Porous clay block wall

A single-leaf wall of cellular clay blocks, where the porosity of the clay body and the geometry of the webs create a dense network of tiny air cells. A single mass that bears, encloses, insulates and stores heat - the best of Mediterranean masonry brought up to modern energy standards.

The porous clay block pushes the idea of the single-leaf wall to its limit: a single element that performs the load-bearing (or infill) duty, the weather seal and the thermal insulation all at once. Porosity is obtained by adding to the clay substances that burn off during firing (wood flour, polystyrene), leaving micro-pores; together with the thin webs and vertical voids, these pores trap still air - the real insulant. The result is a breathing wall, massive and low in conductivity.

The thermal conductivity of a porous masonry depends on two combined factors: the micro-porosity of the fired body and the layout of the voids, arranged in staggered rows that lengthen the heat path through the web. The air held in the micro-pores and cells is still, so it carries no heat by convection: this brings the block's conductivity down to the order of 0.10-0.20 W/mK, far from traditional solid brick. That same mass, however, gives the wall high thermal inertia and a strong decrement delay, decisive for summer comfort.

To avoid throwing away the block's performance, the thermal bridges of the mortar joints must be eliminated. Ground (rectified) blocks, with flat parallel faces, are laid in a thin bed (1-3 mm) of adhesive mortar spread only on the webs, or dry with tongue-and-groove interlocks on the vertical joints. A traditional thick mortar joint, far more conductive than the block, would instead create a grid of thermal bridges. Lintels, ring beams and corners need special care, where the continuity of the insulation must be restored with insulating blocks or thermal breaks.

Porous masonry is non-combustible (Euroclass A1) and offers excellent fire resistance thanks to its mass. It is also hygroscopic and breathable: it absorbs and releases water vapour, helping to regulate indoor humidity and reducing the risk of surface condensation and mould - provided plasters and finishes just as vapour-open (lime, silicates) are used. Its main limit is brittleness in tension and shear in seismic areas: load-bearing masonry needs ring beams, reinforced lintels and, where required, specific seismic design; as infill, the anchorage to the frame must be detailed to prevent out-of-plane expulsion.