How to Install Cedral Lap Cladding: Step-by-Step Guide

To install Cedral Lap, you fix treated timber battens to the wall, add perforated closures and trims, then face fix each fibre cement board through its top edge so the next board overlaps it by 30mm. This guide walks through each stage using the figures in Cedral's own fixing guide, with a checklist of the tools and materials you will need.

Always work from the current Cedral fixing guide on site. It covers details we cannot fit here, such as soffits, gables, mitred corners and high wind areas.

Watch: Cedral Lap Chapter 1, Getting started

How the system works

Cedral Lap is installed as a ventilated rainscreen. The boards are fixed to battens so there is an air gap behind them. Air enters at the bottom, flows up behind the boards and leaves at the top, carrying moisture away. Cedral's guide sets a minimum 30mm clear cavity behind the boards and a minimum 10mm continuous opening at the base, the top, and above and below windows and doors. Using 38mm deep battens gives you that cavity.

Cedral is not an insulator. If you want to add insulation, the guide shows horizontal cross battens or adjustable wall brackets to gain extra depth.

Tools and materials checklist

Materials

• Cedral Lap boards (3600 x 190 x 10mm), plus around 10% for waste
• Preservative treated timber battens: 50 x 38mm for standard fixing, 75 x 38mm at board joints and corners
• Breather membrane, where needed (see step 1)
• Perforated closures (2.5m lengths, in 40, 50, 70 or 100mm depths)
• Lap start profile
• Corner and edge trims as needed: symmetric external corner, asymmetric corner (window reveals), internal corner, end profile and connection profile
• EPDM joint tape such as Walther Strong Cladtape
• Fixings: stainless steel hammer-fix nails or stainless steel countersunk screws, plus colour-head screws for visible fixings
• Touch-up paint for cut edges
• Optional: ventilated cavity barriers if your project needs cavity barriers, and plastic corner caps

Tools

• Tape measure, pencil, spirit level and string line
• Saw for fibre cement: a circular saw with a diamond fibre cement blade, or a jigsaw with fibre cement jigsaw blades
• Drill driver, with a 3mm bit for pre-drilling near board ends
• Hammer, or an adjustable pneumatic or gas nailer
• Gecko Gauge pair (10mm), sold for use with Cedral Lap
• Clean, dry cloth for wiping off cutting dust
• Safety glasses, gloves and suitable dust mask (see the safety section)

You can find all the trims and fixings in our Cedral Lap accessories collection.

Before you start: storage and handling

Store boards flat on their pallet, on a level surface, off the ground and under cover. Keep them dry. Carry boards on edge, not flat, and lift them off the stack rather than dragging them. Cedral's guide also says not to cut boards when they are wet or damp, as the dust will stick and stain.

Step-by-step installation

Step 1: Fix the vertical battens

Fix preservative-treated battens vertically to the wall at a maximum of 600mm centres. Reduce the spacing in high wind areas. Use 50 x 38mm battens for standard fixing and 75 x 38mm where two boards meet and at corners, so both board ends have enough timber to fix into.

Each board must be fixed to at least three battens. If it only crosses two, reduce the batten spacing to 400mm.

If you are fitting a breather membrane, it goes behind the battens. Cedral's guide says it is good practice for solid walls, timber frame and metal stud walls, and generally not required for unfilled or partially filled cavity walls. Follow your designer's or building control's requirements.

Step 2: Fit the perforated closures

Screw or nail perforated closures across the top and bottom of the battens, at the top and bottom of the wall, and at window and door heads and cills. They keep birds, rodents and some insects out while letting air through. Keep the 10mm continuous air gap at each of these points. At window and door heads, Cedral says at least 25mm of the closure should be left open to the air.

Step 3: Fix the vertical trims

Position, level and fix the corner, end and window profiles. Run a strip of EPDM along the batten behind every vertical profile. Cedral's details show a 3mm expansion gap between the board ends and the trims, and fixings at least 20mm from the board edge.

