The mammoth arts infrastructure projects currently under way in Dublin may give the impression that the only tale in town is the one which begins with "spend, spend, spend".

But some construction stories - such as that of the National Library's new storage building on the site of the library's car park in Kildare Street, and the proposed new gallery space next door to the Irish Museum of Modern Art - have a long way to go before they get to the great "happy ever after". According to the institutions involved, these projects are not luxuries, but necessities.

"Not only do we not have enough space, but what we have is pretty poor," says the director of the National Library, Aongus Ó hAonghusa. "This would be a fairly expensive building, but it would address our storage requirements for the next 20 years. It would also be a major statement of support for the library and for the preservation of our documented heritage, a core function of the library and a statutory duty as well."

The library extension has, however, stalled on a technicality - the planning permission lapsed because no building work had been done.

Meanwhile, there's no immediate sign of "new gallery at Imma" on anybody's Christmas list, unless you count Imma's artistic director, Enrique Juncosa. He hopes that under the "per cent for art scheme", the mammoth complex currently under construction between the museum and Heuston Station will - besides apartments, cinemas, car parks, a hotel and a children's museum - contain 5,000 square metres of exhibition space for Imma.

"We're hoping to get a space with two large gallery floors, which is exactly what we lack at Imma," says Juncosa. "Our rooms are very small, and access to the rooms is very small - which is a problem when we want to present large works, or multi-media pieces designed for large spaces."

This new space - next door to the current Imma complex at Kilmainham - would be ideal for temporary exhibitions, while much more of the permanent collection could be displayed in the Royal Hospital. "To have all this work going on is very exciting," Juncosa says. "It moves the centre of Dublin towards the west and the mix of expensive apartments, restaurants, and so on means that people will come to this part of Dublin. I think it will have an impact on visitor numbers."

Waiting for news on the new gallery has proved to be a frustrating experience for everyone at Imma. "There has been an offer to build a gallery space, so this will happen - by law it has to happen," he says. "But I'm a bit concerned because I cannot explain, at the moment, how I would like it to be, and I have not had a meeting with any architect. Of course I understand the negotiations with the companies concerned as well. But I have the board crazy. I say: this is all the information I have."

At the National Library, meanwhile, the success of the big exhibitions on Joyce and Yeats over the past couple of years may - says Ó hAonghusa - give a misleading impression. As chairman of the Council for National Cultural Institutions, he is determined to keep not just the library's case but that of other cultural institutions - including the National Archives, which is seeking funding for a major overhaul - in the public eye. With this in mind, the CNCI recently published its submission to the National Development Plan 2007-2013, and has called for cultural development to form a key element of the next NDP.

But it is, he says, an uphill task. "In a way, that's part of the difficulty we have in getting the message across about our critical storage situation. When people see our new exhibition area and seminar room downstairs and all of that, they think everything is hunky dory. There has been good investment in the library over the past couple of years, and that's all brilliant. But there's still more required. That's the reality."