At 65 Gresham Street, the PCSA period was used to challenge the assumption that an existing façade has to be replaced to meet modern performance expectations.
Instead, OAG carried out an extensive programme of surveys, inspections and specialist testing to prove whether the existing aluminium window systems could be retained, refurbished and upgraded.
Working alongside our supply chain, the testing reviewed the condition, structural integrity, thermal performance, airtightness, watertightness, membrane interfaces and anodised finish of the existing façade.
This evidence-led approach helped confirm that the existing façade could be reglazed and upgraded rather than fully replaced, supporting a lower-carbon refurbishment strategy while extending the life of the building fabric.
Building the evidence during PCSA
The testing focused on the existing EWS-02 aluminium window systems across Levels 2-5. OAG’s own visual and condition surveys reviewed the frames, gaskets, beads, drainage routes, fixings, bracketry and surrounding interfaces, identifying localised areas for remediation, cleaning, gasket replacement and reglazing.
GBG Group undertook a window and bracketry condition survey, inspecting 25 existing frames and associated brackets. Their work included pull-out testing of existing fixings, along with testing of T-bolts and brackets to assess the material properties of the components and support the continued use of the existing window support system.
CTE carried out thermal break shear testing to asses the condition of the existing frames after approximately 25 years in service, helping to confirm whether the retained frames remained suitable for continued use within the upgraded façade system.
Testing performance and durability
Define and NFE completed thermal analysis of the proposed refurbished façade build-up, reviewing the retained frames, upgraded insulating glass units, opaque areas, junctions and bracket interfaces. This helped validate the proposed upgrades to improve thermal performance and reduce condensation risk.
BSRIA carried out air permeability testing of the existing windows before and after remedial works, providing comparative data to assess airtightness improvements achieved through the proposed refurbishment measures.
Aqua Plus carried out on-site hose testing of the existing windows, also before and after remedial works, to assess watertightness and façade integrity. The selected test areas successfully passed the relevant CWCT hose test requirements.
OBEX undertook site testing of membrane adhesion in accordance with BBA certification requirements. Testing was carried out on the existing membrane bonded to concrete, both with and without primer, to confirm the suitability of the proposed membrane and adhesive system.
Clive Plant & Associates carried out testing and measurement of the existing frame finish to assess anodising degradation against expected performance. They also reviewed the proposed cleaning procedures, confirming that surface contaminants could be removed using a controlled neutral pH cleaning method without damaging the anodised finish.
Supporting the refurbishment strategy
OAG’s final report brought together the conclusions and results from the full testing and survey programme, setting out the technical basis for the proposed façade retention strategy.
The report demonstrated how the retained EW-02 window systems could be repaired, upgraded and warranted in line with the project requirements. Subject to the defined cleaning and maintenance regime, the inspection and testing supported the 12-year system warranty strategy for the refurbished window assemblies.
The works include new insulating glass units, replacement gaskets and beads, reinstated drainage paths, upgraded insulation to opaque zones, interface membranes and specialist cleaning of the retained anodised aluminium frames.
At 65 Gresham Street, early PCSA testing turned a technical assessment into a clear refurbishment strategy–proving that, with the right evidence, existing façade systems can be retained, upgraded and given a new lease of life.
