Why are so many of St Petersburg's renowned art-nouveau mansions being left to rot?

peter nasmyth unwraps Exhibit A with elaborate care: a Russian book entitled Deshevia Pastroiki: Dachnaya Arkhitektura – Cheap Buildings: Dacha Architecture. Its pages are falling out, visibly eaten away by time. He'd found it 15 years ago in a second-hand bookshop in sub-tropical Sukhumi – once the Black Sea's smartest resort, latterly the war-torn capital of Georgia's breakaway state of Abkhazia – and it had cost him a dollar. Then he tells me what he's done with it: made a smart new English edition in facsimile – with the more explanatory title, The Art Nouveau Dacha: Designs by Vladimir Story, Published 1917 St Petersburg – and an accompanying exhibition of his own photographs.

"I just loved the drawings in the book," says Nasmyth. "I loved the fact they showed you how to build your own art-nouveau house. And the book was simply going to disappear. I showed it to my friends, who all thought it was great." For the next decade it sat on the shelf, but an idea was germinating. Nasmyth runs his own English café-bookshop in Tbilisi, and had become exercised by the fact that some of the city's loveliest art-nouveau buildings were going to rack and ruin: might the book be used to raise awareness of what was being lost? He investigated the possibility of its re-issue by some Russian publishers, but they didn't see the point. "So I thought, OK, I've got to save this book, so I'll republish it myself." It was safely out of copyright.

One of Nasmyth's architect friends, who had studied at Prince Charles's academy, said that she thought the Prince would love it, so Nasmyth sent it to him. At the same time, another friend suggested he send it to a leading modernist architect, so he did that too. The modernist loved it, and immediately offered to write a foreword. Meanwhile, news had come back that Prince Charles also wanted to write a foreword. This presented an unexpected quandary, as the modernist regarded the Prince as being – architecturally speaking – the root of all evil. The modernist crossly bowed out, leaving Charles to write the foreword.

All of which points to the particular appeal of this book. Its arts-and-crafts ethos, echoing that of William Morris in Victorian Britain, speaks directly to our contemporary traditionalists, but its embrace of functional simplicity speaks just as directly to the 21st-century heirs of the Bauhaus movement. Yet it was simply a collection of patterns. Vladimir Story advertises himself as a humble "building technician", welcoming orders for everything from technical drawings to construction work. He's the prototype jobbing builder, ready to roll up his sleeves and get his hands dirty.

The original book reflects haste: this was its second edition within the space of a few months, necessitated by the inflation which was starting to rocket as the Tsarist empire fell and prices spiralled upwards. The simplest pattern in the book is for a three-room single-storey house costing one thousand roubles (£14,000 today), with the most elaborate one – for an "English-style" house of three storeys with multiple verandas (English style?!) – setting the aspirational buyer back 16 times that amount. In between come designs in wonderful profusion, reflecting a medley of aesthetic and national styles.

Some of these are Norwegian, some are French, and some Islamic, often with Russian-peasant design motifs woven in. Many of the dachas have towers recalling those of Victorian English follies; some designs, including a sun-hatted pergola built on a tree-stump, are delightfully off-the-wall. If you want a "basic swimming house" with a "retractable privacy box", Story is your man. Or do you want a design to accommodate your servants and farm animals, but not in too-close proximity to your own fragrant quarters? Ditto. And he's keen to hear your comments: "The author hopes that his esteemed clients will continue to send their queries, and also valuable pointers to any drawbacks they have found. For their counsel, the author is always deeply grateful."

Those clients would not all have been rich and aristocratic, though the dacha concept itself – the word means "gift" – goes back to the days when Peter the Great used to reward his faithful vassals with such houses. Dachas became integrated into Russian family life in the 19th century, with all who could afford one having their summer home in the country: Chekhov's cherry orchard was felled to make way for a dacha development, while all the great Russian novels were written in them. At the time when Story was in business, self-contained dacha communities had sprung up along railway lines leading out of all the big cities, with their own concert halls and gymnasiums. In Soviet Russia, dachas retained their centrality to social life, being a reward for party loyalty; in hard times, people used their plots to grow vast quantities of fruit and vegetables.

In 1917, Story's book launched into what was in effect a vanishing world, since Constructivism drove out "degenerate" art nouveau in the Twenties. Should we therefore regard its designs as unrealised dreams? Not at all, says Nasmyth, who is mounting the accompanying exhibition of his own photographs to prove the point. He began looking for art-nouveau dachas in Georgia, and soon found some, many of them dilapidated but still inhabited. Then he decided to search in the book's home territory on the pine-clad outskirts of St Petersburg, and what he found was both remarkable and poignant.

Poignant, because many of the erstwhile dachas were just piles of ash – and fire had always been the great fear for dacha-dwellers. But many of the ashes were from recent fires; developers had bought the land, and simply cleared it to build blocks of flats. "If there's anything I can do to stop this beautiful piece of history from disappearing, I'll do it," says Nasmyth. "But the clock is ticking." But he also found much to be cheerful about. The surviving wooden buildings may now largely be inhabited by poor people, with car seats or a bath tub in the garden, but some have been immaculately restored. Retro-chic is invading Russia as it is everywhere else where money can breathe new life into an elegant architectural past. Some dachas still have their original stained-glass windows, or their Islamic eaves-decoration; they tended to be well insulated against the cold. He shows me an art-nouveau shop, just like its contemporary illustration, and puts a period photograph of a grand stone dacha (with servants standing in front) beside the photo of the same building today in perfect condition.

This unusual story has an equally unusual prequel. Two years ago, in a bookshop in north London, Nasmyth found a Romeo and Juliet novel about an affair between a Russian and a Georgian, written in English by a Georgian in 1949. Nasmyth located the author's son, got permission to reprint, and Timeless, by Nicholas Tchkotoua, was republished coincidentally with the outbreak of war between Russia and Georgia. It proved a success, and has now been translated into three more languages.

With this new trouvaille, it looks like Peter Nasmyth is working his magic touch again.

'The Art Nouveau Dacha', MTA Publications, £19.99. The exhibition is open from 16 February to 1 March at the Prince's Foundation Gallery, London EC2