THE RENOVATION OF BUCKDEN TOWERS OUTER GATEHOUSE
The repair of the Grade 1 listed Outer Gatehouse, completed in spring 2021.
The following pictures are from a presentation by Keith Lawrence CEng MIStrucE MICE to the Buckden Local History Society on 7 September 2022.
The text is based on an article written by Conservation Architect, Robert Davies RIBA AABC, for the Buckden Roundabout in February 2021.
After years of fundraising and preparation, the conservation and repair of the Towers' Outer Gatehouse was completed in 2021 thanks to a generous grant from Historic England and funds raised by friends of Buckden Towers and the Claretian Missionaries Trust.
The Outer Gatehouse is located within the boundary wall to the High Street, which was once the Great North Road and the main highway between London and the north. Despite its lack of grandeur compared with the Great Tower and Inner Gatehouse, the Outer Gatehouse, nevertheless, has a long and important history as the main entrance to grounds dating back over 400 years when it was first constructed.
As with all historic buildings, the Outer Gatehouse has long battled the effects of deterioration and decay caused by weather and pollution as well as poor detailing and inappropriate repairs.
MAIN ISSUES
Structual Changes
In the picture above looking west you can see the original north buttress on the right of the arch. It is suspected that a similar buttress was located on the south (left) side of the arch which was removed when the keepers cottage was constructed in the mid 19th century.
Original Gatehouse
The Outer Gatehouse would have had a buttress north and south of the arch
Old and New
The original brickwork of the gatehouse is quite distinct against the 'new' brickwork from the 19th century.
Structural Failures
The removal of the southern buttress caused the gatehouse to tilt which resulted in cracking. Although the new lodge, when it was complted, provided support, structural damage had been done.
GATEKEEPERS LODGE
As completed in 1875 and looking from the High Street (Great North Road).
Ceiling
The combination of decades of weathering and pollution, together with bad workmanship at previous repairs, caused the tiles and leadwork of the roof to fail. This allowed rain to penetrate and rot the timbers and the resulting collapse of the lathe and plaster ceiling.
Brick Vault
During the initial surveys it was suspected that the existing roof was not an original feature of the Outer Gatehouse due to the nature of the materials and method of construction. This theory was confirmed when the rotten roof structure was removed, which uncovered signs of the much earlier vaulted ceiling formed with brick to match the shape of the three-centred Tudor 'flat' arched openings. This brick-vaulted ceiling may have been rendered with a lime mortar. There is also evidence that the original roof had a solid top with a shallow slope finished with clay tiles or bricks.
Records indicate that the Gatehouse roof was re-built sometime after 1870. This corresponds well with the recorded construction of the Gatehouse keeper’s lodge around 1875, and supports the logic that the need to replace the roof was consequent on the demolitions of the old lodge and the associated removal of the SE corner buttress to the Gatehouse structure.
The Outer Gatehouse roof as previously existing.
Exiating Timber Roof
The main timbers of the roof were severely damaged owing to wet rot and were structurally unsound. During repair work the existing central beam had to be supported in case it collapsed.
Existing Roof Covering
There were several design faults within the existing roof.
The clay tiles were unsuitable for the shallow pitch of the slopes and they had not been properly weatherproofed with lead flashings at the abutments to the surrounding masonry. Many of the tiles had cracked and the bituminous felt underlay, which was intended to provide a waterproof barrier below the tiles, had torn in several places.
The central lead valley was designed to discharge rainwater into a cast-iron hopper at the northern end. However, the use of thin lead in over-long lengths had caused the lead to split, allowing water ingress. Over time the valley boards had deteriorated to create a hollow which further inhibited rainwater from reaching the outlet. The constant saturation caused a buildup of debris and moss which compounded the problem.
Existing Parapets
Although some of the existing parapets were in reasonable condition, there were others in a quite dangerous state, including loose and damaged bricks to the decorative merlons. Also, there were several deep structural cracks possibly related to the construction of the Victorian Lodge and the pedestrian gate formed within the boundary wall, both of which may have destabilised the Outer Gatehouse.
REPAIR WORK
New Roof Structure
The new roof was constructed to a similar design as the existing roof but with improved detailing and better materials. However, as none of the original timber structure was suitable for reuse, the roof is entirely new. The new central beam is formed with a pair of air-dried oak beams and a treated softwood framing.
The New Roof Structure
New Roof Covering
The new valley is lined with a thicker grade of lead sheet, with suitable steps and joints to match the length. The roof is finished with natural Welsh slate to match the adjacent cottage and is more suitable for use at the low pitch of 21 degrees. The tiles are weatherproofed with lead flashings at the abutments to the surrounding masonry.
New Ceiling
The new ceiling has been reconstructed with traditional lath and plaster using hand-riven chestnut laths and a 3-coat “hot mix” lime plaster. The decorative oak mouldings from the current ceiling were cleaned, re-stained and reinstated, providing continuity to the roof and maintaining the special character of the ceiling.
Bundle of new ceiling laths
New ceiling laths in position
Completed celing
Brick Repairs
The cracks in the brick were repaired using a modern technique known as crack stitching. Mortar is scraped out and Helifix bars are fixed across the crack and covered with new mortar. 'Rubber Bricks' are made of a light brick material that can be shaped or rubbed easily into the existing structure.
The original brickwork of the outer wall shows signs of 'bleaching' which can’t easily be explained. Underneath, however, can still be seen the polychromatic diapering - typical of the tudor period - which takes the form of diamond patterns made using darker bricks that were burned during the brick making process. This confirms that this was an original feature from when it was first built in tudor days. Similar patterns can be seen in other buildings within the grounds.
