Recommendations from experienced roofers on how to properly lay slate on a pitched roof

For a roofer to achieve longevity and visual appeal, knowing how to lay slate on a pitched roof correctly is essential. Slate roofing is a popular option for both residential and commercial buildings because of its reputation for elegance and durability. But in order to guarantee that the slate tiles are installed accurately and maximize their performance over time, the procedure calls for accuracy and expertise.

Skilled roofers stress how crucial it is to begin with a strong foundation. Make sure the roof deck is adequately prepared and structurally sound before installing any slate tiles. This entails examining the surface for any damage that may already be there, strengthening where required, and making sure it is clear of debris and clean. A strong base keeps the slate from shifting or cracking in the future in addition to supporting the slate’s weight.

Quality is important when selecting slate tiles. Expert roofers advise choosing tiles with consistent thickness and size to guarantee a seamless installation. It can save time and avoid future issues if you check each slate for flaws or cracks before laying them. Selecting premium materials also improves the roof’s overall resilience and aesthetic appeal.

Slate roofing can last a long time, but proper installation methods are essential. To create a water-resistant barrier, roofers recommend overlapping each row of slate tiles starting at the bottom of the roof and working your way up. By using a technique called "topping out," water is diverted from the roof and leaks are avoided. A tight fit that endures the weather is ensured during this phase by paying close attention to details like using the right nails and evenly spacing the tiles.

Slate roofing maintains its aesthetic appeal and increases its lifespan. Skilled roofers emphasize the significance of routine maintenance and inspections, which includes quickly replacing any broken or missing tiles. Eliminating moss and debris accumulation aids in preventing water retention, which over time may cause degradation. Roofers can achieve a long-lasting and aesthetically pleasing slate roof that improves the overall value and integrity of any building by adhering to these recommendations.

Advantages and disadvantages of the design

This material is in demand and well-liked because of its many benefits:

1. Affordable price. Slate is one of the most inexpensive materials used in the construction of roofing structures. Its average market price starts from 150 rubles per square meter. For comparison: corrugated roofing with a thickness of 0.65 mm will cost approximately 200-220 rubles per m2. To install a roof made of soft slate (for example, ondulin) you will need almost 2-2.5 times more money, its price is from 350 rubles. Good quality metal tiles sell for about the same price.
2. Long service life. There are thousands of cases where slate roofing on buildings built more than 50-70 years ago (back in Soviet times) remains in perfect condition to this day. This coating easily withstands changes in humidity and temperature, does not deteriorate due to frequent rain and snowfall, and is not destroyed by ultraviolet radiation.
3. Non-flammability. In case of fire, slate does not ignite and therefore does not contribute to the spread of fire. It can only crack or become covered with soot. But it should be taken into account that the wooden sheathing and rafter system are susceptible to fire – when these structural elements burn, the roof simply collapses, which leads to the destruction of the slate sheets themselves. To avoid such situations, wooden elements should be treated with special fire-resistant compounds.

Nevertheless, the material has certain drawbacks that are significant under certain circumstances:

1. Fragility. Slate sheets are not designed for heavy loads, especially impact. Walking on such a roof, careless handling of the sheets during their installation, as well as the accidental fall of heavy dry branches from trees – this can lead to the material becoming covered with cracks, or large pieces starting to break off from it. Therefore, slate should not be used for roofing buildings next to which tall old trees grow.
2. Heavy weight. One square meter of slate, depending on its thickness, can weigh about 7-10 kilograms. Such a coating places a significant load not only on the roof frame, but also on the load-bearing walls and foundation of the building. Therefore, heavy slate, especially 7 mm, is not recommended for use in buildings built on relatively weak soils and without a reinforced foundation.

Types and basic requirements for roofing material

These kinds of roof coverings fall into a few primary categories based on their composition and production process. Let’s examine the most common varieties of slate:

Asbestos

The ingredients for this material are cement, asbestos, and water. These components usually have the following proportions: 85, 10, and 5 percent, respectively. Because asbestos-cement slate sheets are less expensive, they are among the most widely used roofing materials.

