Larsen Truss Wall Assembly: Complete Guide A Larsen truss wall is an exterior secondary framing system that creates a deep, continuous insulation cavity outside the primary structural wall. For budget-conscious DIY builders, a larsen truss wall offers an accessible route to high thermal performance, reduced thermal bridging, and retrofit flexibility — often delivering Passive House–level envelopes when detailed correctly. This guide explains what a larsen truss wall is, componentry and fastener rules, insulation choices, step-by-step assembly, cost and procurement advice, common installation mistakes, and how the system stacks up against stud walls, double-stud builds, and SIPs. TL;DR: - A larsen truss wall creates a separated exterior insulation(/blog/exterior-roof-insulation-passive-house-performance) cavity (50–200+ mm) to cut thermal bridging and reach U-values as low as 0.12–0.18 W/m²K with 150–300 mm of mineral wool or polyiso. - Build sequence: confirm air/vapor strategy and per...