Westmorland Slates

When setting out for Westmorland Roof Slates, you must consider coverage and sizing.

To form courses you will need to understand the length of the slate on offer, starting with the longest slates towards the eaves the material will then diminish in size towards the apex.

The width of each slate can then be considered to form sufficient coverage with sufficient side lap over each joint to make up the roof area.

Typically, one tonne of Westmorland slate will cover approx 17m2 of roof area.

So, for a 100m 2 roof slope, you will need to consider 5.88 Tonnes of material. However, it is important to factor in wastage and allowance for cuts and interfaces so use an overage allowance of circa 15% when ordering.

Roofing Nails must comply with BS5534.

Generally Copper Nails which are 50mm in length, and 3.35mm in gauge are used to secure each Westmorland roof slate. Each slate should be nailed twice so please consider carefully how many nails will be needed.

Shop 50mm copper roofing nails here. 

When using Westmorland Slates, you will need to ensure a side lap over a joint of at least 75mm or 3″.

This may vary depending upon the pitch of the roof area and generally the more side lap can be achieved, the better the slates will perform.

When it comes to headlap, again this will depend on the pitch of the roof but consider at least 75mm and be prepared to have slates holed at 100mm headlap in some instances.

Yes, new Westmorland Slates can be mixed with reclaimed versions.

However, there will be a distinct colour variation and the colours will depend on where the reclaimed Westmorland Slates have been salvaged from.

In time, the slates will start to blend, but the roof are may look unsightly for several years. Exactly how long will depend upon a number of environmental factors.

Westmorland slate is used for heritage and high specification roofing projects for aesthetic and durability reasons.

As such, it is important to consider an appropriate ridge or apex detail.

Importantly, BS5534 has in recent years considered that the use of traditional mortar bedding of ridge tiles be eradicated.

As such, having taken some advice from a leading Roofing Specialist on this subject, would be to consider the use of a lead ridge.

A lead ridge capping should be formed atop a timber core roll and tabbed at least every 300mm in accordance with BS6915. 

Further, the code of lead used should be code 5 or 6 based upon levels of exposure of a given site.

For certain high profile heritage projects, code 7,8 or even sandcast lead may also be specified.

When specifying Westmorland roofing slates, you should always look to a roofing specialist with significant experience in their use to provide advice on compliance and best practice.

Specialist Installation Required: Why Expertise Matters

The use of Westmorland roof slate, whether new or reclaimed, is a specialist undertaking. Unlike standard roofing materials, Westmorland slate demands precise handling, expert grading, and traditional laying techniques to ensure both its performance and visual appeal are fully realised. Due to its weight, variation in thickness, and specific fixing requirements, most general roofing contractors lack the necessary experience to work with this prestigious material effectively.

Improper installation can lead to compromised aesthetics, premature weathering, and costly repairs—making it essential to choose a roofing team with the right heritage knowledge and practical skillset.

Trusted Installation Partner: GNR Roofing Services

When it comes to high-specification roofing projects, including those using new or reclaimed Westmorland slate, we recommend GNR Roofing Services as the trusted installation partner.

With a proven track record in delivering technically demanding and architecturally sensitive roofing works, GNR Roofing Services offers:

• Specialist expertise in natural slate installation
• Experience with heritage and conservation projects
• Attention to detail and a commitment to craftsmanship
• Seamless coordination with material suppliers like The Reclaimed Company®

Their team understands the nuances of Westmorland slate—ensuring the finished roof not only looks exceptional but performs flawlessly for decades to come.

Are Westmorland Slates Expensive? Understanding Cost vs. Value

Yes, Westmorland slates are among the more expensive roofing materials on the market, but this premium price reflects far more than just aesthetics—it represents long-term value, heritage, and performance.

Why the High Cost?

Several key factors contribute to the price of Westmorland slate:

• Local Sourcing: Quarried exclusively in the Lake District, Westmorland slate is a truly regional material with a limited geographic source.
• Restricted Supply: Only a small number of quarries, such as Burlington’s Kirkby Quarry, are actively producing it. This controlled output naturally drives up demand and price.
• Specialist Extraction: The stone is extracted and split by skilled craftsmen using a combination of traditional and modern techniques—labour-intensive processes that preserve the slate’s unique quality.
• Transport & Handling: Being a dense, heavy material, Westmorland slate requires careful logistics and often specialist installation, which further adds to overall project costs.

