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Choosing Slates and Tiles

Choosing a roofing material is a key decision when building or renovating a home. Claire Lloyd explores the options for pitched roofs, with a look at what’s on offer for flat roofs too.

Your roof slates or tiles not only have to fulfil the role of forming a watertight layer, keeping your home dry, but also need to look good from the moment they’re installed — and for decades to come. It’s a lot to ask of one material, isn’t it? So specifying the right product is an important decision, and one likely to be governed by a number of factors. Choosing between slate, clay tile or even stone roofing could be dictated by the local planning authority who require it to be in keeping with local vernacular; they may even need to approve samples before giving the go ahead.

Both the pitch (the angle at which the roof slopes) and the roof design are key too. As Wienerberger’s Elaine Liversidge explains: “Clay tiles are capable of performing down to pitches as low as 15° (depending on the type of clay tile) whereas slates can only perform down to 25°.” Interlocking slates or tiles in manmade materials such as concrete or fibre cement can offer an alternative on low pitches too. All this needs to be considered at the design stage as a complex, or a low or steep, roof may not marry up with the material you hope to use.

Another key area to investigate when choosing a roof covering (which makes up to 40% of the façade) is whether it will look ‘right’ with the wall cladding, and the joinery. Asking for samples, and creating a small mock up of the wall and roof, will help you reach a decision here. With all these factors to consider, it’s easy to see why choosing a product is important early on.

Clay Tiles

They’re synonymous with rich red roofs, but the beauty of clay tiles lies in the array of shades, not to mention profiles and finishes (more on this later), on offer. From burnt oranges and terracotta to browns; there’s also option for a blend of different shades. “A blend, where the mix and colour variation works to break up large expanses of roof, is a particularly popular choice among self-builders,” says Dreadnought Tiles’ Alex Patrick-Smith. “The important thing with a mix is that the contrast between tiles should not be too great.”

It’s a good idea to find an experienced roofer who will mix tiles on site, preventing patches or ‘bands’ of colour on the roof. Dark blue tiles are also available. They’re particularly prevalent on roofs in the Midlands, and can also be used to emulate a slate aesthetic — at a lower cost.

“The deep blue of our Staffordshire Blue clay tile is produced through the careful control of the kiln atmosphere during the firing cycle, so the colour is actually fired into the product,” adds Alex Patrick-Smith. Here in lies the reason why its difficult to surpass the real thing with manmade alternatives such as concrete (which is typically around 20% cheaper) — the colour is baked throughout the natural material, meaning the clay will mellow and weather with age, but won’t lose its rich aesthetic over the years. Manmade alternatives are likely to lose there surface colour, or if through-coloured, not age like the real thing.

When it comes to building a period-style home or replacing old tiles like for like, the UK is also fortunate to have a number of manufacturers who still offer handmade roof tiles made in the traditional way. But be careful not to confuse these products with those that are ‘handformed’.

Alex Patrick-Smith explains the difference: “True handmade tiles are manufactured by throwing clay into a mould and cutting off the back with a wire, then the nibs and nail holes are formed by hand — so the product is produced entirely by hand. Handformed tiles are produced with an extruded blank which is then manipulated by hand at the end of the process to give the character to the product.”

No two handmade tiles are identical, with an ever-so-slight variation in shape, colour, thickness and size emulating those on century-old roofs. Choose tiles which have been ‘pre-aged’ for a weathered look.

Not all handmade clay tiles, nor machine-made clay tiles for that matter, are made in the UK either. There’s some fine imported products out there. Whatever product you choose, ensure there’s a good guarantee of, say, a minimum of 30 years.

Profile and finish

The surface finish is also important to the overall look. In the south, sandfaced tiles are generally more common; while smoothfaced feature in the Midlands and north. A sandfaced finish can lend to a rustic, aged look, but tends to weather faster; smoothfaced finishes encourage surface run-off more readily and provide a slippery surface which helps prevent mosses from growing.

Different profiles are common throughout the country, with plain tiles (above) most prevalent. S-shaped pantiles are often seen in the east and in Scotland too, while Roman tiles, which feature a double or single alternating roll and flat, are a common sight in the south west of England. It’s a good idea to either stick with plain tiles or a profile common to the vernacular.

