General
In the SA planning code basic restriction is that development shall not result in more than one dwelling on an existing allotment., where an allotment is for such purpose. Some allotments are for group dwellings, and multi-dwelling buildings.
Outbuildings and ancillary buildings are permitted on a residential allotment. Ancillary accommodation however was limited to that used by a member of the family, and the building dependent on the main dwelling for various services, such as bathroom, kitchen and laundry. However the extent of such dependency has become questionable as technology has changed. Obviously before mains services, the main dwelling and ancillary buildings were no different. Now the ancillary building is expected to have electrical power for lighting. With electric kettles and fry pans along with microwave ovens, cooking is permitted in a small space without need of a kitchen. If bedrooms can have ensuites, which maybe desirable for a "granny" flat, then have water supply. If have water supply, then get kitchen sink. The functions of kitchen, bathroom and laundry are available in a small space, and some can share space, and in some countries that is the normal, and technology has developed accordingly.
For example in some places it is normal to have a washing machine in the kitchen, in others to have it in the bathroom, there is thus no real need for separate laundry room. Such separate rooms made sense in the past, where laundry had its own trough and separate boiler, and various other large utensils. These days the equipment used is much smaller. Also some of these rooms were separate buildings, so the ancillary building was likely a laundry. In other situations whilst the laundry is part of the main building it is only accessible from outside.
We can also add the increase in outdoor living, growing veranda sizes, and outdoor kitchens. Thus external space and ancillary buildings can provide functions which overlap with and supplement those of the main dwelling.
Ancillary accommodation maybe required for extended families, or for those assisting the household, such as nannies, tutors, housekeepers, gardeners, and care givers. Given the costs of child care centres and nursing homes, this maybe a more affordable option. Whilst not getting rent, paying less for child care.
Again noting that average household occupancy is less than 3 persons per household, and that birth rate is less than replacement level, population growth is largely due to migration, either between towns or countries. The pressure for housing is largely due to inappropriately sized housing. The housing is inappropriate largely because its built as a financial investment for retirement rather than living in. Or property speculators building largest house for which they can demand the highest rent. The available housing is not compatible with the market need, and needed housing has been opposed because it has been seen as devaluing the over sized and priced monstrosities that are built.
We don't really need more land rezoning and more houses. We need the land using better to provide more appropriate housing. For the most part that is independent sole occupancy units, and two person units, to free up the 3 bedroom dwellings which dominate the supply.
The owners of a property are not necessarily the people who live in an accessory dwelling unit (ADU) or in ancillary accommodation (AA). For example an elderly couple could downsize to the ADU, and rent the main dwelling to others. This way they retain access to their gardens and neighbourhood, and a family gets a dwelling with gardens they don't need to maintain, as the owners do that.
For the following I mostly referred to requirements for the neighbourhood zone in the SA Planning Code, other zones may have different requirements. In some instances the code is not very clear as it just gives long lists of options, but no criteria as to which applies.
Allotment Size
Smallest allotment size permitted per dwelling is typically on an allotment with group dwellings, such as a retirement village or residential caravan park. The smallest site being in a caravan park, in the old council development plans it was commonly 81 sq.m, but the new state planning code has increased this to 100 sq.m. Otherwise the minimum seems to be around 150 sq.m to 250 sq.m. Though in rural areas where using a septic system, the minimum area is 1200 sq.m.
So a block could have been 9m x 9m, whilst now it would need to be 10m x 10m. For an ADU it doesn't really matter as not subdividing the land, just putting an extra building on the land. However, can achieve increased privacy if can partition a piece of the land and set it aside as private to the ADU, and likewise land private to the main dwelling and that which is common space.
Assuming the 1/6th of an acre blocks of the 1970's, then have a block approximately 32m long and 21.333m wide. So to create a 150 sq,m block it would need to be 7.031m long, and for a 250 sq.m block 11.719m long. To subdivide would be looking at two blocks 16m x 21.333 (341.33 sq/m), formed as a hammerhead or battle-axe allotment, which requires using land as an access road, so the areas of the blocks reduce significantly (especially when some of the old council development plans required 9m wide two way access road).
So not really practical to subdivide allotments to create additional properties. Really need to merge allotments, to create group dwelling complexes, or create ancillary accommodation on existing allotments. That is make more suitable rentable accommodation available for 1 and 2 person households, to free up the existing family homes.
Note that these minimums are for the allotment size, not the size of the building. There is no direct limit on minimum size of the building. The minimum size of building just comes from functionality, and meeting required performance criteria, which largely should be determined by anthropometric data and other human factors data.
