Addressing Common Cladding Installation Mistakes

Most cladding installation problems are preventable. They start before the first nail goes in and show up as callbacks, defects, and warranty conversations long after the job is done. This guide covers the seven areas JSC's technical team sees most often.

1. Storage & Handling

   Storing boards wrong before a nail goes in

   How boards are handled and stored from the moment they arrive on site directly affects how they perform once installed. Boards that absorb moisture in storage, or get physically damaged, arrive at the wall already compromised — no amount of correct installation technique recovers that.

   Stack boards horizontally, clear of the ground by at least 100mm, on dry and clean timber bearers at a maximum of 900mm centres. Keep them dry. The best option is storage inside an enclosed building - a garage, shed, or any covered space. If boards have to stay outside, JSC packaging wrap provides some protection, but it isn't enough on its own: add a weatherproof cover and make sure there's sufficient airflow underneath to prevent condensation build-up. Don't store boards over standing water or vegetation - both introduce moisture from below, and boards sitting in damp conditions will absorb it before they ever reach the wall.

   Plan deliveries to minimise the time boards spend on site before installation, and handle boards carefully during unloading. If unloading by crane or hiab, use a minimum of two well-spaced load points to prevent excessive flexing, with packers, slings, or chains to spread the load and protect the boards. A damaged edge or a split from rough handling cannot be fixed once the board is on the wall.

   Storage requirements

   Stack horizontally on dry bearers at max 900mm centres, minimum 100mm clear of the ground. Store in an enclosed building, or under a weatherproof cover with airflow. Never store over standing water or vegetation. If boards do get wet, allow them to fully dry before installation.

2. Coating

   Not coating all four sides before installation, including cut ends

   JSC weatherboards must be coated on all four sides before they go up — face, back, and both edges. The back of the board and the edges are where moisture gets in if the coating is incomplete, and they're surfaces you can no longer reach once the boards are fixed to the wall.

   Coating happens in two phases. Base coat (or coats) go on all four sides before installation; top coats go on all visible surfaces after installation. If you're working with raw boards ordered without a factory finish, the base coat must be applied on-site to all sides and cut ends before installation. JSC strongly recommends factory-applied base coats - the controlled environment removes the variables that cause problems on site, like weather delays, dust contamination, and uneven coverage.

   Cut ends are the most vulnerable point on any board, and the one most likely to be skipped in the rush of installation. Every time a board is cut, raw end grain is exposed, and all cut ends must be double coated during installation, wet on wet. For boards with exposed bottom edges, at the base of the wall, window heads, inter-storey junctions, and soffit junctions - cut the bottom at 15 degrees to form a drip edge and coat 150–200mm up from that edge onto the back of the board.

   Certification compliance

   JSC cladding systems require weatherboards to be coated on all sides in a suitable exterior-grade timber cladding coating to comply with certification requirements. An uncoated board does not comply, regardless of how it's fixed.

3. Fixings NZS 3604:2011

   Wrong fixings, not long enough, over-driven, or not pre-drilled

   For all JSC cladding species, fixing material must be 316 stainless steel or silicon bronze. In exposure Zone D (coastal), 316 stainless steel is mandatory under NZS 3604:2011.

   Nail length isn't optional - the nail must be long enough to achieve the minimum embedment into the framing or cavity batten. With a 20mm cavity batten, the nail needs a minimum of 30mm embedment into the timber framing. With a 45mm structural cavity batten, the nail needs a minimum of 35mm embedment into the cavity batten. A nail that's too short doesn't achieve structural fixing and won't hold the board over time — check nail length against the cavity batten being used and the underlay behind it. A rigid air barrier adds extra thickness behind the batten, so a longer nail will be needed to still achieve the required 30mm embedment into framing.

   Pre-drilling is a must, without exception, regardless of species or profile. Every fixing hole must be pre-drilled before nailing, with a drill bit approximately 1mm smaller than the fixing shank - for a 75 x 3.25mm nail, use a 2.5mm drill bit. This is what allows the nail to grip properly, reduces the risk of splitting the board, and minimises moisture tracking into the timber.

   Don't over-drive. Whether nailing or screwing, the fixing must finish flush to the board surface, not punched or driven into it — over-punched nails and overdriven screws crush the timber fibres beneath the head and create a direct moisture entry path that can't be undone once the board is on the wall. The board needs to be removed and replaced.  If screws are being used, the only acceptable screws are those endorsed by JSC — refer to the JSC Screw Fixing Cladding Guide before using screws on any job.

   Fixing material

   316 SS or silicon bronze

   Zone D (coastal)

   316 SS mandatory

   Embedment - 20mm batten

   30mm min. into framing

   Embedment - 45mm batten

   35mm min. into batten

   Pre-drill size

   ~1mm smaller than shank

   Pre-drilling

   Required always, every hole

   Nail head selection

   Oil and stain finishes: rose head, pentagon head, or flat head. Paint finishes: jolt head is also acceptable, but only for paint - a jolt head under an oil or stain finish will leave a visible mark on the board face. Nail heads must finish flush to the board surface on all finishes, not driven into it.