Non-asbestos

The structure of this material is plastic and flexible. It has a higher crack resistance and can withstand shock loads far better than asbestos.

A notable characteristic of the material is its increased color gamut, which makes it suitable for a variety of unconventional design projects. Materials that are not asbestos include bitumen or soft (European) slate. Ondulin is the most prevalent representative.

Metal

Steel sheets painted to create iron slate. Its qualities are almost exactly the same as those of corrugated roofing sheets; in fact, they are nearly identical. The metal slate’s wavy shape is the only thing that differs.

Such a roof has to meet several specific requirements. First and foremost, the substance needs to be extremely resilient to heat. Asbestos and metal slate, which is semi-soft and capable of smoldering and melting when exposed to open flames, fully satisfy this requirement.

Second, the coating needs to have a smooth surface; otherwise, snow, dust, leaves, and other debris will build up on the roof and ruin its self-cleaning qualities.

The specifications of GOST 303040-95 and GOST 18124-95 also govern the properties of slate materials. Two ratings—40-150 and 54-200 mm—correspond to the standard height of the wave and the separation between the upper and lower points of two adjacent crests. 5.8 to 7.5 mm is the possible range for sheet thickness.

Pie structure

Because slate is wavy, moisture can enter the spaces between the ridges in the lower portions of the roof (specific metal ridges seal the upper portions). It is essential to use a multilayer roofing pie to reduce the detrimental effects of moisture on the wooden components of the roof frame.

Several components make up its structure, and they should be arranged in the following order (from bottom to top):

• internal binder;
• venturezor;
• vapor barrier;
• insulation;
• waterproofing;
• Contracuard;
• crate;
• slate coating.

Inexperienced builders frequently mix up the location of waterproofing and steam because they think these materials serve the same purpose. Because the vapor barrier only traps water vapor and not rain or melted water in its liquid state, this causes a noticeable decrease in the roof’s lifespan.

Consequently, the insulation needs to be adequately shielded from damp air that may seep from the house’s exterior and from precipitation that may seep under the slate from the outside in the event that it is inadvertently damaged or secured incorrectly.

Because of this, the thermal insulation material needs to be positioned in between the waterproofing and the vapor. It will quickly lose its properties if not.

The waterproofing layer shouldn’t be in close proximity to the sheathing. Both above and below it, there ought to be ventilation openings. Condensation will build up otherwise.

Minimum tilt angle

One of the main factors affecting a roof’s dependability, safety, and service life is its slope. This indicator can vary within a wide range depending on the type of slate and the local weather and climate.

The ideal pitch for a pitched roof with asbestos slate is between twenty and twenty-five degrees. Because of the material’s rough surface, snow masses will accumulate on it at lower values and become difficult to remove spontaneously from the roof.

Given that slate has a surface density of 8 to 10 kg per square meter, if the slope is too great, the slate sheets may lift off the fastenings by themselves.

Given that asbestos cement has a lower coefficient of friction than ondulin, soft slate should be installed at an angle of between thirty and thirty-five degrees. Consequently, the roof should have a steeper slope to keep snow from building up on it.

Reducing the angle to 5-8 degrees, or the same value as corrugated roofing sheeting, which has a similar working surface structure, is possible if the building is covered in metal slate. Snow masses slide off the roof surface even with a slight slope because this material is smoother than asbestos or soft.

Read on to find out what the minimum inclination of a pitched roof should be.

Construction of the rafter system and sheathing

Because slate sheets are relatively heavy, the frame’s strength and load-bearing ability are crucial. It is essential to equip the structure with a sturdy and dependable frame in order for it to withstand this kind of load, which increases during the winter.

It is advised to use a wooden beam for rafter legs that is at least 60×150 mm; 100×150 mm is the best size. The maximum moisture content for wood is 15%.

Each slate sheet is positioned on at least two longitudinal supports thanks to the careful selection of the spacing between neighboring rafters. Value standard: one meter.

