Since ancient times, a thunderstorm has been a terrible, incomprehensible natural phenomenon for people, which frightened people and carried the danger of fire and even death. Therefore, for a long time, lightning was considered a punishment sent by the gods to punish sinners. Now the nature of a thunderstorm has been thoroughly studied and is familiar even to a schoolchild, although this has not made it any less dangerous.
To prevent fires as a result of lightning strikes, lightning protection is organized on the roof of a private house. In this article we will talk about the most effective measures lightning protection that is necessary for every building.
Many people, when building their own residential or country house do not think about how roof lightning protection works. A common misconception is that metal types roofs do not need protection from lightning strikes, although this opinion is a big mistake. For a residential or non-residential building, whatever the roof covering, the main dangers are considered to be:
- Direct lightning strikes. Lightning protection of a pitched roof is the key to the safe operation of any home, since the ridge is, as a rule, the highest point in the area, which attracts lightning strikes. Even if a non-flammable covering is laid on the roof, if a charge gets in, there is a risk of fire, since the rafter frame is made of highly flammable wood.
- Static electricity. Roofs made of metal tiles and other metal roofing materials accumulate static electricity well, which occurs when small dust particles rub against the coating. The accumulated voltage can be discharged if a person standing on the ground or ladder accidentally touches the roof surface of a metal-roofed building, which can result in serious injury.
Important! Experienced roofing professionals believe that lightning protection of a roof is required element structures, regardless of the shape of the roof and the type of roofing material used to cover it.
Device
Lightning protection of a roof made of metal tiles or any other roofing material is a set of measures to ensure the safe operation of a building during a thunderstorm and to prevent injuries during roof maintenance due to the discharge of static electricity. In addition, the presence of a well-designed and installed lightning protection is an additional protection of electrical equipment installed in the house from power surges in the network. It consists of the following components:
- Lightning rod. An air terminal is a conductor that meets a lightning strike on the roof. It is a pin, cable or special mesh. The lightning rod must be mounted on the very high point roofs - on a ridge, chimney or ventilation pipe. If the roof has complex structure or a larger area, then for efficient work For lightning protection, a lightning rod is needed not just one, but several at once.
- Down conductor. The lightning protection device for a home must include a down conductor, which carries light along a safe route. electric charge from the lightning rod to the ground electrode. It is made of reliable and durable steel wire with a thickness of at least 6 mm.
- Ground electrode. Houses with a metal roof must be equipped not only with a lightning rod and down conductor, but also with a grounding conductor. A ground electrode is a special device that is connected to a down conductor; it is necessary to ensure that the electric charge is discharged in the ground. A structure welded from metal corners or pipes having a sufficiently large area of contact with the soil.
Note! To determine what kind of lightning protection for a metal roof is required, use a simple rule: it is considered that one lightning rod protects a cone from lightning, the top of which is at its top, and the sides diverge at an angle of 45 degrees from it.
Installation of lightning protection
Lightning protection of a flat roof or pitched roof structure is carried out during the installation of the roof or already during the operation of the building. It is important to correctly calculate the number of lightning rods and the contact area of the ground electrode so that the protection against electrical discharges works effectively. It is believed that the higher the lightning rod, the larger area, which it protects from lightning strikes. It is necessary that this safe area includes not only a residential building, but also the necessary outbuildings. When installing lightning protection, the following requirements must be taken into account:
- The lightning rod is installed at the highest point of the roof. Typically, installation is carried out on a ridge, on a television mast, chimney or ventilation pipe. The disadvantage of this installation method is that the high metal spire creates additional wind load and can also become deformed. An alternative installation location could be a tall tree located near the house.
- The down conductor connects the lightning rod to the grounding conductor. For its manufacture, steel wire with a thickness of at least 6 mm is used, which must withstand voltages of up to 200,000 amperes. The down conductor is laid along the shortest path, and the welding between it and the lightning rod must be very strong so that it does not collapse under voltage. From the lightning rod, the down conductor is lowered first along the roof and then along the walls of the building at the maximum distance from windows and doors. It must be securely fastened to the walls using metal clamps.
- Grounding electrodes are made of stainless steel or copper, as they have good conductivity. It is buried in the ground to a depth of at least 2-3 meters at a distance of more than 5 meters from the driveway to the house, porch, blind area. The soil at the site where the ground electrode is installed must be loamy or clayey and moist. Before a thunderstorm, you can even specially moisten the soil if it is sandy and does not hold water well.
Remember! Lightning protection requires regular maintenance to maintain its functionality. It is recommended to inspect the lightning rod annually, carefully checking the points at which it is attached to the down conductor. Once every three years, weakened contacts should be replaced or strengthened, and once every 5 years, the ground electrode should be dug out and the depth of its corrosion should be checked. If the grounding element is rusted by more than a third, it should be replaced.
At all times, people have been wary of thunderstorms. And this is correct, since lightning carries a very great danger: it can strike buildings, tall trees and even people. A large number of fires occur precisely because of lightning strikes; in addition, a short circuit in electrical networks can occur in the building. Our distant ancestors learned to escape from lightning strikes with the help of lightning rods. Modern architects also do not neglect this element of protection. It is necessary for all types of roofs, although some believe it is not necessary for metal roofing. Let's figure out how lightning protection for a metal roof works, how to install it correctly, and whether it is needed.
