April 28 2021
Behind the Project: Greyfriars Charteris
Recently, we sat down with Associate Andrew Forshaw and Senior Engineer Mike Gauld to discuss Greyfriars Charteris. They took us behind the scenes of the work on the refurbishment of this historic church, just off the Royal Mile in Edinburgh, Scotland.
Entuitive (EN): Thanks for sitting down with us today, Andy and Mike. Tell us a bit about Greyfriars Charteris.
Mike Gauld (MG): The project is a refurbishment and extension to a church and adjoining administrative building located on the Pleasance in the south of the city centre in Edinburgh just past the Royal Mile.
We are working with Konishi Gaffney Architects on this job and we were the winning candidates following a selected competition entry.
The winning bid involved refurbishing the main church and constructing a new four-storey ‘link’ building that connects the church and adjacent administrative building. One of the client’s main goals was to lower the existing raised ground floor from above street level to street level and introduce a lift in the link building to offer step free access to all levels of the church and adjacent building.
Andrew Forshaw (AF): The project takes an existing church and adjacent administration building and remodels those spaces, also linking them together through the creation of a new entrance space.
The result will be a more functional and open administration building, the link building will be a place of circulation, and the Church is opened up significantly while also being made more suitable for modern use.
Entuitive are providing structural engineering services on the project. We’re actually at a critical point in the structural engineering right now – everything is critical, and every decision is urgent. It’s important for us to be responsive to keep things moving forward.
EN: Sounds like a fascinating project. Have there been any challenges so far? If so, how did you solve them?
AF: I think the major challenge that Mike has had to overcome is to engineer the support work, whether it’s steel or timber around the existing stonework. It’s not all square and it’s not all straight. Fitting a lot of steel work has been quite challenging, but it will look great.
MG: Certainly, specifying the new structure to adapt to the existing building was one of the challenges we faced. There are a few others that come to mind as well.
Adding Openings to the Existing Structure
At the main church building and adjoining community building we have added large openings in four of the walls, the thickest of which was 750mm in width. To form these openings, we needed to use spreader frames at each of the new openings. Spreader frames are like box frames with beams at high and low level, connected by posts at each end. The difference is – rather than being utilised to provide stability following removal of a section of wall they are specified to redistribute the loads from above into the wall below to avoid overstressing the existing walls, which would be the case if we simply installed new beams.
Building Two New Staircases
Two bespoke staircases are specified in the church, one at the lower ground floor that connects to ground floor level, and another in the belltower. The feature stairs at lower ground floor are largely in timber with a minimal amount of steelwork, whereas the other staircase needed to be constructed in non-combustible materials and will eventually be overclad in timber.
The other item which jumps out is the use of precast concrete cladding to the front elevation of the link building, which has a secondary timber clad elevation in front.
The link building is four storeys in height and the cladding is located to the three floors above ground. The presence of a lift shaft and large voids that are the height of the link building behind the front elevation meant it was not possible to tie the precast cladding back to any main floor structure. There was also limited potential to resist torsion at the church side of the front elevation.
These factors drove the decision to have the precast cladding as a self-supporting leaf similar to a cavity wall. Steel beams are specified at various levels up the height of the link building and these give lateral restraint to the cladding. Externally, the precast panels stack on top of one another but are supported at high level first floor on a steel beam as the ground floor panels sit in front of the panels above.
One area we didn’t intend to be involved in but had to step in to help out was on the construction engineering. As part of our design there was a new retaining wall to the front of the link building and the flank wall of the administrative building needed to be underpinned to form a basement space for the link building. As for any works below ground, we had indicated two possible ways of building this to demonstrate that these could be built in a safe manner.
Once the contractor was on site and had the opportunity to do further disruptive investigative works, which had not been practical at design stage, it transpired that there were probably simpler ways to construct the below ground works and we tabled a couple of ideas at a design team meeting on how to do this – the grounds worker met with a specialist the next day and adopted a slightly amended version of one of the solutions we presented.
Over the course of the project, we were also asked to produce the reinforcement detailing and schedules for the grounds worker to construct the below ground structure. In addition to this we had some help from David Optyker in Canada to aid in the design and verification of glass where the contractor’s supply chain was incapable of providing calculations for these items. As it happens, we’ve just completed the design of a rooflight and fixings as the glazer was incapable of providing calculations to justify this item, this was done in the Edinburgh office due to pressing time constraints.
AF: There’s several positive aspects to our involvement on this project – one is of course taking advantage of our One Company philosophy to bring in help from our Canadian Building Envelope Group.
Another is that we’re reacting well to the pressures of a construction site. We’re utilising our collaborative approach to minimize any delay by pulling out all the stops to deliver on an extremely tight timeline. There’s a lot of work that goes on behind the scenes which isn’t always apparent.
EN: What has been your favourite part of the project so far?
AF: My favourite part is watching the emergence of the architect’s design. We started with a building that was quite outdated and, already, from the site photographs you can see how the transformation is happening. I can’t wait to see it finished.
MG: For me it’s been working with the architects, Konishi Gaffney. We’ve got a great relationship with them – they’re actually our landlords in Edinburgh, so we share an office with them. Kieran and Adam are always very diligent throughout their projects and their detail-oriented approach will certainly bear fruit on this project.
AF: Incidentally, the same architect is on this project as our James Jones & Sons Visitor Centre, which had a lot of timber. And here again you can expect a lot of timber to be used in Greyfriars.
EN: That’s a great relationship to have! Any final thoughts?
MG: I’m looking forward to seeing it finished. It’ll be a good project to showcase the type and level of complexity of projects we can deliver in Edinburgh. It’s also one of the larger projects we’ve done in Scotland, so it’ll raise our profile locally as well.
AF: It has been a complicated project but quite rewarding at the same time. One regret is that you’ll see the new public face in the link building but unless you’re an avid local churchgoer, you’ll miss a lot of the more complex work we’ve done inside the building.
I’m sure the client is looking forward to seeing it finished as well. It’ll really change the way they operate.
Thanks to Andy and Mike for sitting down with us today. We learned a lot!
Stay tuned for a follow up article once this project is completed in summer 2021.