How Are Mass Timber Schools Designed in the Pacific Northwest?

The engineer sizes every exposed timber member for two conditions: the structural loads with the full cross-section, and the fire condition with the charred sacrificial layer removed. This dual sizing is what makes the fire rating calculable rather than hopeful — the remaining core after the rating period's charring must still carry the fire-level loads. The engineer documents the char assumptions and the resulting residual sections on the structural drawings so the reviewer can verify the rating claim member by member. Connections receive the most careful fire detailing in the building. Exposed steel plates and bolts at beam-column joints are the weak link in a fire, so the engineer conceals connectors within the timber, protects them with additional wood cover, or specifies intumescent protection where concealment is impossible. Panel bearing connections — CLT floors on glulam beams or walls — are detailed so the bearing survives the char period, and the engineer verifies that shrinkage and movement at connections do not open gaps that would let fire into the joint. Every connection detail is drawn at a scale the fabricator can build, because timber connection performance lives or dies in the shop.

The lateral system's ductility lives in its steel connections. The engineer designs hold-downs, shear brackets, and beam-column connectors to yield before the timber crushes or splits — capacity design applied to wood — and specifies the fastener patterns, edge distances, and member thicknesses that make the ductile mechanism govern. CLT shear walls are detailed with vertical panel joints that can rock and dissipate energy, and the engineer checks the overturning restraint at the foundation for the full seismic demand, since a light timber building still overturns. Floor diaphragm design makes the panels act as one. The engineer specifies the spline or lap joints between CLT panels, the screw patterns that transfer diaphragm shear across those joints, and the boundary connections that drag the shear into the walls — then verifies the diaphragm's stiffness and strength under both wind and seismic loads. For acoustics, the engineer works from the consultant's targets: mass-plus-resilience floor buildups for impact isolation, sealed perimeters and penetrations for airborne sound, and isolated ceiling or topping systems where classroom-to-classroom privacy demands more than the bare CLT provides. The MEP engineer routes to planned, sealed penetrations so the acoustic detailing survives construction.