There are several forms of underlay commonly used in roof construction, the most popular being traditional bituminous felts, vapour permeable underlays and impermeable plastic products. 

Vapour permeable underlays, more commonly referred to as ‘breathable’, give many advantages over the more traditional bituminous based underlays and are rapidly becoming the first choice of designers, builders and roofers. Breathable underlays let the building breathe by allowing the passage of water vapour and so cut down, or in some cases eliminate altogether, the need for roof space ventilation. This in turns makes the insulation more efficient because there is less cold air circulating around the roof space. 

Impermeable plastic underlays can be used with adequate roof space ventilation and are particularly good in situations where the roof tiles are being laid on a roof which is below the recommended minimum roof pitch by creating a waterproof sub roof below the tiles.

All tiles have a minimum roof pitch which is always stated in the manufacturers technical information. This minimum pitch is important, if tiles are laid below the recommended minimum pitch there is an increased chance of water getting through which can damage the underlay and battens over a prolonged period.

The general trend is for steeper pitch roofs, which is due partly to the demand for living space in the roof. However there is a frequent need to find suitable roof tiles that perform well at low pitches. Particularly for first floor extensions. As a general rule tiles and slates will perform down to the pitches outlined below: -

• Plain tiles - 35 degrees
• Interlocking clay plain tiles - 15 degrees
• Clay pantiles - 30 degrees
• Natural slate - 25 degrees
• Interlocking concrete and clay tiles - 22.5 degrees
  
  

Firstly its worth checking your options. If you have large format concrete tiles on your roof then you can find various profiled concrete tiles that go down to 15 degrees. Its always best to use a profiled tile rather than a flat tile, as the undulations in the tile help carry the water down the roof and keep it away from the interlocks, which can leak at low pitch. 

If you have plain tiles or slates on the main roof then it will not be advisable to use these on the extension as these traditional do not perform well at low pitch. One option would be to use an interlocking clay plain tile such as the Sandtoft 20/20, which can perform down to 15 degrees and can compliment both plain tiles or slates. Try to avoid low pitch large large format concrete tiles if you have traditional materials on the main roof  as these larger tiles can appear out of character, particularly on an extension where the roof area is smaller and closer to eye level.

It is possible to lay the tiles below their minimum roof pitch, however, your roof will be susceptible to water ingress between the tiles. In these circumstances the structure below the tiles or slates (sub roof) needs to be made fully watertight before the tiles are laid.  

The small pits which are occasionally visible on the surface of clay products are created when pockets of lime immediately below the surface expand, causing the surface above the lime to be pushed up or ‘blown’. This expansion takes place as soon as the tiles leave the kiln as the tiles absorb moisture from the atmosphere.

Lime occurs naturally in most clay and can usually be neutralised, ie prevented from expanding, by submerging the tiles in water. Manufacturers make every effort to prevent lime blows, although occasionally the process can still occur before the tiles have been fully soaked.  The expansion action of the lime only occurs immediately after the tiles leave the kiln. The process stops once the tiles have absorbed moisture and can not re-occur. Therefore there is no risk of further ‘pitting’ to the tile surface after the tiles have been laid on the roof.

It is a common misconception that clay products can be attacked by frost action due irregularities within the surface finish. But there is no possibility that the small pits, or ‘lime blows’, will affect the future durability of the tiles. 

The European Standard for clay roofing tiles, BS EN 1304, does not regard small pits or chips of 7 mm or less in size in the surface of the tiles as faults.

The beauty of clay tiles lies in the way in which they retain the natural colour of the clay material, whilst maturing to a deeper, richer shade.

Colours can be created by applying an ‘Engobe’ to the surface of the tile prior to firing in the kiln. This is a ceramic material, as is the tile itself. Therefore when the tile is fired the engobe and the tile ‘fuse’ together and become one. This means that the surface colours of the tiles are permanent will not fade under any circumstances and any slow change that does take place will be due to mosses, lichens or pollutants attaching to the tile surface.

