Designing ventilated façades in accordance with standards | by Thomas Foschini
Article published in: "Exterior façades: standards and environment"
From a regulatory standpoint, most of the requirements that must be followed when designing an effective, safe and long-lasting anchoring system are set out in the standard UNI EN 11018:2003 “Claddings and anchoring systems for mechanically assembled ventilated façades. Instructions for design, installation and maintenance”.
The standard partly harmonises a number of existing requirements while adding others. More generally, it provides detailed information on the most effective technical and assembly solutions based on real-world experience stemming from the growing demand for these kinds of solutions.
The part of the standard relevant to anchoring systems for ventilated façades is the section on “dry” installation systems (in other words systems in which the ceramic cladding is entirely detached from the underlying substrate) using metal anchors.
There are essentially three parameters that must be taken into account in the choice of type of anchoring system (or rather the choice of the number, type and size of the supports): weight and size of the cladding panels; the specific wind loads they will be exposed to; and the type of wall the panels need to be anchored to (a non-trivial consideration when applying cladding to existing buildings).
The first step in deciding on an anchoring system involves the collection and processing of data and information regarding the type of cladding and the location of the building (seismic criteria, specific wind loads and other considerations such as proximity to high-traffic areas such as pedestrian walkways, etc.).
Another set of considerations concerns the type of building structure. Given the growing importance of renovation within today’s architectural practice, it is no surprise that many companies in the sector (or more frequently specialist partners who work on behalf of major brands) focus on the definition of “secure coupling” solutions even on weak walls such as hollow bricks, mixed surfaces, etc.
It is worth bearing in mind that although UNI 11018 is devoted essentially to new buildings, it is nonetheless applicable to renovations provided the type of building structure can be determined with certainty.
Coupling systems: selection criteria
While UNI 11018 largely limits itself to harmonising the already fairly extensive regulations covering the composition and sizing of the metallic components of anchoring systems (bolts, dowels, etc.), the standard focuses in particular on the selection criteria for the anchoring system and useful design rules (starting from the fairly obvious consideration that each panel must be anchored to the support at at least four points). A separate chapter is reserved for the so-called “thermo-hygrometric design”, given the need to keep the ventilated façade cavity as dry as possible by ensuring proper air circulation.
From design to installation
Although readers should refer to the text of the standard for a full discussion of the subject, it is worth looking at a few key aspects that must be taken into consideration during the design stage to avoid unpleasant surprises on-site (and while keeping safety requirements in mind). For example, special attention must be given to the issue of permitted installation tolerances during assembly. Failure to ensure perfect correspondence between the design specifications (levels, dimensions, distances, etc.) and the actual situation on-site may have serious consequences in terms of the end result, such as non-aligned joints, difficulty in assembling ready-prepared panels (prompting manufacturers to include pre-assembled modular versions in their ranges) and even actual safety issues in the event of incorrect coupling of the panels to the module and of the module to the wall of the building.
For this reason, while effective collaboration between the designer and the installer is important in all fields of application, it is absolutely crucial when installing ventilated façades in order to achieve a satisfactory result in terms of both safety and aesthetics.
Efficacy, durability and scheduled maintenance
A second set of very important aspects concerns effective design of the base of the ventilated façade and the top closure system. Failure to design the base of the façade correctly may allow the ingress of insects, grit and other undesirable materials. As for the top closure, good design and meticulous installation of the top section of the cladding protects the entire wall from infiltration of water, promotes proper air circulation, etc. These are all aspects that have a profound impact on the durability, efficiency and aesthetic quality of the wall over time.
For this reason, following a specific chapter devoted to design and installation of the insulating layer, the standard UNI 11018 focuses on the specific issues of maintenance, setting out the potential causes of deterioration of the wall over time and providing instructions for the drafting of a detail scheduled maintenance programme right from the design stage.
For example, the choice of anchoring system and the design of a ventilated façade in general must take into account the most frequently-occurring issue, namely the need to replace one or more panels over time.
For this reason, all companies in the sector recommend installing a fibreglass mesh behind the cladding to prevent pieces of panel from falling off and to facilitate replacement in the event of accidental breakage (a requirement that must be considered mandatory if the building is close to crowded areas, pedestrian walkways, etc.). The companies themselves explain more or less clearly in the description of their product range the type of operation necessary for replacing the panels or modules (for a given anchoring system and preparation of the panels in the case of concealed anchors).
Finally, we should mention the relatively large corpus of ancillary standards that must be taken into consideration when designing the system. These include standards governing the performance requirements of buildings and claddings (UNI EN 832:2001 and UNI EN 8012:1979), the latest standards on “air permeability” (UNI EN 12152:2003 and the related test method UNI 12153) and “wind load resistance” (UNI EN 13116:2002 and UNI 12179). Further standards concern the “thermal requirements of building components” (UNI EN ISO 13786:2001) and the “product standard” for curtain walls (UNI EN 13830:2005).
Alongside the UNI standards, which are accessible on subscription on the website http://www.uni.com/ but are sometimes made available free of charge or at concessionary rates to architects and engineers by their respective professional associations, the designer’s work handbook must also contain a chapter devoted to Decree Law DL of 19 August 2005 no. 192 (as amended and supplemented by the subsequent DL 311 of 29 December 2006), “Enactment of Directive 22/91/CE regarding the energy performance of buildings”, given that the main function of a ventilated façade is to improve the building’s energy efficiency thanks to the air circulation that occurs in the cavity.
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