External Cladding Selection And Durability

Cladding is the decision with the longest consequence on a building, because it determines both the appearance and the maintenance obligation for the whole life of the asset.

In factory delivery it carries two additional requirements that site construction does not: it has to survive being transported, and the junctions between modules have to be closed on site without weakening the weather line.

What the selection has to satisfy

**Durability in the actual exposure.** A coastal site, an industrial area, a bushfire-prone site and a sheltered suburban site are four different conditions, and a product that performs in one can fail early in another. The exposure is established from the site rather than assumed.

**Fire performance appropriate to the classification and the site.** This is a hard constraint, not a preference, and it eliminates categories of product before anything else is considered. In a bushfire-prone area the requirement is specific and it drives the whole external specification, which is covered in [bushfire and flood resilience](/blog/bushfire-and-flood-resilience).

**Maintenance that can actually be performed.** A finish requiring recoating every few years on a two-storey building needs access equipment each time, and over thirty years that access is a larger cost than the cladding was. This is the main input to the external component of [maintenance and whole-of-life costs](/blog/maintenance-and-whole-of-life-costs).

**Repairability.** Something will damage a panel. Whether the repair is a replaced panel that matches or a patch that is visible for the rest of the building's life is decided at selection, and it depends on the product, the finish and whether the colour is available in small quantities.

**Impact resistance where it is needed.** At ground level, around entries, in parking areas and anywhere a wheelchair footplate, a trolley or a hoist will contact the wall. In supported accommodation this applies to more of the building than people expect.

The transport requirement

A module travels on a truck and is lifted by a crane. The cladding is on it while that happens.

Which means the fixing has to resist dynamic loads in directions the finished building never sees, and the surface has to tolerate the handling. Products that are brittle, that rely on a continuous substrate for stiffness, or that show handling marks are harder to deliver intact.

The practical answers are to select a product with appropriate fixing and impact performance, to protect vulnerable areas during transport, and in some cases to install a specific panel on site rather than in the factory. That is a deliberate decision rather than a failure of the approach.

Module junctions

Every modular building has joints between modules, and those joints pass through the cladding.

Three approaches, and the choice is made at design stage.

**Express the joint,** detailing it as a deliberate line in the facade. Honest, reliable, and it has to suit the architecture.

**Close it on site with a cover piece,** which is simple and has to be detailed so the weather line is continuous behind it.

**Clad over the joint on site,** leaving a strip of cladding to be installed after installation. Gives a continuous appearance and introduces site work at height.

In every case the weather line sits behind the cladding, not in it, which is the principle that makes the junction reliable regardless of which approach is used. The same logic governs [waterproofing in a factory-built building](/blog/waterproofing-in-a-factory-built-building).

The cavity and what sits behind

The cladding is a rain screen. What keeps water out of the building is the membrane, the flashing and the drained cavity behind it.

Which means a drained and vented cavity, flashings at every penetration and opening, and a path for incidental water to get back out. Cladding fixed directly to a frame with no cavity relies entirely on the cladding never leaking, and over thirty years that is not a reasonable assumption.

The cavity also contributes to thermal performance and keeps the frame dry, which connects to [energy and thermal performance in modular](/blog/energy-and-thermal-performance-in-modular).

Penetrations and attachments

Every penetration is a potential leak and every one is known in advance in a factory build: windows, doors, vents, service entries, meter enclosures, taps, light fittings and anything fixed to the wall.

Making those in a factory, in sequence, with the flashing installed before the cladding, is more reliable than cutting them on site after the wall is closed. Which is why the external fixtures are coordinated during documentation rather than located later.

The appearance question, answered last

A selection made on appearance and then checked against performance usually has to change.

Made the other way, the shortlist is the set of products that satisfy the exposure, fire, maintenance and handling requirements, and the appearance choice is made within it. That order produces a building that still looks the way it was intended in fifteen years, which is the part the specification is actually for.

Our standards.

MADEmodular / MADEbetter.