What Should a Residential Site Drainage Plan Resolve Before Building?
Owners, builders and project managers
Residential site drainage needs to be resolved with the footing layout and finished levels, not left as a final landscaping decision. Surface drainage needs to avoid ponding near footings, with several constraints affecting how that is achieved. A line saying drain away is not the same as a coordinated site proposal.
Start with the route the water can actually take
Consider runoff and topography, cut and fill, flooding, landscaping, the legal stormwater discharge level, plumbing, damp-proof-course level and termite management among the matters affecting drainage and floor height. Separate decisions about those items can conflict.
Ask where water arrives, how the finished site will direct it and where it can lawfully discharge. Include uphill ground, side passages, courtyards and later paving. A structural drawing may identify required drainage without including the complete stormwater design; the project scope should explain who resolves it.
Perimeter fall and ponding
Surface drainage should be designed and constructed to avoid water ponding against or near the footing.
The perimeter-fall provision discussed here concerns grading in the immediate vicinity of the perimeter footing, including uphill ground on cut-and-fill sites, to fall at least 50 mm away over 1 m and be shaped to prevent ponding. This is an educational explanation of that particular perimeter context; the requirements applicable to a project need professional confirmation. It is not permission to add fill indiscriminately, cover slab-edge details or treat every drainage situation as a ruler check.
Slab height above finished ground, landscaping or paving is a separate consideration, subject to the relevant exceptions. Those height provisions are not interchangeable with surface fall. Zero-lot-line construction also needs an alternative drainage solution; space constraints do not resolve the water question.
Drainage starts before handover
For the site classes to which these drainage provisions apply, surface drainage needs to be considered in footing design, controlled from site preparation and completed by the finish of building construction. Runoff and water ponding also need attention during construction; confirm the applicable provisions for the actual site.
Where finishing works are deferred, agree the interim arrangement and remaining scope with the responsible team. Keep the intended finished levels, drainage details and completion records together. Repeated regrading after paving is finished can be disruptive; resolving interfaces early may avoid rework, without guaranteeing a cost saving.
For an existing house
Record safe observations during rain: arrival points, flow direction, ponding location, overflow and changes after work. Keep photographs tied to a site sketch. These help define an investigation but do not prove why the building cracked. Do not enter flooded areas or redirect water towards another property as a test. Obtain professional advice for persistent ponding, affected footings or urgent deterioration.