Lightweight insulating concrete roofs, explained by the contractor who builds them.

Lightweight insulating concrete is a cast-in-place insulation systemPortland cement + water + preformed foam or lightweight aggregate. Cast at roughly 20–40 PCF instead of 140–150 PCF for structural mixes. placed as a fluid slurry over the structural deck, usually with EPS insulation boardExpanded polystyrene board embedded between slurry lifts — it carries most of the R-value; the concrete provides the surface, the slope, and the fastening substrate. embedded between lifts. It cures into a monolithic, sloped, insulating substrate ready to receive the roof membrane.

It is not structural concrete — it does not hold the building up. It sits on top of the structural deck and does three jobs at once: it insulates, it builds true slope to drainSlope is screeded in during the pour — crickets, saddles, and compound slopes shaped in place, no taper package to cut and puzzle together., and it provides a continuous, mechanically fastenable substrate for the membrane above it.

The result is a non-combustible deck surface with strong fire classifications and decades of commercial service history — on schools, hospitals, warehouses, and every building type between. The nine guides below cover the rest.