To convert a garage into a bedroom or any other liveable space the following are most important considerations.

1. Vapour Barrier Under Existing Slab

Verify the existing slabs have a vapour barrier (plastic) beneath them.  This is important to stop moisture coming up from under the slab to the surface of the slab.  This is not needed for non-habitable use – but it is for habitable use.  If there are no records of the original slab design plan and inspection records, then the best way to verify this issue is to get an independent structural engineer out to inspect and confirm. This would normally involve a core drill sample of the slab with a concrete cutter. As of 2020, this costs $750+GST depending on location. Other alternatives for checking the vapour barrier are;

  • Physical observation on the side of the house for evidence of vapour barrier.
  • In event of a recent plumbing installation that includes concrete cutting, vapour barrier may be sited.

At CVL Engineers, we facilitate this on behalf of clients.

Where there is no evidence of vapour barrier, topping of slab is recommended which includes installation of a new vapour barrier. Caution – This may affect legal ceiling height. Please contact our office prior to discuss your specific circumstance prior to undertaking any works.

2. Legal Height of 2.4m from Floor to Ceiling

Most garages are set down from the rest of the house and therefore almost always comply with this requirement. It is important to note that where a 2.4m floor to ceiling height cannot be achieved such as topping up of slab to comply with the item 1 above then a Performance Solution would be required for heights less than 2.4. This process takes into consideration other aspects such as number of openings (windows, doors etc) and their sizes. Simply put a Performance Solution is an assessment done by a qualified professional that seeks to demonstrate that the proposal even though not 2.4m as required still complies with the intended outcomes of the National Construction Code.

At CVL Engineers, we facilitate this on behalf of clients.

General Requirements for Building Approvals.

The general requirements for Shed to Granny Flat Conversion are listed below.  For more information on these items please refer to Building Approvals for New Residential Dwelling or Renovations.

  1. Architectural Plans.
  2. Engineering Plans and Form 15 Certificate.
  3. RPEQ Certification of existing slab confirming presence of vapour barrier (as outlined above).
  4. Soil Testing Report (oftentimes not applicable).
  5. Form 4 Notifiable Work (filled by a Plumber).
  6. Energy Efficiency Assessment Report.
  7. Builders Details or Owner Builder Permit.
  8. QBCC Home Warranty Insurance (except where work is done under Owner-Builder Permit).
  9. QLeave (for project costs more than $165,000.00 – oftentimes not applicable).
  10. Build Over Sewer Approvals (oftentimes not applicable).
  11. Amenity & Aesthetics Referral with Local Council (oftentimes not applicable).

We trust that you find this information useful. Feel free to leave us a comment below for further clarification.

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