Pre-Purchase Building Report vs Feasibility — KDR & Duplex (2026)

Two reports, two purposes, completely different value

Pre-purchase building reports cost $480–$880 in 2026 across Sydney. Most buyers order one before settlement on any house purchase. They cover: structural condition of the existing dwelling, visible defects, pest activity, weather damage, cladding type, roof condition.

For a buyer planning to live in the existing house — necessary, sufficient.

For a buyer planning to KDR or duplex on the lot — almost completely useless.

The report tells you nothing about: whether duplex is permitted under zoning, whether 88B restrictions prohibit dual occupancy, what the soil class is, what the bedrock depth is, whether asbestos clearance will cost $6k or $19k, what the council contribution costs are, whether a heritage overlay applies, what the actual buildable footprint is after setbacks and FSR are applied. Buyers ordering a $580 building report and skipping a feasibility study before bidding on a KDR site are making one of the most expensive decisions in residential property — gambling six-figure sums on a report that wasn't designed to answer their question.

What a KDR/duplex feasibility actually contains

A proper pre-purchase feasibility for a KDR or duplex site costs $1,800–$4,500 in 2026 across Sydney depending on complexity. It contains:

Title and 88B review. Confirms what private restrictions apply. Confirms whether dual occupancy is contractually permitted on the title (separate from council planning).

Zoning and planning controls. R2/R3/R4 zoning confirmation. Minimum lot size for dual occupancy under the LEP. FSR maximum. Site coverage maximum. Landscape area requirement. Setbacks. Height limits. Heritage overlay check. Foreshore building line check (where coastal). Bushfire BAL rating (where bushland adjacent). Flood overlay (where applicable).

Soil and ground investigation. Site-specific soil class (AS 2870), bedrock depth, water table, footing system implications, foundation cost range.

Asbestos baseline assessment. Visual identification of likely asbestos-containing materials in the existing dwelling. Indicative removal cost range.

Council contribution forecast. Section 7.11/7.12 contributions, water board contributions, road and drainage contributions where applicable. These can run $25k–$80k on a duplex and are routinely missed by buyers.

Buildable footprint study. Maximum permissible floor area and dwelling configuration on the site after all controls are applied. Often the most surprising number — the 600m² lot the buyer assumed could fit two 200m² duplex dwellings actually only supports two 145m² dwellings after setbacks, FSR and landscape area.

End-value forecast. Comparable sales data for completed builds in the same suburb, suburb-specific market position, realistic range for the proposed build.

Project P&L. Land + design + approvals + construction + holding costs vs end value. Margin or end-equity calculation. Sensitivity to soil class, council contribution and construction cost movement.

A building report tells you the existing house is sound. A feasibility tells you whether the dirt is worth what you're paying for it.

The owners who skip the feasibility and pay for it

Three scenarios I see repeatedly in pre-settlement consultations:

Scenario A: 88B prohibits the build. Buyer offered on a 600m² R3 lot in a 2018 release planning to duplex. Council confirmed permissibility. Pre-purchase building report came back fine. Settled. Engaged a builder. Builder pulled the title and found the 88B prohibited dual occupancy for 25 years. Buyer is now stuck with a single dwelling site he paid duplex-development pricing for. Loss: $180k–$350k of overpayment on the land alone.

Scenario B: soil class destroys the margin. Buyer offered on a 720m² lot in Camden. Comparable duplex sales averaged $1.4m end value per dwelling. Buyer's feasibility worked at M-class soil. Soil report came back E-class after settlement. Foundation cost added $94k that wasn't in the model. Plus the architect needed to redesign for pier-supported slab, adding $11k in design fees and 8 weeks in approval extension. Combined hit $105k that ate the margin entirely.

Scenario C: council contributions weren't modelled. Buyer offered on a 580m² lot in The Hills LGA planning to duplex. Comparable sales worked. Construction priced. Council contributions weren't modelled. Section 7.11 contributions came back at $63k (two-dwelling rate). Water Board contributions added $19k. Road and drainage levy $11k. Combined $93k of cost the buyer hadn't budgeted, eating most of the project margin.

All three losses run from $100k to $400k. All three are preventable with a $2,500 pre-purchase feasibility. The math is overwhelming.

When a building report is enough on its own

Three scenarios where the standard pre-purchase building report is sufficient and a full feasibility is not necessary:

1. Buyer is purchasing to live in the existing dwelling, no major works planned within 5 years.

2. Buyer is purchasing for cosmetic renovation only — kitchen, bathroom, paint, flooring — under $200k of works, no structural or service changes.

3. Buyer is purchasing as a long-term hold investment, no near-term redevelopment intent.

For any other scenario — KDR, duplex, granny flat addition, major extension, second-storey addition — a feasibility is the only investigation that answers the question 'will this work for what I'm planning'.

Pre-offer checklist for KDR/duplex buyers

Before submitting any offer on a site you intend to KDR or duplex:

1. Pull title search and 88B annexure ($14 + $14). Read in full. 2. Run zoning and planning controls check on the council planning portal. 3. Engage feasibility provider for site visit and indicative buildable envelope ($1,800–$4,500). 4. Order indicative soil report (sometimes seller has one, sometimes you order pre-settlement). 5. Confirm asbestos baseline if existing dwelling is pre-1990. 6. Forecast council contributions using council's adopted contributions plan. 7. Confirm comparable sales evidence for the proposed end product. 8. Run project P&L. 9. Sanity-check P&L against worst-case sensitivity (E-class soil, BAL upgrade, contribution upward revision). 10. Decide.

For a free KDR/duplex pre-purchase walk on a site you're considering offering on — covering all 10 points and reading the title and 88B in detail — call 0476 300 300 or visit /advisory/development-feasibility. We've turned away a lot of pursuits at title-read stage and saved owners six- and seven-figure mistakes.