Most of the additional requirements of the planning code, reduce the area of the allotment which can be used to provide buildings . So mostly concerned with ensuring buildings are not too big.
Boundary Set Backs
An ADU/AA will typically be placed in the back garden, though it could be placed side by side with the main dwelling.
The old development plans typically had set backs for front, rear and side boundaries. The new planning code doesn't consistently define these 3 set backs for each zone. It is most likely to define set backs for primary street frontage, and secondary street frontage, and side boundaries, with no mention of a rear boundary. Many of the given set backs typically do not apply to outbuildings or ancillary buildings.
The main rule is wall on the boundary or 600mm from the boundary. It is an access requirement to clear litter and prevent vermin. The NCC/BCA also has a requirement of 900mm from boundary to avoid fire rated construction. Masonry is considered to provide the accepted fire rating, so if closer than 900mm then need masonry.
Old development plan requirements typically had side boundary set backs of 1m. I hazard a guess this was response to the 1970's when for energy efficiency 600mm eaves overhangs became more popular, and several plan drafters , developers and builders, neglected the overhang and the gutter, with the result that the gutters overhung the neighbouring property. Also even if provide for the allowance, still have a continuous roof scape, and a lack of circulation.
Personally I consider the 600mm should be measured from the face of the gutter or other extremity of the building, since need to access the gutters for maintenance, preferably without going on the roof and without entering the neighbours property. So 600mm is just wide enough for small mobile scaffolding, which is considered preferable to ladders and steps. So allowing a maximum of 200mm for width of gutter and 600mm eaves overhang, and 600mm clearance, then wall needs to be at least 1400mm from boundary.
There are also ministers specifications for fire safety in caravan parks which require 3m separation of the cabins/caravans. So allowing equal spacing each property, then need 1.5m boundary set back.
The required set back from a primary street frontage is typically around 5m for the main dwelling or matching existing neighbouring dwellings. The actual value depends on the zone. For ancillary buildings it is 5.5m, it has to be set back from the front line of the primary building.
Set back from secondary street boundaries is typically 900mm, for main and ancillary buildings.
Side boundary set back maybe 1900mm or larger depending on the zone, site area and wall height. For small sites less than 800 sq.m, it is only 900mm.
The rear boundary set back at first floor level is 3m for the main dwelling, it does not apply to ancillary buildings and structures. The setback increases with wall height and site area.
Some websites have indicated a 3m boundary setback. I don't believe this is a requirement and is a misreading of the code. There is a 3m separation requirement but that is a different issue.
Walls on Boundaries
Walls on side boundaries are limited in length, the upper limit appears to be 11.5m depending on zone it could be smaller. But sum of all wall lengths is otherwise limited to 45% of boundary length. So with a 32m long side boundary, then would be limited to 14.4m of wall on the boundary. Whilst for the rear boundary (21.333m) a limit of 9.6m for the building.
As for the additional ruling, I'm not entirely sure what it means, but my interpretation is that if have more than one wall then they have to be separated by 3m. So if I have two walls on the boundary each 7.2m long, then they would have to be 3m apart. Or a single wall maximum of 11.5m, then a 3m gap, and another wall 2.9m long.
Also whilst it maybe permitted to build on the boundary, I personally consider that poor design and contrary to the origin of modern building codes, and contrary to the intent of the 600mm set back.
If two houses are built on the boundary there will be a gap between the two walls and water and other objects can get in that gap. Also note that water pressure is dependent on height not volume. Whilst the pressure may not develop high enough to burst brickwork, it is likely high enough to force water into permeable materials causing damp patches on the interior.
If going to have two adjacent boundary walls then they should be properly capped and sealed together on all sides: which I doubt is permitted. Secondly need to give consideration to circulation around the building. That is circulation for fresh air, and circulation for firefighters to have adequate access to the property.
A whole street of independent houses built boundary to boundary is poor design. Far better to build proper terraced or row houses, with appropriate ginnels to access the rear. Detached houses should be detached and clear of one another.
Separation of Buildings
For fire safety buildings on same allotment need to be separated, and the separation should not be less than 1.8m as required by the NCC/BCA. For caravan parks it is 3m as required by ministers specification. Smaller distances are permitted but that then requires fire rated construction, for which masonry is an acceptable solution. though there are other solutions available, some of which involve multiple layers of plasterboard
Building Floor Areas
Ancillary building floor areas not to exceed 60 sq.m for sites less than 800 sq.m, and not to exceed 80 sq.m for sites greater than 800 sq.m. It depends on zone and can be as low as 40 sq.m.
