The SSQ guide to specifying exceptional slate

Why do thousands of architects, thousands of builders, and millions of buildings all around the world use slate?

Because it’s robust, attractive, and 100% natural. Those are the characteristics that have made it popular for centuries – and that, in an environmentally-conscious age where naturalness and longevity are highly-prized, are fuelling its steady growth today.

So if you’re interested in specifying it, what are the key things you need to know?

When is a slate roof suitable?

Slate is hugely versatile. There’s a common misconception that it’s only compatible with historic buildings, and that the only time it’s used in a present-day context is when conservation guidelines require it.

Replacing historic roofs is one of the key instances where slate roofs are used, of course – either because that’s what the local conservation office demands, or because the homeowners themselves are adamant they want to replicate a slate-roofed building’s original look and feel.

But increasingly, we’re seeing it used in contemporary style projects too. One growing trend is modern-looking properties designed to use traditional materials as much as possible.

Slate, with its combination of authentic looks and outstanding performance, is the obvious choice when it comes to the roof.

What accreditations should you look out for when specifying slate?

Ensure any slate conforms to BS EN12326 standard. If it hasn’t been tested, and doesn’t have CE marking, it doesn’t meet UK Building Regulations and shouldn’t be installed. 

But it takes more than the right BS EN accreditation to distinguish the best slate. In fact, 12326 doesn’t tell you much about slate quality at all – just that it’s been through the standard tests. 

How else can you tell if slate is quality?

Water absorption is one indicator. The less water a slate absorbs, the smaller the risk of delamination, minerals inside the slate swelling up, or damage from the freeze-thaw cycle. 

The British Standard requires slate’s water absorption to be below 0.6%. However, that’s recently changed. It used to demand water absorption of less than half that, 0.3%, and many in the industry would argue that 0.3% is still the mark of excellence. 

Rates of oxidation are another crucial factor to look at. If a slate contains large amounts of iron-sulphur minerals, there’s a high chance a slate will oxidise on the roof. 

Check if the slate you’re considering has been subject to thermal cycling tests – it’s not a 100% sure-fire method, but the test will usually show if there are any iron-sulphur minerals present. 

How much maintenance does a slate roof require?

That really depends on the quality of the slate used. As you’d expect, poorer quality slate deteriorates quicker, and requires more intensive maintenance. 

Individual slates can sometimes crack or break and need replacing, but with high-quality slate that’s an extremely rare occurrence. 

In general, however, a quality slate roof requires very little maintenance at all.

How do slate tiles need to be laid to ensure a high-quality finish that will last for years? 

Slate has to always be laid by a professional roofing contractor with experience in slate roofing. The quality of the craftsmanship is as important as the slate itself.  

For more complicated roofs, we recommend that technical advice is requested prior to installation.

That would include a quantity take off as well as the calculation of the headlap (the length of the overlap). This is the only way to ensure that a slate roof is watertight. 

The best way to get the best

But the most reliable way of ensuring an outstanding slate supply is to work with a company that only offers the cream of the crop. 

For 40 years, SSQ has had an exclusive supply arrangement with the Del Carmen quarry in the Cabrera mountains – one of the only high-grade Spanish quarries to send its best material to the UK as well as France. 

And it’s one of the only companies of its kind capable of supplying phyllite, the stunning architectural stone it sources from its own quarry in Argentina.

If you’re interested in learning more, please contact us here.