Fall arrest systems: basic aspects fundamental for installation
Fall arrest systems on building roofs only made their first appearance in 2003, with the Lombardy Region leading the way in this sector. Installation is mandatory on the roofs of new buildings and in those subject to extraordinary maintenance.
Today, for fall arrest systems we have various UNI standards such as: UNI EN 795, UNI11578:2015 and UNI 11560:2022 to be respected for correct design and installation. But basically, the designer and the installer must always carry out one in-depth study on the morphology and configuration of the roofs existing ones underestimated in the budgeting and sometimes even execution phase, if these works are carried out outside the cases in which the obligation applies, they generally are without either planning or construction management.
Many are increasingly installing these systems even outside of the previous cases, to ensure that the various maintenance workers access the roof and carry out their functions safely.
Case study and analysis of the pathological picture
The case study deals with ainstallation of class A devices, in this specific case, under-tile retaining cords have been installed. The operation took place without any maintenance or reconstruction of the covering, so the installing company worked locally on the covering, removing part of the insulation until reaching the sheet on which to fix the hook, and then proceeding with the relative sealing and restoration.
There diagnosis she concentrated on the aquifer where they were greater infiltration phenomena.
The roof structure was found to be in wood (beams, joists and boarding with closed joints) and has a package consisting of a vapor barrier/waterproof sheet, an insulating panel covered with aluminum foil, with matching tile-bearing sheet metal beams. It has a slope of 21%, while the roof covering has areas with different slopes divided as follows: near the eaves it is 15%, in the area near the ridge it is 13.7% and in the ridge it is found that the last row of tiles has a slope of 12.1%, it therefore immediately appears clear that everything above the structure it is not compatible with the construction slopes.
Semiotic, thermographic investigation and use of tracer liquids
L'semiotic (visual) investigation found that the pathological manifestations with dripping phenomena they mostly occur from different points near the ridge and only in very specific areas along the aquifer. There are no visible signs or residues on the wooden structure and this indicates that the dripping phenomenon occurs canalization and not by filtration therefore it has a short latency time.
Since the end of the installation, the condominium has complained about problems relating, in particular, to the appearance of drips on the intrados of the roof slab in conjunction with atmospheric events.
L'thermographic investigation it is qualitative and was carried out both before the release test of the tracer liquids, where it did not detect ongoing evaporative phenomena, therefore excluding the presence of active infiltrative phenomena, thus allowing an overall evaluation of the physiological picture.
The second, that of monitoring, occurred during the execution of the tests with the tracer liquids and allowed us to have a comparison with the two states and to identify, at the same time, the areas of water entry. The water began to appear in the attic several minutes after the sprinkling, this shows that there is no direct channeling between the entry and exit points.
Localized investigation insights
Running minimally invasive investigationsin order to evaluate some technical details due to its conformation, it emerged that:
- from the movement of the tiles was found a return of water in the overlapping area of the tiles through the phenomenon of the surface tension of the water;
- the hooks protrude from the roof insulationby creating a pocket in the monolithic insulation, subsequently restored with the relevant tapes and seals. The sealing is not tight around the cord, being a mobile element;
- at the base of the hook, the fastening is already torn on the screw, therefore the failure to seal of the cloth at the point where it was torn and the presence of water under the cloth;
- there heap tapingplaced to close the insulating panels, it appears torn. Once the aluminum tape placed on top of the insulating panels has been removed, you can find the presence of drops of water on the end part of the metal batten of the insulating panel and the presence of oxidation phenomena along the entire bar;
- in the area where hooks are not installedin geometric correspondence with the infiltration between the joists, it is found that in that area the stringers at the base have oxidation phenomenaon the underside of the insulation and on the sheet layer there are rust residues;
- again in the area referred to in the previous point, after having made a cut in a random point in the investigation area, it was found that theboarded era completely wet;
- they met infiltrative signs in the areas close to the fixing nail of the insulating panel.
Conclusions
When installing fall arrest systems on roofs, where no renovation or arrangement work is carried out, it is important do not underestimate the morphology of the structure because it provides a information framework in choosing both the most suitable component and the installation method to follow.
As in this case, the roof entrusts its waterproof seal to the sheet placed over the flooring, as all the materials that make up the roofing package, due to the small slope, they are not able to guarantee their waterproof characteristics.
The small installation errors and the choice of a cord hook compared to another with different characteristics, led to the onset of infiltrations, where in situations of roofs with this configuration, but with slopes greater than 30% with high probability they would not have manifested themselves.
Article by Geom. Federico Busi
