Following a fair and thorough tender process, we are pleased to announce that DBR have been awarded the contractor for our big roof project.
They are specialist in quality historic building conservation and have worked on projects such as Wakehurst Place, Hampton Court Palace and Elizabeth Tower. Last month, alongside our architects, Donald Insall Associates, DBR were recognised for their work in the second phase of the repair and conservation project at Westminster Hall. They won the Europa Nostra Award in the Conservation and Adaptive Reuse category. The Europa Nostra Awards are Europe's highest honour in the heritage field.
We are so excited to have them on board!
RIBA Stage 4, also known as the ‘Technical Design’ stage, is the pivotal transition where the vision for the project starts to materialise in a physical sense.
At the end of RIBA Stage 4, the tendering process is a critical phase. This phase is about much more than just picking a contractor; it is about finding a competent contractor who shares the Blenheim vision and understands the project objectives and can confidently face the challenges and risk that this project will bring all whilst considering our guest, visitors and staff.
Bat Emergence & Re-entry Surveys (BERS) help to determine which species of bat are present, how many, and the type of roost (e.g. maternity, non-breeding, hibernation etc.)
Afte the preliminary surveys in November established the presence of bats, a bat emergence survey is required to observe and record bats emerging or re-entering from the roofs. BERS surveys should be conducted from May to September. Emergence surveys are undertaken 15 minutes before sunset and last for up to two hours after sunset, re-entry surveys start two hours before sunrise and last until sunrise or for 15 minutes after sunrise depending on the level of bat activity.
Nearly an acre of the roof is only serviced by just six downpipes which have very limited access, so a CCTV survey is required to survey the historic rainwater drainage serving the roofs.
The exact routes, conditions and sizes of the down pipers are unknown, so CCTV surveys are important to provide a clear picture and can also identify issues such as cracks, splits and displaced joints before they cause problems. Water ingress is one of the key contributing factors to the deterioration of the roofscapes.
Stone fall from a height is the highest priority due to the health and safety risk posed. Getting up high to remove it safely is paramount.
Mobile elevated working platform (MEWP) surveys were undertaken of the south elevation on 23rd, 24th and 26th April 2024, to survey the high-level stonework in more detail as well as to undertake emergency removal of stone at risk of falling. Significant pieces of stone and decorative detailing were loose and came away very easily; the survey focussed on the decorative detailing of the capitals and modillions, the highest risk items.
Specialist masonry cleaning trials were undertaken to demonstrate results, manage expectations, and inform the specification.
Sensitive cleaning to remove surface contaminants has the potential to prolong the lifespan of the limestone.
Cliveden Conservation and Restorative Techniques were undertaking the trials, and Odgers Conservation Consultants provided onsite consultation.
-Thermotech Super-heated steam clean (150°C)
-Thermotech Wet-Air Abrasive clean (a fine abrasive clean)
-Laser cleaning
-2 applications of Sepiolite / 5% ammonium carbonate poultice
It will be critical to complete this cleaning sensitively to avoid disrupting the current appearance and character.
Our Structural Engineers – Clive and Harry from FW Haywood, surveyed the butterfly roof to review the existing structure and have found a high proportion of the original early 18th century structure in situ.
During the surveys, the original roof structure (a lower hipped roof) was clearly visible below the later butterfly roof structure, and this provided an opportunity to not only to improve the detailing of this area but also to reinstate the original roof design.
A scaffold tower was built for a week of specialist inspection and analysis of the ceiling and wall paintings the Saloon and Great Hall. Areas of the paint sampling were tested for chemical composition, colours and layers. This is a necessary investigation to inform the correct approach to conservation. The conservation of the paintings is a unique part of the project and will require the involvement of consultants who are specialists in the conservation of wall paintings and other decorated architectural surfaces.
Opus conservation have been on site conducting these investigations. They bring an experience of wealth of experiencing having previously worked in Hampton Court Palace and The Royal Gallery in the House of Lords. Initial investigations show that the Saloon painting is a lot dirtier than the Great Hall painting, due to the of historical use of coal fires in the Saloon.
We have completed nearly 10 different survey types to date. From ecology to photogrammetry and hazardous material, Surveys are essential for gathering comprehensive information, understanding our requirements, ensuring regulatory compliance, assessing feasibility, and managing potential risks. This information forms the foundation for the subsequent design development stages. The more that is known about the building, the more accurate planning and design can be.
Surveying also allows for a better understanding of the risks – what do we know about the building, what do we need to know more about and what the impact will be of this risk. Whilst some of this data can be sought through desk-studies, on site surveying will often provide the most up to date and accurate information.
Cliveden Conservation were on site to scope out areas for some trial for cleaning of the stonework. Stone cleaning is being considered as an option to stabilise compromised stone which would save significant future replacement costs, and reduce health and safety risk
Changes to the climate (increased rainwater and temperature fluctuations) and airborne pollutions has caused a build up of sulphation crusts and salts on the surface of some stones. This surface grime is contributing to decay of the stone. Carved work is particularly vulnerable to decay because it has a large surface area in relation to its volume, often with exposed fine edges. Through research and specialist discussions a targeted and intelligent approach of stone cleaning emerged as a more cost and time efficient solution instead of adding new stone or replacing whole blocks.
Did you know that in the UK all bats and their roosts are legally protected? Meaning that a special licence is needed for any activities that may disturb them of their habitat. BSG Ecology were on site to conduct bat surveys which involved an initial internal and external inspection to identify the potential for bats roosting or feeding. At the end of this survey a report is written to explain not only if bats are there or not but also how suitable the place is for bat habitation and next steps.
This is extremely important because if there are bats or signs of bat habitation, we have to apply for a mitigation license in order to start the works. After the initial surveys BSG returned to set up bat monitors in the roofscapes that will provide evidence to the presence/absence of bats.
A Mobile Elevating Work Platform (MEWP) was brought on to site for a week to allow for some up-close inspections of the higher-level facades of both the North and South Porticos. The MEWP took the team to over 20 meters high!
During the week the architects from DIA, surveyors from GBG conducted Ground Penetrating Radar (GPR) surveys and stone condition surveys. GPR is a non-invasive geophysical method that uses radar pulses to image subsurface. GPR was used to identify embedded metalwork, fabric construction and locations/routes of embedded downpipe, allowing for the identification of potential conflicts enabling effective planning.
Researchers from our Oxford University Heritage Innovation partnership team also took the opportunity to preliminary survey the stone types to give us an understanding of which quarries/beds the various stones have come from.
Our consultants were on site to get a closer look and discuss progress. Being on site to discuss the works is a vital part of the project as it allows for our consultants to see their areas of interest and report on progress to date any highlight any concerns to work through.
Our first official project meeting with our appointed architects, Donald Insall Architects. Kickstart meetings are crucial moment when everyone involved gathers to set the project off in the right direction. Potential challenges are identified, roles and responsibilities are confirmed and we as the clients can align our expectations with what the team can deliver.
Led by Practice Director Edward Lewis, the team from Donald Insall have worked on other significant listed buildings such as the Palace of Westminster, Kensington Palace, Hampton Court Palace as well as many of the Oxford Colleges.