NELSON BUILDING REPORTS

Floor slab/outdoor ground level issues

Since the 2005 changes to the Building Code, building cladding systems have generally required a drained and ventilated 25 mm cavity behind stucco, or weatherboards, with two layers of building wrap, and comprehensive window flashings. It was good building practice prior to it becoming mandated.

The Building Code requires a minimum height difference between the inside concrete slab and the ground level of 150 mm if paved, or 225 mm if it is unpaved. A minimum of 100 mm, paved, or 175 mm, unpaved, is required under the cladding: weatherboards, stucco, etc, to allow the base of the cladding to remain dry, and keep the drain/ventilation holes free to the air to let out any water that gets into the cavity.

These height differences are intended to prevent water from flowing inside the house in flood conditions.

So. What’s the issue with these levels?

In time the ground level can be raised outside the house through buildup of gardens or paving.

The ground level should always have a minimum clearance of 100 mm beneath the cladding to a paved area, or 175 mm if unpaved.

If this gap is less, or if the stucco or weatherboards are in fact buried, water could fail to drain properly, or seep through the damp cladding, and make its way inside the timber structure. With any weak points in the building wrap water can penetrate the waterproofing and be retained by the wall insulation.

This can lead to the deterioration of the structural timber that is often expensive to rectify.

Maintaining the appropriate ground levels is important to the long-term structural integrity of the house.

Recommendation: remove any excess soil/garden beds/paths against the side of the house where the clearance from the cladding is less than 100 mm, paved, or 175 mm, unpaved.