Requirements, tests, admission conditions

 

Ventilated facades with the use of cladding elements

Requirements, tests, conditions of admission, acceptance.

Participants in the construction process are increasingly turning to the Department of Construction Structures and Elements of the Institute of Building Technology to provide an opinion on the design or acceptance of a ventilated facade.

During the evaluation of the design or acceptance of a ventilated facade it is necessary analyze the calculation part of the project and the technical documentation of the product (facade).

In the calculation part, designers most often make mistakes related to neglecting or not knowing the issues of climatic loads:

•  they perform calculations according to the PN-B-02011:1977 [1] standard withdrawn from the PKN collections (sometimes they insert coefficients from the applicable PN-EN 1991-1-4:2008 [2] standard into the formulas of this standard);

•  they do not take into account the conditions of development in the vicinity of the investment.

The second significant problem is designing the facade casing at inappropriate heights, which puts the life and health of users or passers-by at risk. The greatest problems in assessing ventilated facade designs are related to the technical documentation of the product. Sometimes, after analyzing this documentation, the client is in for an unpleasant surprise – the facade does not have documents confirming its approval for use in construction, even though the individual components (casing, thermal insulation or grid) have approval documents (declarations of compliance with standards, technical approvals).

A ventilated facade should be considered as a whole. Even if individual elements of the façade have approvals for use in construction, it does not mean that the product (façade) will meet the safety and durability requirements. The reason is the incompatibility of individual elements (e.g. different thermal expansion coefficients of the cladding elements and the grid, corrosion of materials when in contact with each other). In order to be approved for use in construction, a ventilated façade should have a technical approval. Technical approvals for this type of products are issued on the basis of ETAG 034 [3].
 

Classification and general requirements according to ETAG 034

According to ETAG 034, a ventilated facade is a set of elements for external wall cladding consisting of:

•  external casing (for example in the form of cement, stone, ceramic, wood, wood-based, plastic, metal, laminate boards) attached to the grid;

• grid (made of metal or wood) attached to the external walls of the building;

• elements fastening the casing to the grid and the grid to the walls;

• insulating materials (for example wool mineral, vapor-permeable foil).

Ventilated facades do not include facades made using double self-supporting insulating boards (according to PN-EN 14509 [4]) and self-supporting sandwich panels covered by ETAG 016 [5]. Depending on the construction and installation methods, ETAG 034 distinguishes eight types (families) of facades.

A layer of air should always be left between the insulating layers and the cladding elements. The ventilated façade structure according to ETAG 034 should meet the following requirements:

• the distance between the cladding elements and the insulating layer or substrate (ventilated space) should be at least 20 mm.

• This space can be locally reduced by 5–10 mm;

• the cross-sectional area of ​​the ventilation gap at the bottom of the building and at the edge of the roof should be no less than 50 cm2 per meter in length.

In the case of leaky facade claddings, the insulation layer should be made of mineral wool (WS or WL(P) according to PN-EN 13162 [6]) and in some parts of polystyrene such as EPS, XPS, PUR foam or phenolic foam.

Specific properties of the ventilated facade are required in terms of:

• fire resistance;

• impact on the environment, health, hygiene;

• safety of use;

• durability and performance parameters.

Scope of verification. Test methods according to ETAG 034

The scope of test methods during the assessment of technical properties of ventilated facades depends on the facade components. For facades consisting of elements with known physical and mechanical properties, the scope of tests may be limited to the necessary minimum, while in the case of unconventional materials – extended.

When assessing a facade assembly in terms of its impact on the environment, health, hygiene should be assessed:

1. 1. Watertightness of the facade. Facades with open joints between cladding elements are considered leaky. In the case of tight joints, the façade tightness test should be carried out according to PN-EN 12155 [7] (maximum pressure 600 Pa).

1. 1. Water drainage. The façade should be designed in such a way that water that forms on the surface of the cladding due to the action of rain, condensate, does not accumulate inside the set and can be drained outside.

1. 1. Content of hazardous substances. In the case of wooden and wood-based elements, the content, type, amount of biocidal agents, flame retardants, and formaldehyde content should be specified.

1. 1. 1. Mineral and ceramic fiber content in cladding elements.

1. 1. 1. 1. Cadmium content in paints and varnishes.

