Two adjoining houses near Bushy Park, Dublin 6 are being sold together to maximise their gardens' development potential. Robert O'Byrne reports

Contrary to what maths teachers have traditionally argued, two into one will go - provided the price is right. That's the case with a pair of adjacent properties in Dublin 6 which have conveniently come on the market at the same time through Colliers Jackson-Stops - with a joint AMV of €10.6 million.

Riversdale House on Riversdale Avenue off Bushy Park Road, between Rathgar and Terenure, was bought in 1959 by the late Douglas Gageby, former editor of The Irish Times. Soon afterwards he and his wife extended the original Georgian farmhouse to accommodate another member of the family and then, at a later date, converted the old stableyard into a fine retirement home for themselves.

Last year, the stableyard and approximately half an acre of grounds were sold for €4.5 million by Gageby's son, John; part of this site is about to be developed to hold four new houses designed by leading architect Tom de Paor.

Meanwhile 25 years ago, the main part of Riversdale House was sold to wine merchant Alex Findlater while John Gageby and his young family moved into the 1960 wing. Now Findlater and Gageby have decided to move on and the two parts of Riversdale have come on the market, offered separately although likely to go to the same purchaser.

So what's on offer? Running to 335sq m (3,606sq ft), the main portion of Riversdale House probably dates back to the 1770s but looks to have been extended and aggrandised in the 19th century.

As a result, there's a fine large drawingroom with marble chimneypiece and handsome cornice, and an equally well-proportioned main bedroom directly above.

The upper floor contains another three bedrooms but only one bathroom; despite a second bathroom tucked onto the stairway return, any new owner will wish to reconfigure the present arrangements.

As for the rest of the ground floor, it holds a cosy study overlooking the rear garden, a diningroom, exceptionally big kitchen and sundry store/utility facilities. There is also a conservatory containing a mature vine currently weighted with grapes; had Mr Findlater not disposed of his wine business some years back, he could now be in the position to sell his own label.

The extension made by Douglas Gageby blends seamlessly into the Georgian property in a way that makes it well-nigh impossible to tell from the exterior where one begins and the other ends.

At 252sq m (2,713sq ft) it too is a big house, certainly ample enough for any family, with four bedrooms, two bathrooms and a study on the first floor, along with a drawingroom, diningroom and spacious kitchen downstairs.

The two main reception rooms have good pine floors and both open through French windows onto a conservatory dating from 1981, complete with its own vine taken from that in the main house.

While obviously lacking the latter's period features, the sensitivity displayed in its construction makes this a house of considerable charm.

Regardless of charm, however, what's most probably going to attract interest is the land surrounding the two Riversdales.

The newer property stands on a little under a quarter acre of gardens, the older comes with approximately 1.6 acres, much of it stretching directly along the banks of the Dodder River.

Given the plans for new housing on the site sold last year, it would be whimsical to imagine several eager developers will not want to buy both Riversdale House and its extension.

Perhaps for this reason the two vendors, acting through the same agent Colliers Jackson-Stops, have opted for neither an auction nor a private treaty sale.

Instead would-be buyers are invited to submit proposals or offers of purchase before October 27th.

By way of guidance on what is expected, an AMV of €8 million is being given for Riversdale House and €2.6 million for the more recent extension. Two houses will go into one ownership, but at quite a steep price.