Note that is an upper limit, not a lower limit. So transportable modules 2.4*4.8 (11.52 sq.m) , or 2.4*12 (28.8 sq.m) are acceptable. If such area meets your needs and the requirements of a class 1 building, then it can be the main dwelling.
The problem isn't that we are prohibited from constructing small buildings, its that they are not being built, and there is a lack of vacant land to build them on.
Site Coverage
It is not permissible to cover all the natural ground surface with impermeable materials. There are thus limits on roof coverage and requirements for private open space and soft landscaping. Stormwater detention tanks may still be required to temporarily hold water on site during a storm even if meet these requirements.
For sites being considered, with ancillary buildings soft landscaping has to remain at 25% of site area for areas greater than 450 sq.m, for sites less than 150 sq.m the limit is 10%.
So for a site 32 x 21.333m site area is 682.7 sq.m, so soft landscaping has to be 307.22 sq.m, or 14.4m wide across the width of the block, or 4.8m wide each side down the length of the block. For a small 100 sq,m site, landscaping would need to be 10 sq.m, so for a 10m x 10m block, a 1m strip garden along any side.
Site coverage by buildings not to exceed 60% of the site, so for 682.7 sq.m site, maximum coverage by buildings is 409.62 sq.m. Given main dwellings are currently up around the 250 sq.m mark, this leaves 159.62 sq.m for additional buildings (which includes verandas). The upper limit for an ancillary building appears to be 80 sq.m, but for this site it would be 60 sq.m. So leaves 99.62 sq.m for sheds, carports and verandas. Though the houses on these sites likely less than 250 sq.m unless they've been extended, their areas possibly down around 150 sq,m. {If have larger floor areas, they maybe 2 storey, rather than the more common 1 storey.}
Private Open Space
Private open space typically has to be provided behind the building line, that is it is typically the back garden, the front garden doesn't count. The area required depends on the area of the site. If site less than 301 sq.m then require 24 sq.m, if over 301 sq.m then require 60 sq.m. With a requirement that at least 16 sq.m is directly accessible from a living room, and has minimum dimension of 3m.
Smaller areas are permitted for multistorey buildings typically in the form of balconies. Cabin and caravan sites are permitted 16 sq.m, no minimum dimension given, but can be used as a second car parking area.
This open space has to remain on an allotment after the ancillary accommodation building is provided. But it may be desirable to provide the ancillary building with its own private open space. Which is why I suggest a 9 x 9m or 10 x 10m site internal partition for the ADU, or possibly larger options of 15 x 10m, or 20 x 10m depending on width of main allotment. Also expecting that the building would only need be between 25 sq.m and 54 sq.m.
Parking Space
Typically site required to provide some off-street parking. Dwelling with 2 or more bedrooms, 2 parking spaces to be provided, one of which is to be covered. For dwelling with 1 bedroom, 1 parking space required. For group dwellings with 3 or more dwellings, space also to be provided for visitors, at rate of 0.33 spaces per dwelling or 1 extra space for every 3 dwellings.
So with ancillary accommodation on allotment, have less than 3 dwellings, and only need 2 parking spaces for main dwelling if has 2 or more bedrooms. So no additional parking spaces required for the ancillary accommodation.
Parking spaces 5.4m long, and 3m wide if enclosed by fencing, or 2.4m wide if uncovered and centre line is 1.5m from obstructions. (pg. 1627)
Storage
For 3 bedroom dwelling not less than 12 cu.m. For 1 bedroom dwelling not less than 8 cu.m. So assuming 600mm wide storage space, and 2.4m high, then would need to be 5.6m long. So a 4.8m long module may not meet the planning requirements for a 1 bedroom dwelling. For a 3 bedroom dwelling it would need to be 8.3m long.
Note this is not necessarily a reference to the dwelling, but the allotment. So additional storage space can be provided by outbuildings, if cannot fit in the main dwelling. So a garden locker, 0.6*1.8*1.2=1.296 cu.m of storage, and place these around the external perimeter of the building.
Waste Bin Storage
Storage space required for bins, area 2 sq.m and minimum width 900mm, and not part of private open space or car parking areas.
Subfloor Space
Space below transportable buildings is enclosed to give appearance of permanent structure. Seems more an issue for light weight construction mounted on pads and piers, with tie-down anchors, than simply transportable buildings. Also assume it doesn't apply to elevated buildings on stilts, especially in flood areas where want open space below, or buildings on sloping ground. That is the pads need to be hidden where inconsistent with neighbouring slab on ground construction, or suspended floors on dwarf walls.
