Inverted Roof Membrane Assembly (IRMA) CLT roof, insulated externally with a moisture resistant high compressive strength XPS insulation that serves to protect the membrane from UV exposure and maintains the CLT roof at a stable temperature. The insulation is weighted down by a stone ballast loaded above a drainage layer with integrated geotextile to manage rainwater above the insulation layer. Required fall in roof can be provided either by the CLT or a cut to fall XPS insulation.