Battens, Membranes and Cavity Barriers for Cedral Cladding
Cedral cladding is fixed to a framework of treated timber battens (or a suitable metal frame) that holds the boards off the wall and creates a ventilated cavity of at least 30mm behind them. A breather membrane goes behind the battens where needed, batten protection tape goes on the battens, perforated closures guard the cavity openings, and cavity barriers may be needed to limit fire spread.
This guide explains what each part of the substructure does, using the figures in the Cedral fixing guide. It also covers where cavity barriers fit in, which is a Building Regulations matter to agree with building control.
Why the substructure matters
Cedral Lap and Cedral Click are installed as a ventilated rainscreen. Air enters at the base of the system, flows up behind the boards and leaves at the top, carrying moisture away. The Cedral fixing guide warns that impeding this airflow could lead to moisture problems within the system. Our post on why ventilation matters on Cedral facades explains the principle in more detail.
The key ventilation figures from the fixing guide are:
- A minimum 30mm clear cavity behind the boards.
- A minimum 10mm continuous opening at the bottom and top of the facade, and above and below windows and above doors.
- A minimum 10,000mm² of ventilation per metre run at the top and bottom of the facade, above and below windows and above doors.
Cedral notes that 38mm-deep battens provide the necessary cavity and are the minimum to resist the pull-out loads generated by the planks.
Timber battens
For horizontal boards, Cedral is fixed to vertical timber battens. The fixing guide specifies battens that are preservative treated and planed on two faces, at least 50mm wide (subject to site location), and spaced at a maximum of 600mm centres. Reduce the spacing in high wind-load areas.
| Batten use | Cedral Lap | Cedral Click |
|---|---|---|
| Standard fixing batten | 50 x 38mm | 75 x 38mm |
| Joints and corners | 75 x 38mm | 100 x 38mm |
| Maximum centres | 600mm | 600mm |
Other rules from the guide:
- Each Cedral Lap plank should be fixed to at least three battens. If it is fixed to only two, reduce batten spacing to 400mm. Lengths over 400mm must be fixed to at least three battens.
- The end of every plank must land on a batten.
- Keep at least 150mm between the bottom edge of the cladding and the ground.
- Any movement joints in the structure must be repeated in the cladding.
- Where wind loading exceeds 1.0kN/m², or exposure is classed as severe or very severe, consult Cedral's technical department.
Vertical boards need counter-battens
To fit Cedral vertically, the fixing guide calls for vertical counter-battens first (minimum 50mm wide x 25mm deep at maximum 600mm centres), with horizontal battens fixed on top (minimum 50 x 38mm, or 75 x 38mm for Cedral Click, at maximum 600mm centres). This keeps the airflow path open behind the boards. Adjustable wall brackets can be used instead of vertical timber battens.
Making room for insulation
Cedral is not an insulator. If you want external insulation behind the cladding, the fixing guide shows extra cavity depth created with horizontal cross-battens or adjustable wall brackets, with the vertical fixing battens fitted on top. The insulation must have no gaps, and the 30mm clear cavity in front of it must still be kept.
Timber or metal framing?
The Cedral fixing guide is written mainly around timber battens, but it does allow for metal framing:
- For Cedral Lap, Cedral recommends its Lap screws for timber battens and says different fixings are available for metal framing. Our Lap fixings, including stainless steel countersunk screws and stainless steel hammer-fix nails, are for timber battens.
- For Cedral Click, clips are fixed with stainless screws onto timber, or with rivets onto metal framing. We stock both the Click clip and screw set for timber and the Click clip and rivet set for aluminium frames.
A metal subframe is usually a specified system with its own brackets, spacings and load calculations. If your project uses one, follow the frame manufacturer's design and check fixing details with Cedral's technical team.
Breather membrane
Where a breathable membrane is used, the fixing guide says it goes behind the battens (behind the vertical counter-battens on vertical installs). Cedral describes it as good practice on solid walls, timber frame and metal stud construction. For unfilled or partially filled cavity walls, it says there is generally no requirement.
