Metal roofing: coating, calculation, device, installation

The choice of roofing material is not an easy task. It is necessary that the roof be reliable, beautiful, durable, and even, preferably, inexpensive. All these requests are answered by a roof made of metal. It must be added to the pluses that it is not the most difficult installation, which even a person without roofing experience can handle with their own hands. 

Types of metal tiles

The metal tile is molded from sheet metal with a thickness of 0,35-0,7 mm, on which protective and decorative compositions are applied. It turns out a multi-layer cake. The basis of this building material is most often steel, but there are options from copper and aluminum. Since aluminum and copper are much more expensive than steel, products made from them have a high price. For this reason, copper or aluminum metal tiles are almost never found, but if desired, they can be delivered to order.

There are on sale both imported and domestic metal tiles. The European version comes strictly from steel 0,5 mm thick – this is spelled out in the standard. In our GOST, from 0,45 to 0,5 mm is allowed.

In addition to different base materials, a different protective coating is applied. First of all, there are two types of steel protection against oxidation – zinc and aluminum-zinc. The second option appeared not so long ago, but it is he who provides better protection, although such processing costs a little more.

There are more different compositions for the top coat, one that, along with weather protection, gives the material one color or another.

Types of protective and decorative external coatings

The outer covering of the metal tile performs two functions at the same time. It protects the base metal from corrosion, and gives the material an attractive appearance. There are the following types of this coverage:

1. The most common metal roofing has a glossy polyester (PE) coating – about 70% of the total number of roofs are covered with this type of material. This is because it has an average price and good performance. Layer thickness 25-30 microns, service life 5-10 years. This coating is resistant to ultraviolet radiation and corrosion, but is easily damaged mechanically – scratches appear even when a large amount of snow comes off. Therefore, polyester metal tiles are not recommended for use in regions with heavy snowfalls. In other areas, to prevent massive snowfall, it is desirable to install a snow retention system. If you cover the roof with such material, you must be careful during installation.
   

2. Matte polyester (MPE) is obtained by adding Teflon. As a result, the film is more durable – the service life is 10-15 years, it can also be used in snowy regions. This composition is applied with a thickness of at least 35 microns. The disadvantage of tile coated with matte polyester is a smaller range of colors (about 20 shades compared to 40 glossy).
   

3. Plastisol (PVC) is a PVC-based compound. It has a beautiful structural surface, is applied in a layer of 200 microns, due to which the coating is resistant to damage. The disadvantage is low resistance to ultraviolet radiation, which significantly narrows the range of use. In addition, in some countries, due to the presence of polyvinyl chloride, this coating is prohibited.
   

4. Pural is a coating based on polyurethane with additives of polymers. Available in glossy (PUR) and matte (MatPUR) versions. Layer thickness – 50 microns, service life – up to 30 years. This is one of the best options: resistant to mechanical damage (worse than palstisol, but better than everyone else), tolerates ultraviolet and aggressive environments well, can be used for roofing on the sea coast.
   

5. Polydifluoride (PVF or PVDF) is a composition based on polyvinyl fluoride with the addition of acrylic (20%). The main advantage is the high elasticity of the coating, due to which, with a small thickness (30 microns), the film is very resistant to mechanical damage. Other advantages are a wide range of colors, fade resistance, long service life – up to 30 years. The disadvantage is the highest price.
   

It is clear that when building a house you do not want to spend extra money. Probably for this reason, most developers choose the cheapest option – polyester-coated metal tiles. But this is not the best solution. Let’s guess. The service life of metal tiles with polyester is no more than 5-10 years, the average cost – with a metal thickness of 0,45 mm – is about 260 rubles / m², with a steel thickness of 0,5 mm – 440 rubles / m². Even if the roofing material lasts 10 years, the price of a square for a year will be 26 rubles and 44 rubles. Now let’s take a very good option – with a pural coating. With a metal thickness of 0,5 mm, the cost is from 510 rubles / m² up to 635 rubles/m² (depending on the manufacturer). Service life – 30 years. For a year of service it will be 12-17 rubles / m². The difference is obvious. And this is without taking into account the work to cover the roof, and this is also time and money.

Profile views

When laying a metal tile, its geometric dimensions and wave parameters are important – a crate is calculated and mounted under them. Also, the wave height determines the degree of rigidity of the sheet – at high wind loads, a material with a high wave (more than 50 mm) is required – the most rigid, under normal conditions, a metal tile with a small wave (less than 50 mm) is suitable.

The waveform is symmetrical and asymmetrical, more rounded or with straight lines. There are quite a few different profiles. The table shows the geometric dimensions (useful width of a metal tile sheet, overlap, wave parameters), which will be useful when calculating the quantity.

Metal roofing in 70% of cases is made from the Monterrey profile. It has a rounded, slightly asymmetrical waveform. There are 7 subspecies with different wave parameters.

