160 Aldersgate Street
About
The extensive redevelopment of 160 Aldersgate Street, 1980’s office block, to provide high quality office space for the City market. Works include replacement of the existing Aldersgate façade to give the building new identity; dramatically reconfigure the building’s atrium; reconfigure floor space to optimise use of the basement and ground floor areas and free-up roof space for terraces.
Key Challenges
This development has an interesting saw-tooth façade architecture as well as a nicely designed brise soliel on the upper levels. This approach creates interesting thermal performance challenges, particularly in light of the exacting heat loss rates required in the specification.
The Brief
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Calculate saw tooth façade cladding U-value
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Calculate bracket Chi-value for various bracket designs
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Review the screen design and cold bridging caused by the bracketry
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Calculate bespoke window U-values
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Advise the overall screen U-value and determine required glazing centre pane U-value
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Calculate and review dew point lines for cill, head and jamb details across the façade
Our Approach
We reviewed the façade drawings to select the details that needed to be modelled for condensation risk analysis. We also reviewed the different bracket types to choose two to model for chi-value calculations. We modelled the façade to ascertain the cladding U-value and jamb Psi-value, these results were then used to calculate the overall screen U-value.
The brise soliel consisted of Portland stone fins which required substantial bracketry. We ran a 3D model of this bracket and calculated its interaction with the mullions on the window screen.
Results
In discussion with the façade company we were able to explore various design changes, including material changes to improve the thermal performance of the brackets; this reduced the U-value of the saw tooth façade and the brise soliel. We were able to show that with design changes it would be possible to hit the thermal emission targets and utilise double glazed units with a centre pane value of 1.1 W/m2K rather than 1.0 W/m2K, the latter is more expensive and has a longer lead time for delivery.