Rising Damp and Mould Under the House on the Central Coast

Rising damp is ground moisture rising up a brick or stone wall, and NSW Health says poor subfloor ventilation, or moisture in the subfloor area, will worsen the problem. Its advice for a raised-floor home is to ensure the weep holes and air vents at the base of the house are uncovered. Mould may grow indoors in wet or moist areas that lack adequate ventilation.

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What rising damp and mould under the house on the Central Coast actually involves

If you rent your home and have taken measures to ensure the building is properly ventilated and mould is still growing, NSW Health says to raise the issue with the owner or real estate agent. People with asthma, allergies or other breathing conditions may be more sensitive to mould.

Fixing the cause, not just the symptom

Where the ground under the floor is sealed with an impervious membrane, the National Construction Code allows the subfloor ventilation rate to be halved, because humidity in the space is no longer affected by moisture from the soil. If the damp looks structural rather than a ventilation problem, NSW Health says an experienced building consultant can check the damp course and recommend ways to fix it.

A white painted skirting board with a patch of dark mould spots and a cracked paint edge above a timber floor — rising damp and mould under the house, the Central Coast. Illustrative example.

Before anything is disturbed

If you have rising or lateral damp, have the damp course checked before assuming more airflow alone will fix it. Cutting or drilling into old wall sheeting is a separate question from ventilation, and asbestos in older walls was not researched for this trade. The high water table page covers the case where the ground itself stays wet.

Ask the provider whether the quote covers the cause (airflow, a membrane or the damp course) or only the symptom.

A gloved hand smoothing a black plastic sheet unrolled across bare soil beneath timber bearers, brick wall vents behind — rising damp and mould under the house, the Central Coast. Illustrative example.

Subfloor ventilation costs and rules check