It is possible to fix rafter legs with or without cutting:

1. When fastening without a notch the eaves are usually provided by the rafter itself. To ensure a tight fit of the rafters to the mauerlat, support bars are used; fastening is done on both sides through special metal corners with holes for self-tapping screws.
2. Fixation with notch requires cutting the rafters so that they fit snugly against the mauerlat. To install a cornice overhang, fillets are often used, which are attached to the rafters with an overlap of at least 1 m. Increased reliability of the assembled frame is ensured by rigid fastening using corners.

Boards are used to create the sheathing. The transverse sheathing elements should be spaced 40–50 cm apart, which is about twice as small as the rafter system. There are various ways to fix lathe elements. Traditionally, long screws or nails have been used.

How to lay hydro- and vapor barrier?

Use premium hydro- and vapor barrier materials to guarantee efficient protection of the roof and under-roof space from precipitation and condensation.

Polyethylene or polyvinyl chloride (PVC) film is most frequently used for roofing felt waterproofing. There is a 15–20 centimeter overlap between adjacent rolls.

Construction tape or a specific adhesive must be used to glue the joints. Using thin galvanized nails or a stapler, the film is fastened between the counter-lattice and the rafters.

A vapor barrier coating is applied similarly to the underside of the roofing pie. Products made of polypropylene or polyethylene can be used as vapor barriers. Their structure can be membrane-like or flat.

If the project calls for it, thermal insulation ought to be positioned in between the waterproofing and vapor layers. If the roof design permits it, the thermal insulation layer improves the comfort level within the building or in the under-roof (attic) space.

The following is a succinct thesis statement for your paper: Skilled installers of slate emphasize crucial methods for installing slate on a pitched roof in order to guarantee its longevity and visual appeal. Understanding these procedures, which include installing underlayment correctly, placing slate precisely, and weatherproofing, improves structural integrity and keeps slate roofing’s classic beauty for many years to come.

Construction stages

Prepare the required supplies and equipment before you begin construction work. You’ll need the slate itself in addition to the following:

• timber for the rafter system, sheathing and counter-lattice;
• construction tape, glue and sealant;
• steam, heat and waterproofing roll materials;
• slate nails, self-tapping screws or special screws;
• fastening elements for a wooden frame (nails, screws or bolts);
• laser or water level;
• roulette;
• drill or screwdriver;
• hammer;
• grinder or hacksaw.

When installing slate sheets, the fasteners chosen should be chosen with consideration for the roofing material.

One slate roof structural component at a time is installed. Installing roof insulation is most practical when done after the roof covering is installed:

1. Rafter system. It is built from wooden beams, the thickness of which is selected individually, taking into account the slope of the roof, its size and other factors. Rafters can be installed using different types of fastenings: nails, bolted connections, etc. Bolts provide a more secure fit, but installing them requires additional time to drill holes. The rafter frame is attached to the Mauerlat.
2. Waterproofing. Moisture-proof coatings significantly increase the service life of wooden frame elements, protecting them from changes in temperature and humidity. For this purpose, roll waterproofing is used. The waterproofing strips are fastened with a construction stapler along the roof, starting from the bottom. The strips are laid with an overlap of 10-15 cm. In the lower part (at the end of the eaves overhang), the waterproofing is glued to the drip line, which serves to drain moisture that has fallen on the membrane into the gutters.
3. Counter-lattice. On top of the rafters, the waterproofing is fixed with counter battens. They will prevent the roofing material from tightly adhering to the waterproofing, which will contribute to a better level of roof ventilation and removal of moisture that forms on insulated roofs, while at the same time they act as a pressing element, which is necessary for waterproofing.
4. Lathing. A sparse sheathing is laid under the slate with a step of 1-2 m between the boards.
5. Slate. Sheets are laid with an overlap of at least 10 cm. If the overlap is too small, moisture will penetrate under the top sheets.
6. Thermal insulation. The insulation is laid between the rafters, pressing it against the waterproofing and shifting each subsequent layer to the side relative to the previous one, so that cold bridges do not arise. The insulation is cut 2 – 3 cm wider than the width of the rafter span (the material should fit tightly, but not bend over).
7. Vapor barrier. Rolls of vapor barrier material are placed on top of the heat insulator. A conventional vapor barrier film is secured with staples using a construction stapler. The first strip of vapor barrier is attached at the ridge, and the subsequent strips are closer to the eaves, with an overlap, and are fixed in the same way as a waterproofing film, only carefully stretched, so.To. there should be no sagging. The glued areas are reinforced with a pressure strip. It is very important to ensure a tight connection to surfaces. In areas adjacent to complex surfaces (chimneys, walls) you need to use glue. The staples from the stapler are glued with tape.
8. Counter-lattice. Mounted along the rafters and made from smaller timber (section 50 mm). These bars will provide a longitudinal ventilation gap. It is possible to have a roofing pie with one ventilation gap, the top one, and the vapor barrier is always adjacent to the insulation.
9. Internal binding. This part of the roofing structure is fixed with nails or fixed with long screws on the lower sides of the rafters.