The next most popular profile is Cascade. About 15% of metal roofs are made of it. It is formed by straight lines, has a clear geometry. It looks very interesting on the roofs of complex shapes with a large number of broken lines.

This profile is used more in regions with average wind and snow loads – the wave height is small, the loads can withstand average.

About 10% of the market is occupied by Andalusia metal tiles. More than anyone else, it looks like a classic semicircular tile. The profile is symmetrical, with pronounced drops.

The profile is designed so that the joint is located on the wall of the wave, it is practically invisible. The impression of a monolithic roofing is created.

If we talk about color, then depending on the type of coating, shades are usually from 20 to 40 pieces. Choose the one that suits you more. The service life or other characteristics do not depend on the color, although it is believed that dark colors fade faster. In fact, the rate of fading depends on the quality of the coating and the pigment, but not on the color.

Calculation of the amount of metal tiles

To calculate the required number of sheets of material, you first need to determine the type of profile and the manufacturer of the metal tile – you will need the exact dimensions of the material itself, and each profile has its own. Then it is necessary to make accurate measurements of the slopes – the length, height, if any, it is necessary to measure all the protrusions or other decorative elements that will need to be sheathed with roofing material. If the roof has a complex shape, it is better to draw its plan, put down all the dimensions and then sit down for the calculations.

Number of rows

It is best to look for metal tiles not in stores or markets. It is advisable to go directly to the manufacturer. It’s not just the price – it may not differ very much, but the fact that many workshops / factories offer to cut sheets of the required dimensions. The minimum sheet height is 0,7 m, the maximum is 8 m. That is, you can order the required number of sheets covering the roof slope from the ridge to the overhang (including the ledge).

This option is good because the metal roof will not have horizontal joints, which means there will be less chance of a leak. The second plus is the minimum amount of waste and a smaller amount of the material itself (due to the absence of horizontal overlaps, several square meters are saved). Cons – difficulties with delivery, lifting long sheets up, inconvenient installation.

When using sheets of standard sizes, the height of the roof slope is divided by the useful length of the sheet. The resulting figure is always rounded up. The useful length is obtained after the horizontal overlap is subtracted from the total length – from 100 to 200 mm. The flatter the slope, the greater the overlap of the sheets is necessary so that precipitation cannot enter the under-roof space. On roofs with a slope of up to 12°, one sheet overlaps the other by at least 200 mm, with a slope of 12° to 30°, the overlap is 150-200 mm, more than 30° – 100-150 mm. The specified amount of overlap is subtracted from the total length of the sheet, this will be the “useful length”.

An example of calculating the number of rows of metal tiles on the roof. Let the length of the slope be 4,5 m, the useful length of the sheet is 2,3 m. Divide 4,5 by 2,3, we get 1,95, round to an integer – we get 2 rows. In this case, only a small part of one sheet will go to waste, but there are times when more than half is cut off. This is very unprofitable, since you can’t use this piece anywhere else.

Number of sheets in a row

Take the length of the slope and divide by the useful width of the sheet. This parameter is indicated in the technical specifications for the metal tile. Most often it is 110 cm (1,1 m). The resulting number is rounded up, we get the number of sheets in a row.

An example of the calculation of sheets of metal tiles in a row. Let the length of the overhang be 8 m, the useful width of the sheet is 1,1 m. When dividing, we get 7,27 pieces, but we round up to a larger integer and get 8 pieces in one row. Moreover, more than 2/3 of one sheet will go to waste.

Features of hip roofs

In hip roofs, the slopes have a triangular or trapezoidal shape. Here it is necessary to select the length of the sheet – to minimize the amount of waste.

The height is chosen so that no more than half goes to waste. It is quite difficult to do this manually, and still there is a solid error – there will be 20-25% more waste than when calculating using programs. They are usually available from vendors and manufacturers. It is better to provide them with an accurate calculation, and at home to pre-measure the parameters of the roof (or call a measurer), and then try to choose the dimensions yourself. Then it will be possible to compare the amount of material needed, calculated by you and proposed.

Determination of the number of additional elements

Roofing from metal tiles requires a large number of various additional elements (additions) that form the ridge, the edge of the overhang, the sides of the slope, the passage of the pipe, the valley (the junction of two adjacent roof slopes). The more complex the shape of the roof, the more the amount of extensions required. With a simple gable roof, ridge elements and plugs, cornice and gable strips will be needed. That’s all.

Despite the wide variety of extensions, they are all considered the same. Take the length of the surface on which you want to mount and divide by the useful length of the element. It is usually standard and is 1,9 m (total length 2 m). The result is rounded up.

What and how to mount

The metal tile is fixed with special self-tapping screws with rubber washers. As well as the main material, they are made of galvanized steel, and on top they are painted in a tone with its coating. During installation, the self-tapping screw must be screwed in strictly perpendicular to the roof surface, its inclination is not allowed.