There are several reasons for coating concrete roofing tiles: 

• Minimises water loss during the critical early cement hydration stage to allow improved concrete strengths.
• Protects the surface from rain water erosion and corrosion (acid rain) during the critical early life period.
• Minimises dust and dirt and inhibits lichen/moss contamination during the early life.
• Minimises the risk of surface salts and efflorescence formation during the critical early life of the product.
• Minimises the variation in colour between product batches and ages, particularly main tiles and fittings, ie "Chequer board effect".
• Reduces the perceived effect of the scuffing which occurs during handling and transportation.
• Enhances the intensity of the tile colours.
• Increases rain and snow dissipation rate from the roof.
• Reduces surface water capillarity, ie improved performance.
• Prolongs the effective life of the cement/pigment rich tile surface.
• Enhances the perceived visual effect of the tile profile by favourably modifying the tile surface reflectivity.

Surface treatment protects the tile during the early, critical stages of the products life, and it is recognised in the roofing industry that the surface coating of a concrete roof tile is temporary, usually lasting for approximately 3 years. 

If some tiles are cracked then these should be replaced straight away. The most probable cause is foot traffic; ie the roofer has walked on the tiles. If the underlay has been installed correctly then the roof shouldn’t leak in the short term, but water leaking onto the tile battens and underlay will cause these to rot in the longer term so it is wise to replace any cracked tiles sooner rather than later.

The short answer is that you should not be walking on your roof tiles! Apart from the damage you can cause to the roof, think of the health and safety risks involved.

Roof tiles and slates are not designed to be walked on, so if they are cracking or breaking when walked on this is not likely to be due to faulty tiles or slates. Generally, tiles and slates must be strong enough to withstand all the handling and transportation between the factory and your roof, as well as being resistant to the weather once they are laid on the roof. But if you do need access over the roof, for whatever the reason, you should make adequate provision to both stay safe and to protect the roof covering. This can be in the form of roof ladders or crawling boards, safely anchored to prevent slipping and with some form of packing over the tiles.

Dentil slips are inserted into the mortar along mortar bedded ridges and hips to help prevent the mortar slumping and cracking. Dentil slips are only required for profiled tiles (which have a curved cross section) where the profile depth of the tile is 25 mm or more.

Very often the dentil slips in a bedded ridge are left partially exposed as a traditional aesthetic feature. It is less common to expose the dentil slips in the mortar bed at hips because of the irregular nature of the cut tiles.

Eaves (or bird comb) fillers are used at the eaves, where the roof slope meets the gutter. They are used when the gap underneath the laid tiles is greater than 16 mm. Eaves fillers close off this gap to prevent birds and rodents entering the batten cavity, the area between the tiles and the underlay.

Some tiles have bespoke plastic eaves filler units, however, universal eaves filler are now available which contour themselves to the shape of a particular tile.

Eaves fillers should not be confused with roof space ventilators. Roof space ventilators allow air to ventilate into the roof space beneath the underlay, whereas eaves fillers are there to prevent access into the batten cavity, ie between the underlay and the tiles/slates.

This effect is called efflorescence and occurs mainly in concrete tiles. Efflorescence is a naturally occurring phenomenon caused by water in the form of rain, condensation or dew penetrating into the pores of the concrete and dissolving lime. The solution diffuses to the surface of the product; the water then evaporates and leaves behind a white film of lime. The lime naturally occurs in the cement which is used in the manufacture of all concrete products.

Since the lime content of the concrete can vary and the weather conditions obviously differ, the level of efflorescence can also fluctuate considerably. The same chemical process which brings the lime to the surface of a tile carries on, enabling it to be degraded and washed away by the rain, so that eventually the efflorescence disappears by itself – usually in a matter of months. Once the lime has disappeared from the surface of the tiles it rarely reoccurs.

If you want to be sure to avoid the possibility of any such problems, use a manufacturer that applies surface treatments on their concrete tiles during manufacture, this generally eliminates any efflorescence.

Roof tiles and slates are very versatile products and can be used on a variety of roof pitches. Tiles or slates can be used at pitches up to 90 degrees (vertical) provided a clip is available to securely clip the tail of the tile (available for most tiles). This is common practice in the south east for instance, where plain tiles are used as a cladding material on the first floor.  In slate areas, such as the south west, natural slates provide an attractive cladding material that was sometimes used to clad entire buildings.  For steeper pitches please note it is a requirement to nail and clip all tiles above 55 degrees.

Ventilation, or to give it a fuller description; roof space ventilation, is required in some form in most circumstances. Ventilation is required to create air movement between the insulation and the underlay. This is a cold space into which air passes from inside the building. As the air passes through the insulation it cools and so loses its ability to hold as much water vapour. So if this cold, moisture-laden air is not driven outside it will form condensation in the roof space.

