Building Assemblies & Specs
How architects specify building assemblies — fire-resistance-rated walls and floors, R-values and U-factors, and STC acoustic ratings — with typical build-ups and where the authoritative tested listings come from.
Building Assemblies & Specs
Architects don't specify materials in isolation — they specify assemblies: layered build-ups whose fire, thermal, and acoustic performance is measured as a system. A rated wall is only rated when built exactly as the tested listing describes; a stud, a layer of gypsum, and an insulation type are meaningless numbers until they are assembled and tested together.
These pages explain the ratings architects put on drawings and in specifications — fire-resistance ratings, R-values and U-factors, and STC — and show typical build-ups that achieve them. Every specific number here is illustrative and meant to build intuition. For a project, the governing values come from a tested assembly listing (UL Product iQ, the GA Fire Resistance Design Manual) or a manufacturer's submittal, referenced by design number.
Pages
- Fire-Rated Wall Assemblies Explained (1-Hour vs 2-Hour)
How fire-rated wall assemblies work — what a 1-hour vs 2-hour rating means, how walls are tested under ASTM E119 and UL 263, and where UL and GA listings fit, with illustrative gypsum partition build-ups.
- STC Sound Ratings for Walls
STC sound ratings for walls explained — what Sound Transmission Class means, typical STC values for single-stud vs staggered vs double-stud partitions, and code/target STC for offices, hotels, and multifamily party walls.
- Typical Exterior Wall Assemblies (Layer by Layer)
Typical exterior wall assemblies layer by layer — wood stud, steel stud + continuous insulation, mass masonry, and rainscreen walls — with illustrative whole-wall R-value ranges and the control-layer logic behind them.
- Understanding R-Value and U-Factor
R-value vs U-factor explained for architects — definitions, the reciprocal relationship, how layered R-values add in series, and how thermal bridging reduces the effective whole-assembly R-value.