Vehicles
So from previous, a vehicle assembly line can produce 100,000 vehicles per year, and vehicles can exit the line at the rate of 1 vehicle per minute or 4 minutes. The line operates continuously, and some lines can produce more each year. The total production time used to be indicated as between 2 and 4 weeks, though now appears to be 18 to 35 hours so less than 1 week. However, apparently can expect it to take a few months when order a vehicle, even though there are acres of land covered with unsold vehicles. So whilst the vehicles can be produced quickly, the right vehicles are not necessarily getting made in the right places.
If everything was right, then the next vehicle of the production line a minute from now would be yours. However, if want custom features, then your vehicle has to flow from the start of the production line to the end acquiring all the custom features. So if your vehicle can be put on the line immediately, then will have to wait 18 to 35 hours. But if there is a waiting list or orders to be filled, then it could takes weeks before your order reaches the production line. What really want is, to be able to go to the car sales lot, pick a car and drive away the same day. So cars being sold are not necessarily the cars which are desired, they are the cars which are available, which can otherwise fulfil the dependency on a car.
{Global market apparently around 57.5 million units each year}
Shipping Containers
The largest manufacturer of shipping containers produces 2 million containers each year in 11 factories, so averaging 181,818 containers per factory.
{Global Market apparently 1.04 billion twenty foot equivalent units (TEU) each year}
Housing
The housing crisis is global not just a local issue. A housing shortage has existed for decades. Currently there is an estimated 1.6 billion people lacking adequate housing, and expected to grow to 3 billion by 2030. Back in the 19080's there was also an indication that 75% of global housing was inadequate, I'm not aware that this has been changed. One prediction is that maximum sustainable population is 10 billion. The world reached a population of 8 billion in 2022, so we are getting close to the limit. However, the limit is still greater than the current population, and only an estimate, so still useful for planning. Whilst some countries are experiencing population decline, the world population is still growing. So assuming an industrial city-state of 100km diameter, and maximum population of 10 million, then 1000 such cities will be needed. Assuming population distribution matches current distribution, then each country has more cities than needed, and population can be distributed to smaller cities over larger area.
If consider most of the population is going to live in sole occupancy units, then need 10 billion units, if population to be coupled up then need 5 billion units, if families of 4 then will need 2.5 billion units. Given average household occupancy of less than 3 persons, then will need 3.3 billion units.
Given that average household occupancy is less than 3 persons and we have a housing shortage, the implication is that average household occupancy needs to be 1 or 2 persons. So assuming in the next five years need to produce housing for 3 billion, then 0.6 billion each year sole occupancy units. A sole occupancy unit is typically adequate for a couple, and may just be tolerable for a young family. In any case if aim for modular sole occupancy units they can be combined to create family units. The number of modules basically remains the same, though can possibly save a few modules on family units compared to multiple sole occupancy units, as facilities like kitchens, bathrooms and laundries can be shared.
If only make 0.6 billion units each year, then maybe considered as not adequately addressing the current shortfall. Should want to see currently shortfall removed as quickly as possible, not a 5 year plan, or 15 year plan and certainly not a 30 year plan. Shortfalls should be eliminated in less than 1 year. So that would be 1.6 billion sole occupancy units in 1 year, or 0.4 billion family units. which would then leave 1.4 billion to be provided in remaining 4 years, so drops to 0.35 billion sole occupancy units each year.
Assuming 99% of buildings already exist, then possibly only need to cater for the shortfall. However, if 75% inadequate also need improvements. The main inadequacies are kitchens, bathrooms, and laundries, that is water supply and sanitary drainage. Here in Australia, expect around 5% of households to undertake renovation involving bathrooms, kitchens, verandahs, or outdoor decks, or possibly adding an extra bedroom.
So if have a city with zero population growth, and it has a population of 10 million, in 5 million dwellings. Then estimate a need for production of around 250 thousand units every year for replacement and maintenance. Which if a single factory can produce 100,000 units, would need at least 3 factories to each city.
