The importance of the fixations in apparent waterproofing systems

The roof of buildings is the element most exposed to the weather. The actions of the wind can bring irreparable damage to the waterproofing systems, and it is essential to develop a project with the calculation of the quantity and distribution of the fixations, when it is not foreseen the placement of a finishing and heavy protection on the waterproofing system.


Learn more about the different mechanical fixation systems and their features in the article below.



Important components before making decisions

The constructive solutions for roofs of limited accessibility of buildings, without heavy protection (as is the example of the rolled pebble or pebble), are formed by the support, separating blades such as steam barriers and geotextiles, thermal insulation, waterproofing membranes and mechanical fixings.

The type of support used in the rooftops, which serves as the basis for the other components of the system, will determine the choice of fixations to be applied, as it will be the support that will ensure a consistent foundation for anchoring these fixations. There are three types of supports: concrete, wood and profiled steel plate.


Additionally, we can choose different types of isolation that can be rigid or compressible, which will determine, once again, the type of fixation and the most appropriate length.


There are also different types of waterproofing membranes whose resistance per fixing point, once the coefficients and safety factors are applied, may vary among themselves. Therefore, you can opt for thermoplastic waterproofing membranes, applied in a single layer or bituminous membranes, applied in a bi-layer, with self-protection mineral in the surface layer of the exposed face.


Before determining the fixing system it is essential to carry out membrane tests to calculate wind resistance and thereby define the density of the fixations to be applied and their arrangement, in order to compensate for wind suction and avoid problems in the roofs. Otherwise, vulnerabilities resulting from the action of the wind, such as membrane rupture and therefore leakage, may be recorded.

The most drastic consequence would be the total destruction of the system resulting in the isolation and waterproofing materials “flying” from the roof.

For the various solutions mentioned a fixing system that complies with European regulations must be chosen.



Prudêncio’s Work – Rehabilitation of the roof, Pingo Doce Aveiro


Types of mechanical fixation systems

There are two types of mechanical fixation to be taken into account, depending on the determination of the other elements that compose the cover:


1. Traditional system of fixation (by superposition)

This system can be realized in two ways:


1.1 Screw system, double thread and metal plate

In this case, the screw must be equipped with an adequate corrosion resistance of at least 15 kesternich cycles according to European standards and have a double retention thread preventing it from rising under the feet.


However, in a long-term it is necessary to be aware that the circulation of people in the roof may cause ruptures in the membranes in the areas of the metal plates or damage in the double screw thread, no longer guaranteeing the protection to the perforation of the membranes that it ensures.


1.2 Plastic cannula and screw

It consists on the natural evolution of the previous system, producing a thermal rupture, therefore benefiting the thermal efficiency of the system and allowing a safer circulation. This solution addresses the challenges imposed by the previous proposal since it presents better fixation points, when the coefficients and safety factors are applied. In this sense, despite the circulation of people, the cannula follows this movement of compression of the isolation being, at times, a better option compared to the metal plate and screw.


This system also presents a versatility of combinations for different isolation thicknesses with different cannulas, but with the same screw or the contrariwise.


2. Induction system

Compared to the traditional fixation system, the induction system has multiple advantages by allowing greater resistance per fixation point on any type of support and with different types of screws, coupled with the fact that they all guarantee anti-corrosion protections above 15 kesternich cycles.

Additionally, this system allows a better tension distribution in the waterproofing membranes and brings more versatility and speed to the application of the total solution. As it has greater resistance it is necessary a smaller number of fixations and the waterproofing membrane is never perforated at any point by this fixing system.




Difference of tension distribution in membranes between traditional fixing systems and induction system


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