Ventilation grills are fitted in or near the eaves. These allow air to enter and leave the roof space through the action of the wind. If ventilation grills are also fitted at or near the ridge, fresh air is drawn in through the eaves vents and so this is much more efficient than relying on eaves vents alone.

Eaves ventilation can be in the form of over fascia¹ vents or soffit² vents. In some circumstances it could be in the form of tiles vents, spaced at regular intervals just above the eaves course.

Ridge ventilation can be in the form of a dry ridge system³ or ridge or tile vents spaced at regular intervals on or close to the ridge

1 - The fascia is the vertical board behind the gutter. The over fascia ventilator sits on top of the fascia directly underneath the eaves tiles.

3 - A dry ridge system mechanically secures the ridges without the need for mortar and can ventilation into the roof space.

A dry fix roof offers many advantages over the traditionally mortar bedded roof. Mortar requires regular maintenance, whereas dry fix systems are maintenance-free. Dry fix systems also provide other advantages, such as mechanical fixing to ensure security against wind damage; also ventilation at ridge and hip. 

On some old traditional roof coverings or heritage buildings, mortar still has its place. But where possible it should be used in conjunction with other fixings such as nails, screws or clips for security. Although a strong mortar mix can resist wind uplift, if there is any movement within the roof structure then the mortar will crack and leave the fittings vulnerable to wind, whereas dry fix systems are able to cope with some structural movement.

Dry fix (or dry roofing) systems offer a number of advantages over the traditional method of using mortar bedding. These include;

• Allows all weather installation, whereas mortar cannot be installed in wet weather
• Essentially maintenance free
• Overcomes problems associated with mortar such as cracking and loss of ridges in high winds.
• Provides full mechanical fixing of all components to resist highest wind speeds ever likely to occur.
• Provides continuous ventilation along the ridge – this is particularly useful in many modern buildings where the use of insulation between or above the rafter precludes the use of traditional ridge vents.
• Provides a consistent attractive finish.

Building Regulations acknowledge that when stripping and re-tiling an existing roof the replacement tiles or slates may impose a substantially heavier load than the original roof covering. Also, there may be occasions when the new material imposes a substantially lighter load than the original roof covering.

If the replacement roof covering was significantly heavier then there is the risk that the roof structure may collapse if it is not designed to carry the extra weight. If an heavier roof covering is to be used, then a qualified structural engineer must carry out a survey and advise on any roof structure strengthening which may be required.

If the replacement roof covering was significantly lighter then there is the risk that the roof structure may be lifted or otherwise damaged in high winds. Many older roofs are not physically fixed to the building and instead rely on the weight of the tiles or slates to prevent uplift. If a lighter roof covering is to be used, then a qualified structural engineer must carry out a survey and advise on any roof structure strapping and bracing which may be required.

Very often each roof in a row of terraced or semi-detached houses will need to be replaced individually; therefore the joint between the old and new tiling or slating between two houses must be weathered. 

Sometimes this is done by simply mortaring a row of tiles or ridge tiles over the joint. Unfortunately, this can often lead to leaks and is not to be recommended. 

A far better solution is to incorporate a ‘bonding’ or ‘jointing’ gutter. This can be formed from lead, or alternatively, there are a number of proprietary systems available. A bonding gutter not only provides an effective means to weather the junction, but it also gives a neat appearance, with old and new materials finishing closely together and the gutter being almost completely hidden.

If some tiles are cracked then these should be replaced straight away. If the underlay has been installed correctly then the roof shouldn’t leak in the short term, but water leaking onto the tile battens and underlay will cause these to rot in the longer term so it is wise to replace any cracked tiles sooner rather than later.

The most probable cause is foot traffic. This means that either the roofer, or another tradesmen, has walked on the tiles. Roof tiles and slates are not designed to be walked on, so if they are cracking or breaking when walked on this is not likely to be due to faulty tiles or slates. Generally, tiles and slates must be strong enough to withstand all the handling and transportation between the factory and your roof, as well as being resistant to the weather once they are laid on the roof.  But if any access is required over the roof, for whatever the reason, always ensure the relevant tradesmen makes adequate provision to both stay safe and to protect the roof covering. This can be in the form of roof ladders or crawling boards, safely anchored to prevent slipping and with some form of packing over the tiles.

