The Mackintosh 3D model scanned by point cloud and augmented by Page/Park. Credit: Glasgow School of Art

Much discussion on the nature of the rebuild followed the devastating fire that destroyed most of the west wing of Charles Rennie Mackintosh’s Glasgow School of Art in 2014. Contemporary intervention or replication? Now the school, undergoing a £51 million restoration under the guiding hand of Glasgow architect Page/Park, will to some be almost unrecognisable. Yet there’s no contemporary intervention on the Category A listed structure, far from it. This restoration is mostly about the forensic evaluation of the damaged 1909 building to ascertain what it actually looked like – about how Mackintosh, with his skills, aesthetic intent and the economic means at his disposal created his Gesamtkunstwerk; one so good, it’s absorbed into the identity of the city itself. After a fire that saw the accretions of 100 years seared or soaked away, Mackintosh’s masterpiece will return to us in 2019 a far more nuanced thing; not a building of over-painted monochromatic polarities but with a revealed materiality of subtle hues. Making the building perform better, with a reduction in demand for heat and conditioning and the discreet hiding of modern services, has been the key other consideration. This is ironic, since it was the increasing need to make space for cables and pipes that helped the 2014 fire to spread so quickly from the basement to west wing roof. Page/Park depute of conservation Iain King explains that the brick north duct wall of the east west spine corridor had thus become riddled with holes ‘like Swiss cheese’. The fire raged through these ducts up and along to the west wing, completely destroying the library there.

West wing first floor studios during the strip out. Note the absence of Mackintosh’s original roof light ‘dwangs’. Credit: Alan McAteer

Given the tonal subtlety that will be in evidence in the GSA’s new iteration it’s surprising that the only real full documentation of the building as it was completed is a set of black and white plates from photographer Bedford Lemare in 1910, explains Page/Park architectural historian Natalia Burakowska. But these show that the brick walls of the upper east west spine were never painted white, as perceived in recent history, but left as exposed, roughly pointed brickwork. This is the condition that they and their arches have been returned to. King says that as far as possible, services will be embedded in the Douglas fir ceiling soffits or run at low level in narrow containment channels, and pop up locally where needed. New galvanised sprinklers and fire detection tech, however, remain exposed.

The north studios were treated with a pale green paint pigment and linseed oil

For homogeneity, undamaged white- painted walls in the east end will be taken back to the bare brick too. It’s clear from the walkabout of the site that gradual revealing of the building has forced some adhoc decisions on the Mackintosh Operational Group design team, with its ironic MORG acronym. Some were driven by interpolation of the original photographs along with analysis of burned remnants by specialist architectural paint research consultant Crick-Smith. It ascertained that the north studios were treated with a pale green paint pigment and linseed oil wash. New timber panelling in the first-year architecture studios, on the rebuilt west side, will be treated in this manner. On the east however, undamaged white painted timber panelling will remain. The GSA’s Liz Davidson, senior project manager for the restoration, explains that whereas formerly the walls would have been a backdrop as students used easels, now they are the work surface. As a result they decided to keep them white to accord with current art pedagogy.

But the shock of the new is felt in the restored upper level hen run, the glazed corridor that was the last to perish before the fire was brought under control. Previously white painted timber, these were identified by Crick-Smith’s research as having been originally treated with a raw/burnt umber paint and linseed oil wash. This is how they’ve now been finished, turning the structure a dark but vibrant brown. Not only that; the timber joists supporting the roof have been lowered to their original 4º pitch, and the ‘dwangs’ (noggins) between the joists reinstated so the square module in elevation is repeated along the roof. It’s also now to be found back in place on all the north studio roof lights. Mackintosh’s grid detail in dark, thin timber suggests a delicate sense of chinoiserie not in evidence before, and in places, says King, it even helped with running fire detection conduit. In the hen run, as elsewhere in the building, a view was taken on glazing and especially how wide expanses of north facing glass could be treated to minimise heating load. Shattered west side south elevation glass was replaced with single-glazed hand-blown glass sourced, for reasons of economy, in Germany, but the more challenging north face required any original glass panes as well as replacement ones to form the outer face of a bespoke argon filled double glazed unit with 8mm gap. Perhaps the most radical intervention is on the north roof lights, where from east to west flat, state of the art, double glazed units have replaced those lost, introducing technology to the roof that even Mackintosh would have raised an eyebrow at. King says the former, sloped glazing and lead detailing have been brought up to modern standards, noting that ‘if we were to have rebuilt it to Mackintosh’s details it simply would have failed again.’

This proved to be the case in Studio 58 – the rooftop space above the library, also completely lost in the fire – most noted for its Japanese construction influences. In its predominantly glazed roof, even Mackintosh had attempted to install a prototypical form of secondary glazing, the interior pane dapple frosted to mediate light ingress. Having failed and been replaced in the intervening years, replacement double-glazed sand blasted units will, says King, ‘return the light quality to one that no-one remembers in recent history.’ They’ll be warmer too; 100mm of PIR insulation was installed behind the original Douglas fir soffit line. This detail maintains the exact interior proportions but has pushed the exterior apex line of the roof up. To emulate the north American yellow pine of its Japanese influenced columns, a heritage building in Massachusetts undergoing demolition supplied timbers with similar density, strength and grain characteristics. Delivered by a ship that probably plied the same Scottish/American trade routes as in Mackintosh’s day, their precise selection criteria now, thinks Burakowska, stands in relief against the economic contingency with which the originals were specified.

Page/Park constructed a full laser scan of the building to ascertain the damage

Yet what marvels may come from on-the-hoof solutions. Mackintosh’s desire to see the library built in oak like his Ingram Street Tea Rooms fell at the first hurdle, but the decorative American tulipwood he could afford and used throughout didn’t have oak’s intrinsic strength. Burakowska explains that the fire revealed how he got around it, sandwiching stronger spruce between tulipwood sections for his library posts, hiding it all away in a tulipwood fascia. These posts are now being assembled with cut nails to hold up a reconstructed mezzanine. Above it all is the lovely new umber-stained Douglas fir ceiling, suspended by steels from the concrete beams of Studio 58 above. Between the two lies the library’s ‘hidden’ book storage room. On the west elevation, the thicker 1946 Crittall sections that replaced Mackintosh’s failed originals will be replaced with bespoke, single glazed steel windows being manufactured in Austria. This, it’s hoped, will return crystalline delicacy to the architect’s Baronial oriels. And students will be able to get closer to them now. Radiators installed in the bays soon after opening at the governors’ behest – vehemently opposed by Mackintosh as they prevented students sitting beneath his triple height voids – will disappear and be replaced by underfloor heating. ‘We took a view that if we can improve the performance of the space and in doing so get nearer to the design intent, then why not?’ says Burakowska. Most contentiously, the only black to be seen now is salvaged stone from the west gable wall. New blocks of snecked rubble Giffnock sandstone, hand-cut by modern masons, is positively creamy by comparison.

The Mackintosh building before the fire. Credit: Alan McAteer