An environmentally controlled mixed-media archive store, designed to occupy a spatially restricted site and to integrate with existing storage buildings on the National Library of Wales estate. The building resolves the various angles and undefined spaces at the north-west corner of the NLW site and improves the appearance of the existing machine house area. The structure and all external and internal finishes are designed for maximum, long term durability with minimal maintenance. The materials and detailing of the envelope are designed to be consistent with distinctive features of the key existing buildings on the Grade 2 listed Library estate.

The 5 storey building provides 7.35km ( circa 850 m³) of shelving and has an internal floor area of 980 sqm. Storage facilities are designed in compliance with BS EN16893-2015. The building follows passive environmental principles. The superstructure is in-situ concrete, with 20cm blockwork walls, insulated to achieve U-value 0.1 W/m²K through all external surfaces, and internally sealed to achieve0.03-0.05 air changes per hour.

The archive store is designed for long term, low access storage. Air-lock lobbies are provided to each of the vaults. Temperature and humidity are regulated by electric under-floor heating and low-volume MVHR with de-humidification. An array of photo-voltaic panels covers the whole of the roof of the archive store. Detailed modelling indicates that the PV generation should provide for all of the energy requirements of the building, with the possible exception of periods of prolonged, extreme heat or cold. By applying a strategy of monitoring and fine-tuning over the early years of operation, it is hoped and intended that the new archive store will by fully self-sufficient in energy, and operate at zero-carbon, if not for the whole of the time, then for the great majority of any calendar year.