It is known that metal roofing is laid directly on wooden sheathing or roofing felt. And it's not safe. There have been cases when lightning, striking roof elements, caused burns and melting, which became the cause of a fire from the ignition of the lining material. In addition, a direct lightning strike heats the metal deck to a temperature higher than the fire temperature of wood. rafter system, which can also lead to a fire.
A metal roof can serve as lightning protection only if it is attached to a non-combustible material, and also when reliable connection all metal elements and the presence of electrical connections between them. A good addition to this would be grounding the metal coating.
Lightning protection intercepts a lightning discharge and directs it to the ground
Lightning protection device
Lightning protection can not only protect a building from fire, but also preserve electrical equipment. There is external and internal protection. The external part of the system provides protection from direct lightning strikes, and the internal part ensures the safety of the electrical network from strong surges. electric current.
In internal system Lightning protection uses special discharge devices for electrical networks that limit voltage. The cheapest and in a simple way internal protection is to turn off all electrical appliances, especially if lightning follows thunder in less than 8 seconds.
External system comprises:
- lightning rod;
- grounding.
The task of external lightning protection is quite simple - the lightning rod meets the lightning at the roof itself, then it passes in a safe channel along the down conductor, and the grounding conductor neutralizes it in the ground. This system You can make it yourself, and in a fairly short time. For this you will need a lightning rod, a down conductor, a grounding conductor, and also welding machine and metal brackets or clamps for connecting down conductors.
The number of down conductors is determined by the size of the object, but in any case there must be at least two of them
Installation of lightning rod for metal roofing
A lightning rod is a conductor that is fixed to the roof of a house so that it receives electrical discharges. Install it at the highest place. If near the building complex design or it is very large, then it is advisable to install several lightning rods.
According to their design, they can be of several types:
- in the form of a metal pin;
- metal cable along the roof ridge;
- lightning protection mesh.
For metal roofing, an air terminal in the form of a long metal pin (0.2-1.5 m) is usually used. It is installed vertically at the highest point of the building. The pin must be made of metal that is not subject to oxidation under open air, for example, made of galvanized steel, copper, duralumin or aluminum. The cross-sectional area of the upper part of such an air terminal must be more than 100 mm. sq., diameter – about 12 mm. If a hollow tube is used, then its upper end must be welded.
Important ! You cannot paint or insulate the lightning rod.
The higher the lightning rod, the large territory it protects against lightning
If there is a television mast on the roof (metal, unpainted), then a good lightning rod can be made from it. You can also use a tall metal weather vane for these purposes. The main thing is not to forget to ground it all. Sometimes a lightning rod is installed on a chimney, but this is not always correct, since the attached metal pin will create strong wind loads that can damage the pipe.
How alternative way When constructing a lightning rod, you can use a tall tree (higher than the roof) standing close to the house. In this case, the lightning rod is attached to the very top of the tree so that it rises half a meter or more above the crown.
It has been established that a lightning rod protects from lightning an area falling within an imaginary cone, the apex of which is located at the end of the lightning rod, and side surfaces– at an angle of 45 degrees to the device. The resulting circle is the safe zone. From this we can conclude that the higher the lightning rod, the wider the safe zone. In other words, the height of the lightning rod is equal to two sizes of the safe zone. It is desirable that not only the house, but also outbuildings fall under the protective cone.
Video review of active lightning rods
A down conductor is that part of the protection that diverts lightning from the lightning rod to the ground electrode. It has the form of a steel wire (6 mm), which is welded to the lightning rod and, in connection with it, can withstand loads of up to 200 thousand amperes. The welding between the lightning rod and the down conductor must be reliable so that there are no breaks in strong winds or when a snow layer falls.
The down conductor is lowered from the roof along the walls. It is nailed with special brackets and directed to the ground electrode, into the ground. If there are several down conductors, the distance between them should be at least 25 meters. They need to be laid away from the windows and doors of the building.
Important ! Under no circumstances should down conductors be bent, as a spark charge and further ignition may occur.
To disguise the down conductor, you can lower it down the drainpipe, securing it with clamps
According to the rules, down conductors should be as short as possible and they should be laid closer to the edges of the gables, dormer windows, sharp protrusions, that is, to the most dangerous places.
Grounding device
The ground electrode is a device that ensures contact of the down conductor with the ground. Its main element is a metal structure, which has a fairly large surface for better contact with the soil.
It is very convenient to use a welded structure made of pipes or angles as a grounding conductor. You can also bury a sheet of thick iron, a large piece of thick wire mesh, or an old metal barrel in the ground. If you don’t have the time or desire to dig a deep hole, you can use steel rods for grounding, which can easily be driven 2-3 m into the ground.
Great importance It also has grounding material. If regular iron (steel) is used, there is a high probability that it will rot over time. Galvanized iron is no better, since zinc quickly dissolves in an aggressive environment. The best materials for grounding are stainless steel and copper (a thickness of 2-3 mm is sufficient). You can also use iron, but it must be thick so that it does not have time to rot.