Natural Slate

Slate roofs dominate the vernacular of many a region for the simple fact that the UK was, and still is, fortunate in having a number of quarries producing some of – if not – the world’s finest slate. Indeed, Welsh slate and those such as Burlington from the Lake District are reputed for their excellent quality and centuries of longevity.

As such, British slate commands top-end prices. But the options available to the modern-day self-builder and renovator do not just include those quarried here, but from across the globe, with some imported products closely matching the colours of native slates.

A slate’s origin should really be one of the first things you check. Good-quality alternatives to Welsh slate are available from North America and Canada. But in the main, imports are from Spain, China and Brazil. The biggest attraction is arguably the price, with Chinese and Brazilian slate among the lowest priced available.

Not all slate is of the same quality. “The reality is that slate quarries that are only miles apart can produce slates of widely differing quality and cost,” advises Ashbrook Roofing’s Bez Walker. “Spain produces much of the world’s roofing slate (the Cupa Slate company alone is said to produce one out of every four). However the very best Spanish slate is far superior to the best Chinese and Brazilian slate. While the poorest Spanish slate is beset with high metallic inclusions, is not durable and will fade over time,” he adds.

“It is normally true to say ‘you get what you are pay for’ with regards to strength, durability, performance, and aesthetics,” furthers the NFRC (National Federation of Roofing Contractors)’ Technical and Training Manager, Kevin Taylor. “As slates get cheaper, the risk of staining tends to increase, they become less regular making them harder to lay and they may not last as long. That said, it does not necessarily mean that the slates are not fit for purpose; just that homeowners need to be aware not all slates are the same; so it always pays to do your homework.”

Essential to such homework is ensuring the product meets European Standard BS EN 12326, and taking a look at the test certificates. Slates are tested for variables such strength, water absorption (low absorption is linked to longer life, and should be under 0.6% in the UK), carbonate content (high levels may cause slate to discolour quicker), how they perform in repeated freeze/thaw cycles, etc. “Better quality slates are denoted by the letters A1 (absorption), T1 (thermal cycle) and S1 (sulphur dioxide exposure),” says Kevin Taylor. Some Brazilian ‘slates’ are not actually slate at all.

“Much of the slate quarried in Brazil comes from ‘sedimentary mudstone’,” says Bez Walker of Ashbrook Roofing (01629 732988). As such, it’s not tested under this standard. Whatever the slate, Walker recommends: “Asking for detailed written quotations (specifying the name and grade of the slate) from two or three suppliers. And, checking the price includes pre-holing to the correct head-lap.”

Adding to the cost of a natural slate roof is its installation. It’s laid double lapped (meaning the slate above overlaps that below to form a watertight layer), and as a natural product with slight variations, then it’s a good idea to hire a professional to undertake the task — find one on the NFRC’s website (nfrc.co.uk).

Alternatives

Manmade alternatives range from concrete products which emulate clay plain tiles to fibre-cement roof slates to emulate natural slate. They do not age like their natural counterparts (and are unlikely to last centuries, like Welsh slate for example), but the attraction usually lies in their lower cost. Many products available today offer a marked improvement to those of old — responsible for the many dull grey roofs which scorn the landscape.

What’s more, the uniform size, shape and thickness of manmade alternatives make them easier and thus cheaper to lay; many can be specified as interlocking to help with the task. “Leading manufacturers are now able to offer an alternative interlocking tile solution which is fixed with only a single nail and clip, and are able to be laid to pitches as low as 22.5° and only require 16.3 tiles per m² (compared with 60 tiles per m² with traditional clay roof tiles) — a significant reduction,” adds John Lambert, General Manager of Forticrete (01525 244900).

Manmade slates and tiles can also provide a solution where a light-weight covering is required. There are some interesting products to look out for in this market. Marley Eternit’s Ludlow EcoLogic, for example, features a photocatalytic upper coating which can absorb air pollutants like nitrogen oxide.

Stone Roof Tiles

If you’re repairing a period home (particularly if it’s listed or within a protected area) or building a new traditional home where roofs in the vernacular are predominately stone, then you may be required by the local planning authority and/or conservation officer to follow suit.

