Contingency and hidden-condition planning for a 150 m² Sydney renovation

[LightStory]

Either I spend more on investigation before tendering or hold a sizeable contingency for discoveries during the work; neither option feels cheap. The preliminary budget is A$130,700 for an older 150 m² detached Sydney home. It covers the kitchen and bathrooms, new floor finishes and paint, checks to the electrics, and limited energy improvements. I am not proposing an extension.

My main concern is what happens once walls or wet areas are opened. Moisture, access to pipes or cables, and any resulting structural work could disrupt both cost and sequence. Material lead times may do the same. What assumptions and exclusions should surveyors and contractors state, and what targeted checks would make the budget credible before work starts?

 

[TheoCalder]

With an older building and limited investigation, I’d initially allow around 20% rather than relying on a tight contingency. Ask each contractor to state assumptions and exclusions for demolition, waste removal, wall repairs, plumbing access, electrical upgrades and moisture damage. Also clarify whether the quote includes reinstating every surface disturbed while reaching pipes or cables.

 

[FieldCairn]

How many bathrooms are involved, and will the house be occupied during the work? Those two details could materially affect sequencing and cost. “Moderate energy upgrades” also needs defining—otherwise different contractors may price completely different work. I’d arrange targeted investigation of the wet areas, accessible plumbing and electrical system before comparing tenders.

 

[sailsAndVale]

I’m not convinced a blanket 20% is the best answer. A large contingency can hide an incomplete scope without making the final cost more predictable. Spend some of the planning budget reducing uncertainty first: identify moisture sources, establish where plumbing can be accessed, and find out whether any walls being opened or altered have a structural role. Then set the contingency around what remains unknown.

 

[talia_plans]

Build decision points into the programme. Complete design and investigations first, confirm whether any approvals are required in the relevant Sydney jurisdiction, then lock in materials with significant lead times. After strip-out, pause before rough-ins so hidden conditions can be documented and priced. That prevents electrical and plumbing changes from being discovered after walls or new finishes have gone in.

 

[sasha_page]

For contractor comparisons, ask for a line-by-line list of exclusions, provisional allowances and who carries each risk. Useful questions include: What happens if moisture damage extends beyond the visible area? Is access and making good included? What electrical work would trigger a revised price? How are suspected hazardous materials handled? Keep the contingency under your control rather than absorbing it into the contract price, and require written approval before it is used.