What installation tolerances and site-preparation steps are required for curtain wall to achieve weatherproofing?

Achieving reliable weatherproofing for a curtain wall begins long before panels arrive on site. Critical site-preparation steps include ensuring the primary structure around openings is plumb, level, and within specified dimensional tolerances; providing a continuous, drained substrate or cladding support system; and installing a compatible air- and vapour-control layer where required. The structural frame interface must be detailed for thermal movement and water management with continuous flashings, back-dam details at sills, and deflection heads where applicable. Installation tolerances typically require absolute limits in both plane and setting: typical maximum deviation for opening plane flatness is often ±6 mm over a 3 m span (project-specific), anchor hole positional tolerance may be ±3–5 mm depending on connector type, and cavity widths for sealant must conform to manufacturer minima and maxima (for example 6–12 mm). Anchors must be located within load-bearing zones and verified against as-built conditions with templates or laser layout prior to unit installation. Weatherproofing depends on a watertight load path: specify pressure equalized drainage systems, positive drainage for sills, and redundant seals at joints. Gaskets and sealants must be installed in clean, dry conditions and to manufacturer temperature ranges; where field seams are required, backer rods and primer treatments should be used to achieve the correct joint geometry. Protection of installed units from site trades and temporary weathertightness strategies during construction (e.g., temporary seals) prevent damage and water ingress prior to final sealing. Finally, produce shop drawings with clear tolerance callouts, perform pre-installation mock-ups, and require installer certifications to ensure that site preparation and installation tolerances align with weatherproofing performance expectations.