Interpreting the rules around wall linings for wet areas
When it comes to keeping homes sturdy and moisture-free, the interior is just as important as exterior cladding and framing. Using the wrong wall lining can allow water to get into structural timber and floors, destroying a home’s integrity from the inside out.
When it comes to splash areas, like those around laundry tubs, kitchen sinks and bathrooms, clause E3 of the Building Code says wall linings and finishes have to be impervious and easy to clean. Acceptable Solution E3/AS1 of the Building Code lists suitable linings and finishes, including:
- fully waterproof sheet material (such as PVC) with sealed joints
- ceramic or stone tiles with 6% maximum water absorption and waterproof grouted joints
- sheet linings finished with a semi-gloss or gloss coating or a hard-wearing low-sheen latex paint containing mould inhibitors
- water resistant sheet linings finished with decorative high-pressure laminate or factory applied polyurethane or resin, installed with impervious joints
Each material has its own dos and don’ts when it comes to achieving compliance. Here are some general guidelines for linings in wet areas, according to the Level website.
Timber - not included under E3/AS1 when it comes to wet areas because it can warp, so it must be consented as an Alternative Solution. If consented as a wall lining in damper rooms, timber should be finished with a minimum of three coats of semi-gloss or full-gloss paint and sealed or primed on the edges and back face before installation.
Plywood - the same finishing requirements as Timber. It also needs to be treated using a water-based preservative like Chromated Copper Arsenate (CCA) (Light Organic Solvent Preservative (LOSP) isn’t suitable) and be at least 9 mm thick. While properly finished plywood may be used as a substrate under tiles, it can’t be used as an exposed finish in showers.
Compressed sheet - mostly used under tiles but can also be a substrate for vinyl wallpaper in bathrooms. It should never be used only with a painted surface.
Sheet vinyl – suitable for shower areas, but it requires heat- or solvent-welded joints to be fully watertight, and substrate surfaces must be totally smooth.
Ceramic/stone/terrazzo tiles – ideal for wet areas, but glazed tiles should have glazed edges. E3/AS1 also requires waterproof grout joints, a stable, rigid substrate such as concrete, plywood or fibre-cement sheet and flexible, mould inhibiting sealant joints at junction points. If you’re using tiles in showers, a waterproof membrane is required, but a membrane is recommended in any splash area.
Plasterboard – even with water-resistant versions available for wet areas, plasterboard must be protected by a membrane or waterproofing system when used as a tile substrate in high-risk areas. Standard plasterboard is suitable for other areas, where it should be treated the same as plywood.
Vinyl-coated wallpaper – moisture is known to cause peeling, so wallpaper should only be used in drier areas. Plasterboard and fibre-cement substrates used underneath must also be sealed with a water-resistant sealer.
Paint and clear finishes - paint should not be used on surfaces that are regularly splashed or exposed to condensation. In well-ventilated kitchens and bathrooms, you can use water-based acrylic enamel paint over a solvent-based sealer coat. For best performance, use water-resistant plasterboard underneath. High-gloss coatings should be used in areas where regular cleaning is required.
