Stone ventilated façade

A façade clad in natural-stone slabs hooked onto a metal subframe, held off the insulation by a continuous air cavity. The stone acts as an advanced screen that intercepts rain and sun; the air flowing behind it carries away moisture and heat. The open joints between the slabs do not seal but drain: tightness is entrusted to geometry and the cavity, not to silicone.

The stone ventilated façade is an «advanced screen» (rainscreen) cladding: the stone slabs are not bonded to the wall but hung in front of it, on a subframe of aluminium or stainless-steel profiles, with an air cavity between the cladding and the insulation. It is an envelope of separate layers, in which each element does a single job.

Driving rain strikes the stone, but most of it runs off the outer face; the little that gets through the open joints meets the cavity at once and drains away, without reaching the insulation. The air in the cavity, warmed by the sun, rises by the stack effect and is continuously renewed from eaves to top: it carries off moisture and heat, keeping the insulation dry and the wall cool in summer.

Stone is heavy, and the system lives on its anchors. Each slab is held by clips or undercut anchors set into holes or kerfs on its back and edges, which carry its weight and restrain it against the wind (and the earthquake). The subframe transfers the loads to a few fixed points on the structure, while the other anchors slide to follow thermal movement without restraining the stone.

The open joints give the typical regular pattern and let a single slab be removed and replaced. Durability is high because the insulation is protected and dry and the stone, ventilated at the back, holds no moisture. Care goes to the flatness of the subframe, the thermal bridges of the brackets (with thermal-break spacers) and the edges: eaves, corners and the base where the cavity takes in and exhausts the air.