← All Insights

Building Advice

Top Knockdown Rebuild Mistakes Castle Hill Homeowners Make

The most common and costly knockdown rebuild mistakes Castle Hill homeowners make in 2026 — from skipping soil tests to keeping the old slab — and how to avoid them.

TL;DR Most Castle Hill knockdown rebuild regrets come down to a handful of avoidable mistakes: skipping the soil test, trusting low site allowances, keeping the old slab, designing before checking zoning, lodging incomplete approvals, and underbudgeting. Each is easy to avoid once you know it's coming. This article runs through the big ones, with the local context that makes them matter in Castle Hill specifically. Mistake 1: Skipping the soil test Castle Hill's suburban core sits on reactive Wianamatta Shale clay, with sandstone to the west. Budgeting without a soil test means guessing at your footings — and engineered foundations here commonly run $24,000–$42,000. The test is cheap; the surprise isn't. Always test before locking your budget. Mistake 2: Trusting an unrealistically low sit…