The view from the top of the new Theatre Royal, Glasgow extension is fabulous.

Looking west, on a good day indeed rather like the day I visited the building site this week, you can see the serried spires of Great Western Road framed by distant hills. Turning to the north, the cityscape is backed by a clear view of the Campsie Fells. If you turn to your left, you can see all the way down Hope Street and a spectacular view of the southside. The problem at the moment is that, despite two deadlines coming and going, the only way one can see this view is with privileged access, wearing gloves, a hi-vis vest and a protective helmet.

Scottish Opera planned to open the Page/Park designed, £14 million new foyer extension to its Theatre Royal home in May. That deadline slipped, undone by bad weather over the winter - in particular hindering the use of high cranes - and some of the same problems that Scottish Opera's general director Alex Reedijk outlined to The Herald this week. These are various, and have also stopped the company from opening the new extension this month, in time for the Commonwealth Games.

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What has happened? "Stuff has happened," Reedijk said, simply. Mainly, the task of adding a brand new, 21st-century building to a very old theatre, on a tight site of only 480 square metres, has thrown up all kinds of unexpected problems. In particular, the wall of the Theatre Royal that joins onto the new cylindrical foyer has provided surprises, diversions, and tricky issues. This wall, more than 100 years old, is full of pipes and services, blocked windows and different materials. New discoveries have been made over the months, Reedijk said, which have necessitated their own solutions, which, he and the contractors, Sir Robert McAlpine, perhaps reasonably thought they should not rush. A powerful electrical cable, perhaps laid when the building was used by STV as a studio, was one unexpected find - it had to be removed. The upshot is the new building, costing more than planned (Mr Reedijk would not say how much, beyond "a few thousand") will not be open to the public until late September. However, the shows will go on - planned performances of Madama ­Butterfly and a special Glasgow Commonwealth Games show, Anamchara - Songs of Friendship, written by Alexander McCall Smith will go ahead.

But the new build, as far as one can tell when you are in the midst of a busy building site, will be a dramatic addition to Scotland's public and cultural sphere. Its design features clean but powerful lines in concrete and wood, and the sense of space is notable given its cramped footprint. There will be a notable new tapestry by painter Alison Watt adorning one wall. The spectacular spiral staircase is at the foyer's centre, an airy public space which will lead audiences naturally, the designers hope, into the theatre space. The naming rights to 39 window boxes, designed to give visitors some privacy as well as views of the city, have each been sold. Good coffee is promised, there are lifts, wifi and cloakrooms, and the roof terrace will be unlike any other public space in Glasgow. But it is a shame the public have to wait so long to see it.