In terms of safety of use, special attention should be paid to the resistance of the façade to impacts, wind (pressure and suction), changes temperature, humidity, thermal expansion. The elevation should be designed in such a way that in the event of damage (due to the above factors) it does not expose users or passers-by to injury due to dangerous (sharp) edges or falling parts.

Wind resistance testing involves checking the resistance of a selected section of the façade to negative pressure and positive pressure. The dimensions of the tested section depend on the type of façade. diagram_komory_elewacje_wentylowane. In the case of façades of type a, b, f, g (Fig. 1), the minimum façade area should be at least 1.5 m2, in the case of types d and h, a model consisting of three vertical and three horizontal rows of cladding should be tested, while in the case of types c and e – a section of the façade consisting of four elements. The test should be carried out in a pressure chamber (according to the diagram given in Fig. 2) exerting a load (from 0 to 2400 Pa) evenly distributed over the surface of the tested facade. The test is carried out until significant irreversible deformation is observed. During the test, the deformations of the cladding, grid, etc. should be observed. The test results should be used by designers when designing a ventilated facade. It is important that the ventilation is resistant to a greater wind load than the calculations indicate. The diagram of the pressure chamber for conducting the tests is illustrated in Fig. 2.

Cladding elements should have specified basic mechanical parameters: impact resistance test, bending strength and modulus of elasticity. Depending on the type of façade, the resistance of the cladding to tearing out the fasteners, the action of shear forces, long-term loads, etc. is also to be determined. The façade must be adequately resistant to the action of a horizontal force (e.g. against the support of a ladder). The appropriate test consists of loading the façade with a horizontal force of 500 N within one minute. The force is transferred to the surface of the façade through two spacers measuring 25 x 25 x 5 mm, spaced 400 mm apart. After removing the loads, the façade should not show any damage or deformation.

A ventilated façade should be resistant to hard body impact (1–10 J). The scope of application of the façade depends on the degree of impact resistance. The test is performed according to ISO 7892 using steel balls weighing 0.5 and 1.0 kg, falling from a height of 1.02 m (in the case of a 1 kg ball) and 0.2–0.61 m (in the case of a 0.5 kg ball).

The possibility of using individual types of cladding elements on a façade is also influenced by the resistance of the cladding element to soft body impact (impact energy in the range of 10–400 J). The test is performed according to ISO 7892 [8], using bags weighing 3 and 50 kg. Bag drop height: 0.34–2.04 m (for a 3 kg bag) and 0.61–0.82 m (for a 50 kg bag). The general view of the test is shown in the photo.

The possibility of using different types of cladding in individual parts of the building depending on impact resistance is specified in the table. Ventilated facades are subject to requirements regarding resistance to hydrothermal changes:

1. 1. 1. • • resistance to heating cycles – rain (the test simulates the resistance of the facade to thermal shock possible during a rapid change in temperature, for example during a summer downpour). The facade should withstand 80 heating cycles (air temperature 70oC, humidity 10–30%, duration 2 h) – spraying (water temperature 15oC, spray intensity 1 l/m2) without damage);

1. 1. 1. • • resistance to variable temperature cycles; the elevation should withstand five temperature change cycles without damage.

Cladding elements should be resistant to frost.

The number of freeze-thaw cycles is determined depending on the climate zone of the building’s foundation.

The frost resistance of cladding elements can be determined using three options: option 0 (0 frost resistance cycles); option 1 (25 frost resistance cycles), option 2 (50 frost resistance cycles).

For individual elements of the facade, any signs of corrosion that impair the proper functioning of the set are unacceptable. Steel or aluminum elements of the grid should be identified and have a specific scope of use (atmosphere with a large amount of chemical contamination, marine atmosphere, industrial atmosphere, etc.).

Acceptance of ventilated facades

Unfortunately, the technical conditions for the acceptance of ventilated facades have not been specified directly in any of the versions of the Technical Conditions for the execution and acceptance of construction and assembly works.

Due to the similar structure of works during the acceptance of ventilated facades, it is reasonable to apply requirements analogous to the acceptance of stonework (PN-B- -06190:1972).

Before starting the assembly of the cladding elements, it is necessary to check the compliance of the insulation layers with the design: thermal insulation (thickness, method of attachment to the substrate, whether appropriate materials have been used in individual zones of the facade), wind insulation (continuity of the veil, compliance of the documentation with the design assumptions). The grid and the elements fastening the grid should also be accepted.

