Model showing new structure to support class AA extension
Model showing new structure to support class AA extension
RESIDENTIAL
AIRSPACE
DEVELOPMENT
ENFIELD
Ross House is a three storey office block next to Enfield Chase Overground station. Our client Dominvus commissioned Milestone to develop the detailed design for a two storey addition to the building which would be constructed under a class AA permitted development prior approval.
The existing office spaces were also to be converted to residential use under class e permitted development rights. The building would then provide 42 1 and 2 bedroom apartments.
'The greenest building is one that already exists'
The existing structure is a concrete frame with clay hollow pot infill floors with a thin structural topping. Tully's faced two scenarios in designing the structural solution. Could they prove that the existing structure could take the additional load and if not they needed to knit in additional structure within the existing frame to do the job instead.
Time is always a factor in construction and in order to verify the existing structure a detailed survey of the existing piles would be required as there was not enough as built information due to the age of the existing structure.
The team sought tenders for concrete scanning service which had a lead time in excess of six months so it was decided a new structure inside the existing was required.
The engineers primary request to POW and the team was to save weight wherever possible so we targeted three key areas
Light Steel Frame Structure for new floors
Lewis Deck and thin screed for Slabs
StoCleyer B Brick Slips on insulation for the new façade
No plant on roof
A light steel frame was designed in conjunction with a specialist contractor, this would be delivered to site in panels and craned into place, the panels were typically 89mm wide so comparable to a standard stud wall.
The Lewis deck is a trapezoidal metal deck that can be fixed to steel or timber, it only requires 40mm of lightweight screed to gain the required fire certification and saved weight.
Finally using the StoCleyer system saved weight on the external façade which meant the existing edge beam could take most of the load and majority of the new structure could be inbound from the façade edge allowing us to achieve the required design of the façade without new columns next to windows.
Additionally the StoCleyer system is also available in class A and A2 variants which allowed the building to get EWS1 certification which is required by the clients lenders.
The existing structure also needed to achieve an hour fire rating and this was achieved via a simple plaster finish to the underside of the slab before the ceiling grid was installed.
The existing fabric needed to be upgraded too and we added internal wall lining to the inside which was full filled with rockwool insulation. The existing windows were also replaced to allow residents to open the windows for ventilation and fresh air.
Mechanical ventilation and hot water were provided by an innovative KERS system. The system converts waste heat energy from bathrooms and kitchens to low cost, renewable hot water. Saving energy and also allowing the design to pass SAPS.
The system also only needs one external vent which simplified the architectural resolution of the window systems and minimised penetrations in façade which adds up when trying to achieve low air tightness figures.
The whole building was fitted with a sprinkler system to provide the highest level of protection to the residents in the event of a fire. We designed a subterranean supply tank in conjunction with the specialist sprinkler supply company, which maximised lettable space for the client.
Existing office block
2 storey rooftop extention
Existing office block