Or from another perspective Australia with a population around 25 million, only needs 3 industrial city-states, and therefore a total of 9 factories. It has more cities and potential for more factories. If it has more factories then it can produce more units, and if it has more units available, then more dwellings can be renovated or replace each year.
Modular Buildings
To be clear offsite prefabricated does not equate to modular. If have true modular then floor plans are determined from the available modules. If don't like the floor plan after a few weeks, can rearrange the modules, if want more floor area can acquire more modules, if want to increase the number of storeys can again add more modules. If at some point in the future want less space, then can remove and sell the modules which are surplus to current requirements.
If simply have offsite prefabrication, then floor plan is fixed, and future renovations are hindered. As simply offsite prefab and custom designed, new customised transportable segments have to be designed and fabricated to fit the existing segments. It is time consuming and expensive, compared to buying off-the-shelf modules. It is possible that off-the-shelf volumetric modules can be delivered within 24 hours, and within a day the house is extended. No waiting for design, approvals or fabrication.
Production of Prefabricated Buildings
Mean while manufactures of modular buildings are only able to produce a few thousand (ie. 4000) modules per year or tiny house builders and transportable house builders are only producing around a few hundred (ie. 250) each year. Time frames for supply are also suggested at around 4 to 12 weeks, or longer at 18 months.
Is the short fall for builders a consequence of process, a technical limitation or a consequence of low demand?
There is a global shortage of houses, and prefab buildings have to be designed as transportable segments or units. These segments/units have to be constrained to the same dimensions as vehicles, this puts them into the same size range as cars and shipping containers. The buildings can be shipped to the world. It would appear that the demand far exceeds the willingness to supply.
From previous, a box from composite panels can be produced in 10 minutes, a caravan with kitchen and washroom in 7 hours, and the shell for a larger building in one day (say 8 hours). A tiny home can be framed in cold-formed steel in 4 hours.
Assuming the following production stages:
- Floor Assembly
- Wall Assembly
- Roof Assembly
- External Roof Cladding
- Electrical Systems (1st)
- Plumbing Systems (1st)
- External Wall Cladding
- Internal Wall Linings
- Internal Ceiling Linings
- Electrical Systems (2nd)
- Plumbing Systems (2nd)
- Windows and Doors
- Internal Decoration
- Bathroom Fitout
- Kitchen Fitout
- Quality Checks
and 1 day at most for each stage, then expect a upper limit of 16 days., so at 5 work days per calendar week, then needs around 4 weeks to produce. But clearly the caravan industry can complete all these stages in one day, and a typical module is not expected to be larger than a caravan, furthermore a typical module is empty space. So just looking at the shell:
- Floor Assembly
- Wall Assembly
- Roof Assembly
- External Roof Cladding
- External Wall Cladding
- Windows and Doors
- Quality Checks
This appears achievable in 1 day, leaving:
- Electrical Systems (1st)
- Plumbing Systems (1st)
- Internal Wall Linings
- Internal Ceiling Linings
- Electrical Systems (2nd)
- Plumbing Systems (2nd)
- Internal Decoration
- Bathroom Fitout
- Kitchen Fitout
- Quality Checks
Now if the electrical and plumbing were integral with floor, wall, and ceiling panels, along with internal linings. Then remaining stages would be reduced to:
- Internal Decoration
- Bathroom Fitout
- Kitchen Fitout
- Quality Checks
The vast majority of modules are empty space, and don't need bathrooms, kitchens or laundries, so that just leaves internal decoration and final quality checks. So if we make wet areas as separate modules, then we can speed up the provision of basic shelter. Wet area modules can be produced on a separate production line, and then they are plugged into basic space modules to create a whole dwelling. As modules for wet areas are smaller then the shell can be produced faster. The rooms possibly expect in a dwelling with recommended dimensions for resale are:
- Kitchen (3m x 2.7m.)