To some extent, the very fact that you need to source stone slates from the local quarry (there’s a comprehensive list of these on the Stone Roofing Association’s website: stoneroof.org.uk) can make the specification an easier process. The task becomes more complex however when trying to match like for like on an old roof and the original quarry has ceased business; meaning you’ll have to source a stone from another local quarry.

Stone for roofing is typically a local form of limestone in the Cotswolds, the Purbeck district of Dorset and areas of Somerset, for example, or a type of sandstone in parts of Caithness, Cumbria and Hereford.

It’s not just the rock type which varies from region to region, by the size, thickness, how the edges are finished/dressed too. It’s an expensive option, which will require experienced skills to lay, but its none-the-less a very attractive look. Your local conservation officer should be a good source of knowledge on the vernacular stone, but English Heritage and the Stone Roof Association also provide some great information on the subject.

And for flat roofs…

Contemporary architecture, together with material innovations, has contributed to the resurgence in flat roofs. “Just several years ago it would have been a common expectation for self-builders and architects to suggest that unless the design absolutely required it, the best solution for a flat roof was not to have one,” says Allan Frizzell, Technical Manager of GRP specialist Topseal (01423 886495), whose systems are backed with a 25-year guarantee. “This is not surprising as traditional roofing systems have always relied on using sheets or rolls of material which are then glued together along joints and patched over one another to protect pipework or other extrusions. The joints are the most common cause of failure on a flat roof, making it difficult to satisfy modern demands for large skylights with confidence.”

In addition to GRP, options for flat roofs include metals such as aluminium (try Euroclad: 0292 079 0722) and copper (see come-home-to-copper.co.uk for advice on the latter), single ply, built-up felt and liquid membranes.

“Cold liquid-applied systems are a modern and reliable solution to waterproofing,” says Nick Roberts, Operations Director of Polyroof (0800 587 7775). “Manufacturers of quality liquid roofing systems will have the confidence to back their products with an insurance-backed guarantee, so always ask for evidence of this. They also tend to offer free specification service to ensure that the roof design is correct before its installation. At Polyroof, all our installations are carried out by a national network of independent and fully approved contractors.” Further contacts: Sika Roof Assured: 01603 709360; Glasplies: glasplies.co.uk

In the Gallery

1. The Heathland Manor House Mix from Redland is actually a concrete plain tile, which can be specified with a sandfaced finish for a rustic look. POA (0870 560 1000) 
2. Cembrit’s Westerland fibre-cement slates, POA (cembrit.co.uk)
3. Dreadnought’s Staffordshire Blue Smoothfaced clay tile costs £400/1,000 excl VAT. This product is machine made, but they also offer handformed tiles too (01384 77405)
4. Lovell Purbeck’s hand-fetted stone roof tiles are made bespoke to order. Tiles are sold in the traditional unit — a finished roofing square (10ft x 10ft) which includes all the required overlap, POA (01929 439255)
5. Sahtas’ County Sandfaced tiles are handmade in Turkey, and come with a 30-year insurance-backed guarantee (01908 311411)
6. SSQ’s Brazilian Ultra Riverstone Grey comes with a A1-T1-S1 rating and is covered by a 75-year guarantee (0208 961 7725)
7. Stoneleaf Building Products’ Del Sil is a blue/black Spanish slate with riven edges; it’s A1, T1 and S1 rated (01277 841555)
8. The Tudor Roof Tile Co.’s handmade Tudor Antique clay tiles, shown here in a blend of 10% Dark, 65% Medium and 25% Red (01797 320202)
9. These handcrafted Alban clay plain tiles in the Sussex Blend colour from Sandtoft (0844 9395 900) are made from alluvial clay from the plain of the river Humber.
10. Vermont Structural Unfading Green is a prime quality slate from North America. From £50/m2 at David Wallace International Slate UK (01539 559289)
11. Welsh Penrhyn slate from Ashbrook Roofing Supplies. From £2.10 excl VAT per slate (01629 732988 ashbrookroofing.co.uk)

 

All prices correct at time of going to press in March 2013