Identify the existing slate arrangement
Record whether the roof uses regular or diminishing courses, along with slate dimensions, thickness, texture, colour variation, edge character, headlap pattern and details at eaves, verges and ridges. Photograph representative slopes and transitions rather than relying on one loose slate as the whole specification.
The Engine Shed explains that many traditional Scottish roofs use relatively small, thick slates in varied sizes and that diminishing courses contribute to their distinctive character. The existing roof, not a generic product description, should therefore be the reference for matching and setting out.
Diagnose why slates are slipping or breaking
A missing slate may reflect isolated impact, wind lift, a failed nail, decay around the fixing hole or a support problem. Map how many slates are displaced, whether the pattern follows particular courses or exposures, and whether debris or staining suggests repeated movement.
Inspect connected leadwork, masonry, gutters, valleys and the accessible roof void because water can enter away from the internal mark. Where the condition of sarking, battens or widespread fixings is unknown, state that limitation rather than treating surface replacement as a complete diagnosis.
Retain, sort and match usable slate
Retention starts with condition. Sound removed slates may be sorted by size and quality for reuse, while fractured, heavily weathered or otherwise unsuitable pieces should not be put back merely to maximise a salvage count. Agree storage and handling before dismantling begins.
Where replacements are needed, compare size, thickness, weight, texture, tone and weathering with the retained covering. A slightly similar colour does not compensate for a visibly different thickness or laying pattern. Record the proposed source and use a sample area where the match remains uncertain.
Decide between targeted repair and reslating
Targeted repair is strongest when defects are limited, surrounding slates and supports are serviceable, and replacement can be integrated without excessive disturbance. Wider reslating may need consideration where failures are repeated, fixings or support are broadly unreliable, or safe access would disturb a large connected area.
The decision should show quantities or mapped zones, not rely on age alone. Compare the likely disturbance, salvage potential, support repairs, junction renewals and consent implications of each option. If opening-up could change the conclusion, identify it as a pre-specification step.
Protect vulnerable slate during access
Traditional slate can be damaged by direct loading and repeated movement across the covering. Define safe access and material routes before work, including how valleys, gutters, ridges and finished slopes will be protected and how different slate sizes will be kept organised.
Photograph the roof before access and record accidental damage or newly exposed weakness as the work progresses. A repair scope should allow evidence-based adjustment, but changes to quantity or detail still need to be documented and reviewed where they affect material matching or an approved proposal.
Coordinate slate with lead, mortar and drainage
Slate performance depends on more than the field of the roof. Check widths and cuts at valleys, abutments and skews; the condition and movement of lead; mortar at ridges or masonry junctions; and whether gutters and outlets receive water without backing up into the covering.
Specify interfaces in sequence so one repair does not compromise another. Lead or masonry work may require nearby slates to be lifted, sorted and reinstated. The record should show who owns each interface and how the finished laps and water path will be inspected.
Document matching, permissions and next steps
Major reslating or a change in material, pattern or visible detail may need planning-authority advice depending on the property and location. Keep status checks, existing-roof photographs, proposed samples, quantities, salvage method and junction details together so the actual proposal can be assessed.
When requesting an assessment, share safe external and internal photographs, the number and pattern of visible defects, any loose slate already recovered, known building status and previous repair information. Do not climb or lift slate to create evidence for the enquiry.
