Selection & Wastage Rates

As there is no European or Industry benchmark, there is little or no consistency across the market defining what makes a particular grade. Every quarry will aim to produce the highest possible proportion of best quality slates, with the lower grade slates more keenly priced.
However, it is important to note that any potential savings made from using lower grade slates may be offset by increased time and labour charges involved in additional sorting and grading.

To ensure you have greater transparency when selecting natural slate, all SIGA slates are categorised into ‘Excellence’, ‘Specification’, ‘Commercial’ and ‘Classic’.

Depending on the quarry (and even the seam of rock in that quarry), the selection process usually results in a mixture of the following grades:

The finest SIGA Slates from the most reputable quarries are selected to provide a long-lasting, beautiful roof with minimal grading & sorting. All slates are W1(≤ 0,6%) T1 W1 to comply with NHBC requirements and offer a 75 Year Warranty.

SIGA Specification slates are a popular choice with homeowners, self-builders and developers, due to their consistency, quality, smooth roof finish, and market-leading warranties.

All Specification slates are W1(≤ 0,6%), T1, W1 to comply with NHBC requirements and have a 75 Year Warranty.

Ideally suited to professional installers, these are good quality slates with a 30 year warranty, and can provide an economic solution to both new and refurbishment work.

SIGA commercial slates are rated to T1 classification, with a distinct price advantage over our specification and excellence ranges. However, additional costs required to sort, grade and install should be taken into account.

SIGA Classic slates require careful sorting and grading in order to produce a good roof finish, however meet the same strict testing and certification criteria as the higher grades. Ideal for small patching jobs or budget conscious projects, all slates are W1(≤ 0,6%) T1 W1 to comply with NHBC requirements.

Note: all natural slates must be sorted prior to installation. When deciding on the most appropriate slate we recommend that you consider all of the costs associated. These include wastage rates, grading, sorting and trimming required with the lesser quality slates along with transportation costs needed for distribution.

Wastage chart