Measuring the Variability of Outcomes of the New Natural Daylighting Requirements in the Basque Country's Habitability Decree

TL;DR

This study evaluates the variability of natural daylight outcomes in residential spaces under the Basque Country's new lighting regulation, analyzing geometric and architectural factors through simulations to assess their impact on lighting quality.

Contribution

It provides a detailed analysis of how geometric proportions and architectural variables influence daylight variability under new regulations, highlighting limitations of fixed geometric rules.

Findings

Lighting variability depends on window proportions and room depth.

Architectural features like courtyards and street width significantly affect daylight levels.

Geometric rules alone may not reliably ensure lighting quality.

Abstract

The Basque Country's Habitability Decree of 2022 redefines natural lighting requirements in residential spaces, increasing the Wall-to-Floor Ratio (WFR) compared to previous municipal and sectoral standards, based on the depth of the space considered. This regulatory adjustment seeks to optimize the quality of natural light, a key factor for well-being. However, the application of a geometric rule based on fixed proportions raises questions about the variability of achievable lighting results and their suitability for residential comfort needs. This study analyses the implementation of the regulation in two bedroom models, BR1 and BR2, selected as the typical and the deepest, but with less than 4 meters and meeting the rest of the dimensional requirements, respectively. Through simulations of the Daylight Factor (DF) using window proportions of 1:1, 3:2, 2:1, and 1:2 under a CIE overcast sky model, the dispersion in the obtained natural lighting has been examined. Such analysis allows for the quantification of lighting result variability within the regulatory parameters, exploring the complexity of meeting lighting requirements through an approach based exclusively on geometric proportions. Additionally, the impact of architectural and urban variables such as building height, the presence of courtyards, street width, and balcony depth has been considered. These factors, often overlooked in regulations and indirectly considered in D80/2022, play an important role in modulating natural light and lighting quality. At the end, the paper comments on the advantages and limitations of regulating natural light through arithmetic or geometric rules like the WFR, comparing this method with approaches based on detailed room-by-room analysis.