Customers often ask us why the mast mounting system is sometimes more expensive than the lattice itself. They are skeptical to learn that a standard eye nut is not suitable as a guy wire anchor, and that a chimney or fire wall are the last places where you should anchor ropes. Let’s take a look at the forces that a mast exerts on a building’s structure.
Tension cables operate under tensile force—the greater the surface area of the antennas on the mast and the greater the wind exposure of the structure itself, the stronger the force. These forces, combined with the initial tension of the cables, act on the mast shaft, pressing it against the roof surface. Below are a few examples taken from structural calculations performed for our clients:
| Mast type | Height | The force that pulls out the anchor | The force driving the mast into the roof |
| M500 | 16 m | 480 kg | 1100 kg |
| M1000 | 24 m | 1300 kg | 2900 kg |
| M1000 | 28 m | 3700 kg | 4000 kg |
| M500 | 50 m | 3800 kg | 4500 kg |
| M750 | 28 m | 2000 kg | 3500 kg |
Several important conclusions can be drawn from the figures cited:
- Even for a small and generally standard mast, often installed on old buildings, i.e. M500-16 - the anchor pulling force reaches 500 kg... a standard M12 cast eye nut can transfer a maximum of 340 kg of force, but only in the axis, which is the case when the masts are anchored in basically does not occur. The load at an angle of 45 degrees drops to 240 kg. So we see that we do not have any strength reserve, but rather the risk of tearing off the ear in a more serious storm. Another question - can half a ton of load overturn a chimney - often consisting of a pile of damp and eroded bricks with crumbling mortar? Our experience shows that this can happen easily.
- Is it safe to place M500-16, e.g. on a non-supported rafter, or directly on a sandwich panel on the roof of the hall, in a random place, if we realize that our mast will introduce a point load of over a ton in the place of its location? We have seen such cases and we have seen masts that "fell inside".
- The example of the above-mentioned M1000 masts shows how quickly the forces increase with the height and windage of the structure, and how they are differentiated by the additional load from the antennas (the 28-meter one was designed for 1 m2 of antenna area more than the 24-meter one). The difference in tearing... almost three times. Moreover, the values themselves are impressive... nearly 4 (!) tons of pulling power. Let's imagine that we plan to hang two off-road vehicles on the planned anchor - this gives an idea of the scale of forces.
- You can see why we almost never ask about the number of antennas you plan to install on the mast, but we often pester you about their surface area. Considering the vertical force in the mast shaft is counted in tons, several dozen additional kilograms in the mass of the antennas are practically irrelevant, but the additional surface quickly increases the forces, and these differences are counted in tons and not in single kilograms.
These figures give us pause for thought—it’s clear why we choose the location for the mast on a building so carefully and why it can’t be just any point on the roof. The forces we’re talking about can easily tear through thin screeds on flat roofs, break floor beams that are several decades old, or shatter firewalls. It is not uncommon for adapting a building to withstand the planned loads to require the installation of steel anchoring structures spanning several stories, the use of chemical anchors, and major construction work. In other cases—when dealing with a poured slab, a roof point supported by a load-bearing wall, and good access to the ring beam—even a large mast can be installed with a moderate amount of work. This variety of situations results in a wide range of prices for anchoring preparation, and without an on-site inspection or a design, we are unable to estimate how much the installation will cost.