Design Solution · Structural Systems
Design Solution · Dream about it
A lightweight CLT-and-glulam storey added atop a retrofit.
A new top floor is built entirely from cross-laminated timber panels on glulam frames, light enough to add over existing structures behind retained mews facades while meeting fire standards. The low self-weight of mass timber lets new area be added without major foundation or frame strengthening. It adds lettable space with low embodied carbon.
Adding a CLT and glulam top floor to an existing building behind retained mews facades exploits mass timber's primary structural advantage over concrete and steel in this context: self-weight low enough that existing foundations and frames can carry additional area without costly strengthening, provided the structural survey supports it. This is a commercially attractive proposition for a retrofit developer — new lettable area with low embodied carbon added without disrupting the ground-floor uses below — and mass timber rooftop extensions have enough UK precedent that fire strategy, planning and procurement are navigable rather than experimental. Evidence state is claimed, so the specific performance in terms of actual embodied carbon, construction programme and the fire-standard compliance route are asserted by the project team rather than independently verified in this record. The design dependency that demands early attention is the existing structure's actual capacity: a structural survey that verifies load path, foundation bearing and facade wall stability under the new load case is a gate item before the scheme can be committed to, and facade retention at this scale adds its own temporary works and sequencing complexity that must be factored into the programme and prelim costs. The fire strategy for a CLT top floor on a mixed masonry and steel building in a conservation area needs specialist input early, as the route to compliance shapes the detailing in ways that affect both cost and exposed-timber ambition.
#CLT #glulam #rooftop extension #embodied carbon