The Value Proposition

While upfront costs may be higher, Westmorland slate offers exceptional value over time:

• Lifespan: Often exceeding 100 years with minimal maintenance.
• Low Maintenance: Its natural durability resists frost, algae, and weathering far better than many other roofing materials.
• Heritage & Resale Value: Adds prestige and character to any property, particularly valuable in conservation areas or luxury developments.
• Eco Credentials: When sourced reclaimed, it’s a sustainable choice with virtually no embodied carbon compared to manufactured alternatives.
• In essence, Westmorland slate is not just a roofing choice—it’s an investment in the long-term beauty, performance, and value of your property.

What Are the Alternatives to Westmorland Slates?

While Westmorland slate is widely regarded as one of the most prestigious natural roofing materials available, there are alternative options that may be considered for projects where budget, availability, or architectural constraints are a factor.

Viable Alternatives

1. Vermont Slate (USA)

• Origin: Quarried in the northeastern United States, Vermont slates are available in a range of colours including greens, purples, and greys.
• Qualities: Durable, consistent, and widely respected, Vermont slate performs well in harsh climates and offers a high-end finish.
• Suitability: An excellent alternative when Westmorland is unavailable, though colour and texture will differ subtly.

2. Burlington Slate (UK)

• Origin: Also quarried in Cumbria, often from the same geological beds as Westmorland.
• Products: Burlington offers a range of green-grey slates, including Burlington Blue and Burlington Sage Green, which may visually resemble Westmorland to some degree.
• Availability: More readily available than reclaimed Westmorland but still produced in limited volumes and to premium standards.

3. Other Natural Slates

• Welsh Slate: High-quality and historic, but typically darker in colour.
• Spanish Slate: More cost-effective, widely available, but typically lacks the depth, texture, and prestige of British or American slates.

Is There a True Equivalent to Westmorland Slates?

In short — no.

Despite the quality and beauty of the alternatives, Westmorland slate remains unmatched in terms of its:

• Distinctive green-grey colouration, subtly mottled with olive or blue tones
• Fine-grained texture, which gives a softer, more refined surface
• Cultural and architectural heritage, especially in Northern England
• Exceptional durability, often outlasting the building it protects

For listed properties, period homes, and prestige new builds that aim to match traditional materials, there is simply no true substitute that replicates both the visual impact and historical authenticity of Westmorland slate.

Westmorland slates are natural green slates from Cumbria, prized for durability, colour variation and suitability for diminishing courses on heritage and premium builds. See our current stock and related roofing supplies.

Reclaimed offers authentic patina and is ideal for conservation or matching works. New provides uniform thickness and can simplify setting-out. Blend both via our Matching Service if needed.

Sort slates by length; lay large eaves to smaller ridge pieces keeping a consistent bond. Balance visual lines course-to-course and trim as required.

Coverage depends on size mix, pitch and headlap. Allow 5–10% contingency on reclaimed lots for selection, cuts and wastage. Share area + pitch via Contact for guidance.

Use non-corroding fixings. Copper slate nails are the standard; stainless may be specified in severe exposures. Hooks can assist on thin slates or windy sites. Shop: Copper Slate Nails (BS 5534).

Select a quality roofing underlay and design ventilation to manage moisture in line with guidance. See Proctor air/open membranes.

Derive batten gauge from chosen headlap (pitch & exposure dependent). Maintain side lap and correct nail-hole distances to prevent spalling.

Detail abutments, valleys and penetrations using appropriate lead codes and fixings. Choose ridges with mechanical restraint in exposed locations. Explore Roofing Supplies.

Many Westmorland roofs are in conservation or listed contexts — consult your local authority and refer to Historic England guidance.

Plan safe pallet offload and a clean sorting area. Store on edge under cover. Replace any cracked or delaminated slates promptly after installation.