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A concept design for the seismic strengthening of Taranaki Cathedral has been received from Holmes Consulting. Architect Jenny Goddard has summarised the detailed report for us:
What is being proposed?
These are the key physical actions:
- Removal of the slate roof (to get at the structure)
- Laying of plywood sheets on top of the existing timber linings (the linings we can see from inside the Church)
- Fixing flat steel plates over the plywood and in to each roof truss
- Fixing steel angles over the roof ridges and valleys and bolting through to important timber structural members. Some steel connections will be visible inside between the wall and the roof
- Re slating the roof (over all this new structure). This probably means new slates
- Re positioning or renewing all gutters and downpipes as the roof will now be higher (30mm approx. because of the steel)
- Removal of approx. 400mm of stone from the top of every external wall (done in sections, not all at once!)
- Temporary propping of the roof while these wall sections are removed
- Boxing up for a reinforced concrete beam to be poured (bond beam) where the stones were.
- Steel anchors drilled down from the concrete beam in to the stone walls – mostly 1metre, 2m down at the corners
- Low pressure grout pumped in to the walls where the anchors are to be sure they are binding the wall
- Stones put back covering the new concrete beam, (inside and outside)
- Steel plates fixed to the gable end wall (west) and transept wall (east). These will be visible.
- Vertical steel rods drilled down in to south wall either side of opening to Vestry
- New concrete footing dug under these sections of wall (rods go in to new concrete)
- 4 vertical steel rods drilled in to east wall either side of Sanctuary with extensive new foundations required beneath.
- Every buttress (20?) has to be anchored to the stone walls with rods. This requires stone removal similar to as for the bond beam. Stones replaced after rods tensioned and grout injected
- New connections between the roof and walls and floor and walls in the Vestry. This will require removal of all floor coverings. Removal of roof covering would be required to work on roof. Reroof after work done. No visible impact.
GABLE END CROSSES
- Gable crosses supported with steel strops behind. Attach to new steel work being put in the roof.
What Does This Mean For The Cathedral?
Visually the impacts will be quite minor- some steel will be visible at the wall to roof connections and across the gable walls but for the most part, the work is happening within the walls, within the roof and in the ground under the walls. While this is pleasing it makes it all very difficult, very time consuming and obviously expensive! Rightly they have discarded an option that would have seen lots of steel forming a ceiling within the Church.
The Cathedral Advisory panel has met, and more information will be forthcoming soon.