Over fascia ventilator strips can be adapted to a variety of different situations. As its name implies, the ventilator is designed to fix on top of the fascia board, tilting the tiles to their correct plane. However, where there is no fascia the ventilator can be fixed, for example, directly onto corbelled masonry. Over fascia ventilators can also be used in internal box gutter situations, junctions between sloping and flat roofs and even at monopitch ridge junctions. 

When the roof pitch is 35 degrees and above, or when the building is 10 metres wide or more, then the British Standard BS 5250 recommends the use of ridge ventilation combined with eaves ventilation. This actually provides a much more efficient system because air passing over the ridge will draw fresh air into the eaves. When there is only eaves ventilation there needs to be enough wind to force air in through one side of the building and out through the other.

You don’t normally need planning permission to reroof a property so long as  the building is not listed and is not in a Conservation area.

If there are any alterations planned to the roof such as the addition of roof lights or skylights, then the alteration must project no higher than 150mm from the existing roof plane and must not project above the highest part of the roof.

There may be restrictions on the roofing material and colour you will be allowed to use. Chances are you may be required to replace ‘like for like’. Contact your local Planning office for advice.

You don’t normally need planning permission to fit solar panels to the roof as long as the building is not listed and is not in a Conservation area.

Solar panels must project no higher than 200mm from the roof plane and must not project above the ridge line.

If your property is in a conservation area then planning consent is required if the panels would be visible from the highway. 

If the panels were to be visible from the highway then planning consent would be required.

If your property is a listed building then you will need to apply for listed building consent, even where planning permission is not needed.

The roof structure should be checked by a competent person to make sure that it is strong enough to carry the solar panels. Strengthening work should be done if necessary.

Building regulations also apply to other aspects of the work, such as electrical installation.

If you visit your local Planning department’s web site you can enter your postcode for an immediate answer. Alternatively, contact the Planning office. If you need an answer in writing then you will need to write to them.

Your local Planning department’s web site contains lots of information on Planning. Also you can visit the Government’s Planning Portal at www.planningportal.gov.uk.

Bats are a protected species therefore you must plan the work to avoid any undue disturbance. A survey may be needed before work commences and you may require a licence. Contact Natural England at www.naturalengland.org.uk for more advice.

If you are reroofing the whole property, or more than 25% of the roof area, then you will need to apply for approval. This is so that the building inspector can check your loft insulation thickness. As a condition of granting approval, you will be required to increase your loft insulation to meet current legislation; ie a minimum 270mm thickness.

Yes. Because of high number of relatively old houses in England and the slow rate of replacement new rules were introduced in 2008 to improve the thermal insulation of properties having building work done. This is part of the government’s drive to lower carbon emissions.

So, as a condition of granting approval, you will be required to increase your loft insulation to meet current legislation; ie a minimum 270mm thickness.

If the new roof is lighter than the existing then the roof structure may require extra ties and fixings to the building walls to prevent the risk of the roof structure lifting in high winds.

Building regulations require that the weight of a replacement roof covering is similar in weight to the old tiles or slates. If it is significantly different then a survey of the roof structure must be carried out by a competent person.

If the new roof is heavier than the existing then the roof structure should be surveyed by a competent person to determine if strengthening is required to support the extra weight.

Your local building control department’s web site contains lots of information on building regulations. You can also visit the Government’s Planning Portal at www.planningportal.gov.uk.

It is a good idea to inspect the inside of your roof at least once annually to check that it’s still weatherproof and there is no woodworm infestation.  Repeat your check in different weather conditions. A check after heavy rain will reveal any water ingress as a result of any defects in the structure. A check in winter weather will reveal any condensation within the roof space.

When inspecting you roof from outside at ground level use binculars to look for slipped or dislodged tiles. If tiles or slates have slipped there may be a difference in colour to those around them. At the ridge line check for missing ridge tiles and gaps in mortar and at flashings around chimneys. One of the most obvious signs is pieces of mortar laying on the ground or on the other tiles on the roof.

Why does moss grow on tiled roofs?

The main reason moss is able to grow on roofs is that the surface of roof tiles filter out dirt from rainwater over time. This can be aggravated by dead leaves blowing onto the roof, becoming lodged and then decaying. Spores and seeds of mosses, weeds and lichens can then be blown on top of these elements and sooner or later they begin to grow.

 

Which roofs are most affected by moss?

