Reiach and Hall’s Inverness Justice Centre combines the honesty of an exposed in-situ structure with the civic dignity of a glistening precast colonnade, writes Tony Whitehead
Few buildings have quite so many roles to play as the new Inverness Justice Centre. It is the first of its kind in Scotland – a new bringing together of criminal and civil courts with a range of related functions including citizens advice, women’s aid, victim support and social services. But it is also something of a frontier project, the first of a different type of development in an area of north Inverness, previously a rather featureless ‘shed-land’.
“The planners are keen for the city to develop in this direction, and the Justice Centre is very much part of that plan,” explains Neil Gillespie, director of architect Reiach and Hall. “So the design had to help open up the area to encourage new investment. Because of this, and because it is an important civic building with a serious purpose, the design needed a certain gravitas.”
For this, says Gillespie, concrete was a natural choice: “Scotland is predominantly stone built, especially prestige buildings in cities. So unless you have a very generous budget, concrete is the material that can provide that minerality, weight, and a sense of permanence and civic dignity.” Looking at the impressive, 115m-long front elevation of the two-storey Justice Centre, it is easy to see what he means. Tall, white precast concrete pillars punctuate the rain-screen of the front facade, and continue as free-standing columns supporting sheltering canopies at either end of the building.
They give the centre an appearance which is unmistakably classical, imposing, yet unfussy and essentially modern. It is no surprise that it was named 2021 Public Building of the Year in the Scottish Design Awards. But it was not just the “serious” look of concrete that led the Reiach and Hall team to specify it. “The exterior columns and cladding are precast, but the frame is in-situ concrete,” explains Gillespie. “There are environmental reasons for that – the ceilings and columns are exposed – so we are using the thermal mass of the concrete to even out temperature differentials and improve the efficiency of the heating and cooling system.
But even more than that, and perhaps the overriding reason we chose concrete here, was because of a very specific set of acoustic concerns and requirements.” Courtrooms, he explains, have to be free from any kind of noisy distraction from outside – be that from an adjacent corridor, or from outside the building. “Trials can collapse if defendants can claim they could not hear what is being said,” says Gillespie. “This was made very clear to us by the client. So we were very concerned about traffic noise – the centre is next to the four-lane A82 which can get very busy, and we are also next to a police station, so you have constant blue-light activity going on there.” This led to a favouring of concrete’s solidity and mass to block out noise cheaply and effectively.
“We were nervous of featherweight, contemporary construction styles of the steel frame and stud partition type,” says Gillespie. “We didn’t have the budget to start building acoustic boxes within boxes, so we thought if we could have some solid concrete walls, together with a flat concrete soffit, then any partition walls could fit simply and snugly against the ceiling because there would be no complexity like downstands to work around. It’s almost primitive – but it works.”
The building’s reinforced concrete structure is arranged on what Gillespie terms a “tartan” grid. This was driven by the need for the courtrooms (two civil on the ground floor and four criminal on the first floor) to be column-free to enable all parties within them to see each other clearly. This resulted typically in 9.5m x 6.9m bays. Adjacent to the courtrooms are associated rooms such as those used to accommodate witnesses. Though the courtrooms themselves have no windows to minimise distractions for the trial’s participants, Gillespie wanted waiting witnesses and staff outside the courtroom to have access to natural light and ventilation. “So there are internal courtyards.
A finely judged facade
The defining feature of the Inverness Justice Centre is its long front facade, comprising 30 precast concrete columns plus a further 19 similar free-standing precast columns that support canopies at either end of the building.
Designed by Etive Consulting, and made by Plean Precast, the 7.2m-high columns were all manufactured as single units. “It made for heavy pieces. Those in the facade typically weighed 2.8 tonnes,” says architect Neil Gillespie at Reiach and Hall. “But to erect them in sections would have created difficulties with getting the pieces perfectly aligned – and they just look better as single units.”
Those in the facade are not structural, being attached via a thermal break to slim, in-situ concrete columns behind them. Each of these is 250mm deep, chamfered at the edges, and 680mm wide where it meets the widest section of the precast pillars. “The grid of the facade structure is completely different to that of the main building grid,” says structural engineer Jeremy Grant at Arup.
