One project that pushed us hard was a midrise where the developer wanted exposed mass timber and a clean ceiling line. A coordination meeting sticks with me. We chased a two hour fire rating by encapsulating only the beam sides while leaving the soffit exposed, then stacked a tested topping slab and acoustic mat above, which felt odd at first because everyone expected more drywall. One short moment mattered. The assembly passed with added mineral wool and resilient channels tuned for IIC and STC. Sound complaints dropped fast. Fire officials were cautious but open once we showed test data instead of renderings. The lesson was involving the AHJ early. Next time, I'd mock up acoustics sooner. Assumptions cost time. Data saved it, abit nervy but worth it.
On multifamily mass-timber projects targeting a 2-hour rating, the most reliable path has been tested encapsulated CLT assemblies rather than fully exposed timber. Assemblies using multiple layers of Type X gypsum (often 2-3 layers) on resilient channels, combined with a concrete or gypcrete topping slab, consistently achieve the 2-hour fire rating while meeting STC 55+ and IIC 60+ targets. For exposed conditions, success has usually required an AHJ-approved alternate method, supported by listed fire-test data, char-rate calculations, and a performance-based fire engineering analysis. Acoustically, adding acoustic mats under the topping slab and carefully detailing perimeter flanking paths was critical small gaps easily killed IIC performance. What I'd change next time: engage the fire protection engineer and acoustical consultant earlier, and push for mock-up testing before finalizing details. Early coordination avoids last-minute encapsulation increases that compromise the exposed-timber aesthetic and budget.