Also note the NCC/BCA requires minimum openings for ventilation to the subfloor space. Also floor framing has ground clearance requirements. If no termite inspection requirements then 150mm ground clearance to underside of lowest framing, if termite inspection required then 400mm clearance. Note this is a poor crawl space. If want to access the space below to crawl around on knees, then 800mm clearance is preferable, and if want to squat and work, then 1250mm clearance. (Refer new metric handbook )
Storm water
Development may require rainwater tanks for both detention and retention. Generally these are additive, not shared storage space. For sites less than 200 sq.m 1000 L retained and 1000 L detained. so total 2000 L. Flat rectangular water tanks would suit these requirements.
Paving and Foot Paths
Generally the first metre of ground around a building should have a fall away from the building, and preferably should be paved. If the building is only 600mm or 900mm from the boundary, then the required fall is not met as the last 100mm to 400mm is on the neighbouring property and falling in the opposite direction. Also the triangular trough formed by the two neighbouring properties, has a smaller section area than provided by 1m of paving, and therefore a smaller volume of water which can be held in its length, and it will be closer to the two buildings than desirable.
So preferable that building walls are greater than 1000mm from the boundaries. The required fall depends on rainfall intensity and is either 25mm or 50mm.
Floor Level.
Required Finished floor level (FFL) is typically given relative to the Australian Height Datum (AHD), it may otherwise be given as some height above street kerb level. Typical values in the past have been 100mm to 300mm above kerb level.
For a slab on ground the finished slab level should be 50 to 150mm above the ground. It depends on rainfall intensity and whether the ground is paved.
Conclusion
The above outlines requirements of the SA Planning Code and some issues of the building code which overlap with planning as regards providing ancillary accommodation or for that matter the main dwelling.
As far as I can tell there are no minimum size dwelling or room requirements in either the planning code or the NCC/BCA. The only minimum is a ceiling of 2.4m and there has been increasing number of situations in which lower is permitted.
In Australia we don't have the confusion of manufactured buildings to HUD specifications that they have in the USA. In Australia all buildings are to the NCC/BCA: transportable, modular, manufactured. Constructed on-site or off-site it doesn't matter.
Building Code of Australia, BCA-1 is similar to the international building code (IBC) and BCA-2 is similar to the international residential code (IRC). According to the HUD website they have adopted the national models codes, which as far as I know are the IBC/IRC. And the IBC/IRC are adopted by states and cities, So the houses should be the same, except HUD indicates they have imposed additional durability requirements. Beyond that the HUD specifications require a chassis and wheels. Which is weird given HUD=housing and urban development. Point is shouldn't really be any confusion, though could do with changing the name, so the word "manufactured" can be used properly. So really have houses to HUD specification or to the IRC, either of which can be fabricated or manufactured in a factory. If choosing to supply globally, then American manufacturers would require design to another specification like the NCC/BCA. Whilst Australian manufacturers choosing to supply to the USA would have to choose HUD versus IRC. I don't know why they would choose HUD over the IRC.
Tiny Homes
The tiny home movement. Not sure I understand its emergence in Australia. Tiny homes appear to be poorly designed vehicles, poorly designed caravans and poorly designed houses. The dimensions of a shipping container (2.4x2.4 section area and 6 to 12m long) has dimensions which are most transportable, but still likely to encounter problems. The Australian design rules (ADR) limits 2.5m wide, 4.3m from ground to top, and length possibly 12m. Length limits are somewhat confusing, and depend on type of vehicle, and likely have difficulty finding trailers and vehicles which meet the maximum. Making a vehicle to these dimensions is not sensible, it may still encounter problems with low bridges, and narrow tunnels. The dimensions are for compatibility of new vehicles and new infrastructure. They are not for suitability with existing infrastructure.
For most part people are aiming for light vehicle less than 4.5 tonne which can drive or tow with ordinary drivers licence. In SA towing limit imposed by licence is typically defined relative to capabilities of vehicle, the towed vehicle typically has to be less than the towing vehicle, and that typically puts the trailer at 3.5 tonne. Either way there are few light vehicles which can tow such weight in Australia. So likely will have to get it towed or transported on a truck. Or keep it small, streamlined and light, like a proper caravan.
For the most part in Australia a tiny-home is either a small transportable building to the NCC/BCA or if its on wheels (THOW) then its considered a caravan. There is little value in it being considered a caravan. You are typically not permitted to live permanently in a caravan, nor a class 10 shed. You can live in a small transportable building which meets the NCC/BCA and planning code requirements for class 1 building. There may be some Australian states which have dimensional constraints on housing, South Australia is not one of them. The constraint is the size of the allotment of land, and the number of dwellings permitted on that allotment in a planning zone.