The ground electrode is buried in the ground to a depth of 1-2 meters
It happens that even a very good grounding conductor does not perform its functions well, for example, on sandy soils or during dry summer times. Water will help correct the situation. It is advisable that the soil in the grounding area is always moist. You can drain water from the washbasin into this place or intentionally moisten the ground, especially before a thunderstorm. To increase the electrical conductivity of the soil, you can drill small holes in the soil once every few years and pour nitrate and salt into the holes.
Important ! The ground electrode should be located at a distance of 5 or more meters from the porch, paths, passages and at least a meter from the walls of the building.
Maintaining lightning protection in working order
- Every year, before the start of the thunderstorm season, it is necessary to inspect the lightning rod and all attachment points in order to replace and paint them, if necessary.
- Once every 3 years, it is necessary to tighten or replace loose connections and clean the contacts.
- Once every 5 years it is necessary to open the ground electrode and check the depth of the corrosion that has formed. If it is rusted by more than 1/3, then it must be replaced.
Protection zone from external influence lightning
Installing lightning protection for a building may not be a very simple matter for unprepared people. Everything needs to be calculated correctly, taking into account the size and type of building, type of roof and other parameters. Specialists in this matter will not only competently perform all calculations and build reliable protection from lightning strikes, but will also ensure that the system does not spoil the appearance of the building.
The modern approach to the safety of buildings of any type is complex measures, where one of the positions is responsible for protecting roof structures from lightning strikes. This system is called lightning protection. In this article we will talk about the production of lightning protection for a gable roof, what it consists of, what types there are, what criteria should be used to select it, and whether it is possible to do without this system. Let us immediately note that lightning protection is a technically complex system.
What is lightning protection
This is a set of certain measures, which includes design, installation and maintenance, which are aimed at protecting the roof from direct lightning strikes, as well as from electrical phenomena accompanying it. It is imperative to protect roofs from lightning, because this a natural phenomenon has a powerful electric discharge, under the influence of which even sand melts.
Therefore, lightning protection is installed on the roofs of buildings, especially on those that are higher than all other neighboring objects. If this system is not installed, then there is a high probability that lightning striking the roof will cause a fire. But this is not the only reason for the installation; it should be noted that during a thunderstorm the air becomes electrified. And this is an opportunity to provoke high-power electromagnetic pulses that negatively affect the electrical network supplying the house. It can also generate pulses of large amplitude, which will certainly affect voltage surges. And this, in turn, will cause the failure of household and computer equipment, various types of short circuits and fires.
Many owners of private real estate, especially low-rise ones, believe that lightning only strikes tall buildings. And if the roof of the house is covered with metal roofing material. This is a false opinion. Lightning can strike any object, especially if it is located far from other buildings. As for the roof covering, during a thunderstorm the roof becomes wet. And everyone knows that water is an excellent conductor of electricity. Therefore, it does not matter what material the roof is made of. For the zipper, it is enough for it to be wet.
Types of lightning protection
Roof lightning protection is divided into two categories:
external;
internal.
The first is a design that everyone knows. It consists of a metal pin that rises above the roof of the house. This element is called a lightning rod. A current conductor comes from it. Usually this is large-diameter wire (rod) and small-diameter steel reinforcement. Or a steel strip 3 mm thick and 5 cm wide. And the last part is a grounding system located in the ground. Essentially, these are several pins driven into the ground and connected at the upper ends by tires. Going to external lightning protection exactly in this order, where the down conductor is the connecting part between the lightning rod and grounding.
It should be noted that all of the above mentioned parts of the protection system can be assembled from steel, aluminum or copper elements. Depending on the choice of material, their cross-section is also selected. Because all metals have different electrical conductivities. And this must be taken into account at the lightning protection design stage.
The table shows the dimensional parameters of lightning protection system elements depending on the selected material.
The second, that is, internal lightning protection, is special devices, inserted into the home's electrical power supply system. Such devices are called surge protection devices for internal networks, or for short – SPDs. This device is selected according to the location of the lightning strike. There are two categories here:
Strike straight. This is the most dangerous situation, which often leads to unpleasant consequences.
Impact indirect. Here the impulse strength is 20 times less than in the first case. But this is also a dangerous situation.
The purpose of our article is to talk about external lightning protection.
Lightning protection device on a roof structure
It should be noted that the pin sticking into the sky, installed on the roof of the house, is simplest system drainage of electricity. And they call it passive. That is, if lightning strikes it, it will be removed. Today, manufacturers offer an active system, but more on that below.
What, other than a protruding pin, are offered by companies involved in calculations and installation of lightning protection systems? In principle, there are few proposals. This:
Cable system. Typically, a cable is pulled along the roof ridge (along) and secured to the roofing material with special brackets.
Mesh system, for which they use a cable or wire rod, which is installed on the roof slopes in the form of a mesh.
Typically, the type of lightning protection is selected taking into account the area of the roof slopes, their angle of inclination and the material with which they are covered. It is clear that the most difficult option– mesh. Here you have to accurately calculate the distance between the laid lattice elements, and then carry out the installation correctly.
Let's use the example of roofs covered with different roofing materials to consider the rules for installing a mesh structure.
On our website you can get acquainted with the most popular projects – from construction companies, presented at the exhibition of houses “Low-Rise Country”.