The elevation should be made in accordance with the design specifying the dimensions of the framework and the shape and dimensions of special fastening (anchoring) elements, their number and method of fastening, adapted to the type of cladding.

The number, shape and dimensions of fasteners should be determined based on detailed static calculations, taking into account the effect of external and internal forces on the cladding and the structure of the frame.

During the acceptance of the elevation, special attention should be paid to the method of making surfaces adjacent to door and window openings and to compare the existing condition with the design assumptions.

In order to ensure long-term use of the elevation and prevent degradation of thermal insulation, it is necessary to look at the contact point of the window sill and the structure of the elevation. External window sills should ensure proper drainage of rainwater after installation. The horizontal joint between the window sill and the edge of the vertical cladding element located under the window opening, as well as the window sill joints with the window construction elements should be filled with waterproof flexible putty.

When accepting the elevations, it is necessary to check the quality of workmanship near the building expansion joints and the compliance with the design of the implementation of compensatory expansion joints (if provided) allowing the cladding elements to move. In the case of stone cladding, the distance between expansion joints should not exceed 20 m. The solutions for individual expansion joints should be provided for in the technical documentation.

In order to meet the assumed thermal insulation requirements, it should be checked (by removing the cladding) whether the appropriate distance between the cladding and thermal insulation has been maintained. The number of removable claddings should be agreed between the parties to the construction process in an annex to the contract.

When accepting the façade surfaces, the condition of the cladding should be checked – the use of damaged cladding is unacceptable. It is also worth checking the colours and shades of the built-in cladding elements and comparing them with the design assumptions.

The technical condition of individual claddings should be assessed based on the requirements of the subject standards. The thickness of the joints and the correctness of their course is checked by means of external inspection, and in cases of doubt by measurement with an accuracy of 1 mm.

The straightness and correctness of the joint layout in claddings made of regular elements should be checked by stretching a thin string or wire along two randomly selected joints over their entire length and measuring the deviations with an accuracy of 1 mm. The perpendicular direction should be checked by applying a mason’s square to this string or wire and measuring the deviations with an accuracy of 1 mm. Deviations of weld lines from straight lines should not exceed 1 mm over a length of 1 m (this does not apply to elements of irregular shape).

The face of the facing should create a surface shaped in accordance with the requirements of the technical documentation.

Deviations from the designed surface should not exceed half the sum of deviations for individual elements of the facing with a specific texture according to the requirements of the subject standards for these elements.

The correctness of the cladding surface should be checked by applying a 2 m long control rod in two perpendicular directions to any place on the surface and measuring the gap between this rod and the cladding surface with a feeler gauge to an accuracy of 2.0 mm.

If, in accordance with the documentation requirements, the cladding does not form a plane, appropriate templates should be used for checking instead of a control rod.

dr inż. Oleksiy KopylovInstitute of Building Technology

Literature

1. 1. 1. • 1. 1. PN-B-02011:1977 Loads in static calculations – Wind loads.

1. 1. 1. • 1. 1. PN-EN 1991-1-4:2008 Eurocode 1: Actions on structures – Part 1-4: General actions – Wind actions.

1. 1. 1. • 1. 1. 1. ETAG 034 Guideline for european technical approval of kits for external wall claddings Part I: Ventilated cladding and associated fixing, Brussel 2010.

1. 1. 1. • 1. 1. 1. PN-EN 14509:2010 Self-supporting insulating and structural sandwich panels with double-sided with metal cladding – Factory made products – Specifications.

1. 1. 1. • 1. 1. 1. 1. ETAG 016 Composite sandwich panels – Part 1: General information, Brussels 2005.

1. 1. 1. • 1. 1. 1. 1. PN-EN 13162:2009 Thermal insulation products for buildings – Factory made mineral wool (MW) products – Specification.

1. 1. 1. • 1. 1. 1. 1. 1. PN-EN 12155:2004 Curtain walls – Watertightness – Laboratory tests under static pressure.

1. 1. 1. • 1. 1. 1. 1. 1. ISO 7892:1988 Vertical building elements – Impact resistance tests – Impact bodies and general test procedures.

1. 1. • 1. 1. 1. 1. PN-B-06190:1972 Stonework – Stone cladding – Requirements for execution and inspection upon acceptance.