create a large storage space underneath for the battery modules, water tank and extra storage both accessible for the inside and outside of the bus. A wooden finishing (Ecoplex) will be applied to cover all visible aluminium framing as to create a warm and coherent interior. The two wall panels at either side of the bus create a somewhat more private and cosy bedroom.
Carbon compensation: See "aluminium framing" task.
Acknowledgement:
Remote or homeworking from the bus is another must :) Hence, we'll need some large and multi-functional desk space as we won't be working all the time.
Final design: A desk can never be too big. The current design foresees a 140 x 72 cm table top, which should create a spacious and comfortable work space. Along with the outdoor landscape views, be ready to boost your creativity or simply dream away :D For the dining configuration, the table top will slide towards the center as to create a large dining table for 6 persons. Additionally, for the sleeping configuration, we should be able to lower the table top as well, to create an extra double bed together with the sofa (a must for friends to sleepover :D). A first 3D concept was designed which will be further optimized in the coming weeks. Happy to receive further ideas or suggestions.
Carbon compensation:
A warm shower is heaven and definitely not to be excluded from the design (we will however need to be careful with the shower durations, the water supply is not endless :D). As we wanted to maximize the headroom and showering comfort, the shower is located in the center and near to an air extraction point.
First ideas: To avoid water spilling in all directions in the bus or making everything wet in the bathroom, a separate shower cubicle will be constructed (part of the aluminium framing). We're looking into unique and practical designs along with sustainable materials for the cubicle finishing.
Carbon compensation:
Acknowledgement: Thomas
The rear wheel wells are often tricky to integrate into the design as they stick out more than 20 cm above the steel subfloor and have this large curved shape. This raised area however seems like an ideal location for the toilet, the throne or king's seat of the bus :D
Final design: To avoid additional plumbing and a separate black water tank, a composting toilet will be installed (final model not yet selected). There's some additional space foreseen in the bathroom for a small sink and storage. Note that the emergency window is conveniently located next to the toilet and opens via a top hinge, enabling additional ventilation should it be needed :D
Carbon compensation:
Fresh water, both hot and cold, seem essential for a comfortable living. To allow for remote and extended adventures, a decent amount of water storage will be required onboard of the bus. In the end it's all about being careful and efficient with your water usage.
Final design: A big bus allows for a big fresh water tank, hence a 450 liter food-grade MDPE water tank (from Wydale Plastics Ltd) was selected for the project. This water tank is rotationally moulded as a single piece and has a central baffle to reduce sloshing whilst driving. The water tank will be installed indoors (for better protection against freezing temperatures) and near the rear axle (left side) for better load distribution. Given its length of 115 cm, the tank will partially slide underneath the bed.
A water pump (LILIE SOFTSERIE) will supply the cold fresh water to the bathroom, shower, kitchen and boiler. Some quick technical specs: 11.3 L/min (max. flow rate), 2.1 bar (max. pressure), 12 V (power supply).
In the corner of the kitchen, hidden in the cabinetry and near the diesel (HVO) heater, a hot water boiler will be installed (roughly 25 liter, final type not yet selected). The boiler will allow for both electrical heating and diesel (HVO) heating via an internal heat exchanger.
The grey water tank (collection of waste water, not to forget) will be mounted underneath the bus (same location as the fresh water tank) and fixed to the chassis. The capacity of this tank will be somewhat smaller though, roughly 200 liter.
Carbon compensation:
Acknowledgement: Cedric (Vanderer) - thanks for sharing your professional knowledge and providing useful tips regarding water supply and plumbing in a van or bus.
Belgium has a rather mild climate; it tends to freeze a couple of times during winter, whereas temperatures above 30 C are limited during summer. However, we never know where the adventure might take us, so we should be prepared for both moderate cold and moderate hot climates. Sahara or North Pole expeditions might be a little too extreme in this case :D
Final design: In terms of heating (most important), both an electrical system and a back-up (booster) diesel system will be installed. The electrical heating will consist of small electrical air blowers (roughly 500 W each) and should be suitable for mild conditions or short trips with sufficient battery level. The diesel (HVO) heater from Webasto (Thermo Pro 90) will ensure a cosy warm bus in winter season where the electrical heating would simply consume too much energy and drain the batteries in no time. The diesel (HVO) heater, mounted underneath the chassis, will heat up a coolant (glycol) and pump this to small air heat exchangers in the bus (Florida 3 No Noise, each 3 kW). The hot water boiler will be included in the heating loop as well, to allow for optional or back-up heating via the diesel (HVO) system.
In terms of cooling (more for comfort), a small roof-mounted air conditioning unit will be installed in the bedroom, to allow for comfortable nights in hot climates. The final model of the air conditioning unit will be determined soon.
Carbon compensation: Initially the aim was to design a full-electric heating system using efficient heat pumps, however, the required heat load in cold winter conditions is simply too large (doesn't surprise in a way). As not all processes can be electrified (is sometimes also not the most sustainable option), the diesel heater will run on HVO (100% renewable diesel) similar to the engine of the bus. There's a small carbon footprint linked to this biofuel, which should be compensated for during the lifetime of the bus. It's however a very clean alternative to fossil fuels and an ultimate combo of a high-density energy carrier, sustainable fuel and limited carbon emissions.
Acknowledgement: Toon - thanks for initiating and assisting with the heat loss simulations of the bus ;)
Proper ventilation is critical to ensure sufficient fresh air in the bus and extract humid air to avoid or limit possible condensation. As probably most of the windows will no longer be able to open or slide, we will need an active ventilation system.
Final design: The central emergency hatch in the roof of the bus will be removed and replaced with a MaxxFan Deluxe from Maxxair. This central location is right above the cooking area, allowing to immediately extract the hot and humid cooking air to the outside. Throughout the day, the fan will ensure continuous ventilation of the living area. The shower cubicle and toilet (wet areas) are located in the vicinity of this central extraction point (by design) and will be connected via appropriate openings and ducting. As the required opening for the fan is somewhat smaller than the hatch (40 x 40 cm), a transition piece was designed with durable Trespa material.
Carbon compensation: ongoing
Acknowledgement: Cedric (Vanderer) - thanks for sharing your professional knowledge and experience regarding ventilation in a van or bus.
Coming from the renewable industry as project engineer and driving electric for a couple of years now, I initially wasn’t too keen on driving around with a V8 7.3L diesel engine from 1996 (despite the iconic look and feel of the bus). At some point it popped up our minds to convert the bus into an electric one. A quick calculation on the required battery pack for a basic range of 300-400 km soon made us realize this was not an option for the bus (with the current batterytechnology). The ecological impact and cost of this gigantic battery pack would be difficult to justify as well.
Instead, looking at the alternatives for heavy duty transport, we came to know HVO100 (hydratedvegetable oil) also known as “renewable diesel”. This fuel is produced from 100% renewable waste streams and blended with hydrogen in a specific process to create the renewable diesel. It’s claimed to reduce the CO2 emissions by 90% compared to conventional diesel. It’s a little more expensive at the station (as somewhat expected) but perfectly fits the project philosophy and allows for some great mileage with a single full tank (160L).
First ideas: We would like to go even a step further here and are currently looking into the option to install some additional EGTS (exhaust gas treatment system). The idea would be to install a diesel particulate filter which we would regenerate manually from time to time by dismounting the filter and placing in a small industrial oven.
Carbon compensation: We still need to compensate for the remaining 10% of CO2 emissions somehow. We keep track of all trips with the bus, have a look at the project overall statistics.