Metal roof protection
Lightning protection of a metal roof requires a special approach. After all, the metal coating itself is an excellent conductor of electricity. Therefore, it is not necessary to use a lightning rod as such in their design. This is even indicated in the “Instructions for the installation of lightning protection of buildings and structures.” But even in such a situation, experts recommend installing a pin or cable as an addition to increasing the efficiency of lightning removal.
If, nevertheless, a metal roof has been adopted as the main element of lightning protection, then a down conductor will have to be rigidly attached to it, for which welding must be used. If for some reason it is not possible to carry out hot work on roofs, then it is allowed to use bolted connection, which will have to be examined once a year for joint corrosion.
And yet, experts unanimously assure that metal coating– not the most reliable lightning removal device. In a roofing structure, there is always the possibility of poor connections between metal sheets, panels or pieces. This means that efficiency drops sharply. Therefore, it is recommended to equip even such roofs with rod or cable lightning rods.
And one moment. A lightning strike on a metal roof causes an increase in temperature at the point where the electrical discharge strikes. And if the thickness of the metal is insignificant, then the probability of fire of wooden rafters is high. Therefore, there are thickness standards that must be taken into account. For example, if the coating is a steel material, then its optimal thickness is 4 mm. It is clear that this size does not exist on the roofing market. Therefore, there are three ways out of this situation:
Conduct rafter insulation systems from roofing material.
Use not wooden, but metal rafters.
Install lightning protection.
For obvious reasons, the third position is the most optimal.
Now let’s talk about the steps at which the elements of the mesh structure should be installed. Everything will depend on the height of the roof. The higher it is, the larger the step. Approximately the ratio is:
roof height 15 m, installation pitch – 3 m;
25 – 4 ;
35 – 5 ;
45 – 6 .
As for the fastening elements on which the mesh lightning rod is “mounted,” there is a fairly large assortment. The photo below shows one of the varieties.
Protection on soft roofs
Lightning protection on a soft roof requires a special approach. After all, installing a large number of mounting brackets means punctures that become places for leaks into the under-roof space. Therefore, it is optimal to use either rods installed along the edges of the ridge girder of a gable roof, or a cable stretched along the ridge, or perfect option– install active protection.
Pay attention to the photo below, which shows how on a roof covered soft tiles, a rod lightning rod is installed, connected to the same rod on the opposite side of the ridge by a cable. That is, two methods were used to protect the house: cable and rod.
As for active lightning protection, today this is the most ideal option. Especially for roofs covered with non-metallic roofing materials. What is active lightning protection?
Video description
The video shows how an active lightning rod works:
On our website you can find contacts of construction companies that offer. You can communicate directly with representatives by visiting the “Low-Rise Country” exhibition of houses.
Active lightning protection
This is a proactive system. Purely structurally, this is an ordinary pin installed on the roof of a house, at the end of which is attached electronic device. It generates high-voltage pulses that propagate over a certain distance from the pin, forming a kind of pulse circle. Its diameter varies from 17 to 44 m.
So this pulse circle simply captures lightning and carries it along the down conductor to the grounding system. Surprisingly, there is no need to connect this device to an electrical power supply. During a thunderstorm, the electric field in the air rises to 20 kV/m. And this is enough to charge the device.
Let us add that active lightning protection is an economical system. After all, it only requires the installation of one pin, and not necessarily on the roof. By choosing a device with the maximum range, you can cover not only the house, but also nearby buildings with a pulsed field. The only drawback- high price. Although all this is compensated by the smaller amount of materials used and the aesthetic appearance. We add that the pulse device must be installed above the roof at least 2 m.
Video description
The video shows two systems that protect the gable roof of a house from lightning strikes: passive and active:
On our website you can find contacts of construction companies that own own production, which will pick up and . You can communicate directly with representatives by visiting the “Low-Rise Country” exhibition of houses.
Flat roof lightning protection
The optimal option for a lightning protection device for flat roof– mesh modification. Cell size in in this case selected taking into account the lightning protection category. Here are the ratios of the two indicators:
Regarding the technology for assembling a lightning protection system, there are certain rules. Here are some of them:
To fasten the elements of a mesh lightning rod, special brackets, made of plastic. They can be hollow or filled with concrete mortar.
Distance between fasteners – 1-1.2 m.
Today, concrete-filled brackets are being abandoned. They create point pressure on soft roofs flat roofs. They were replaced fasteners with self-adhesive tape from the reverse mounting side.
Please note that the installation of lightning protection on the roof is carried out in a passive way . That is, brackets of any type are not attached to the roof of the house. They hold the mesh structure only by their weight.
Along the perimeter lay the cable or wire rod along the parapet with fastening to the ends.
If there are pipes, antennas and other structural elements on the roof, then each of them must install a lightning rod in the form rod and connect it to the grid.
Conductor and grounding
So, we’ve sorted out the lightning rod located on roofs of different configurations and covered with different roofing materials. Let's move on to consider the question of how to install a down conductor and grounding.