- Bathroom (1.8m x 2.4m) /WC (1.8m x 1m)
- Laundry (2.7m x 2.1m)
- Dining Room (3m x 3m)
- Lounge (6m x 3.6m)/Living Room
- Master Bedroom (3.6m x 3.6m)
- Additional Bedrooms (3m x 2.7m)
In South Australia, minimum housing standards require a room to have a minimum area of 7.5 sq.m to be considered a bedroom (ie. 2.74m x 2.74m). Also note that these dimensions are internal usable space, however most of the dimensions are recommendations not requirements. Also broad loom carpet is 3.6m, so anything wider and the carpet has to be cut and has a seam.
So if we have 3.6m wide rooms and a 1.2m wide corridor between then get a maximum width of around 8.4m, allow 0.3m for external walls and 0.1m for internal, then add an extra 2*0.3+2*0.1=0.8m bringing over all width to 9.2m. So don't expect to span further than 9.2m: which wouldn't need to do as have modules providing walls at 3.6m centres or less.
Possible modules:
- Narrow (2.4m high x 0.6m wide x maximum 12m long)
- Small (2.4m high x 0.9m wide x maximum 12m long)
- Basic (2.4m high x 1.2m wide x maximum 12m long)
- Wide (2.4m high x 2.4m wide x maximum 12m long)
These would be internal dimensions, so assuming external walls do not need to be more than 150mm thick, then over all width of wide module would be 2.7m and not readily transportable. Though the basic module wouldn't need walls, and these can be transported separately and installed on site, in which case the thickness of the walls can increase to 300mm or so each.
So to create a lounge or bedroom would need either 3 basic modules side by side, or one wide module and a basic module, to get width of 3.6m. Modules can be made with two opposite walls missing, or open on one side only. So a 2.4m wide module never has side walls as it would make it too wide to transport, whilst the smaller modules do have one or both the side walls as they wouldn't be too wide to transport. Also the smaller modules can be defined by over all width, or internal width only.
So assuming 200mm insulated wall to one side only, then a 600mm wide module can be considered as providing an additional 400mm of internal space. So fitted to each side of a 2.4m module provides an additional 800mm of internal width, to get 3.2m of internal space.
To create the 8.4m requirement, as 2 segments 3.6m and central corridor 1.2m wide, can use 2 wide modules and 3 basic modules. One basic module, the corridor, can be provided with walls on both sides to provide internal division into rooms. The other basic modules can either be combined together, or placed on the exterior of each room. If placed to the exterior then these modules can have the external walls fitted.
Then the other approach considers that 8.4m is less than 12m, so can place 2.4m x 8.4m modules end to end to create a building 8.4m wide of any length. So when comes to basic rooms and empty space the modules are not such a problem.
Creating rooms which have to be fitted out before transported can be a problem, as may not be possible to create a room large enough which can be transported. Creating a WC seems viable, whilst a bathroom at 1.8m x 2.4m is viable if adopt a 1.8m wide module and as long as needed. A laundry at 2.1m x 2.7m is relatively large, and probably more often about 1.8m wide. This allows 900mm width for equipment on one side and a 900mm walk through to the back door. So again a 1.8m wide module as long as needed, or alternatively adopt 2.4m wide modules. That primarily leaves the kitchen as a problem, it being 3m x 2.7m, with neither dimension suitable for transportation. But then again tend to have cupboards going along one wall, or opposite walls creating an aisle between. So could use a 2.4m module and a 0.6m module, or two modules 1.5m. Or module could be 3m wide on open faces, and then 2.4m wide strip, which are placed end to end to create any length.
So to create longest buildings, do not span the 2.4m maximum width of segment, instead span the 12m maximum length of segment and add 2.4m segments end to end to create buildings of any length. In general wouldn't expect a need to span more than 9.2m. These segments can then have internal walls to create rooms from multiple segments.
So assuming that an empty shell can be completed every day, and that if the shell is assembled from 6 composite panels it takes a 10 minutes to assemble. Then in a 480 minute day, assuming an adequate supply of panels, can produce 48 modules each day. So with 250 productive days, 12,000 modules each year. If have 3 shifts then 36,000 each year. If operate continuously with as many shifts as needed, then can produce 365.25*24*60/10 = 52,596 units each year.
