Where would you buy an 8ft carved eagle from the Philippines, a giant swan bath used by Faye Dunaway in the film The Four Musketeers or a Roman aqueduct from Dijon? How about the 1960s royal box from Ascot racecourse or the interior of London’s bombed Baltic Exchange? These are just some of the past highlights from Salvo Fair, an annual open-air jamboree of architectural eccentrica, still more or less unknown outside the trade.

Next weekend, salvage dealers will gather in the grounds of Knebworth House, Hertfordshire, to sell 500 tons of materials reclaimed from building sites and demolitions across the globe. If you fancy a makeover, but would rather avoid the mass-produced offerings of the high street, Salvo is the perfect place to shop for inspiration.

Though the stars of the show are the plus-size pieces, you don’t need to think big. Among the spiral staircases and cast-iron verandas are thousands of affordable antique fixtures and fittings: patinated brass doorknobs, elegant wrought-iron railings, oak floorboards weathered to a driftwood-pale hue. For imaginative homeowners, buying reclamation is the smart way to acquire objects of unrepeatable craftsmanship on a reasonable budget. The tradition of using reclaimed architectural elements dates back to antiquity. Greek decorative devices were purloined by Roman architects; Roman bricks and capitals, in turn, were reused by medieval builders. In the 18th century, English gents returned from the grand tour laden with columns and busts to incorporate into the decor of their stately homes.

Nowadays, there are environmental arguments for continuing this ancient form of recycling. “We use 3 billion new bricks a year in the UK and we destroy 3 billion old ones,” says Thornton Kay, who organises the fair. “Every 12 bricks embodies the energy of a gallon of petrol - where’s the logic in that?”

Truthfully, though, the fair’s devotees aren’t eco-warriors; they are on a quest for curiosities. Jocelyn Burton, a silversmith, has been a reclamation addict for almost 40 years. Her designs for monumental silver chandeliers have inspired the decoration of her home, a converted stable in Holborn, central London. Burton, who exhibited goblets and a gilt tea set at British Silver Week earlier this month, decorates her high-ceilinged interior with her latest finds. She has cut-glass ceiling lights from “an old cafe or a rather superior pub”; bulkhead lamps, made for an exterior wall, but displayed on the stairwell; and, in pride of place upstairs, “a larger-than-life-size crucifix”.

Perhaps surprisingly, such ecclesiastical pieces are increasingly in demand. Steve Williams, of Church Antiques, says his plaster saints, which start at £20 and 10in tall, are extremely popular: bestsellers include St Sebastian and Our Lady of Fatima. Williams’s stock, rescued from old churches, doesn’t always end up in living rooms. Choir stalls discarded from St Martin-in-the-Fields, in Trafalgar Square, were recently redeployed to St Agatha’s in Portsmouth. Most of his treasures, however, go to private homes. “People like to have a hymn board in the kitchen as a noticeboard, and some customers use pews as dining chairs,” he says.

Vintage ironwork is a speciality at Salvo. Sam Coster, of Mongers, will be showing a fabulously crested and curlicued pair of Georgian wrought-iron gates for £13,000. John Bodrell, of Cast Iron Reclamation Co, will bring a stock of hundreds of antique radiators, priced at £390 and upwards, including 19th-century examples from the Houses of Parliament. “They’re furniture, but some are more like art,” Bodrell says. “The older radiators go well in contemporary interiors – we’ve done several loft apartments in New York.” His favourites are four doughnut-shaped versions from the 1860s, each costing £2,500 and elaborately cast with leaf motifs, that were designed to wrap around the columns of a church in Somerset. “I almost sold one to Madonna, but she didn’t have any vision,” he says. “I told her to put it in the middle of a room, with a glass top on, but she wasn’t having it.”

Another Salvo stalwart, Justin Miles-Booy, of Arc Reclamation, has a missionary’s zeal for old timber. “If you were going to buy a 6ft by 2ft mirror or painting, what would you pay?” he asks. “So why not spend that on a beautiful door? Don’t spoil a lovely room with something that cost £50.” His stock of 1,300 doors includes a six-panelled Victorian pine one for £160.

One of Miles-Booy’s keenest clients is Alan Booton, who has been restoring his 17th-century farmhouse in Hampshire for the past six years. Purchases have included Tudor bricks, to repair his inglenook fireplace, and acres of 17th-century flooring. “There’s just nothing to match the look of old wood,” says Booton, who commissioned Miles-Booy to make a bed from two salvaged pews, as well as numerous reclaimed elm doors to replace the unsightly modern ones installed by previous owners.

Doors will be on offer at Drummonds Architectural Antiques, too. The firm, which specialises in elements rescued from well-known country houses and London landmarks, will exhibit walnut, mahogany and oak doors, priced from £100 to £4,000, some of which were salvaged from Hurst-bourne House, in Hampshire, and Chidswell House, near Halifax, Yorkshire. This year, despite a reputation for big-ticket items, the Drummonds marquee will feature a haul of small-scale, inexpensive pieces. “We’ve been going through the various stores we have hidden away,” says Drummond Shaw, the proprietor, “and will be selling all the small items we have spent 15 years collecting.”

Storeroom finds include vintage window locks and switches, as well as cobbles and flagstones. Prices start at £10 for light switches (usually from £30), £15 for brass door furniture (usually from £35) and £195 for batches of six sash-window catches (usually £270) - so it’s worth making the effort to truffle them out at the fair.

Tempted to invest? Before you buy, make sure your potential purchase will work once you get it home. Above all, be precise about your measurements. Know the exact size of your chimney breast if you are buying a mantelpiece, or the amount of space you have for a cast-iron roll-top bath (and check that the floor is strong enough to take its weight). Ensure bathroom paraphernalia is already adapted for modern plumbing, or that the dealer knows someone reliable who can install it for you.

You should also keep an eye on budget. Vat is charged on all prices, so factor this in. And think about how to get your treasures home: the heavier pieces can cost hundreds of pounds to deliver. It is worth asking whether the dealer will throw in carriage as part of the price. Truth be told, however, the only potential pitfall is the weather. “Some years, it’s like the Somme,” Miles-Booy says cheerily. So go and enjoy, but take an umbrella. And you’ll need vision. Take note, Madonna.

Salvo Fair is at Knebworth House, Hertfordshire, on June 28 and 29, 11am-5pm; 0870 011 5007, www.salvo-fair.com . Admission is £7.50 per person; a family ticket costs £26

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