Down conductor requirements
There are quite stringent requirements for the conductive section of lightning protection. After all, an electric discharge of enormous power passes through it. Here are some of the basic requirements:
the down conductor must be straight section, without turns, loops and other branches;
its length should be the shortest distance from the lightning rod to the grounding system;
optimal if connect the lightning rod to grounding several parallel down conductors;
distance between outlet elements depends on the perimeter roofs and categories lightning protection, average value– 20 m, but not less than 10 m;
The down conductor must be laid at a distance half a meter from window and door openings;
if the house is made of non-flammable materials, then outlet circuit can be laid right along the walls or lay down inside them;
if they were used flammable materials, then distance from walls to the site gaskets should not be less than 10 cm;
it is impossible to install a down conductor inside the drainage system.
Some building structures contain metal elements that can be used as a down conductor. But if their cross-section corresponds to standard indicators and are solid products along the entire length. For example, steel reinforcement that is part of a reinforced concrete product.
Video description
The video shows how the down conductor was installed on the façade of the temple:
Requirements for the grounding system
The purpose of the grounding loop is to drain electrical discharge into the ground. There are two options for organizing a grounding system:
Flat. This is when the contour is laid at a shallow depth in the form of a steel strip around the perimeter of the house. Down conductors are connected to it from different sides.
Deep. These are several pins driven into the ground to a depth of at least 2-3 m, tied together with steel tape 3 mm thick and 40-50 mm wide.
Can be used as pins steel reinforcement with a diameter of at least 18 mm, a pipe with a diameter of at least 32 mm with a wall thickness of 3.5 mm. The pins are usually driven in at the ends of an equilateral triangle. All connections are made by electric welding, soldering or using bolts. The joints must be covered with insulating materials.
Video description
The video shows how to properly and professionally install grounding for lightning protection:
Conclusion on the topic
So, we have dealt with lightning protection for roofing structures. Despite the apparent simplicity of the system itself, it is actually a complex structure in terms of correctly carried out calculations and design. To do this you will need to contact specialists. And the installation itself is not an easy process, and you can’t do it without qualified help.
Lightning protection for roofs made of soft materials allows you to protect buildings, especially wooden ones, from the effects of a thunderstorm. A lightning rod can be installed in several ways. At self-installation system, it is important to follow the recommendations given in instructions RD 34.21.122-87.
Roof part of lightning protection
A lightning strike into a building leads to fire and damage to property and poses a direct threat to human life. Roof lightning protection systems consist of:
- receiver;
- down conductor;
- ground electrode.
The lightning strike receiver is the device that comes into first contact with the current. Based on the characteristics of the building, it is possible to use natural sources of protection, however, in most cases the installation of special structures is required.
A down conductor is a wire that connects the receiver to the ground electrode. Installed on a building wall or drainpipe. Neutralization of lightning occurs in the ground. Approximately 50% of the total discharge is taken over by grounding, the rest of the voltage is distributed between the cable sheaths and water supply pipes.
The appearance and size of the device depends on the height of the building, the type of roof and the individual wishes of the customer, including aesthetic ones. In some cases, it is possible to combine several protection systems (active and passive).
The roof part usually consists of a lightning rod in various modifications. It can be a classic spire or mesh. For soft roofs, passive protection is usually used, however, each installation case is individual. When installing a lightning rod, all recommendations set out in the installation instructions must be followed. Otherwise, the system will be unreliable and will not cope with its task.
Active lightning protection on soft roofs
This type of device is a mast that is installed on the roof. The receiving head with the ion source actively attracts the high-voltage discharge. This design allows you to catch lightning without leaving it a chance.
A significant advantage of this system is that the soft roofing structure of the building is not damaged, while the level of protection is an order of magnitude higher than that of others. Installation of active protection is convenient, since a minimum number of movements on the roof is required. When working, take into account the following points:
- The number of lightning protection masts depends on the roof area, the area that needs to be protected from strike, and also on the type of roof (flat or pitched).
- The receiver rod is installed at the highest point of the building, and rises at least 2 meters in height.
Important! When installing lightning protection for a soft roof, you should think in advance about the system for attaching the spiers (to the chimney or water pipes).
Passive lightning protection on soft roofing
This type of lightning rod dissipates electrical discharge due to its special structure. Passive protection is used quite often, especially in low-rise residential buildings and industrial facilities. The lightning rod may look like this:
- Metal pin. The structure is installed on the edge of the roof ridge. A wire with a cross-section of 6 mm or more is lowered from it to the ground loop. The peculiarity of this protection is that its part located in the ground is located 30 cm below the soil freezing level.
- Cable. It is attached to the main lightning rod and extends across the entire roof. Grounding is arranged in any convenient way.
- Lightning protection mesh. Installed directly on the roof, on top of a soft covering or under it. This lightning protection on a flat roof is a mesh with a cross-section of 6 mm. For gable roof two structures are set up: first for one half, then for the other. Grounding cannot be done combined.
Note! When installing lightning protection under a roof, it is important that the insulation material is resistant to high temperatures. Recently, due to the risk of roof fire, this installation method has not been used.
The advantage of passive lightning protection is its ease of installation. In addition, qualified workers will be able to install any of the listed installations without harm to the flat roof covering.
Down conductor
This soft roof lightning protection element supplies an electrical discharge to the ground loop. The current conductor is made of thick wire (more than 6 mm), most often copper. This device, together with a lightning rod, is capable of extinguishing a voltage of 200 thousand amperes.
To reduce the likelihood of sparks, this lightning protection element is positioned so that the discharge is evenly distributed along two parallel paths, the length of which should be minimal. All connections in the structure are made by welding.