Naturally, the roofs most susceptible to moss and lichen growth are those near to trees and vegetation – and parts of the roof that are shady or damp will be particularly affected. Steeper pitched roofs are less likely to spark moss and lichen growth, as they shed water more quickly and gather less dirt from the rainwater. North facing slopes that remain damper for longer may experience moss and lichen growth more than others.

 

What are the effects of moss growth?

There is every chance moss growth has little or no impact on the function of your roof, although it can slow the flow of water to gutters, which means water is held against tiles for a much longer period of time. If the moss or lichens affect the drainage of water down valleys and guttering, they should be removed. However, a lot of the time harmless moss growth can provide an elegant touch of character and is even sought after by some homeowners.

 

Removing moss

Method one: Toxic wash

Although a relatively cheap method of removing moss, as the name suggests, undertaking a toxic wash requires great care to be taken. It’s a job best suited to professionals with a proprietary toxic chemical in order to avoid the potential risks. Any wash that is toxic to moss will also be toxic to garden plants in the vicinity of the roof and potentially those in your neighbours’ gardens. It can also be potentially hazardous to birds and wildlife – so make sure you’re aware of the risks before getting started.

 

It takes a few days for a toxic wash to take effect, and it’s best to apply the wash in dry weather if possible (rain can wash the chemicals off before they have had time to act). You can speed up the process by removing thick patches of moss before the wash is undertaken.

 

One treatment is usually sufficient, but in rare cases it may need to be repeated the wash process. The dead growths will weather off and disappear quite quickly. Some contractors will recommend using a pressure washer to washing moss off. Even if you ensure the spray is only aimed down the roof, to reduce water penetration into the roof space, this is not advisable due to the damage that could be caused.

Some washes leave a residue that stops subsequent growth, but even in the best circumstances this will only last two or three years.

 

There are Environmental and Health & Safety regulations relating to the removal of moss using toxic washes, so be careful to check the Building Research Establishment (BRE) Digest 139, “Control of lichens, moss and similar growths” or make sure the professionals you hire already have.

 

Method two: Copper Wire

A more permanent way to avoid moss and lichen growth on your roof is to trail copper wires across the roof surface. These can be fixed at intervals across the entire roof, or just affected areas, below the front edge of the tiles. They work because with every rainfall, the copper slowly oxidises in the atmosphere and provides the roof with a thin layer of copper salt which prevents renewed moss growth. The Copper Development Association can provide full details on how it works – contact them on mail@copperdev.co.uk or visit www.cda.org

 

Method three: Scraping

This is exactly what it sounds like – scraping moss from the roof. This method is never recommended as it usually results in damaged roof tiles and can leave permanent, ugly scrape marks on the roof. It also offers no form of long term prevention whatsoever.

 

Things to remember

-       Generally, moss and lichen growth is not unsightly and in many cases adds character to a roof.

-        If moss is affecting the discharge of water from the roof, it needs to be addressed.

-        Removal is best undertaken by toxic chemical wash. Garden centres do sell washes, however it advisable to take professional advice.

-        Copper wire can prevent moss and lichen growth, but does not work in all cases.

There are key reasons for a roof to leak: - 

If the mortar is dropping out at the verge this is a sign that the roof is ready is for some maintenance. It would worth checking the whole roof for signs of failure.

The best way of treating the verge in this situation is to fix a dry verge system over the existing mortar bedded verge. This is usally straightforward once safe access has been set up; ie some form of scaffold.

Some of the dry verge systems on the market can be fitted retrospectively; ie without removing the existing verge tiles. In most cases it is simply a matter of fixing a timber a batten to the gable wall, underneath the existing verge tiles and mortar bedding. The new dry verge units can then be nailed or screwed to this timber batten. See manufacturer’s installation guides for further information.

Inspect the underside of the roof slope in good daylight. Look for tears in the felt or if the roof is not felted check whether the roof battens or slates or tiles are visibly damaged or missing. If the damp is close to an abutment wall the flashing may have failed and will need replacing.

There are two possible causes for this. One could be leaking pipework or water tank in your loft space. If you can eliminate this as the cause then it is very likely that this moisture has come from long term condensation in the loft space.   

The remedy is to provide your loft with better ventilation.

Take advice from a professional roofing contractor about how to provide this. 

