What is an open-jointed cladding system?
An open-jointed cladding system is a façade cladding whose outer layer has many openings — open joints between the boards — so that the space behind it is well ventilated. The cladding stops most of the water, but the actual weather barrier sits behind it, in the form of a façade membrane.
That is the reverse of a closed façade. In a closed system the outer skin itself has to be watertight. In an open system you accept that some water gets behind the boards; that water runs down the membrane and is drained away at the bottom, while the ventilated cavity dries everything quickly.
Build-up
From outside to inside:
- Cladding with open joints — boards, panels or louvres, vertical or horizontal.
- Ventilated cavity — a continuous air layer with an open inlet at the bottom and an open outlet at the top.
- Battens — horizontal battens behind vertical cladding and the other way round; counter-battening keeps the cavity continuous.
- Water-resistive, vapour-permeable façade membrane — protects the structure behind against wind-driven water and against UV exposure through the joints.
- Insulation and structure, usually timber frame or an insulated inner leaf.
Points to note
- Choose a membrane rated for open-jointed façades. Not every water-resistive membrane is UV-stable; an ordinary one degrades behind open joints within a few years. Check the maximum joint width and the permitted UV exposure period given by the manufacturer.
- A black background. Behind open joints you see the membrane or the battens. A black membrane or black-painted battens make the joints read as deep and calm.
- Let horizontal boards fall slightly outward, so water does not stand in the joint. With vertical cladding the same applies to the battens behind.
- Keep the cavity open. Insect mesh at top and bottom keeps vermin out without blocking ventilation; use a coarse mesh, not a fine fly screen.
- Expect debris in the cavity. Leaves and dust come through the joints; make sure the bottom cannot silt up.
- Suitable materials include zinc, stainless steel, hardwoods, thermally modified timber and composite panels. The system is used mainly in commercial buildings and on timber frame houses.
Related terms
- Cladding
- Vapour-permeable membrane
- Timber frame construction
- Ventilated cavity
- Hardwood
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