The down conductors are located as follows:
- both outside and inside (provided that the insulation material is non-flammable) of the facade;
- 0.1 mm or more from a flammable surface, if the facing material of the building is fire hazardous;
- away from door and window openings.
Important! When laying a down conductor, they try to create the shortest possible path to the grounding loop, avoiding loops and twists.
If wire connections cannot be avoided, their number should be kept to a minimum. The down conductors are attached as securely as possible to avoid the conductors breaking due to wind or other physical influences.
It is possible to use nearby structures or design features building as a down conductor, subject to the following parameters:
- metal carcass;
- interconnected steel reinforcement;
- the thickness of the elements is at least 0.5 mm;
- Half of the fastenings are made using welding or hard methods (bolts, tight twisting).
If reinforced concrete reinforcement or the building frame is planned to be used as down conductors, then laying horizontal chords may not be necessary.
Installation of the ground loop
Effective lightning protection is impossible without a structure that absorbs and neutralizes the electrical charge. The grounding must be located 5 meters from the entrance to the building and inaccessible to children and pets. The material from which this part of the lightning protection is made can be any, but stainless metals are preferred: copper, aluminum and brass. The circuit consists of several rods, the minimum value is 3–4 pieces per one- or two-story house.
The rods are connected to each other with an electrical conductor. In this way, a closed system is created that looks like the letter “W”.
On a note! The connection of the ground loop is made using welding or bolts. Under no circumstances should twisting be used. The structure is located at a distance of 1 meter from the walls of the house. To enhance the conductivity effect, it is recommended to periodically wet the ground in the grounding area with water.
Circuit testing
Before commissioning a lightning protection system on a soft roof, tests are carried out to identify possible violations and inconsistencies in the design regulatory requirements. The check includes several stages:
- Comparison of lightning protection of a building with the standards given in document RD 34.21.122-87. Check the correct choice of range and design.
- Inspection of lightning protection system elements for connection strength. Special attention pay attention to the quality of fastening and the absence of corrosion on the metal.
- Welding areas are checked using physical impact (hammer blows) for strength.
- Measuring resistance values on the ground loop. It should not exceed 10 ohms.
A three-pole test is used to measure the resistance of a lightning protection system. To perform this, the ground electrode is inserted into the socket of a special device. The current meter is dug into the ground at a distance of about 40 m from the lightning protection and connected to the measuring device. A metal potential probe is driven into the soil 20 m from the lightning protection system and is also connected to the device. All elements line up in a single line, switch to measuring installation is moved to position RE 3p. After this, by pressing the Start button, you can read the readings.
Important! According to SNIP, every year it is necessary to check the grounding conductors for a reduction in the thickness of the section and, if it decreases by half, carry out repair work.
Right installed system Lightning protection on a soft roof will help save property and people’s lives, so its installation must be carried out in compliance with all regulatory requirements.
Protection of cottages, garages and country houses from lightning discharges Our state is not yet involved. The owner takes care of the means of preventing the fire of private property from lightning. He independently chooses the type of protective system, most often constructing it with his own hands.
In arranging flat roofs, this is not a very tricky matter, although it requires detailed information about the basic technological principles. A home craftsman should thoroughly know how the lightning protection mesh on a flat roof is structured and what rules must be followed for the result to work flawlessly.
About the real facts of destruction residential buildings and commercial buildings as a result of lightning damage we rarely hear. True, this is not a reason to relax and neglect measures to protect against natural negativity.
Each impact poses a serious threat to homestead owners and their pets, even if specific impacts are not initially detected.
The following may be damaged by lightning strikes:
- People and animals. A discharge penetrating into a building through air communication wires can affect a living organism. It causes sparking at the connection points and connection points of devices powered by electricity. If the home does not have a grounding system or grounded metal piping, currents can pass through the body. The consequences are extremely dangerous.
- Residential and commercial buildings. Especially buildings whose walls are made of flammable material - wood. For concrete and brick houses Lightning current discharges are also highly undesirable. From the point of impact to a grounded object or ground, a high pressure along with the temperature. This area is susceptible to internal damage. There are known cases when brick and wooden walls, which had previously withstood several thunderstorms, were split when struck by lightning.
- Private garages and small fuel depots. A lightning discharge is accompanied by a sharp increase in the temperature of a kind of branched or linear channel through which currents flow. Contact of the channel with flammable products will definitely lead to ignition and fire.
Lightning currents do not threaten metal conductors with a cross-section of 35 mm² or more. They are not dangerous for metal structures, the parts of which are reliably connected to each other by a metal bond and the lower elements are grounded.
For example, a metal sheathing is connected by welding to reinforcement reinforced concrete walls, and it in turn is connected with the foundation reinforcement. The roof elements receive the discharge, distribute it and forward it to the reinforcing bars of the walls. The currents are then transferred to the foundation reinforcement, which releases them into the ground with relief.
In addition to foundation reinforcement, the transmission of lightning discharges to the ground can be carried out by structures laid in the ground. metal pipelines and cables in metal sleeves.
Lightning protection device
We found out that to protect buildings from lightning strikes, it is necessary to build a system. It is called a lightning rod and includes three parts of equal importance:
- Lightning rod– a device that directly receives a lightning strike.
