The existing property is a combination of the main 3 storey residential building with a small basement level, together with a single storey extension between the edge of this building and the neighbouring property. The existing vertical structure to the building comprises of a number of both exterior and interior flank walls, both formed with solid masonry. The upper level floors are formed from timber joists spanning between external/internal walls whereas the ground and basement floor construction is ground bearing concrete slabs. The proposed development will comprise of a new basement level under the full footprint of the house and a new rear 2 storey extension, together with internal structural alterations.
The existing brick perimeter walls will be underpinned in mass concrete following a hit and miss sequence. Reinforced concrete L shaped retaining walls will be cast inboard the mass concrete underpinning. The new basement slab will be formed using a suspended concrete slab, tied back into new retaining walls, whereas the new ground floor slab will be formed using concrete cast onto a metal deck, spanning between steelwork placed within the depth of the floor. The new steelwork will typically span between new steel columns forming goalpost frames and loadbearing masonry walls. A new 2 storey steel portal frame spanning from basement level to 1st floor level will provide the stability to the building in the new arrangement.