For open-jointed vertical installations, where more rain reaches the cavity, the guide calls for a breathable, watertight membrane directly behind the vertical battens. That membrane should meet EN 13859-2 and have increased UV stability.
Batten protection tape and joint strips
Water can run down behind board joints and sit on the face of the batten. Cedral specifies a protective strip, which the guide calls an EPDM strip, on the battens:
- Cedral Lap: along the batten behind every plank joint and behind all vertical profiles, and on battens at movement joints.
- Cedral Click: on every batten, not just behind the joints, before any profiles or planks go on.
- If the joint strip is exposed to light, it must be UV resistant.
We stock Walther Strong Cladtape, a UV-resistant, non-butyl batten protection tape (50mm x 20m), and a PE foil DPC roll (100mm x 30m) for use behind cladding joints and battens. Cedral's fixing guide also lists a 100mm x 30m PE foil joint strip among its accessories.
Perforated closures
The cavity has to stay open to air but closed to birds, rodents and insects. Perforated closures do both. The fixing guide says to screw or nail them to the top and bottom of the battens, at cills and window or door heads, and at the top and bottom of the facade. At least 25mm of the closure should be left open to the air, for example at window and door heads.
Closures come in 2.5m lengths and different depths to suit the cavity, including where external insulation is used. We stock 30 x 50mm perforated closures, along with 40mm, 70mm and 100mm versions, in the Cedral Lap accessories and Cedral Click accessories collections.
Cavity barriers
A ventilated cavity is also a route that fire and smoke can travel along. Cavity barriers close off the cavity at set points to limit that spread. Whether you need them, where they go and what fire performance they must achieve are set by the Building Regulations. In England the guidance is Approved Document B, and Scotland, Wales and Northern Ireland have their own requirements. The answer depends on the building type, its height, how it is divided into compartments and the wall construction behind the cladding.
The Cedral fixing guide does not set out cavity barrier positions, so agree them with your building control body, architect or fire engineer before you order materials.
Ordinary solid cavity barriers would block the airflow that Cedral needs. For that reason, ventilated (open-state) barriers are often used behind rainscreen cladding. We sell the Tenmat FF102/50 ventilated cavity barrier. Its manufacturer listing describes a 6mm-thick intumescent strip (1000 x 75mm) for ventilated cavities up to 50mm deep, which leaves an air gap in normal conditions and expands in a fire to close it. Tenmat lists fire performance of up to 120 minutes depending on the wall construction. Check the manufacturer's installation instructions and certification against your wall build-up, and confirm the product with building control.
Cedral itself is classified A2-s1,d0 to EN 13501-1. That classification does not remove the need for cavity barriers where the regulations require them, so always check your project's fire requirements with building control.
FAQs
What size battens do I need for Cedral Lap?
The Cedral fixing guide specifies 50 x 38mm treated timber battens for standard fixing and 75 x 38mm at joints and corners, at a maximum of 600mm centres.
And for Cedral Click?
75 x 38mm battens for standard fixing and 100 x 38mm at joints and corners, also at a maximum of 600mm centres.
Do I need a breather membrane behind Cedral?
Cedral calls it good practice on solid walls, timber frame and metal stud walls. It is generally not required on unfilled or partially filled cavity walls. Where used, it goes behind the battens.
Do I need cavity barriers behind Cedral cladding?
It depends on the building and the wall construction. This is a Building Regulations question, so check with your building control body before you start.
What does batten tape do?
It protects the face of the timber batten from water running behind board joints. Cedral requires a protective strip behind every Lap joint and on every batten for Click.
Get your substructure right first time
Send us your wall areas and openings through the Cedral quote form and we will price the boards, trims, closures, tape and fixings together. Still choosing a colour? Order free Cedral samples, and see the full range on our Cedral hub. For every detail, download the Cedral fixing guide (PDF).