- Purpose and principle of operation
- Heating cable selection
- Electrical equipment
- Roof heating installation
- Anti-icing of the drainage system
We offer you a number of technical solutions for roof heating, which will help to combat icing of the roof and gutters. Ice and icicles can form on almost any roof. This is due to natural design flaws and is fraught with various consequences: from leaks to damage to the drainage system.
Purpose and principle of operation
Even in a well-designed roof, thermal protection is not absolute. As the snow cover accumulates, heat leakage into the atmosphere decreases, the temperature of the roofing rises, which is why it gradually melts. Flowing down, the water reaches the bottom of the slope, where it finally freezes, forming an ice bank. Above this shaft, new portions of water are collected, the risk of leaks increases, and the snow cap continues to accumulate, increasing the load on the supporting system. At the first thaw, the entire accumulated mass of snow and ice comes off the roof like an avalanche, damaging the drainage system and posing a threat to people and property..
Roof heating is an active anti-icing measure, the main task of which is to melt the resulting ice and facilitate the smooth removal of melt water. Depending on the roof structure, the specifics of the operation of the snow melting system may differ. Conventionally, roofs are classified according to the numerical value of heat losses:
- Roofs over cold attics or unheated rooms are called cold roofs. The snow cap on them melts only on a sunny day near the bare areas of the roof; ice practically does not form. Heating of such roofs is required in cases where the amount of precipitation is high, and an independent fall of the cover is impossible due to the small slope. Basically, cold roofs do not heat.
- Roofs over warm attics or mansards with good insulation are called moderately warm. This is the most difficult case: snow melting occurs with low intensity, due to which the thickness of the ice layer is slowly but steadily growing. The task of the snow melting system is to speed up the melting of snow, while the system operates in a semi-automatic mode with infrequent but rather long intervals.
- Roofs with poor insulation are conventionally considered warm, the snow melting on them is very active. As a rule, the formation of ice is recorded in the lower part of the slopes and gutters, therefore, heating elements are placed only in these areas. Their power is quite high, the system works in a repeated-short-term mode..
Heating cable selection
Two types of two-core heating cables are used for roof heating. The first option is a heating section of fixed length and power, this is the most convenient way to heat gutters and pipes. There are also self-regulating cables consisting of two parallel conductive cores, the space between which is filled with a weak dielectric, the resistance of which increases abruptly when heated to a certain temperature. Thanks to this, the self-regulating cable can be connected in segments of any length, only the maximum line length is limited.
Both types of cable have a rather complex structure. Heating conductors or steam are wrapped in a heat-resistant sheath with good dielectric properties. A shielding braid is wound over the shell – a protective measure in case of damage to the main electrical insulation. The cable is also covered with outer insulation, which protects against both breakdown and mechanical damage. The self-regulating cable also has an additional layer under the outer sheath that eliminates the friction of the flat heating core against the outer insulation to maintain its shape.
All heating cables are divided according to specific power, which can be 15-50 W / m. Cables up to 20 W / m.p. used on warm roofs, up to 30 W / m. – in cold areas of moderately warm roofs, up to 50 W / m. – for heating the drainage system.
Since the electric heating system is operated in rather harsh conditions, and safety measures are much stricter than when heating open areas, the system requires the use of a number of electrical products and protective devices..
Electrical connections require the most attention. In high humidity and ultraviolet conditions, standard heating cable connectors do not perform well. Therefore, they are used only for connecting heating cables to each other or in conditions where the installation of a secure connection is impossible. In other situations, the connection of the heating cable to the power cable is carried out inside the junction box with the degree of protection IP66 through screw terminals. The box is placed below under the eaves of the roof, which somewhat increases the consumption of the heating cable, but is guaranteed to protect the vulnerable spot.
The worst that can happen to a heating system is insulation breakdown and a short circuit between the conductors or to the metal roofing. Therefore, the circuit breaker for protecting the line is selected in exact accordance with its power and the effective supply voltage. It is required to select the machine closest to the nominal, and then adjust the thermal splitter according to the instructions. The second stage of protection is a fire class RCD designed for leakage currents of 200–400 mA. For its correct operation, the shielding braids of all heating cables must be reliably grounded..
The self-regulating cable is used in systems with manual activation and does not require the installation of a thermostat. An exception is heating systems for roofs of houses that are not designed for permanent residence, or if the goal is to make the heating work completely autonomous. In such cases, the thermostat turns off the heating when a positive air temperature is reached, and the automation can also use the readings of the humidity sensor to determine the presence of precipitation. For heating sections, the installation of a thermostat is mandatory, the cut-off temperature is selected in the range of +3 … + 10 ° C, depending on climatic conditions. In this case, the temperature sensor is not located in the open air, but is rigidly fixed 20-25 mm from the heating element.
Roof heating installation
The arrangement of cables on cold and warm roofs is different. In the first case, the heating elements are lifted in parallel lines along the entire length of the slope with a step of 30-40 cm. Such a heating system is used only on flat roofs with a slope of less than 10 °, where the snow cap is not possible to fall off on its own.
In all other cases, only the lower cold edge is heated, where ice accumulates. For warm roofs, the width of the heating strip is equal to the projection of the coating beyond the outer plane of the wall. On moderately warm roofs, heating is arranged on the width of the eaves and walls plus 10–15 cm. The cable is laid with a triangular snake with a distance between the tops from 25 to 100 cm, depending on the density of the heating elements. It is determined by the required specific power of the heated area, which for moderately warm roofs is 250-300 W / m2, and for warm ones – about 400 W / m2. Depending on climatic conditions, the manufacturer may provide additional recommendations for adjusting the power.
Fastening the cable to the roof with a snake pitch of more than 50 cm is carried out with point clamps, which are attached to the coating with self-tapping screws or rivets. Before fastening, a special seal is placed between the retainer and the roof. With a fairly frequent step of the snake, it is better to mount it on a perforated mounting tape. It is attached with two parallel lines at the bottom of the slope and with the required indent from the edge, after which the cable is pressed by bending the cut petals. This method is especially often used on steep slopes, where there is a high likelihood of a snow cap coming off: the cable will not be damaged, the mounts will simply be unbent.
Particular attention should be paid to wind eaves and valleys. At each overhang, the cable should rise from the bottom by 2/3 of the slope height. An excessive amount of ice forms in the valleys and gutters, so the specific heating power should be increased by 1.5 times. As a rule, this is achieved by laying two or three parallel heating cable lines on both sides of the valley with a pitch of 10-12 cm.
Anti-icing of the drainage system
With an existing roof heating system, it is imperative to lay heating cables also in gutters and drain pipes. Without this, the melted water will not be able to drain freely, will freeze and, most likely, damage the drainage system..
As a rule, two cables with a specific power of more than 25 W / lm are sufficient for gutters. One of them is laid along the outer side, the other along the bottom of the gutter. Fixation is carried out on special brackets, which are fixed inside the tray with a step of 20-30 cm. If during operation water freezes in the drain, you can add another heating cable.
Pipes are the most vulnerable part of the drainage system, due to entanglement of the cable, plugs can form inside them, and the entire system will become unusable. Therefore, usually for pipes, cables with a capacity of up to 50 W / m are chosen. with a high operating temperature. They are mounted in a taut state: the heating cable of the trough is lowered to the very bottom, fixed at the bottom with a double bend to prevent freezing of the outlet socket, and then pulled back up. Particular attention should be paid to the receiving funnels: in them the heating elements are laid with one or two rings around the perimeter.