In Montpellier (34), in the Antigone district, the Nombre d’Or residence is undergoing a large-scale window renovation project, led by ACM habitat and entrusted to Lorillard Bâtiment Occitanie. This work, carried out in an occupied site, combines heritage and architectural requirements, logistical constraints, and improvements in energy performance.

Commissioned by ACM Habitat, the renovation of the windows of the Nombre d’Or residence, listed as “Remarkable Contemporary Architecture,” takes place within a highly regulated architectural context. Built in 1984 by Ricardo Bofill, this complex of 275 apartments in a R+6 building, located on Place du Nombre-d’Or in the Antigone district, is one of the emblematic landmarks of Montpellier’s urban landscape. The project involves the replacement of 1,518 window units, with a dual objective: improving the thermal performance of the buildings while faithfully restoring the original aesthetic of the site. The main challenge of the project lay in preserving the proportions and rhythm of the façades (directly inspired by the golden ratio: see box), which structure the openings and decorative modules. Once this specification was established, Lorillard Bâtiment Occitanie defined a precise intervention protocol based on a like-for-like approach. The original wooden windows, with inefficient double glazing, were replaced with pine elements of similar appearance, incorporating higher-performance glazing.

Occupied site

Started in May 2025, the installation of the windows was completed in March 2026, representing more than ten months of work in an occupied building, with particularly significant logistical constraints. Located on a lively pedestrian square hosting shops and weekly markets, the operation required strict organization, with no possibility of on-site storage and limited daytime access. To address these constraints, Lorillard implemented a just-in-time logistics system, supported by an off-site depot located near the construction site. Daily deliveries made it possible to maintain a steady installation pace, with three teams deployed and up to 16 window units installed per day. This organization relied on close coordination with manufacturing, carried out by the Aveyron-based company Molenat Bois (Lorillard Group), capable of producing between 70 and 100 window units per week, including large-format units (up to 2.40 x 2.10 m) intended for the upper floors of the building. Vertical supply required the use of a furniture lift for the highest levels. As an additional constraint, the project was subject to a specific asbestos removal protocol under subsection 4. During dismantling, the affected elements were sealed according to strict procedures, with appropriate protective measures implemented in each apartment to ensure the safety of both occupants and workers. The simultaneous management of these technical, logistical, and sanitary constraints was key to the success of the project.

Performance

From a technical standpoint, the new window units incorporate approximately 24 mm insulating glazing, combined with effective sealing gaskets, achieving a thermal transmittance coefficient below 1.3 W/m².K. This improvement enhances residential comfort while meeting current energy performance requirements. The issue of solar shading, absent in the original design but expected by occupants, was carefully addressed in order to preserve the architectural reading of the façades. The chosen solution was internal shading in the form of double thermal and blackout curtains in neutral tones, consistent with the building’s color palette. This solution improves summer comfort without altering the exterior appearance of the buildings, illustrating how contemporary uses can be reconciled with respect for the original architectural design.

Beyond the intrinsic performance of the windows, the project highlights the ability to intervene on 20th-century heritage with high standards, both in terms of restoration and execution. The synchronization between manufacturing and installation, the management of a complex occupied site, and the precision of technical choices made it possible to successfully carry out a large-scale renovation without altering the identity of the site.

By Adèle Cazier

Photo credits: ©Lorillard

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