A growing number of Southern Highlands homeowners remove a pool specifically to create the space and site conditions needed for a granny flat or secondary dwelling. The freed site, combined with NSW planning reforms making it easier to build secondary dwellings, makes this a logical sequence. But there are specific requirements for building over or on a previously-filled pool excavation that you need to understand before committing to either project.
Quick Answer (BLUF)
Building a granny flat on the site of a removed pool is achievable in most Southern Highlands residential zones, but it requires: full pool removal (not just partial fill-in), appropriate engineered backfill with compaction testing, a geotechnical report, and a development application (DA) or Complying Development Certificate (CDC) for the secondary dwelling. The pool removal and the granny flat are two separate approvals, though they can be planned and sequenced together. Allow 6-12 months from decision to occupancy of the granny flat.
Why Pool Removal Creates the Opportunity
A granny flat (secondary dwelling in NSW planning language) typically requires:
- A lot size of at least 450m² (under the NSW Housing SEPP rules)
- Sufficient setbacks from boundaries and the primary dwelling
- Adequate private open space for the principal dwelling
- An unobstructed building envelope on the lot
Many Southern Highlands properties have a pool occupying the exact location that would otherwise be ideal for a granny flat, close to the boundary, away from the main house, with potential for separate access. Removing the pool creates both the physical space and the potential building site simultaneously.
The Two-Approval Sequence
Approval 1: Pool Removal (CDC or DA)
Before the granny flat approval can proceed to construction, the pool must be removed with council sign-off. This is because:
- The granny flat site investigation (geotechnical report) needs to assess the filled pool excavation
- The certifier for the granny flat will want evidence that the pool was removed with appropriate compaction
- Building over an unapproved fill without documentation creates defect risk
Pool removal approval (CDC pathway for most standard residential properties in Wingecarribee Shire) takes 10-20 business days from a private certifier. See Wingecarribee council pool removal guide for the approval process.
Approval 2: Secondary Dwelling (Granny Flat)
Once the pool is removed and compliance-certified, the granny flat approval proceeds through:
- CDC pathway (if the property and design meet SEPP Housing conditions): processed by a private certifier, typically 10-25 business days
- DA pathway (if the property has heritage overlay, is in a conservation area, or doesn’t meet SEPP criteria): through Wingecarribee Shire Council, typically 8-16 weeks minimum
Key SEPP Housing criteria for CDC secondary dwelling approval:
- Site area ≥ 450m²
- Floor area ≤ 60m²
- Compliant setbacks from all boundaries
- Compliant parking provision
- No heritage listing or conservation area overlay
Many older streets in Bowral and Mittagong with pool-aged properties also have heritage overlays, check this early.
Geotechnical Requirements When Building Over a Pool Site
Building any structure on a previously-filled pool excavation requires geotechnical consideration. The concern is differential settlement, the filled zone may settle at a different rate to surrounding undisturbed ground, causing the structure to crack or tilt.
For a granny flat on a pool fill site:
| Requirement | Why It Matters |
|---|---|
| Geotechnical investigation | Confirms fill quality, compaction and bearing capacity |
| Footing design | Footings may need to extend below fill into natural soil |
| Fill specification confirmation | Engineer certifies fill meets standards for building load |
| Settlement monitoring period | Some engineers recommend 6-12 months after fill before building |
See geotechnical report for pool fill-in for what the investigation involves and what it costs.
Full Removal vs Partial Fill-In for a Granny Flat Site
A partial fill-in is not suitable as a granny flat building site. The shell left in place creates voids and structural inconsistency that cannot reliably bear building loads.
A granny flat on a pool site requires full removal, complete extraction of the shell, engineered backfill in compacted layers, geotechnical testing, and a compliance certificate. See building over a filled-in pool for the full picture.
Backfill Specification for Future Building
When the pool removal contractor backfills the excavation with a view to future granny flat construction, the specification must be appropriate for building loads:
Recommended fill specification:
- Base zone (bottom 40% of fill): Compacted road base or clean granular fill, maximum 200mm layers, compacted to 95% standard Proctor density
- Intermediate zone: Continued granular fill at same standard
- Upper zone (top 300mm): Topsoil for landscaping, compacted to 90%
- Testing: Nuclear density gauge testing at each layer
Tell your pool removal contractor upfront that you intend to build on the site. Backfill suitable for a granny flat is more expensive than garden-only fill, typically $2,000 to $5,000 additional for higher specification material and testing.
Lot Size and Zoning in the Southern Highlands
| Zone | Secondary Dwelling Permitted? | Notes |
|---|---|---|
| R1 General Residential | Yes (CDC or DA) | Most Bowral, Mittagong suburban lots |
| R2 Low Density Residential | Yes (CDC or DA) | Many Moss Vale, Bundanoon lots |
| R5 Large Lot Residential | Yes (DA required) | Lifestyle blocks 1-2+ ha |
| RU1 Primary Production | Generally no | Rural farming land |
Most properties with pools in Bowral, Mittagong, Moss Vale, and Bundanoon are R1 or R2 zones.
Cost Summary: Pool Removal for Granny Flat Site
| Item | Indicative Cost |
|---|---|
| Pool removal (full concrete) | $18,000 to $30,000 |
| Engineered backfill upgrade for building | $2,000 to $5,000 additional |
| Geotechnical report | $1,500 to $3,500 |
| Pool removal compliance certificate | $500 to $1,200 |
| Secondary dwelling design and approval | $8,000 to $20,000 |
| Granny flat construction (to 60m²) | $120,000 to $200,000 |
| Total project estimate | $150,000 to $260,000 |
In the Southern Highlands rental market, a well-built granny flat commands $350 to $550 per week, a reasonable yield on construction cost over time.
Frequently Asked Questions
Do I need to remove the pool before applying for a granny flat approval? You need the pool removed (or committed to removal) before granny flat construction begins. Some manage both approvals concurrently, but the pool must be removed, backfilled and certified before the granny flat footing is poured.
Can I build the granny flat directly over the pool excavation? Yes, if the fill is done correctly with engineered backfill, compaction testing, and geotechnical sign-off. Footings will typically extend deeper to reach undisturbed soil beneath the fill zone.
How long after pool removal should I wait before building a granny flat? Most geotechnical engineers recommend 6-12 months of settlement monitoring on significant fill areas. Enhanced compaction and testing may reduce this wait period, discuss with your geotechnical engineer.
Will removing a pool and building a granny flat increase my property value? Significantly. A well-built 60m² granny flat adds $150,000 to $250,000 to property value in many Southern Highlands suburbs. The pool removal cost ($20,000 to $30,000) is a fraction of this uplift.
Can I use a CDC for the granny flat if my Bowral property has a heritage overlay? No. Heritage properties and conservation area properties require a full DA through Wingecarribee Shire Council, the CDC pathway is not available.
Planning to remove a pool and build a granny flat in the Southern Highlands? Contact Southern Highlands Pool Removals for a free quote with building-specification backfill included.