A sandwich panel is a three-layer construction product consisting of two coloured galvanized steel sheets and core between them.
The technology of sandwich panels production appeared due to American architects Frank Lloyd Wright and Alden B.Dow, who were the first to use it in their projects. Already in 1959, the American company Koppers Inc. started mass production of sandwich panels. The oldest sandwich panels manufacturers in Europe are the Finnish company Rannila now known under the Ruukki brand, the Irish company Kingspan, and the Italian company Cannon.
Sandwich panels possess good aesthetic properties, excellent energy saving characteristics, as well as can quickly assembled and thus are widely used for construction of trade and office buildings, prefabricated frame buildings, including warehouse complexes, industrial objects, and agricultural structures.
Depending on their use, sandwich panels are divided into wall and roof panels. In selection of wall sandwich panels, the key parameters are heat engineering, strength, and fire protection characteristics, while for roof panels, bearing capacity and long life are also of relevance.
Roof sandwich panels have to ensure full air-tightness and necessary roof strength, that is why it is recommended to use panels with special profile of external facing in the form of ridges.
The energy saving properties of sandwich panels are determined by the type of core, air-tightness of the lock and availability of seal in it.
A seal can be of butyl, installed at the time of panels installation, or EPDM (ethylene-propylene-diene-monomer) installed into panels’ lock during production, which ensures better air-tightness and energy efficiency of the sandwich panel lock.
A critical sandwich panels’ energy efficiency parameter is thermal resistance (R0), which takes account of heat losses in the lock part of the structure. The minimum reduced thermal resistance (at 25°C) for quality sandwich panels of leading European manufacturers is presented in the following table:
|Panel thickness, mm||Thermal resistance R0, m2*K/W|
|Mineral wool||Foamed polyurethane|
Panels with thermal resistance below the mentioned parameters, are not recommended for usage in construction of energy efficient buildings.
Usage of modern cores, such as mineral wool and PIR, enable construction of buildings with even zero energy consumption. Construction of passive buildings and warehouses with regulated gas environment requires usage of technical solutions on sealing of all abutments, as well as application of sandwich panels with increased energy efficiency, allowing to almost completely exclude energy losses. A sandwich panels building structure can be considered energy efficiency, if its air-tightness comprises less than 1.5 m3/m2hour.
Sandwich panels with integrated photovoltaic modules (solar batteries) are the most innovational energy saving solutions.
The sandwich panel core (insulation layer) ensures such characteristics as durability, thermal and sound insulation, and fire protection properties.
Various types of cores are used in sandwich panels production; mineral wool, foamed polyurethane (PU, PUR) and its modification – polyisocyanurate foam (PIR, IPN), as well as foamed polystyrene (plastic foam) are the most widespread.
Panels filled with foamed plastic, possess the worst operational characteristics, therefore, as a rule, they are used for construction of temporary structures having useful life of up to 10 years and no fire protection requirements, because foamed plastic is combustible. Apart from that, foamed plastic has low sound attenuation and gives rise to mold spreading. The only advantage of foamed plastic sandwich panels is their low price.
Being the most widespread material, mineral wool is always used in sandwich panels with increased fire rating requirements (up to EI360), for instance, in fireproof partitions. The mineral wool U-value varies within the range of λ=0.038-0.044 W/mK. Depending on the necessary characteristics, mineral wool of various density is used in the sandwich panels structure: low density (less than 90 kg/m3) – for internal partitions, medium density (95-115 kg/m3) – for external walls and roof panels, or increased density (120 kg/m3 and more) – for fireproof partitions and wall panels having increased bearing capacity. The mineral wool characteristics have caused wide usage of sandwich panels with such a core in construction of warehouses for combustible materials, fire-hazardous productions, as well as buildings with increased acoustic requirements.
Sandwich panels from foamed polyurethane are convenient in installation due to their small weight (in most cases, foamed polyurethane density in panels comprises from 32 to 40 kg/m3) and possess higher energy saving characteristics (λ=0.020-0.021 W/mK) compared to mineral wool.
