Garage Conversions Into Granny Flats

Garage & Granny Flat Conversions

The NSW State SEPP Legislation, called the ‘Affordable Rental Housing SEPP’ is your first port of call when considering garage conversions. The document is not by any means the easiest Government document to decipher, especially since it also includes Boarding Houses and In-fill accommodation. You can, however, head over to our Granny Flat Approval Guide Page, which lists the main pre-requisites for garage conversions into granny flats.


Garage Conversions

The Legislation

Garage conversions from a Class 10 (Outbuilding) into a Class 1A (Granny Flat Dwelling) is not specifically stipulated in the legislation, so it’s not easy to see whether your garage can legally be approved or not.
Private Certifiers needs to be satisfied that garage conversions are structurally adequate in order to be approved as a habitable dwelling, so this is a difficult aspect of compliance. The following lists how garage conversions must meet the Building Code of Australia:

  1. The Slab- The existing concrete slab will need to be certified by a Practicing Structural Engineer as being adequate for habitation. Depending on the engineer, this may require ‘core-drilling’ of the slab to ensure it has adequate hardness, thickness and steel reinforcement. This can cost a few thousand dollars, so be sure to shop around for a willing engineer. The engineer is certifying the slab, so he must accept all responsibility for the slab’s strength as well.
  2. The Frame – Again, an Engineer should be consulted to ensure structural adequacy of the walls and roof sections. Garages can be either single-skinned brick structures or timber-framed, so it’s wise to ask the Engineer to certify or suggest ways to bring the frame up to standard, especially for brick garages. Brick garages usually don’t have a timber frame, instead having ‘engaged piers’ which support the roof trusses.  It’s also important to have something for the plasterboard and insulation to sit in, so the frame may need to have additional studs and battens installed to support the lining.
  3. BASIX- Granny flat conversions must meet the NSW BASIX Legislation, which is a special algorithmic certificate for energy-efficiency. This includes adequate insulation, glazing, circulation, heating and cooling, hot water and cooking facilities to name just a few.
  4. Termite protection– Garage conversions must be protected from termites in accordance with the relevant Australian Standards. There are a few ways to achieve this depending on the existing foundations and risks in your area, so we recommend hiring a suitable experienced drafts-person or termite contractor to ensure the building is going to be protected from termites.
  5. Water Proofing– The new wet areas will need to be adequately sealed from hydraulic inundation. A suitably qualified plumber must carry out all plumbing works and provide a certificate for water-proofing of wet areas for garage conversions.
  6. Sewer Connection– Sydney Water (or your local authority if in Rural NSW) will need to be notified and the Site Plan stamped by a Sydney water Quick-Check Agent, ensuring your granny flat isn’t going to affect the Sewer mains pipes.
  7. Electricity– A licensed electrician can run conduit from the main dwelling for lights, power, stove and air-conditioning plus phone and data as needed. He will need to be hired early in the game to run these for you.
  8. Insulation– If the garage is already internally lined, the walls will need to be exposed for pumping insulation material between the studs but this can be quite expensive; otherwise the walls will need to be removed to allow for insulation and batts to be fitted.
  9. Glazing– Most garages don’t have enough windows in them, so walls need to be opened and lintels fitted (if brick) or cross-plates (for framed dwellings) to support the openings for the new windows. Also, since most garages don’t have eaves, windows will need to be double-glazed to pass BASIX for adequate insulation.
  10. Plumbing– The concrete slab will need to have channels cut for running plumbing lines (including metered gas), otherwise all lines will be exposed which can be unsightly.
  11. Minimum Wall Heights– Habitable buildings must bee minimum 2.4m in wall height throughout all living spaces. If it’s a raked (cathedral) ceiling, just measure the highest wall height and add it to the lowest wall height then divide it by 2 to get the average wall height. Many garages are only 2.1m high (floor to ceiling) which does not meet the Building Code of Australia, so the roof needs to be raised to meet this requirement- not cheap!
  12. Roller Doors– The roller door will need to be removed and the wall reinstated to adequately seal the building. This is probably good place to fit a glass sliding door if possible.

The points (above) are just a few of the Building Code of Australia requirements, which must be met for garage conversions, from a garage into a granny flat. As you can see, it’s not a simple process and can often be more expensive than just starting from scratch.

Site Considerations

Other other aspects of garage conversions which should be considered are:

1. If converting a garage into a granny flat, where will you now park your car?

2. How will the granny flat look? In the end it will still look like just a garage, usually with no eaves and with fibro or metal lining,

3. How large is the structure? Many garages are quite small, so may not provide adequate space for your secondary dwelling needs.

We have done a few approvals for garage conversions and have noted that some clients wished they had just started from scratch, mainly due to the restrictive nature of the conversion and the fact that in the end you’ve lost your covered parking.

The compliance costs are also quite high; more than building from scratch, so this needs to be considered.

I hope this article has helped with your decision to convert a garage or shed into a granny flat. It’s fair to say that most people don’t realise just how much additional work goes into a garage conversion, so we hope these guidelines enlighten you to the pitfalls and the process of conversion.




Serge Panayi- Granny Flats Sydney.



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