Mathematical tiles really do add up and, in the case of Althorp House in deepest Northamptonshire, they equal a country home that really is enshrined in the British psyche.

The impressive grade 1 listed building, well known as the ancestral home and resting place of Diana, Princess of Wales, has undergone a £2.5 million restoration that included the replacement and refurbishment of its illusory façade with York and Manchester based building and restoration specialists William Anelay Ltd as principal contractor for the overall twenty month long project.

Successfully completed in six phases, William Anelay started on site in September 2009 with the brief of refurbishing the two wings, State dining room and complex roof area of the main house on behalf of the Althorp Estate.

The lead consultant, London based conservation and historic building architects Giles Quarme and Associates, undertook weekly site visits to assist in the smooth running of the project and were ably assisted by quantity surveyors, Sawyer and Fisher and by structural engineers, Hurst Peirce + Malcolm LLP.

Set within 14,000 acres of beautiful countryside and encompassing over 30 farms and 200 cottages, Althorp has been the ancestral home of the Spencer Family since the 16th Century. The original red brick Tudor building underwent a dramatic makeover in the 18th Century when renowned architect Henry Holland was commissioned to make extensive changes.

That particular makeover involved thousands of clay mathematical tiles being placed over its facade to create the impression of brickwork. Mathematical tiles were a popular building material across the Home Counties in the 1800s and early part of the 19th Century. Not only did they create an attractive exterior, they also saved money at the time of the Brick Tax between 1784 and 1850.

The tiles are laid in an overlapping pattern with the thicker, lower section remaining visible and the upper section hidden beneath the row above. They are attached to the underlying structure and then tuck pointed to form a flat surface.  For this scheme, tens of thousands of stainless steel fixing pins designed by the structural engineer were discretely inserted before being lime pointed to ensure that the tiles remain in situ for many years to come.

William Anelay Site Manager Gary Wilson explained: “Mathematical tiles cover all aspects of Althorp House and surround the ninety or so windows so their refurbishment or replacement covered all of the phases of the project. Whilst a number of our own masons have been involved in restoring and repairing the stonework and producing carved composite capitals, Bowden and Ward, a locally based masonry contractor have proved themselves a key member of the team as they have carried out a significant element of this specialist work.

“Phase one of the project involved the roof, facade and stonework on the south west wing and it was there that we started to uncover a number of substandard repairs from previous years. That’s common in our industry and we’re regularly called on to make good past mistakes.”

Phase two involved work on the State Dining Room roof as well as re-pointing and reformation of guttering. The removal of the slates revealed some cracked timber beams that threatened the integrity of the structure but the expertise of a team of joiners and of plaster repairers Stevensons of Norwich helped to mitigate that issue. Phases three and four covered the North East wing and main house area with the last two phases covering the remaining elevations.

“The project involved extensive lead work to the roofs. In excess of 100 tonnes in fact! That’s a big roof surface area to cover but it’s a challenge that we’re used to, having carried out similar work at Harewood House, Bowes Museum and Manchester Cathedral to name but a few,” added Gary.

According to Gary there were a number of challenges to working on the roofs: “We had to remember at all times that we were working directly above some much loved and valued artwork. Whilst earlier leadwork carried out in the 1950’s had been executed well, lead roofing techniques have moved on considerably since then.

“There was less consideration for expansion and contraction then which over the years can cause lead to crack and allow water to leak in.  Lead Sheet Association approved techniques go a long way to avoiding this situation and will serve the building well for decades, even centuries.  We’ve reinstated much of the existing roofing with many tonnes of Welsh and Westmorland reclaimed slate installed to match the existing.”

Preserving the historic building fabric with minimum impact on the house itself was a main project stipulation for the professional team.  The Structural Engineer would not allow scaffolding to be tied in to the main structure other than at one particular point at roof level.

“Given these restrictions and the scale of works, a very complex scaffolding system was put in place that took 17 weeks to erect and used 36 one-tonne water filled containers to provide kentledge.  On one occasion, extremely high wind speeds gave some cause for concern but the scaffolding held its own,” explained Gary.

Many of the building’s window heads and sills were repaired or replaced using Cadeby Stone. The weather created a few problems during the winter months as the Anelay team had the December deep freeze and resultant frosts to contend with which caused delays to lime mortar works during the sub-zero temperatures.

“Another factor to consider was that the building remained in use throughout the construction period and is open to the public during the months of July and August with thousands of visitors walking around the house and grounds. It goes without saying that safety remained a priority at all times,” added Gary.

Architect Dr. Archie Walls of Giles Quarme and Associates closely monitored the work carried out by Gary and his team and comments:

“As architects, our aim is always to provide a client with a successful outcome and one that enhances and benefits the building.  In order to achieve this, it requires the consultants and contractors to work closely together as a team.  The success of the conservation project at Althorp House proves that this strategy works well and that William Anelay has performed their functions superbly.”

Giles Quarme and Associates, like William Anelay, are well established as experts in preserving Britain’s historic architecture. Indeed few firms offer the longevity and experience of William Anelay in the field of building conservation and restoration having been founded in 1747!

Edward Crookes, Althorp Estate Director concludes: “The decision to award this contract to William Anelay was absolutely the right one. As well as carrying out the work to an impressively high standard, their project management has been second to none and the whole team has been a pleasure to work with from the outset.”

The stunning new mathematically challenged aspects really do sum up the craftsmanship and knowledge that’s gone into this very special project.

Work on Althorp House was completed in April and the House opens again on 1st July when visitors can witness this new-look, iconic building in its entirety. For further details visit www.althorp.com and www.williamanelay.co.uk