When fixing a metal tile, it is also necessary to monitor how tightly the fasteners adhere to the surface. You can’t tighten it too much, bending the metal, but you can’t allow a loose fit either – the connection will not be airtight.

Lathing for metal tiles

A metal tile is a rather rigid material, therefore a sparse crate is made under it, which consists of planks that are located along the roof overhang.

What material

If the metal tile roof has a simple design, an inch edged board (24-25 mm thick) 100 mm wide goes to the crate. On a roof of complex shape or in regions with large snow loads, it is better to use a board of 32 mm thickness or a beam of 50-50 mm. The beam is also used with a large distance between the rafters (more than 80 cm).

Sheathing step

Installation of a metal tile on a roof has one important feature. There is the strongest place in the profile – under the step of the wave in the hollow. This is where you need to screw the screw. The crate must be made so that the middle of the bar is just under this place. This is precisely what causes difficulties: the profiles have different sizes, therefore, each of them requires its own installation step for the battens. This value can be determined by measuring the already existing material, but, usually, this parameter is indicated in the instructions for the metal tile.

There are several important points of the device of the crate under the metal tile. Please note that the first plank along the overhang is thicker than all the others – the step height for this profile is added to the selected plank thickness. In addition, this plank is made wider than all the others – a dropper will be attached to it, which closes the cut, protecting the wood from precipitation.

Also note that the second bar is not stuffed with a standard, but with a shortened step, otherwise you will not get further into the wave. The step is also different when installing the last bar near the ridge – it is obtained in fact, as well as the height of the bar. We remind you that there should be sufficiently large gaps in the area of ​​uXNUMXbuXNUMXbthe ridge – and the crate and roofing material should not be joined. This is necessary for proper ventilation of the attic.

Installation procedure and features

Before you cover the roof with a metal tile with your own hands, you need to familiarize yourself with the rules for working with the material:

• First of all, you need to take care of proper storage – in ventilated stacks, arranged in bars.
• When cutting, do not use an angle grinder (grinder), but cut only with a jigsaw or scissors for metal. The grinder overheats the metal, due to which the zinc evaporates, in the places of the cut the material will begin to rust.
• Start laying the sheets from the lower right corner (the installation diagram of the metal tiles is in the photo below).
• When mounting, wear soft, well-fitting shoes, step only in the lower part of the wave.

Next, we will talk about the device. Metal roofing comes in two versions: with a cold or insulated attic. Depending on the type chosen, the order of work changes – when arranging a warm attic, two more layers are added – a heater and a vapor barrier membrane from the side of the room.

Cold metal roofing

This type of roof is suitable if the attic is planned to be non-residential. Then all the insulation is concentrated in the ceiling, and the function of the roof is only to protect from rain and wind. The order of work is as follows:

• The first lath of the crate (higher) is installed along the overhang.
• A drip bar is attached to it.
• A waterproofing membrane is spread over the rafter legs. Installation begins from below, the film is rolled out along the overhang. The lower edge of the film comes to the drip bar, ending after the inflection line. The film is fastened with planks 30-35 mm thick to each rafter leg, not in tension, but with obligatory sagging of 2-2,5 cm. The second row of the film overlaps the first by at least 15 cm, the joint is glued with a special adhesive tape (sold in the same place where and membrane). The membrane is attached to the drip bar with self-tapping screws (galvanized or stainless steel).
  

• Boards (bars) of the crate are attached to the planks that hold the film with the selected step. Use galvanized or stainless steel screws, the same nails with a large flat head. The length of the self-tapping screw and nails is three times the thickness of the battens.
• Sheets of metal tiles are laid on the crate, exposing them strictly along the overhang (if you have it exactly horizontally). Neighboring sheets overlap in one wave, installation is carried out from the bottom up, with the obligatory horizontal overlap by the required amount (see above).
• Mount ridge elements, end strips. They are fixed with the same self-tapping screws as the metal tile, in increments of 10 cm.

On this we can assume that the cold roof of the metal tile is ready.

Warm roofing

When constructing an insulated roof made of metal tiles in the roofing cake, another heat-insulating material is added, which is fixed between the rafters, and a vapor barrier film, which is stuffed onto the rafters from the attic side. Further, the entire installation process is similar.

How to attach sheets

When we cover the roof with a metal tile, we must correctly position the screws. There are several rules to follow:

• Self-tapping screws are installed in the lower part of the wave, 2 cm below the step.
• The bottom row, along the overhang, is attached to each wave. Fasteners are also installed in places of horizontal and vertical joints.
• The waves between the horizontal joints are fastened through one in a checkerboard pattern.

These rules are clearly shown in the diagram. In a graphic image, some things are easier to understand.