External Shiplap Cladding
How to fit DuraKlad 150mm horizontal PVC-U shiplap cladding over a drained and ventilated batten cavity.
Safety Warning — Working at Height & Scaffolding
Plan and risk-assess all work at height. Avoid work at height where reasonably practicable and use suitable collective protection, such as a correctly erected scaffold, tower or work platform, where a fall could occur. A ladder is only suitable for low-risk, short-duration light work when the assessment justifies it. Use competent installers, inspect access equipment and secure loose boards against wind.
Product Scope
These instructions cover Kalsi DuraKlad smooth shiplap, 150mm cover × 7mm, installed horizontally. They do not cover 170mm Featheredge, Double Embossed, Woodland Timber or slatted cladding. The supporting wall, battens, fixings, cavity barriers and flashings must be designed for the building height, exposure, local wind load and applicable Building Regulations.
What You'll Need
Tools
- Scaffold tower or full scaffold
- SDS drill (for masonry fixing)
- Drill/driver with countersink
- Circular saw or fine-tooth handsaw
- Spirit level (1200mm minimum)
- Tape measure and chalk line
- Snips or multi-tool
- Caulking gun
Materials
- DuraKlad 150 × 7mm shiplap boards (5m lengths)
- Starter trim (base profile)
- J-trims and F-trims (window reveals)
- External corner trims
- Preservative-treated structural battens, minimum 25mm deep
- Substrate fixings selected for the wall and project loads
- 30mm stainless-steel cladding nails
- Ventilation/insect profiles and vapour-open membrane where specified
Technical Specifications
Technical basis: Kalsi's current 150mm Shiplap product specification and established cellular PVC-U cladding practice. Obtain the current Kalsi-controlled fixing, movement, ventilation, opening and fire-performance schedule for this profile and the project before installation.
Step-by-Step Installation
1 Inspect the Wall and Plan
Confirm that the wall is structurally sound and resolve cracks, leaks or damp before covering it. This cladding is a non-structural rainscreen and must not be used to brace a wall. A competent designer must confirm the wall build-up, insulation, vapour-open membrane, cavity barriers, fire performance, fixings and wind-load spacing for the particular building before installation.
2 Install the Batten Framework
Fix preservative-treated battens vertically, straight and in one plane, leaving a minimum 25mm clear cavity. Space battens at no more than 600mm centres for white boards and 400mm for Anthracite Grey, Black or exposed locations; reduce the spacing further where the project wind-load design requires it. Support every board end, trim and opening without adding a continuous horizontal batten that blocks drainage or airflow.
3 Fit Trims and Starter Profile
Fit the starter, corner, edge and joint-trim bases level and plumb to supported battens. Use corrosion-resistant trim fixings compatible with the chosen trim. Provide a continuous ventilated opening at the base and top, protected against insect entry without reducing the required free area. Keep the base arranged to drain water outwards; do not seal the starter or ventilation path closed.
4 Fit the First Board
Seat the first board in the starter trim and check it is level. Fix through the concealed nail groove into every vertical batten using a 30mm stainless-steel cladding nail. Start at the board centre and work towards both ends. Do not fix through the decorative face or drive the head so tightly that it restrains movement. Leave 5mm at each end of a white board or 8mm for Anthracite Grey and Black.
5 Continue Up the Wall
Fully engage each shiplap joint and fix through the concealed groove at every batten. Use the matching centre joint or cover-joint trim where a run exceeds one board. Locate each joint over supported or doubled battens and retain the same 5mm white or 8mm dark-colour movement allowance at both board ends. Do not use an improvised open butt joint or backing strip.
6 Detail Windows and Doors
Support board ends and trim bases around every opening. Use the matching edge/reveal trims and provide a head flashing or drip that discharges water onto the cladding face. Sills, flashings and membranes must direct water out of the cavity. Retain the colour-specific movement gap inside trims and seal only the interfaces required by the designed opening detail; do not seal cavity drainage paths.
7 Top Edge and Ventilation
Cut the final board where necessary, support its cut edge at each fixing centre and finish it with the matching top or edge trim. Maintain the continuous air path to the top outlet and protect the opening against insects. Size the free ventilation area to the wall design or current Kalsi detail rather than assuming that the visible trim gap provides enough airflow.
8 Final Sealing and Inspection
Fit the trim covers and seal only junctions and penetrations identified by the designed detail, using a sealant compatible with PVC-U and adjacent materials. Confirm the base drainage and top ventilation remain open, boards can move within trims, flashings discharge correctly and every board end is supported. Clean with warm water, mild detergent and a soft cloth.
Common Mistakes to Avoid
- No drained cavity — Maintain at least 25mm clear behind the boards and keep its base and top openings unobstructed.
- Untreated battens — Battens in the cavity will be exposed to moisture. Untreated softwood will rot within a few years. Always use tanalised or pressure-treated timber.
- Pinning through the face — Fix through the nail flange only. Face pins create visible holes, allow water ingress, and look unprofessional.
- Blocking cavity ventilation — The cavity must be open at base and top. Blocking either end defeats the purpose of the ventilated cavity and traps moisture.
- One movement gap for every colour — Leave 5mm per end for white and 8mm per end for Anthracite Grey or Black.
- Poor window detailing — Rushed window reveals are the most common aesthetic failure. Take time with cuts and trim junctions — they're at eye level and highly visible.
Related Products
Need Technical Help?
Our technical support team can talk you through any installation query. Available Monday to Friday, 8am–5pm.
0121 693 0373 Contact Technical Support