Original designers return to Senedd to celebrate latest expansion

To mark 20 years since the opening of the Senedd building the original designers will return to celebrate the completion of the Siambr expansion.

The new debating chamber has been enlarged to accommodate the increase in Members of the Senedd from 60 to 96 at the election on 7 May 2026.

Originally designed by the architects at RSHP and opened in 2006, the Senedd has become an emblematic building for Wales, conceived as an expression of democratic openness, transparency, and participation. The practice has returned to the building to expand and enhance the debating chamber with a design that champions reuse, accessibility, and long-term adaptability.

The building’s original design anticipated the future expansion of the chamber. Two key interventions, that were allowed for in the original design, have increased the number of seats within the debating chamber.

The original rear corridor, which served as an entrance lobby, has been removed to create an additional row of seating. New entrance lobbies have been repositioned exterior to the Siambr.

Additional seating

The removal of the timber ceiling at the perimeter allows natural daylight to penetrate deeper into the space, ensuring that the new rear row of desks benefits from the same quality of light as the existing seating.

Desk widths were slightly reduced to accommodate additional seating, while retaining the original geometry to enable the reuse of existing curved components. A key development since the building was first opened is that standing to speak has become the norm.

In response, folding lecterns have been integrated into every desk, enabling Members to stand and speak comfortably. An integrated pocket for laptops has been incorporated as part of an overhauled and flexible IT strategy. Original floor structure and desk materials have been reused wherever possible.

New desks are crafted from solid Welsh oak –a locally sourced, robust material –supported by durable stainless-steel sub-frames housingIT equipment. The new desk inserts, folding lecterns and integrated IT are designed on modular principles to maximise future flexibility, allowing room for any future technological upgrades without dismantling the desk.

Drop-in sessions

Drop-in sessions were held with Members of the Senedd to understand how they interacted with the space.

The reconfiguration ensures that Members seated in the new row experience the same visual connection, acoustic quality, and sense of participation as those in the innermost seating, reinforcing the chamber’s democratic ethos.

Existing steps and platform lifts have been removed and replaced with gentle ramps between level changes, allowing step-free access to seats. The Llywydd’s position (the Presiding Officer) has been modestly raised to optimise clear lines of sight across the chamber.

Media 

Broadcast and media requirements have been integrated through a new ceiling-mounted curved technical ring, providing future-flexible mounting positions while keeping cabling contained.

Sound, translation, and media booths have been subtly re-profiled to maintain visual continuity and inclusivity for the new rear row. The rear wall is formed from sound absorbent fabric panelling which is facetted for acoustic performance

RSHP won the competition to expand the Siambr in 2023, building on its long-standing relationship with the building and its commitment to inclusive, sustainable design.

Both the original building and the Siambr expansion maintain exemplary sustainability standards, combining elevated public spaces, extensive natural daylight, durable locally sourced materials, and a layered environmental strategy to create a highly sustainable civic building.

The brief required that the extension be designed for an 80-year lifespan to align with the original building’s 100-year design life.

As a leading example of passive design, it achieves major energy and water savings through 75% natural ventilation, ground source heat pumps made up of 27 100m deep boreholes and a biomass boiler for top-up heating, rainwater harvest covering most of the non-potable water demand, and renewable systems, resulting in 50% lower energy use than a comparable conventional building and the first BREEAM ‘Excellent’ rating in Wales, the highest rating at the time of the original design.

Turning point

The completion of the Senedd twenty years ago marked a turning point for Welsh politics and will be celebrated over the weekend of 28 February and 1 March, where the building will host St David’s Day festivities, including dance and music performances, art and craft workshops, circus skills, and more.

Visitors will also be able to see the redesigned Siambr from the public viewing gallery.

Ivan Harbour, Senior Design Director, RSHP said:“Twenty-five years ago, we set out to create an emblematic home for Welsh democracy, with the Siambr at its heart, designed to encourage the public to witness and engage with political life.

“Today, this sensitive expansion, planned for all those years ago, allows the Siambr to accommodate more Members of the Senedd while preserving its openness, transparency, and the original spirit of participation that has shaped the Senedd’s identity.”

Important milestone

Daniel Wright, Associate Director, RSHP said:“The Senedd was designed with longevity as one of its guiding principles and this expansion demonstrates how forethought in the flexible design has supported the building’s evolution 20 years later.

“We set out to preserve the original aspects of value and the unified character of the circular Siambr space while carefully reworking its organisation to increase capacity.

“By retaining and adapting much of the existing fabric –from the seating geometry to the desk components –we were able to minimise material waste while improving accessibility, performance, and preserving long-term flexibility.”

Llywydd of the Senedd, Rt Hon Elin Jones MS, said: “This return to the Siambr marks an important milestone for our Senedd. Our debating chamber has been transformed to meet the needs of a larger parliament and a new era of Welsh democracy as we look ahead to the election on 7 May.

“This is a building shaped around openness, sustainability and the people we serve, and the changes reflect the next chapter in our democratic journey.