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An Engineering Practice:

Based in the Heart of the Fens, North of Cambridge, Anthony-Johnson offers Structural, Geotechnical, Civil and Environmental Engineering services to Homeowners, Architects, Builders and Businesses in Wisbech, Kings Lynn, Downham Market, Thetford and surrounding areas

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Grade II* listed Georgian Property in a Conservation Area

The North Brink in Wisbech is synonymous with Georgian Architecture, much of which was designed and commissioned by the Peckover Family. I was contracted by the owners of North Brink Medical Practice as Structural Engineer to a project that would see the internal re-modeling of the third floor to this historic structure. The work involved was considerable and involved:

  • Removal of the existing Plaster and Lathe Ceiling
  • Installation of a new Ceiling at a height that allowed full use of the new space.
  • Removal of an internal single skin brick partition

An initial site visit allowed me to carry out an inspection of the existing ceiling timbers and notably, two of these formed ties to the wall plate, thereby preventing the spread of the walls due to roof loads. The ties also acted as main structural supports, carrying the ceiling loads themselves.

My key concern when carrying out the designs for this project was to retain the existing historic features of the structure as far as possible. This meant limiting structural alterations so that the original fabric of the building remained intact.


The construction techniques used in a building of this age clearly dictate it’s longevity. Timbers were included in the construction of it’s external walls, providing some “elasticity” that would otherwise not be present in a building with walls formed from “bricks and mortar”. The existing masonry still retains it’s original lime mortar with pozzolan clearly defined against the white of the lime on freshly “opened up” faces. Timbers were ungraded at the time of construction but appear denser than those used in modern construction today. Lead flashing is thicker than the gauges employed in roofing today. Movement and true levels in the building itself,  whilst clear against straight edges, is lost through the use of skilled construction techniques and use of traditional building materials.

In designing the new ceiling, it was important to check that the existing timber rafters could accommodate the new loads imposed by new joists that would be attached to them. Vertical loading at the connections could quite feasibly cause undue sagging of the roof. Purlins spanning perpendicular to the rafters could be subjected to greater stresses in bending and these needed to be checked. Loads on these were determined using the “Stiffness Matrix” method, whereby the rafters were analyzed for spanning over four supports.

Interestingly, the new joists were slender about their minor axis, so I introduced Noggins between them to prevent buckling. This had the added benefit of making the new connections between the joists and rafters act in shear, taking out the risk of the timbers failing at the new connections. With stress in the timbers being within tolerable limits, a final design was drawn up that would inadvertently strengthen the existing structure for years to come!

However, the removal of the internal wall, which clearly was not carry any vertical load proved an eye opener to all those involved in the project. In carrying out wind load calculations, it soon became apparent that the wall did indeed carry loads- horizontally! In effect, the central wall, formed from a single skin of brickwork, acted as a support to the main external wall when buffeted by wind from the South. It prevented the wall from bowing out as the wind tried to “suck” at it and took load when the wind tried to “push” on it. My solution to this was to design a single column, fixed to the spine wall of the building below and rafters above. Formed from a Structural Hollow section (SHS), the column was fixed back to the wall at every fourth brick course and acts as a mid-span support to the wall itself.