How big does a block need to be to subdivided?

If you have noticed development in your local area, you have no doubt looked out in to your backyard and wondered what your options are.  We receive many calls from people looking in to the potential of their own properties to make the most of the very strong housing market right now.  The most common question is “How large does a block need to be to subdivided?” and the answer can sometimes be unexpected, especially when we let people know their expectations were far higher than their property will allow.

So, is there a minimum site size you need to subdivide? Unfortunately, the short answer is no. However, there is a quick and easy set of steps you can follow to work out the subdivision potential of a block. There are typically five types of subdivisions in established neighbourhoods:

  1. Mid street blocks, retaining the existing house and building one at the back;
  2. Mid street blocks, demolish the existing house, construct two or more;
  3. Mid street blocks demolish the existing and construct two houses side by side;
  4. A corner site, retaining the existing house and building one at the back;  
  5. A corner site, demolish the existing house and build two or more. 

Select which site type is applicable to you and apply the process set out for it below to get an indication of the subdivision potential of the site. It is important to point out that this DIY process is for use as a helpful indicator only and once you have done it is important to confirm your results with a subdivision expert in your local area to confirm if you are accurate. 

1. Mid street blocks, retaining the existing house and building one at the back.

  • The distance between the side boundary fence and the side of the house must be 3 metres or greater to provide car access to the rear for the new house;
  • The distance from the back of the house to the back boundary fence should be 16 metres or greater;
  • The width of the backyard between the two side boundary fences should be 18 metres or greater.

There are situations where your site may not meet the required distances above but still may be suitable for subdivision. For example, if the distance between the back fence and the house is 14 metres it would fail to qualify for subdivision by applying the above rule. However, in this example the shortfall in the length may be compensated if the site width was greater than 20 metres. If your site fails one of the distance tests above but is well in excess of the requirements of the second distance test you must speak to a professional with local expertise to confirm a house will fit in the backyard.    

2. Mid street block demolish the existing house, construct two or more

  • The front setback of the front house must be the average of the two neighbours or nine metres from the front property boundary, whichever is the lesser. It must be the average of the two neighbours even if the existing house is set forward of the two direct neighbours. For example – if we were to demolish the house with the blue roof in the image below. The front house of the new development would have to be setback the average of the two neighbours. It would not be permitted to take the setback of the current blue roof house.

 

  • Subtract the required front setback distance from the overall length of the site. Divide the result by 13. The answer is the likely maximum number of houses you can achieve on the site. Examining the photo above, you can see the front setback of the neighbours is 8.56 metres and 7.02 metres giving a required front setback for development on the site of 7.79 metres. The overall length of the site is 34.07 metres and subtracting the required 7.79 metres from this gives a remaining length of 26.28 metres. Dividing this figure by 13 gives a result of 2.02. This means this site can be developed for 2 house site if the existing house is demolished.

3. Mid street blocks demolish the existing and construct two houses side by side

  • These are the simplest sites to qualify;
  • If the width of the site is 15 metres or greater and the depth of the site is greater than 20 metres then it is possible to achieve a side by side development.

4. A corner site, retaining the existing house and building one at the back 

  • The depth of the site from the back of the house to the back fence should be equal to or greater than 15 metres (this allows for the required carport/garage for the existing house to be newly built);
  • The width of the site should be equal to or greater than 15 metres. 

5. A corner site, demolish the existing house and build two or more

  • Check the front setback of the direct neighbour, the front house of the new development that faces the same street will have to align with this setback or be setback 9 metres, whichever is the lesser. Refer to the below example – If you want to demolish the house on the corner site – the new house that faces Hampshire Road would have to be setback 8.5 metres from the boundary along Hampshire Road. The side setback to Vanbrook Street can be 2 metres for this house.

  • Subtract the required front setback distance from the overall length of the site. Divide the result by 13. The answer is the likely maximum number of houses you can achieve on the site. Examining the photo above, you can see the front setback of the neighbours is 8.51 giving a required front setback for development on the site of 8.51 metres. The overall length of the site is 37.62 metres and subtracting the required 7.37 metres from this gives a remaining length of 30.25 metres. Dividing this figure by 13 gives a result of 2.32. This means this site can be developed for 2 house site if the existing house is demolished.

These DIY steps are provided to give readers an indication only of the likely yield of the site and this advice is general in nature. These steps do not account for specific planning controls such as minimum lot sizes your local council have applied to your site. You should therefore discuss your findings of this excercise with a subdivision expert prior to making any decisions to move forward with an application.