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Case Studies » TCosy2 retrofit, Great Yarmouth

TCosy2 retrofit, Great Yarmouth

Enhabit’s Head of Building Physics & Consultancy Dr Sarah Price has been project manager and technical advisor for the BEIS-funded deep retrofit project of a block of six council flats in Great Yarmouth, working alongside Beattie Passive and Oxford Brookes University. The project completed in early January 2021 and is in the process of applying for EnerPHit certification

Enhabit undertook Passivhaus Planning Package (PHPP) modelling of the project to show its carbon emissions reductions and predicted reductions in energy bills. Enhabit also undertook some of the thermal bridge modelling for Beattie Passive’s TCosyTM retrofit system and advised on the ventilation strategy.


This block was chosen due to its traditional 1950s style terrace, and thus any solutions to the challenges presented by this project will be able to be rolled out across the country more widely.

The project aimed to develop a fast, efficient and cost-effective solution to deep retrofit. The aim was to create a super-insulated envelope around the building, in which the thermal bridges can be addressed.

The project is in the process of applying for EnerPHit certification (the Passivhaus retrofit standard), meeting a space heating demand of 25 kWh/m2 annum and an airtightness of less than 1 ach-1 @50Pa.

Project challenges
  • Working on terrace style flats created challenges as to how the newly retrofitted structure would interact with the neighbouring properties
  • How to deal with the existing balconies on each flat
  • Tenants were to remain in their homes, with as little disturbance as possible
TCosy2: King Street retrofit, Great Yarmouth
TCosy2: King Street retrofit, Great Yarmouth
Project innovations and solutions

The retrofit involved a completely new innovation of the TCosyTM retrofit system, developed by Beattie Passive during the project.

The main improvements were:

  • GRP (fibreglass) cladding fixings were used to fix a fireproof board to form a cavity, into which the Ecobead insulation is injected. This forms a continuous layer of insulation around the building.
  • The project’s airtightness strategy involved, at one point, the whole building being sprayed purple, using airtightness paint Purple Passive.
  • The 6 MVHR units were located in the warm roof void above the stairwell with ducting threading its way down the external insulation to the flats below.
  • Tenants remained in-situ for the whole retrofit and access to the flats was only required 3 times during the build – to install the ventilation valves, to remove windows, install new ones and to install new window reveals.
Modelling & monitoring

The modelling in PHPP shows that the retrofit measures could potentially result in an 80% reduction in CO2 emissions and therefore energy bills. The modelling of the pre-retrofit building agreed with the monitoring data from Oxford Brookes when real occupancy and internal temperature conditions were input into the PHPP model.

Rajat Gupta, Professor of Sustainable Architecture and Climate Change at Oxford Brookes University and Director of the Oxford Institute for Sustainable Development and Low Carbon Building Research Group, and his team have been monitoring energy use and indoor air quality throughout the project.  The first post-retrofit report is due in summer 2021.

More information

Read Beattie Passive’s regular blogs on the project


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