“We don’t actually need an in-situ column behind each of the precast ones which are arranged at 3m intervals. On the plainer rear facade they are every 6m. But it was easier and visually better for the interior in-situ facade columns to reflect the rhythm of the exterior precast.”
While it would have been possible to have the precast columns perform structurally, he adds, the hybrid column design naturally allowed for a thermal break between the two types of concrete. “Also, it meant that the in-situ and precast contractors had the freedom to operate almost independently as far as the structure was concerned.”
While the free-standing precast units are square or rectangular in section, those in the facade are roughly triangular, 680mm x 350mm, arranged in a sawtooth pattern. They are made with Skye marble, a very white and reflective aggregate, says Gillespie. “Because the facade columns are not flat to the facade but canted, first one way, then another, you get a pleasing light effect as they reflect the rays of the low sun.”
Complementing the white precast columns are matching pale precast cladding units over much of the nonglazed area of the facades. In addition, matching precast blocks or bricks, 460mm long, have been arranged to form a low perforated wall between the free-standing columns at one end of the building. “The blocks are arranged with spaces between, so you can see through the wall,” says Gillespie “We originally designed it with larger spaces, but the client asked us to reduce the gaps to improve privacy for those inside the building.
This typified a key challenge for us: reconciling the tension between creating a place with some openness and transparency as to the functions inside – justice must be seen to be done – but at the same time ensuring the centre provided security and privacy for those who need it.”
The courtrooms and courtyards alternate, giving rise to a structure which, in a long building like this, looks a little like a ladder, or tartan, on plan.” Like the foundations, the columns and supporting sheer walls in the building were all constructed from a concrete mix containing an unusually high proportion of cement replacement. Replacing 70% of the cement with GGBS (ground granulated blast-furnace slag) saved around 360 tonnes of CO2 compared with a traditional CEM1 mix. Further carbon reductions were achieved via the specification of post-tensioned (PT) reinforced concrete slabs for the floors and roof slab.
“The slabs make up about 40% of the concrete in the building, so we looked at how PT slabs might help make the structure more efficient,” says Arup’s Jeremy Grant, structural engineer on the project. “They span up to 9.5m with no downstands, so basic flat slabs would have to have een about 375mm thick – quite substantial to damp out noise and vibration. But by changing to PT we found we could reduce the thickness by 50mm.”
It doesn’t sound much, but a number of advantages resulted from the switch to PT slabs: “It saved 261m3 of concrete which, quite apart from the material and carbon saving, means many less movements of vehicles carrying just 8m3concrete at a time. You also save on reinforcement, and reducingthe dead-load of the structure just makes it all much more efficient.” Grant adds that under normal circumstances, the slabs could have been even thinner, perhaps 300mm. “But we had to consider the effect, for example, of a crowd of people moving down a corridor outside a courtroom. We didn’t want distracting vibrations to be felt inside, so 325mm slabs were the slimmest we could go to keep the response factor down to <4.”
The need for sturdy floors was also a factor when it came to designing the grid’s main columns. These are 800 x 300mm in section, and positioned at the edges of the courtrooms and courtyards. This results in rows of columns in a “double blade” configuration, the double columns running either side of the corridors that run past the courtrooms from to the rear of the building. “To maintain a consistent aesthetic, we kept the double-columnarrangement even where it wasn’t strictly needed,” says Grant. “It did, though, come in useful when it came to designing a movement joint for this length of building.”
Arup decided to split the 115m-long structure in two, to accommodate inevitable expansion of the concrete due to changing temperatures. “The question was where to split it. A courtyard was considered as there was less structure to split, but a joint would have spoiled the look of the courtyard facades.” The solution was to place the 25mm joint along the length of a central corridor: “And because we had the double-blade column arrangement, we didn’t need any additional support around the joint.
We just cantilevered the two slabs towards each other from the columns on either side of the corridor. It’s covered by the raised floor.” Inside, the exposed slabs and columns, together with some exposed services such as ducting for lighting, give the centre an almost industrial feel. However, the look is tempered by the use of steel and glass around the precast concrete staircases and also, especially in the courtrooms, by generous amounts of oak acoustic panelling.
The result is an aura of calm solemnity and functionality. Appropriately, Gillespie describes the finish as “honest”. “Because of budget limitations, it’s not the finest interior finish in the world – but when you see it against the strippedback pallet of glass and oak it really starts to work.”