Step 4: Fix the start profile

Fix the start profile level along the bottom of the wall. It covers the first batten and kicks out the bottom of the first board so it sits at the same angle as the rest. Leave at least 150mm between the bottom edge of the cladding and the ground.

Step 5: Fix the first board

Sit the first board on the start profile and fix it to every batten it crosses. The end of every board must land on a batten. Any board longer than 400mm must be fixed to at least three battens.

Keep all fixings at least 20mm from the edges of the board. You can fix without pre-drilling when you are at least 50mm from the end of the board. Closer than 50mm, pre-drill (Cedral specifies a 3mm bit for nails) and countersink for screws.

Cedral's minimum fixing specs are:

• Screws (recommended): stainless steel, minimum 4.0 x 45mm
• Nails by hand: stainless steel ring shank, minimum 2.8 x 45mm, 7 to 10mm head
• Pneumatic nails: stainless steel, minimum 45mm long, 2.5 or 2.8mm diameter, round head 6 to 7mm, ring shank preferred. The gun must be adjustable, and you should trial nail first to set the depth.

Nail heads should sit flat on the board surface, not be driven into it.

Step 6: Work up the wall

Overlap each new board 30mm over the one below and fix it through the upper edge, so the next board covers the fixings. Fix every board at least once to every batten.

Butt board ends loosely together without forcing them, with the joint landing on a batten. Put a strip of EPDM on the batten behind every joint to stop moisture getting in. Choose your joint pattern (straight, free or broken bond) before you start. If the building has movement joints, repeat them in the cladding.

Step 7: Finish the top course and corners

The fixings in the top board will stay visible, so use colour-matched screws. Where Cedral meets another material with no end trim, the end of the board should not sit more than 100mm past the last fixing. On gable ends, fix the boards top and bottom to the batten that follows the roof slope, as an unsecured bottom edge can curl.

For corners, you can use the aluminium trims, an overlapping corner, or a mitred corner. Mitres only work on a true 90 degree corner and need careful cutting, so check the guide for the exact cut dimensions.

Finally, apply touch-up paint sparingly to cut edges with a small brush, and wipe any overspill off the face straight away with a clean, dry cloth.

Cutting Cedral and dust safety

You can cut Cedral with a handsaw, a guillotine (Lap only), a jigsaw or a circular saw. Cedral recommends a diamond blade, 180mm in diameter with 4 teeth, and cutting from the back of the board for a clean face. Test cut first. Cut in a dry, well-ventilated place and wipe dust off with a clean, dry cloth.

Cedral's guide warns that cutting dust can irritate your airways and eyes, and that long-term exposure can harm your health. Fibre cement contains cement, so treat the dust seriously:

• Cut outdoors, with the wind carrying dust away from you and others.
• Use a saw with dust extraction where you can.
• Wear eye protection and a properly fitted dust mask. HSE guidance for similar silica dust tasks recommends FFP3 level protection.
• Do not dry sweep dust. Vacuum it or dampen it first.
• Read the safety data sheet for Cedral Facades on cedral.world (technical section).

Frequently asked questions

What size battens do I need for Cedral Lap?

Cedral's guide gives 50 x 38mm treated battens for standard fixing and 75 x 38mm at joints and corners, at a maximum of 600mm centres.

How much do Cedral Lap boards overlap?

30mm, which gives a 160mm cover width per board when installed horizontally.

Can I nail Cedral Lap or should I screw it?

Both are allowed. Cedral recommends screws, but stainless steel ring shank nails are fine by hand or with an adjustable nail gun. Pre-drill within 50mm of a board end.

How high above the ground should Cedral start?

Leave at least 150mm between the bottom edge of the boards and the ground.

Ready to start?

Browse Cedral Lap boards and trims, or order free samples to settle on a colour first. Send us your measurements through our Cedral quote form and we will put together a full list of boards, trims and fixings. You can also read our guide to ventilation behind Cedral.