In recent years, many cities around the world have pledged to upgrade their building stocks to carbon-neutral. However, the literature does not yet provide a shared definition of carbon-neutral building (CNB), and the assessment objectives and methodological approaches are vague and fragmented. Starting from the available standards and scientific literature on life cycle assessment (LCA), this paper advances an operational definition for CNB on the basis of an explicit calculation approach. It then applies the definition to an urban case study, comparing it against a state-of-the-art nearly Zero Energy Building (nZEB) scenario, with the intent of highlighting the major practical limitations connected to the application of a methodologically sound carbon neutrality calculation. The case study shows that carbon neutral objectives can hardly be achieved by single urban buildings because of the lack of spaces that can provide onsite carbon offsetting actions. Carbon neutrality may be better approached at the city, regional, or national scales, where overarching policies may be defined.

Previous studies dealing with dynamic insulation technology neglect the microscopic interaction between the solid matrix of the porous material and the air flowing through the pore structure. The main goal of this work is to investigate this interaction, and its effects on the heat transfer phenomena at macroscopic scale using the Volume Average Method. At first, the microscopic geometry of two samples of rock wool is investigated through image analysis, leading to the evaluation of porosity and granulometry. Then, the volume averaging technique is applied to the microstructure of fibrous materials. Thermal dispersion and thermal tortuosity are introduced and evaluated through numerical simulations of simplified geometry in laminar and low-Pe conditions, and two regression equations are defined

Breathing Walls are air permeable envelope components based on porous materials. In contra-flux operation air flows opposite to \ud conductive flux, while in pro-flux they have the same direction. The Breathing Wall behaves either as a ventilation heat exchanger \ud or as an active insulation. \ud In literature an analytical model describing steady state heat transfer across a Breathing Wall can be found. Since it lacks an \ud exhaustive experimental validation, a facility developed at the Energy Department of Politecnico of Milano was used to investigate \ud the thermo-physical behavior of a no-fines concrete based Breathing Wall in steady state Dirichlet conditions and contra-flux \ud operation