- Down conductor– a system of metal linear parts that receive currents from the lightning rod and transmit them to grounding. The elements of the down conductor can be the already mentioned reinforcement bars, metal drain pipes, etc.
- Ground electrode– linear or closed metal outline. It consists of vertical pins driven into the ground, connected by a rod or strip. The ground electrode is buried at least 0.5 m. The length of the pins and the distance between them are determined by calculation methods.
A lightning rod of any architectural type must include all three listed parts, otherwise there will be no point in designing the system. The differences lie in the type of components depending on the roof and building configuration.
For example, pitched roofs are protected from lightning by installing rod receivers. Lightning rods with cable receivers are installed above elongated houses. The use of these varieties somewhat spoils the architectural ensemble, but in the end it turns out to be the most economical.
Features of lightning rods for flat roofs
Lightning protection for houses and outbuildings with a flat roof is carried out according to a standard, practice-tested scheme:
- The lightning rod is made in the form of a mesh made of horizontally laid round steel Ø 6-8mm. Instead of wire rod, a steel strip with a cross section of 4×20mm can be used. Lightning rod as branches
- The current conductor consists of metal conductors made of round steel with a diameter of at least 6 mm connected to grounding. the underground part is made of rolled steel Ø 10mm. Pipes and fittings can serve as current drainage elements on flat roofs, if their use as a current drain was taken into account when designing the structure. The recommended distance between down conductors is 25 m.
- The grounding system is closed loop, covering the perimeter of the protected object. The distance between the ground loop and the wall of a house with a flat roof is no more than 1 m.
The lightning rod of a flat roof can be a metal roof connected to metal lathing or directly with down conductors using a metal connection. For such schemes only suitable metal roofs, connected by folds. In such cases, there is no reason to install a protective mesh, but this is a completely different, “integumentary” story.
Profiled sheets with protective coating and excluded from possible options due to the lack of connections sufficient for the passage of currents, as well as due to the polymer shell affecting the properties of the material.
The installation of a mesh lightning rod can be carried out during the construction process or a protective system can be installed after laying the covering.
Option No. 1 is possible if non-flammable insulation, waterproofing and coating are used. The mesh is placed under the waterproof layer. The implementation scheme for a lightning rod of this type is developed at the design stage.
Option No. 2 is used without restrictions. Its design has virtually no effect on appearance Houses. The mesh is laid on top of the coating and fixed in holders specially designed for it. In the case of constructing lightning protection for a soft roof, the holders provide a distance gap of 10-12 cm between the flammable material and the lightning rod conductor.
The first scheme predetermines the installation of a protective mesh over the floor slabs before laying the roof. To connect the branches of the mesh with the reinforcement of walls or columns, connecting devices are installed in the seams between the roof slabs, to which the mesh is welded on one side and the reinforcement on the other. In the construction of a lightning rod system of this type, only welding is used.
The second scheme involves installing receiver elements on top of the roof. She also needs a basic design to provide for the possibility of cleaning winter precipitation and the unimpeded flow of rainwater. Metal elements systems must be protected from corrosion.
It is recommended to install lightning rods with mesh receivers on roofs with a slope of 4º to the internal or external drainage. Often, mesh systems are combined with rod counterparts, which are mounted in the corners of the building and at the intersection of conductors.
Rules for the construction of lightning protection mesh
We admit that most home craftsmen will probably have problems implementing the first option. After all, reliable welded joints must flawlessly connect the mesh with the reinforcement of the walls and foundation.
Quite high demands are placed on their quality and timeliness. Let's look at the rules for constructing the second option of lightning protection on a flat roof, which we can handle with our own hands.
General rules for installing lightning protection mesh:
- The lightning rod branches are laid perpendicularly, forming cells with equal sides.
- In accordance with the IEC (International Electrotechnical Commission) regulations, the pitch between the mesh branches is above residential buildings should not exceed 12m, above garages with fuel storage up to 5m. Domestic requirements are somewhat softer: 15m and 7m. However, it is advisable to adhere to international standards.
- All devices that rise above the level must be equipped with additional rod receivers. These are pipes and antenna masts that should be connected to the general network.
- Welded connections are given priority, but bolted analogues are also allowed. Especially if universal die clamps are used for their installation, which significantly facilitate installation procedures.
- It is recommended to connect the branches of the mesh receiver to the down conductor on each side.
More stringent IEC regulations dictate that each grid cross connection be equipped with rod receivers. The height of the rod requires 25 cm. Down conductors are required to be grounded with two grounding rods and detachable ram contacts are installed on them for testing operations. There is no doubt that it is time to get used to international norms, but our financial capabilities often come into conflict with them.
Domestic standards numbered RD34.21.122-87 do not make such draconian claims, and systems built in accordance with them have not yet failed. It is possible that our lightning rod, which is not too sophisticated, works well for us due to the moderate lightning load. It is still better for residents of the southern regions of the country to focus on international standards.
Let us remember that in the range of coverings for a flat roof there are flammable and non-flammable materials. Let's classify them according to combustible characteristics and analyze the most common schemes.
Lightning protection mesh on a fireproof base
The category of fireproof bases includes concrete screed, galvanized roofing, sandwich panels and gravel backfill used as ballast in inversion roofing systems.