4. Single Fixing

   Pinning the lap or putting a nail through the face of the board

   Each weatherboard gets one nail per batten crossing. That single fixing is deliberate - it allows the underlap to move freely as the timber expands and contracts. Add a second nail anywhere along the lap or through the face of the board, and you've locked the board at that point. The timber will still try to move; it just can't. This can result in the board splitting.

   Don't pin the laps. Don't put a nail through the face of the board. Don't use a brad nail as an additional fixing point. Clinch nails are available as an optional aid to hold boards in position while nailing off, but they serve no structural purpose and must not be relied on as a fixing - they don't reduce the number of weatherboard nails required, and they can't substitute for accurate packer alignment.

   Single fix only, no exceptions

   One nail per batten crossing. Never pin the laps. Double fixing locks the board, which can cause splitting — the timber will try to move regardless of how many nails you put in.

5. Timber Movement

   Not leaving the expansion gap between boards: timber will always move

   Timber is a natural material. It responds to its environment - gaining moisture in winter and losing it over summer, and that means it moves. This is the nature of the product; the question is whether the installation gives the timber room to do it safely, or fights it.

   JSC weatherboards require an expansion gap between boards. The exact detail varies by profile and cladding system, so always confirm the required gap against the relevant profile drawing and installation guide before starting. This negative space at the face keeps the weather grooves aligned, and is what gives the finished wall its clean, consistent line.

   Some species move more than others. Radiata Pine has more dimensional movement than thermally modified timber or Western Red Cedar, which is part of why its expansion gap requirements are more stringent. Thermally modified timbers (TMT Taiga, TMT Taxon, TMT Amba, ThermoPine) have reduced hygroscopic movement because the modification process restructures the cell walls - but even these will move to some degree. The gap is not negotiable regardless of species.

   Tight boards installed with insufficient gap will close up as the timber swells, and the boards will cup, buckle, or push against each other. By that point, there's no fix short of removing and reinstalling.

   Expansion gap

   The required negative detail varies by profile and cladding system. Always confirm the correct gap against the relevant profile drawing and JSC installation guide before starting. Radiata Pine profiles require a larger negative detail than other species due to greater dimensional movement. When in doubt, contact the JSC technical team.

6. Cavity Battens at Flashings

   Not machining cavity battens down at junctions

   Where flashings and other building elements create a buildup, the cavity battens must be machined down. At window heads, jambs, and other junction details, multiple components stack up behind the cladding - wall underlay, flashing tape, the flashing itself, and the cavity batten. If the cavity batten isn't machined down to account for this buildup, the total thickness at those points is greater than the rest of the wall. The weatherboard then bridges a step rather than sitting flat against the batten, and gets forced into a position it wasn't designed to hold.

   The consequence is stress in the board at exactly the point where it's most exposed to weather. JSC's technical team has seen boards splitting at window heads and jambs where the root cause is not moisture, not the species, and not the coating - it's mechanical stress from a buildup that was never resolved during installation. The board is being bent by the detail, and timber under sustained bending stress will eventually crack.

   Cavity battens must be installed at the same plane across the whole wall. Where accessory components (flashings, cavity closures, flashing tape) add to the thickness at a junction, the cavity batten must be planed/ machined down by up to a maximum of 5mm to compensate.

   At window heads and jambs

   Account for the total accessory buildup (underlay, tape, flashing) before installing the cavity batten at that location. Machine the batten down as needed, up to 5mm maximum, so the back of the weatherboard makes full, even contact across the batten face. Boards that bridge a step will be under stress from day one.

7. Ground Clearances E2/AS1

   Missing clearance requirements at the base of the wall, decks, and roof junctions

   Clearance requirements exist to keep standing moisture away from the bottom of the cladding system. They're Building Code requirements under E2/AS1, not preferences, and they get checked at inspection. Getting them right is straightforward when factored in at framing stage - much less so once the slab is down and the framing is up.

   At the base of the wall, the cladding must finish a minimum of 100mm above a paved surface, or 175mm above an unpaved surface. The cladding must also extend past the bottom plate by 50mm minimum. A minimum 35mm clearance is required to roof claddings and decks. Where a slatted timber deck meets the wall, E2/AS1 requires a 12mm minimum gap between the deck, its stringers, and the wall cladding, easy to miss when the deck framing is going in, and by the time the cladding is on, recovering that 12mm means cutting back either the deck or the boards.

   Cavity closure and vermin proofing must run continuously around the base of all walls, at open horizontal and raking junctions, and over openings. The vent openings in the closer must be kept clear - they're the air path that keeps the cavity dry, and blocking them, even accidentally with construction debris, defeats the purpose of the drained cavity.

   Above paved surface

   100mm min.

   Above unpaved surface

   175mm min.

   Past bottom plate/bearer

   50mm extension

   To roof claddings & decks

   35mm min.

   To slatted timber decks

   12mm min. gap