Also several years back, as I recollect there was a law introduced to SA which prohibited buying empty blocks of land and holding onto it and selling it for a higher price. The requirement was to either put a house on the land in 1 to 2 years or sell the land to someone who would. This was primarily concerned with the scattering of empty blocks around suburban streets, which hadn't been developed, and so there was land available for needed housing without need for rezoning anything.
So cannot live on a suburban or rural block permanently in a caravan or shed. Nor can set up a village on farmland. Though a farmer could set up a village for seasonal workers or farm tourism. These would likely have to provide facilities similar to a caravan park, though the planning code does have a workers settlement zone for seasonal workers in rural areas. There is no need to put the buildings on wheels, and buildings can be transportable without need of their own wheel set.
Developing Land to Rent for use with Transportable Buildings
Humans have legs and are meant to be mobile. To be mobile need somewhere to move to, which suggests a need for more residential caravan parks. If the objective is to be mobile. That however doesn't seem to be the objective, its just a desire for a smaller building. Possibly a desire not to own land, and only rent land whilst own building. So may be opposed to the tie-down anchors to prevent wind blowing building over: though anchorage connection doesn't have to be permanent. May also be opposed to some of the energy efficiency performance requirements which keep increasing and increasing the cost of housing: thus oppose the NCC/BCA hence building on wheels to avoid compliance.
So first thing is that housing sites can be developed to move buildings in and out. Secondly landscaping to front gardens is not consistent. So landscaping can be used to hide a house, if not consistent with other houses. The house frontage can be made to match other houses, whilst the house behind is different.
Instead of having slab on ground with all services embedded in the concrete, can just have a simple slab and a utility service box. The slab can just provide for the maximum rectangle permitted on the site, or define a smaller area.
The site is rented, and tenants provide their own house. So tenants responsible for maintenance of own house and can do as they wish with the house. So landlords using other peoples money only have to pay for the land, their costs are lower, therefore rents are lower. Whilst tenants are paying for a house they can own. House owners can start with tiny-house and trade up to larger house.
When I was at school in 70's, current affairs shows, indicated that people in Adelaide were moving interstate to work, that they were renting interstate whilst they had mortgages on houses in Adelaide. They couldn't sell the houses, because no one interested in moving to the city, due to lack of employment.
Land allotments don't have natural water supply, and are not large enough for growing food. Land is basically useless, it just provides space. All really need is a licence to occupy and use the land, no real need to own. If people have transportable house then it can go where they need to be, and they don't have to settle for what ever rubbish is already built on the land. A lot of development wastes the available land, and deprives people of access to land. Development does not require constructing a building, it requires making the land more useful.
Developers can assess that the buildings on an allotment of land are worthless and put a bulldozer through them. Then possibly merge allotments or subdivide allotments, followed by constructing new houses and making a profit. The typical person cannot afford to buy a property and remove the house.
But change the situation. The house on the land is not suitable. The land has the required space, its in the appropriate location and the neighbourhood is acceptable. The house is moveable and reusable. The house is removed and sold to others, and the desired house is moved in.
Thus developers don't need to build houses, they just need to make the land more useful. They demolish the existing houses, improve the site. Then future occupants choose the house they want, and the developer puts the appropriate transportable house on the site.
This is better than property speculators building oversized houses asking for extortionate rents and having problems finding tenants, and otherwise using up land which could be put to better use. Now some of these over sized properties can be changed into boarding houses, and get more people in.
To prevent future waste however, leave the sites empty, but with appropriate development to accommodate transportable buildings. The future tenant then chooses suitable house. The property investor may buy the house, and rent both to the tenant, or just rent the site. The tenant may have the option to rent to buy the house. The property investor likely doesn't have much use for the house, as unlikely suitable for future tenants.
Transportable houses can be moved off-site and renovated, then moved back. During the renovation the occupants can live in a substitute house delivered to site, with contents placed in temporary storage. A property investor could have more houses than allotments. They can have houses being renovated, whilst others are occupied.
With movable houses, and rented land, we can expand and contract the housing supply as needed. Plus we can more readily upgrade housing, or change the nature of housing. So can have 3 bedroom house one day, and a sole occupancy unit the next. Plus property investors can change a site from having a family dwelling one day to having multiple sole occupancy units another day. They are not stuck with an empty building which doesn't meet the needs of the market. A fixed building which costs too much to renovate, and too much to demolish and replace. Transportable buildings can be moved in and out, and relocated to where they are needed.
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Revisions:
[13/03/2024] : Original
