What is a Philibert truss?

A Philibert truss is a curved roof truss built up from short sawn boards in staggered layers — the forerunner of the glulam arch.

What is Perspex?

Perspex is a brand name for PMMA (acrylic) sheet: crystal clear, light and weather-resistant, but scratch-prone and highly expansive.

What is the Perpendicular style?

The Perpendicular style is the last phase of English Gothic, recognisable by strictly vertical tracery, vast windows and fan vaults.

What is permeability?

Permeability is the extent to which a material lets liquid or gas pass through — governing groundwater flow, concrete durability and how well soakaways work.

What is perlite?

Perlite is an expanded volcanic rock used as granules for insulation, lightweight mortars and plaster — non-combustible and rot-proof.

What is a round timber stake?

A round timber stake is a pointed round wooden pile driven into the ground for revetments, bank protection and fencing.