St Mary Redcliffe Project 450 RIBA 2 Stage End Report

4. Substructure
4.1 Foundations
Any foundation solution will be dependent on the ground conditions and no design can be carried
out in this area prior to completion of the site investigation
Given the ecclesiastical nature of the project and the historic nature of the site, obstructions
and burials in the ground are likely. A raft foundation or piled raft foundation could be the most
suitable solution as it will allow flexible support locations whilst avoiding the need for deep
excavations. See diagram in sub-section 1
4.2 Ground Floor Construction
As noted above, the results of the intrusive site investigation will be required before the ground
floor construction can be confirmed. If a raft slab foundation solution is adopted this will also
form the ground floor structure
A suspended slab will be required to the Events Space in the South Churchyard due to the
presence of trees. This could take the form of a lightweight steel and timber structure with a void
below. See diagram in sub-section 1
4.3 Basement
5. Superstructure
5.1 Conceptual Design
Crucial to the architectural concept is the differentiation between a rooted, heavy-weight base,
with visually-lighter linings and upper components. This is reflected in the proposed approach to
superstructure
5.2 Northside Building
An in-situ concrete frame will achieve the following key benefits:
• Common form of construction, familiar to most contractors
• Inherent fire protection
• Flat soffits, avoiding disruption to service runs and permitting a free-flow of ventilation air
• Simplified detailing of partition heads
• Thermal mass to minimise cooling and diurnal swings
Quality fair-faced concrete can be produced with careful forethought and thorough specification,
provided that the concrete contractor is appropriately skilled and experienced
An additional cost allowance should be made for a high-quality, exposed, board-marked finish
Two new basement structures are proposed to the north of the site. The first provides WCs
adjacent to the existing C20 Undercroft, the second provides a service corridor, kitchen areas
and further WCs adjacent to the chancel aisle / ambulatory
Both basements sit immediately adjacent to the existing church, in areas of apparent previous
excavation. so trial pitting will be required to confirm both the existing foundation details to avoid
undermining
The level of the groundwater is also currently unknown but, as noted, existing structures already
exist at these levels. Nevertheless, it is assumed that two layers of waterproofing will be required,
most likely in the form of waterproof concrete and a drained internal cavity
The suggested site investigations will confirm the nature of the ground for basement excavation,
but it is likely that there is a large depth of fill on site which will require temporary support during
construction. As noted above, the level of groundwater is currently unknown but temporary dewatering
should be allowed for at this stage
Finally, whilst the new basements occupy areas that appear to have been disturbed previously,
they remain within the historic church boundary and so burials are a risk. If burials are
encountered during the intrusive site investigations, this aspect of the spatial strategy may need
to be reconsidered, as the implications of exhumation may prove prohibitive
An Example of a Board-Marked Concrete Finish