If some tiles are cracked then these should be replaced straight away. The most probable cause is foot traffic; ie the roofer has walked on the tiles. If the underlay has been installed correctly then the roof shouldn’t leak in the short term, but water leaking onto the tile battens and underlay will cause these to rot in the longer term so it is wise to replace any cracked tiles sooner rather than later.

The short answer is that you should not be walking on your roof tiles! Apart from the damage you can cause to the roof, think of the health and safety risks involved.

Roof tiles and slates are not designed to be walked on, so if they are cracking or breaking when walked on this is not likely to be due to faulty tiles or slates. Generally, tiles and slates must be strong enough to withstand all the handling and transportation between the factory and your roof, as well as being resistant to the weather once they are laid on the roof. But if you do need access over the roof, for whatever the reason, you should make adequate provision to both stay safe and to protect the roof covering. This can be in the form of roof ladders or crawling boards, safely anchored to prevent slipping and with some form of packing over the tiles.

Tile noise is known as chatter, and occurs when the wind lifts the tail of the tile and causes a chattering noise when the tile drops back down. This can generally happen in small ‘local’ areas on the roof. The problem is often highlighted in roof designs where there is living accommodation in the roof space. The sound created by the movement of the tiles/slates can be amplified by forms of roof construction where the ceiling is fixed directly to the rafters.

To eliminate this, the tiles need to be clipped. On steep roof pitches or in exposed locations slate hooks can be used to secure the tails of the slates.

Experience has proved that the correct mix of mortar (ie 1:3 cement:aggregate) is more than adequate to resist the highest winds ever likely to occur in the UK. However, where there is movement within a roof structure, particularly where the roof passes over masonry walls, the mortar bed can crack, leaving the ridge tile vulnerable to wind uplift. In new buildings in particular, where timbers etc are drying out and shrinking, differential movement can be a problem. For this reason, the current British Standard for slating and tiling, BS 5534, recommends that where differential movement can take place, such as at gables and abutments, ridges should be mechanically fixed as well as bedded.

Experience has proved that the correct mix of mortar (ie 1:3 cement: aggregate) is more than adequate to resist the highest winds ever likely to occur in the UK. However, where there is movement within a roof structure, particularly where the roof passes over masonry walls, the mortar bed can crack, leaving the ridge tile vulnerable to wind uplift. In new buildings in particular, where timbers etc are drying out and shrinking, differential movement can be a problem. For this reason, the current British Standard for slating and tiling, BS 5534, recommends that where differential movement can take place, such as at gables and abutments, ridges should be mechanically fixed as well as bedded.

Efflorescence is a naturally occurring phenomenon caused by water in the form of rain, condensation or dew penetrating into the pores of the concrete and dissolving lime. The solution diffuses to the surface of the product; the water then evaporates and leaves behind a white film of lime. The lime naturally occurs in the cement which is used in the manufacture of all concrete products.

Since the lime content of the concrete can vary and the weather conditions obviously differ, the level of efflorescence can also fluctuate considerably.

The same chemical process which brings the lime to the surface of a tile carries on, enabling it to be degraded and washed away by the rain, so that eventually the efflorescence disappears by itself – usually in a matter of months. Once the lime has disappeared from the surface of the tiles it rarely reoccurs.

If efflorescence does appear, it has no detrimental effect on the long term performance of the tile.

There are several reasons for coating concrete roofing tiles, as follows;

•  Protects the surface from rain water erosion and corrosion (acid rain) during the critical early life period.
• Minimises dust and dirt and inhibits lichen/moss contamination during the early life.
• Minimises the risk of surface salts and efflorescence formation during the critical early life of the product.
• Minimises the variation in colour between product batches and ages, particularly main tiles and fittings, ie "Chequer board effect".
• Reduces the perceived effect of the scuffing which occurs during handling and transportation.
• Enhances the intensity of the tile colours.
• Increases rain and snow dissipation rate from the roof.
• Reduces surface water capillarity, ie improved performance.
• Prolongs the effective life of the cement/pigment rich tile surface.
• Enhances the perceived visual effect of the tile profile by favourably modifying the tile surface reflectivity.

Surface treatment protects the tile during the early, critical stages of the products life, and it is recognised in the roofing industry that the surface coating of a concrete roof tile is temporary, usually lasting for approximately 3 years. 

The beauty of Natural Red clay tiles lies in the way in which they retain the natural colour of the clay material, whilst maturing to a darker, richer shade.