How to lay different types of slate?

When laying asbestos sheets, they are typically fastened with unique nails that have shock-absorbing rubber rings and metal washers in them.

It is strictly forbidden to use nails that are not meant for slate roofing. The edges of the holes may crumble if the wrong fasteners are used, which is why they will progressively get bigger and allow rainwater to enter the roofing pie.

When driving slate nails, it’s important to drill holes beforehand using an electric drill bit with a thin enough diameter to keep the delicate material from crumbling.

The best way to lay asbestos slate sheets is to do so staggered, or in a checkerboard pattern. This indicates that the top rows’ sheets should be shifted by roughly half of their width to the left or right of the bottom rows. This is not the same as overlap, where sheets lie on top of one another along their longitudinal axis.

Using a specialized power tool, self-tapping screws or screws with rubber washers are used to secure metal and soft slate; this is an inconvenient and challenging task to perform with a hand tool. Staggered laying is not required, unlike asbestos. The metal sheets fit together more tightly, so they can be mounted without lateral displacement.

Typical mistakes of novice builders, useful recommendations

It takes a lot of labor to lay a slate roof, especially one made of asbestos, because this material is easily harmed by negligence.

Errors are common among inexperienced builders, leading to substantial material deterioration, needless expenses, and decreased installation quality.

Clogging nails into the lower sections of the waves is a fairly common mistake. This is incorrect because even if you score a nail half a million times deeper than necessary, the material may crack due to such fixation. The upper regions of the crests are where the fastening points should be found.

The fasteners placed in the center of the sheets constitute the second mistake. Additionally, this causes fractures and allows rainwater to seep beneath the roof. Along the edges of the sheets, where there is lateral overlap, slate needs to be fixed. Every nail needs to be simultaneously scored between two sheets.

The incorrect order in which slate sheets are laid is the third and most significant error. They must be mounted from the bottom up, in the direction that runs from the cornice to the top of the roof. If not, the overlap is incorrect.

The lower portions of the upper sheets must inevitably be beneath the upper parts, which are higher on the roof slope, and not the other way around. If not, water will seep beneath the joints.

Careful planning and execution are necessary for installing slate correctly on a pitched roof. Skilled roofers stress how crucial it is to begin with a strong foundation. This entails making certain the roof deck is stable, clear of obstructions, and oriented correctly. Before installing slate, any necessary reinforcements or repairs should be taken care of.

When choosing a slate, quality is very important. Skilled roofers advise selecting slates that are flawless, consistent in thickness, and long-lasting. Additionally, they emphasize how crucial it is to order a little bit extra slate than you’ll need in case any breakages or cuts occur during installation.

Paying close attention to details is essential when installing something. To ensure appropriate water shedding, roofers recommend overlapping each slate correctly and working upwards from the bottom up. Additionally, proper nailing techniques are essential; in order to prevent cracking, nails should be driven flush with the slate surface without being overtightened.

Last but not least, maintaining a slate roof on a regular basis is crucial. Roofers advise doing an annual roof inspection to check for damage, loose slates, and debris accumulation. Water intrusion should be stopped as soon as possible because it can eventually cause more serious damage. Through adherence to these guidelines, homeowners can guarantee that their slate roofs maintain their aesthetic appeal and functionality for an extended period of time.

Video on the topic

frame for a pitched roof under slate 🏡nabane

Budget construction. Part 21. How to lay slate without gaps

how to fasten slate