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Slated for success

Restoration of an early nineteenth-century gate lodge in Regent's Park to create unusual accommodation has required the complicated reconstruction of its hexagonal slate roof

John Nash's original plans for Regent's Park, London, provided for 26 villas of which only eight were built. Gate lodges adjoining two of these original villas remain:

Hanover Lodge, close to Regent's Park mosque, and South Lodge, at the entrance to Regent's College - formerly Bedford College. South Lodge has recently been restored and saved from collapse by architect Giles Quarme and Associates.

Dr Archie Walls, project architect at South Lodge, points out the similarities between Hanover Lodge, by Nash, and South Lodge and believes one was the model for the other. South Lodge predates Hanover Lodge and originally stood within the grounds of the demolished South Villa which the young Decimus Burton was working on in 1818.

A plan dating from 1827 shows South Villa with a small building on the exact site of the existing lodge.

Dr Walls, in collaboration with Dr Anne Saunders, former borough archivist for St Marylebone, believes that this was probably South Lodge and that there is a strong possibility that the architect was Burton; if not Burton, perhaps Nash, who was responsible for the design of all the park facades.

The interest of this little building, which belongs to the Crown Estates, lies in its hexagonal structure. A rectangular room was added later to provide adequate space to house a gatekeeper. In its refurbished state, it provides unusual but charming one-bedroom accommodation - ideal for visiting academics.

Archive photographs existed, showing the roof, but the actual structure had collapsed and the broken remains of the original slates littered the site. The geometry of the building had never been perfect: the chimney was off-centre, the wallhead was uneven, the angles of the sloping slate roof surfaces were not symmetrical and a concealed drainage channel behind the cornice had never functioned efficiently, causing the timber roof members to rot.

If quarrying methods had not changed in the past 200 years these irregularities might not have mattered; slates could have been sawn on site as they had been during construction. But mechanised slate production meant that all slate slabs (66 in the restored version, 54 originally) would have to be pre-cut to exact measurements.

A new concrete ring beam was installed on the wallhead, and laid so that it provided a level base for the roof. The concealed drainage channel above cornice level provided additional flexibility for eliminating irregularities. With the help of the ring beam and variable width gutter, it became possible to construct an accurate plywood template, which fitted all six facets.

A further complication, again a feature of modernised quarry techniques, meant that the large original slate sizes used on the two lower courses could only be supplied in 20mm thickness, instead of the original 12mm. This would have made the roof unacceptably heavy. Dr Walls overcame the problem of maintaining the 12mm thickness by using two half slates, instead of one, with an invisible junction between; the solution is a half-slip joint, secured by Sika adhesive, and virtually invisible. The slates used are Heather Blue Bangor Slate from Aberlleenni Slate Quarries in Bangor, an exact match of the green flecked originals, in compliance with the Listed Building Consent conditions.

The new roof, as the old, has narrow throatings, running parallel to the six hip joints; these were discovered after detailed examination of slate remains, and were evidently discreet drainage channels to protect the lime mortar beds for the hip covers from being washed away.

The hip and intermediate cover pieces are solid chamfered slate sections bedded in lime mortar with red lead.

At a late stage during reconstruction the mortar started to crack and as a result the ridges were found to be shifting. Going back to the remains of the original cover sections, remnants of holes and handmade screws were discovered: clearly the same problem had occurred with the original roof. Dr Walls corrected the defect in a similar manner by inserting countersuck screws, pelleted with slate dowels.

Restoring the roof on South Lodge has been a painstaking task, and the architect has derived obvious satisfaction in solving the construction conundrum it presented. But Nash intended Regent's Park to be a profitable enterprise and whether he or Burton was the architect at South Lodge, this particular form of construction was not repeated when the similar Hanover Lodge was built a few years later in 1822.

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