The Burrell Collection is majestic and abundant, a rich man’s hoard of 9,000 objects, industrial wealth transmogrified into Chinese porcelain and medieval stained glass, paintings by French impressionists and Scottish colourists, Persian carpets, suits of armour, Roman and Egyptian antiquities. Amassed by the Glaswegian shipping magnate Sir William Burrell, it was given by him and his wife, Constance, to the city of Glasgow in 1944. Eventually, in 1983, a new building was completed to house it, in Pollok Country Park, the city’s largest green space. It’s an exceptional work of architecture whose conception goes back to 1971, when the young Cambridge-basedarchitects Barry Gasson, John Meunier and Brit Andresen won a competition to design the collection’s home. Its principal aim was to make the most of its natural setting, in high, pillared, glass-walled galleries that allowed you to see a Rodin bronze or a Ming sculpture against a woodland backdrop. But it didn’t get you there immediately. As Meunier now puts it, you experienced “a gradual immersion into the magical world of the collection”. First, you wandered through rooms in red sandstone and timber, part castle, part domestic, part glasshouse, both crafted and industrial, intimate and grand, eclectic and varied like the collection, and responsive to both its personal and public aspects. Gothic doorways and window surrounds were built into the fabric. Confident concrete columns and robust timber beams stood alongside the art in relationships of mutual respect. The art and architecture worked together in a three-dimensional composition. Next month, the Burrell reopens after a £68.25m renovation lasting more than five years. The aim was to fix defects in the ageing fabric and reverse declining visitor numbers, from 1 million a year when the building opened to 150,000 by 2015. A rearranged interior allows a 35% increase in gallery space, enabling more rotation of the exhibits, which it is hoped will attract more visitors. A “hub” has been formed in the heart of the building, an atrium with stepped seating for events. A new main entrance has been formed, so as to encourage more passersby to enter from the park. In the original layout you entered through a portal in the end of a long pitched-roof wing that looked like a fragment of a monastery. This was felt to be too “ecclesiastical” and off-putting by the architect for the renovation, John McAslan + Partners, and the route through the wing protracted and awkward. The new entrance takes you across an open “piazza” through glass doors into the centre of the complex. Necessary steps have been taken to fix leaking roofs, improve climate controls and bring the collection up to current standards of sustainability, conservation and display. The engineer Arup has meticulously worked out a way of upgrading the extensive glazing, such that it looks the same as the more primitive system of the original structure. It is certainly welcome that more of the collection can be shown in better conditions than before. Most of the building’s magic is still there. It is like a man-made version of a walk in a park, where the glass-walled galleries achieve as close a connection as possible between art and trees. There are frequent inversions of inside and out: some internal walls are made of thick stone, as if they were external, and much of the glazed exterior skin wishes itself towards invisibility. From deep inside the building you see greenery through layers of space and objects. Daylight comes from many directions, sometimes flooding through a glazed roof, sometimes glimpsed at the end of a vista. There is also a pleasing contrast of building techniques: the stone is hewn and carved, made to last for ever, while the assemblies of concrete and timber have a basic, just-bolted-together feel. John Meunier, though, is not happy. He has publicly decried the relocation of the entrance, which has entailed the displacement of some stained glass. The original design also included the reconstruction of three rooms from Burrell’s home, Hutton Castle, two of which have now gone. Meunier objects, he tells me, to “the crassness of the abrupt transition from outside to inside, as opposed to the carefully orchestrated transition from the quotidian life outside to the exquisite, almost timeless life among the objects in the collection, a transition of light levels as well as space”. John McAslan says that the changes are necessary for ease of circulation, and that the lost rooms were little visited. What’s at stake here is a clash of cultures. The Burrell represents a road that turned out to be less travelled in modern British architecture, where buildings were considered as things composed, like music or poetry, an attitude that includes the possibility that a less than obvious route to a desired destination might be desirable. McAslan, who once worked for Richard Rogers, comes from the more dominant hi-tech approach, which is more about problem-solving and directness. His way aligns with that of modern museums, which seek accessibility and permeability. The old Burrell, says its management, no longer met “visitor expectations or standards required for a major cultural building”. They will do what they have to do to work with a listed structure such as the Burrell, but they don’t want the architecture to get in the way of their objectives. The subtle qualities of which Meunier speaks can get blown away in the process. The Burrell is run by Glasgow Life, a charity that “delivers a wide range of services on behalf of Glasgow City Council”. You can’t blame them for wanting the building to meet its needs, and conceivably there was no alternative to moving the entrance, but something has certainly been lost. Every part of the original building had personality and intent. Or soul, if you like. McAslan’s most significant interventions in the Burrell don’t really do soul: they do the job, often with quality and skill, but without particular feeling for this unique place. The main new moves – piazza, sliding glass doors, atrium – are the stuff of corporate and cultural buildings everywhere. The Burrell is a collection like no other, for which reason it had a building like no other. It still has, and in important ways it’s better than before, but it has become a little more normal. The Burrell Collection at Pollok Country Park, Glasgow, reopens on 29 March