Re roofing Chester | The Bishops House

Project Details

The Property

Located in Abbey Square, the Deanery, now known as The Bishop’s House, dates from the mid 18th Century.

The external facades are Flemish bond brown brick under a Westmorland Slate roof.

Additions are present under lead roof areas and include an entrance vestibule to the principal elevation.

The building is Grade II listed and is depicted by Historic England as such.

Moreover, the project has been documented as part of the history of this magnificent historic house.

Importantly, the building acts as a residence for the Bishop of Chester and performs functions relevant to this position in the Church of England.

The Location

The Grid reference for the property is SJ4055166568.

The House is secluded close to Chester Cathedral in a private square called Abbey Square.

Hidden behind some traditional iron gates the property is set within its own grounds in the shadow of the Cathedral.

Access is gained via Northgate in Chester and the Abbey square is positioned behind a section of the city wall. 

Specification of work

The work involved complete replacement of the high level roof coverings.

The specification encompassed replacement of the roof areas covered with Westmorland Slate and some of the lower level lead roof areas.

Further, as part of the scheme, all of the lead valley linings lead gutters and flashings were replaced,

Moreover, to bring the leadwork up to modern standards, changes were made to the substrate as part of our work.

Furthermore, in accordance with current Building Regulations, improvements were made, so far as practicable, to the insulation levels within the various roof voids.

To one of the lead roof areas on the rear, a new fully vented substrate was formed in advance of the lead bays being replaced in code 6 rolled lead sheet.

Additionally, some work to repair the chimney stacks was carried out as part of the scheme inclusive of installing some replacement, reclaimed chimney pots. 

The existing rainwater goods were checked and overhauled to ensure that they were fit for purpose.

Access scaffolding was erected to the full perimeter of the property for the duration of the work.

Sadly, the project saw significant delays due to the Covid-19 pandemic which meant that our teams of specialist roofers and lead workers had to leave site part way through the work.

However, once we were able, we returned to complete the project for our clients as quickly as we were able.

The Materials

The materials used on this project were mainly salvaged to make good shortages of the existing slates that were re used.

However, as part of the scheme, it was necessary to source second hand Westmorland slates for certain roof areas.

Further, some roof areas, covered with Welsh slate, saw a need for us to source reclaimed Welsh slates to match. The Reclaimed Company were instrumental in helping us find and bring to site an array of second hand roofing materials.

Rolled lead sheet…

Further, the leadwork was carried out using code 4, 5 and 6 rolled lead sheet, depending upon the application.

New substrates were formed for lead lined gutters and flat lead roof areas using 18mm exterior grade plywood.

Moreover, our membrane of choice, as always, was Proctor Roofshield and the battens used were treated and 25mm x 50mm to comply with BS5534.

The fixings for the slates were 40mm and 50mm copper nails, the gauge of the nails used was 3.35mm again to ensure compliance with BS5534 and amendments.

As a matter of course, where reclaimed roofing materials are used our go to supplier is The Reclaimed Company. 

The Project

Re roofing a listed building can be a complex undertaking and careful consideration is required in terms of materials and methods employed.

The project consisted of a number of elements requiring various skilled sets.

At GNR, we are fortunate enough to have a fantastic team of slaters, joinery and leadworkers and can undertake all elements of work on a project such as this in house.

Usually, the only sub contract elements are limited to access scaffolding.

In brief below, we will outline each stage of the project and how it was done.

Access scaffolding | Site presence

As with all projects of this size, the access requirements are considerable.

A full perimeter scaffolding was erected to the building to provide large working areas on which we could store and sort the roof slates ready for reinstallation.

Further, working areas were important to carry out the fabrication of the new lead roof components which were purpose formed on site as work progressed.

Further, easy access and egress for our operatives was key and a stair tower was erected to provide this.

Strategically placed, a loading bay was formed to allow our hoist to be erected so that waste materials could be removed and new materials easily and safely lifted to the area of work.

Our site presence was small in this instance due to access constraints.

However, we were allowed to use the basement of the property for our own welfare and a garage formed a storage unit which was utilised throughout for materials and plant.

Roof slating | Random Widths diminishing courses

As mentioned above, the main roof areas were covered in `Westmorland slates laid in random widths and diminishing courses.

However, other roof areas were covered in Welsh slates laid in tally courses.

All slates were fixed onto new treated softwood battens using copper slate nails.

Double courses were formed at the eaves onto a new eaves tray. The function of the tray is to carry the underfelt and eliminate UV degradation at the eaves where otherwise the felt may be left exposed.

Leadwork | Quality lead roofing services by GNR

As part of the project, all of the existing leadwork to the roof areas was replaced.

The detailing included the following key elements:

• Lead flashings, aprons and back gutters to chimneys.
• Lead gutter linings at interface points between roof slopes.
• Code 5 Lead valley linings.
• Lead hips and ridge details to certain areas.
• Decorative lead details to a feature finial.
• Code 6 Flat lead roof areas, fully vented and interface flashings for the same.

Chimney repairs | Masonry work

As part of the project, we were required to repair some of the chimney stacks.

Further, we were also tasked with installing an opening in the basement for a new boiler flue.

The work to the chimney stacks was minor and involved re pointing using lime mortar and new cement flaunchings.

However, as it was reactive, additional access scaffolding needed to be erected and costs presented in progress to our client.

Re roofing a Bishop’s House | Conclusions

Notwithstanding delays caused by the global Covid pandemic, the project was successful and our client was pleased with the finished result.

It is often important to reflect on the success of roofing projects afterwards and consider if anything different could have been done.

In this instance, proper planning was important before the project was undertaken. From our perspective, we would not have done anything different and the end result is a roof covering that will protect the building for a further century.

If downtime on site could have been eliminated then this would have been preferable.

However, we were obliged to listen to Government advice and take leave from the project for a period of time.

Skills Required

• Roof slating in diminishing courses.
• Tally slating.
• Joinery.
• Specialist leadwork.
• Masonry work.
• Site and project management.

Materials Used

• Reclaimed Westmorland slates.
• Reclaimed Welsh slates.
• Treated battens.
• Code 4, 5 and 6 lead.
• Copper nails and stainless steel clips.
• Exterior grade plywood.