Construction generates heterogeneous data across many disciplines, while ESG reporting demands structured, traceable clarity. Retrofitting projects face this conflict directly: planning documentation, execution records, reality-captured surveys, invoicing, and monitoring data must be turned into ESG indicators that an auditor can trace back to source. Current Common Data Environment (CDE) implementations manage files; they do not extract, structure, and interlink granular data points with their source documents. This paper presents three coupled concepts. BRIX (Building Readiness Index for Computational Exploration) classifies a single building data point by its structural position in the data lake: source container with creation purpose (BRIX-0), foundational parameter extracted from a source (BRIX-1), and calculation parameter derived from sibling values (BRIX-2). Because every generated report re-enters the lake as a new BRIX-0, the typology is cyclically closed. A bidirectional reference mechanism preserves the evidence chain through every stage of refinement and yields source-, calculation-, and effect-checkability. Input lines, finally, model information that a use case needs but does not yet hold: a data-point type bound to a responsible role, a trigger, a deadline, and an acceptance criterion, instantiated as a BCF topic when the trigger fires. Separating creation purpose from consumption use case removes a recurring ambiguity in BIM data semantics. The framework is applied and prototyped on Austrian social housing retrofitting within the FFG-funded RECAP4ESG project. The reference structure also fits naturally with on-premise large-language-model assistance for auditable report generation under European data-protection constraints.