But if split the task into stations, then assume have 5 panels to attach to a base, so have 5 stations and each takes 2 minutes. So flow along line is at rate of 1 completion every 2 minutes. So in 24*60/2=720 units each day, and for the year 720*365.25 = 262,980 units.
If a sole occupancy unit requires 2 modules, then can produce 131,490 dwellings each year, and 2 factories would be required to produce 250 thousand dwellings each year. This is based on an assumption that takes 2 minutes to install a panel: it likely takes longer than that simply to move panel into position.
If the panels are light enough then an empty box can be fabricated relatively quickly. The panels have to be fabricated away from the main assembly line, and they have to be produced relatively quickly. So assuming 12m long, 2.4m high and 2.4m wide, and basic panel is 1.2m wide. Then need to produce 2 floor panels and 2 roof panels each 12m long, so total of 48m of panel. Similarly 48m for side walls, and 4.8*2=9.6m for end walls. So total of 105.6m of panel. {Alternative 10 panels x 1.2m wide x 2.4m high gives 24m each side wall, so 48m for both side walls.} Assuming panel formed at the rate of 2m per minute, then it will take 52.8 minutes to produce, which is slower than the building is assembled. Stock piling doesn't help, as will still eventually run out off panel, and have to wait. Therefore need more than one machine producing panels in parallel. Alternatively accept a lower production rate for the boxes and a need for additional factories or building production lines.
Also note our bench mark is 10 minutes to assemble a composite panel box, and 30 minutes to assemble cold-formed steel framing. The latter than needs to be clad both externally and internally, pushing production times still higher. But should still be talking about production times in minutes, not days or weeks.
A bathroom or kitchen renovation is likely to take 1 or 2 days, a week at most once they get on site. Most of the cupboards are fabricated offsite in any case, then adjusted to fit on site if necessary. It takes more than a day on site then really need to know what they are doing. So I don't expect wet area modules to take more than 1 to 2 days to produce. Also expect that most of the tasks involved would be less than 2 hours duration, so have potential flow at rate of 1 unit every 2 hours. So production of 12 modules each day, and 3000 modules each year, for 250 productive days.
Also note that depending on nature of building if less than 15 sqm here in SA, then may not need development approval. A factory can build laundry buildings (5.67 sqm) all day every day. Also a 6m shipping container is 14.4 sqm. Need extra bathroom (4.2sqm) space for the kids, then install a module, which can be accessed from the back laundry door. The laundry walk through is extended and the back door relocated, so don't have to walk outside to access the new bathroom. When no longer need the extra bathroom facilities then get rid of the module.
So modules are not simply for constructing new dwellings, they are useful in own right for extending existing dwellings. The modules have to be readily available, faster supply, and lower price than onsite construction. Simply shifting on site processes off site into a factory offers little benefit. There has to be concurrent design of product and process, and process has achieve consistent output so that have higher quality in a factory than on site. Simply shifting into a factory does not improve quality, nor productivity.
A single work team, with appropriately scheduled work processes, should be able to produce at least 250 modules each year: assuming no task takes longer than 1 day. If tasks can be further reduced than greater production can be achieved.
Note that whilst work can be staged, and crews can move between construction sites, such travelling is a waste of time. By shifting into a factory, only one site crew needs to travel to the site, most workers only travel to the factory and along a production line. A lot of subcontractors or trades will charge for a days work, even though only a few hours or even a few minutes work, and this is because getting to the site wastes the day. In a factory they can more readily move from building to building, and therefore can complete more buildings in a day, than they can if working on site. Therefore the price of factory built buildings should be lower. However have extra costs of transporting large object, and possible crane fees. But have these transportation and crane costs for large fabricated components. If building can be delivered by tilt trailer then transportation costs should be low.
So need more process time information, so that can move away from estimates based on hours and days, to estimates based on minutes, and get the flow rates better. So not interested in a day to fitout a bathroom or kitchen, really interested in how that time is built up, and if its possible to get such modules flowing from a production line at so many units per minute.
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