The Healthy Homes moisture and drainage standard, explained
Every damp house has a supply line. The moisture and drainage standard is about cutting the two biggest ones: rainwater that is not carried away from the building, and ground moisture rising into an enclosed subfloor. It is the least glamorous standard and, in wet parts of the country, the one doing the most work.
Efficient drainage
The property must have drainage that efficiently carries away rainwater, surface water and ground water, gutters, downpipes and drains doing their jobs. "Efficiently" is the operative word: a downpipe that discharges beside the foundation technically exists and practically fails. The best inspection is a wet one: walk the outside during real rain and watch where the water goes. Overflowing gutters, pooling against cladding, and moss lines on paths all name their problem.
The ground moisture barrier
If the house has an enclosed subfloor, a ground moisture barrier, in practice a heavy polythene sheet laid over the soil, is required where one can practicably be installed. It is a modest job that meaningfully dries the air under the floor, which is the air that ends up in the house. The classic evidence problem: the barrier is invisible once the access hatch closes. Photograph it installed, before that happens.
Moisture ingress
Beyond drainage and the barrier, the intent of the standard is a home without unreasonable moisture entry. Leaks around flashings, failed sealant, cracked cladding: none of these improve with time, and each one found during a routine inspection is dramatically cheaper than the same fault found by a tenant's mould photo. In high-rainfall districts, make the exterior walk a fixed part of every inspection.
Evidence worth keeping
- Invoices for drainage work, gutter replacement or clearing.
- Dated photos of the ground moisture barrier before the subfloor closes.
- Inspection notes from the wet-weather walk, even two lines with a photo.
Drainage evidence has a second life: it answers insurance questions after storms and supports the compliance statement for new tenancies. File it against the property and it keeps working for years.