Depending on the type of fireproof base, the installation scheme for the lightning protection mesh is selected:
- For profiled sheets, which does not have a polymer coating, installation is carried out across the direction of the corrugation. The metal rod is laid with a planned step and welded to the surface of the corrugated sheeting wave every meter. An excellent alternative to welding are metal bolt holders, which allow installation of a mesh receiver of any degree of complexity.
- On concrete roofs According to the design data, plastic holders with concrete filling - weighting material - are installed. Filling weight from 12 to 17 kg depending on the brand of product. The impressive weight of the products guarantees the stability of the system and resistance to gusty winds. There are holders on sale without weight filling, for installation of which a load of frost-resistant concrete is poured independently on site. For low-rise buildings in regions with low wind activity, holders are produced with fastening with self-tapping screws or gluing to bitumen mastic.
- On gravel backfill for ballasted roofs, holders are installed with and without concrete ballast. If you want to fix the holders to the base, they are mounted before adding ballast. In such cases, it is recommended to use spacer models glued to the base using mastic.
The maximum installation step of holders should not exceed 1 m for all listed schemes.
It is not recommended to install a lightning rod with a mesh conductor on metal roofs made of material thinner than 4 mm. A direct blow to the coating can easily burn through it.
Therefore, it is customary to equip roofs made of thin corrugated sheets with mesh on remote holders, the protection zone of which is still larger than that of devices in contact with the roof.
Mesh receiver on a combustible base
We will include among them roofing coverings low-flammable category and materials that support combustion, because unquestionably flammable materials are not used in construction. The list of flat roof coatings that are hazardous according to combustion criteria includes bitumen and bitumen-polymer waterproofing materials and – i.e. soft roofs.
In order to prevent direct contact of the lightning discharge receiver with the bitumen and polymer coating, so-called distance holders are used. The essence of the design of simple devices is that an air gap is created between the roof surface and the mesh branch, sufficient to attenuate a possible spark.
According to the requirements of SO 153 3.2.2.4. this distance should be at least 10cm. IEC requirements indicate the need to use insulation coefficients of materials indicated by the letters km in calculations.
Insulation gaps are created using vertical rods included in the spacer holder kit. They are fixed in a plastic stand on which a concrete weighting agent is placed. The task of fastening the wire is solved by the bushing that completes the fastening device.
Algorithm for installing an air-termination mesh with remote holders on a soft roof:
- We mark out the work site according to the developed project. The holders are installed every 1 m along the lines corresponding to the grid cells. The maximum distance between devices is 1.2 m, the possibility of increasing is specified in the manufacturer’s instructions. Design development must take into account that the areas for connecting branches to down conductors and down conductors to grounding should be minimal. Do not forget that the function of a branch can be performed by a metal parapet shield and similar long metal parts.
- Rods made of fiberglass are cut or chopped to a pre-calculated amount required to form an air insulating gap.
- We install according to the markings plastic stands, the center of which must coincide with the marked point. In the case of a polymer membrane roof, we place a rubber gasket under each stand so that heavy parts do not damage the coating.
- We place concrete weights on the supports.
- We freely place the cut rods in the channels located in the center of the stands.
- The tops of the rods are equipped with fastening devices with bushings designed to fix wires up to Ø 8 mm.
- We lay the branches of the lightning protection mesh, simply snapping them into the bushings of the holders.
Pipes and antenna masts protruding above the surface must have an electrical connection with the lightning rod. They are equipped with rod receivers or metal aprons and connected to down conductors with die clamps. Similarly, the edges of the branches are joined to the down conductors, which is much more convenient than welding. In addition, an inexperienced performer will be able to create high-quality units with their help at a high pace.
Connection of down conductors with grid branches
Assembling a mesh discharge receiver is only the first stage of a lightning protection device and a full-fledged grounding system. It must be properly connected to the grounding circuit so that the received currents flow into the ground without obstacles.
Rules for laying and connecting down conductors:
- Down conductor routes must be designed taking into account the shortest distance between the connection points to the lightning rod and grounding.
- Down conductors are attached to flammable walls using spacer brackets. The distance between the wall and the conductor is at least 10cm. Contact between the metal bracket and the wall material is allowed.
- Down conductors can be fixed to drain pipes with metal clamps.
- It is allowed to lay down conductors made of galvanized round steel directly on a brick or concrete wall.
- The distance between the fastening points for horizontal sections is 1 m, for vertical sections is 2 m.
- Laying to form loops is not allowed.
- When choosing a location for laying a down conductor, it is recommended to select areas of the building with the least likelihood of people being present.
It is customary to lay down conductor routes in the corners of houses being developed. The maximum distance between them is 25m. The lower edge of each down conductor is lowered into the ground, where it is attached to the grounding system using a bolt device. It is recommended to wrap the areas where the conductor enters the soil with anti-corrosion tape.
Video instructions for home craftsmen
The video will introduce you to the general principle of installing a lightning rod for a private home:
The technology of constructing a lightning protection mesh for a private home protection system can be mastered without having fundamental knowledge in the field of electrical safety. The installation devices currently available for sale will help carry out the work in a short time and without much hassle. The main thing is not to forget about the rules of the device so that the property protection system is complete.
