5 New Street Square

A deep retrofit of an office building in the City of London set to achieve NABERS 5* certification.

Climate Change Adaptation Health, Wellbeing and Social Value Resource Use Advancing Net Zero Circular Economy Case Studies

Member written

Project Overview

*This case study is featured in UKGBC’s report, Building the Case for Net Zero: Retrofitting Office Buildings

With the main lease coming to an end, a key motivator for retrofit was retaining the existing tenant, for which net zero operation and well-being had become increasingly significant factors. A major lease event provided a clear opportunity for a deep retrofit.

A net zero carbon roadmap was developed and modelled to establish the most effective measures for meeting the energy use intensity targets. Despite a potential improvement in overall u-values from 1.9 to 1.4, it was quickly established that a replacement façade was not only costly and disruptive, but also that the improvement in energy performance was insufficient to offset the upfront carbon impact, however, this may be considered at the next lease event. The focus of the strategy has therefore been on centralised plant and floorplates, combined with a move to all-electric operation. The Energy Use Intensity Target for the project has been set in line with a NABERS 5-star rating, and an EPC minimum of B.

Company name

Landsec, Bennetts Associates, Cundall

Location

New Street Square, London

UK availability

Yes

Date added

Jan, 2024

Completion date

Q1 2025

Project partners

Client: Landsec, Architect: Bennetts Associates, MEP Engineer: Cundall

Project status

Design stage

Project size

28,734 GIA (exc. basement)

Case Studies submitted by

Landsec

Bennetts Associates

Cundall

Key Sustainability Objectives/ Outcomes

Operational energy performance

The four most significant energy savings that had relatively little impact on the use of the building were – in descending order – ASHPs, HVAC upgrades, lighting improvements, and mixed mode operation. More noticeable changes, such as tenant IT (mostly cloud servers) and behaviour (temperature set points, dress codes and remote working approach) are ones over which the landlord has limited operational control, but which do still have a marked influence.

Demand Control Ventilation: New variable air volume (VAV) terminal units will provide demand-based control of the ventilation system. The VAV units will extend from the reused main riser ductwork and be controlled via CO₂ sensors used to measure the equivalent level of occupancy. This will significantly reduce the amount of ventilation air required during periods of lighter occupation.

Partial Mixed Mode Operation: The existing smoke vents within the perimeter facades will be re-tasked to provide natural ventilation to the office floors. Actuators will be refurbished or replaced as required and interface units provided to allow connection and control to the building management control system. This will allow passive ventilation to the perimeter zones during the shoulder period (spring and autumn). When either too cold or too warm the whole building will revert to sealed operation.

Resource use and circular economy

The ethos is to minimise the embodied carbon associated with the project via the retention and refurbishment of as much of the existing building as feasible, including the façade and centralised MEP. The existing air handling plant and secondary pump sets will be comprehensively refurbished. Pipework and ductwork installations, main electrical infrastructure and distribution are to be retained (following testing).

Health, well-being and social value

Common spaces are to be revitalised, roof terraces updated, with planting and bio-diversity increased. Demand controlled ventilation will lead to improved air quality while also reducing energy consumption.

Lessons Learnt

Operational and upfront carbon need to be carefully balanced.
Retrofit results in much lower upfront carbon than even the very best new builds.
Central MEP and HVAC systems have a significant impact on overall energy use intensity and therefore can result in substantial savings.
Landlord and tenant split in reducing energy consumption is important to understand.
MEP is potentially a significant part of upfront carbon in a reuse project.

134-138 Edmund Street

Building performance optimisation of a Birmingham office, achieved through embedding a data analytics software tool to provide actionable intelligence to property managers, building contractors and tenants.

Climate Change Adaptation Case Studies