Colours are created by applying an ‘Engobe’ to the surface of the tile prior to firing in the kiln. This is a ceramic material, as is the tile itself. Therefore when the tile is fired the engobe and the tile ‘fuse’ together and become one. This means that the surface colours of the tiles are permanent will not fade under any circumstances and any slow change that does take place will be a steady darkening of the red colour.

The small pits which are occasionally visible on the surface of clay products are created when pockets of lime immediately below the surface expand, causing the surface above the lime to be pushed up or ‘blown’. This expansion takes place as soon as the tiles leave the kiln as the tiles absorb moisture from the atmosphere.

Lime occurs naturally in most clay and can usually be neutralised, ie prevented from expanding, by submerging the tiles in water. 

The expansion action of the lime only occurs immediately after the tiles leave the kiln. The process stops once the tiles have absorbed moisture and can not re-occur. Therefore there is no risk of further ‘pitting’ to the tile surface after the tiles have been laid on the roof.

It is a common misconception that clay products can be attacked by frost action due irregularities within the surface finish. But there is no possibility that the small pits, or ‘lime blows’, will affect the future durability of the tiles. 

Yes definitely. It’s hard for roofing contractors to keep up to date with all the developments in roof tiles and consumer trends. Because of this, the contractor will possibly recommend a material, tile or brand that he uses regularly.

If you know what you want on your roof or would like something different don’t be afraid to ask.  A good roofer will be happy to get hold of the tiles you want for your roof.  There are only two reasons why you would be prevented from using a tile of your choice.  Firstly where the minimum pitch of the tile or slate is not suited to the pitch of your roof or secondly where the local planning department guidance dictates the use of a certain tile. 

There are many things to consider when choosing a new roof.
 

1. Roof Pitch

Each roof tile is different and each will perform at different roof pitches. It is important that you select the right tile for your roof.


2. Material

Roof tiles are manufactured in clay, concrete and slate.

Clay – clay brings warmth and character to a building and is available in a wide variety of permanent colours and textures which over time will never fade. Clay roof tiles will perform in excess of 60 years.

Concrete – concrete is the most common roofing material used in Britain. Concrete provides an economic alternative to natural materials.

Slate – there are many options available, natural slate, recycled slate or slate appearance products which are manufactured from clay.


3. Colour/texture

Think about colour and texture. Consider what kind of effect you want from your roof; do you want it to look new or weathered so that it blends in with the older surrounding buildings?

Do you want a solid, even colour or a varied effect?

Does the surface need to be smooth or coarse (sandfaced)?


4. Profile

Roof tiles vary in shape and are available in numerous profiles:

Plain Tiles – a small tile (265 x 165mm) which is cambered and has no other feature except for nibs and nail holes.

Pantiles – A tile which is moulded into an S shape which gives the appearance of ‘waves’ and ‘troughs’ on the roof. A Pantile can be either Single (one ‘wave’) or Double (two waves).

Roman Tiles – a tile which is flat in the middle with a slightly tapered roll at one end. Roman Tiles are available as Single (one roll) or Double (two tapered rolls).

There are also many other profiles available, please talk to your local stockist for more information. A full list of Roofing Advice Centres is available on our Homepage (please insert link to the ‘roofing advice centres’).


5. Sustainability

Intelligent product design can also add to the ‘true value’ of roof tiles by reducing the environmental cost of a building.

Each roof tile will have a BRE (British Research Establishment) rating. Ratings account for the performance of the product in relation to its environmental impacts. An A+ rating will have the lowest overall environmental impact.


6. Weight

Some roof tiles weigh more than others so if you are replacing concrete then a switch to plain tiles may not be an option. Most trussed rafters are normally designed to take a roof tile loading of up to 60kg/m².


7. Roof Complexity

How complex is your roof? Roofs that require many cuts and careful setting out need a tile that can cope easily.

Is your roof curved? There are some tiles which will cope easily, for example plain tiles, however, interlocking tiles will not be suitable.


8. Rafter Lengths

Long rafter lengths in certain areas, especially at low pitches with flat tiles can cause problems with water drainage. A profiled tile may be a better option.


9. Local vernacular

Look at your neighbouring buildings to see which roof tiles are popular in your area, roof profiles vary dramatically across the UK.

You may need to consult your planning officer if you have a listed building or are in a conservation area. Your local planning department’s website will have lots of information on Planning; also you can visit the Governments Planning Portal at www.planningportal.gov.uk