Foamed polyurethane does not absorb moisture and thus can be successfully used in panels for carwashes, swimming-pools, productions with increased humidity (malt houses of breweries, mushroom farms etc.), as well as objects located close to bodies of water.
Sandwich panels with foamed polyurethane core are used at objects with low fire safety requirements, as well as at cold storages (refrigerators and freezers, including with regulated gas environment). In this case, polypropylene inserts have to be used on panel fixings to prevent from cold bridging and reduce heat losses.
It is worth noting that foamed polyurethane belongs to combustible materials (G1 combustibility group) and is flammable (M1-M1 group), while fire rating of sandwich panels with foamed polyurethane core is EI15.
Foamed polyisocyanurate (PIR) represents a new generation of polyurethane core (λ=0.020-0.021 W/mK) with fire rating up to EI45. E-PIR type foamed polyisocyanurate core has EI15-EI30 fire rating, while X-PIR – up to EI45.
IPN is a trademark of modified foamed polyurethane (λ=0.020-0.022 W/mK) used in Kingspan sandwich panels. In this case, IPN according to its characteristics more corresponds to X-PIR type, while IPN-L is close to E-PIR. A drawback of IPN is the absence of this type of core among those recommended in the European standard DSTU B EN 14509:2014, which complicates confirmation of quality characteristics for products with such core and does not guarantee its long life.
The range of sandwich panels represented at the Ukrainian market, provides almost endless possibilities of creation of unique architecture. Rich colour solutions, variations in installation direction, a variety of types of profiles and décor enable an architect to use sandwich panels not only as structural, but also a design element of a building.
Sandwich panels with polymer-coated steel facing can have standard (always available by manufacturers in their warehouses) and bespoke colours. The range of possible colour shades of panels is determined according to the RAL, RR, or NCS international colour standards.
When selecting the colour of a sandwich panel, it is necessary to take account of the ability of metal having various colours to heat and expand, because this largely determines the long life and aesthetic characteristics of panels. The darker the colour is, the more the external facing is heated, therefore dark colours are not recommended for use on the roof, where panels would be heated stronger by the sun and might become wavy, while the facing can peel off from the core. It is also not recommended to install dark sandwich panels on the southern façade, because there panels can get bent, thus creating waves, especially if panels are over 6 m long.
There exist several types of profiles of sandwich panel facing: microprofile, linear, corrugated, smooth, stamped, and sinusoid. Due to technical peculiarities of production, smooth and sinusoid surfaces are possible only for panels with foamed polyurethane core. For premises where it is necessary to exclude dust accumulation or where frequent washing is planned, panels with smooth or microprofile surfaces should be used for convenience.
Sandwich panels can be installed horizontally, vertically or at a slope. It is allowed to use sandwich panels even for erection of curved walls, if the curve radius comprises 30 m or more. For even accommodation of panels deformation, it is recommended to install them in one span.
A series of leading sandwich panels manufacturers offer additional possibilities for their decoration, such as application of any colour images onto the surface of panels, or installation of ventilated façades with decorative lining above sandwich panels.
Apart from the external facing, visual perception of panels is also influenced by the fixing, which can be visible or hidden, as well as joint and framing elements, battens, special corner sandwich panels etc. Such seemingly insignificant details are decisive in the façade architecture of a series of objects. Therefore, if it is necessary to create an expressive building design, involvement of experienced specialists into project development is recommended.
The optimal choice of external facing material of sandwich panels is polymer-coated galvanized steel, ensuring long life and preservation of operational characteristics of a product.
Prior to purchasing sandwich panels, it is worth paying attention to the steel facing characteristics. Under DSTU EN 10346:2014, S280, S320, S350 structural steel grades with flow limit 280-350 MPa can be used for manufacturing sandwich panels. In spite of that, to reduce the price, many producers use DX51 steel grade, which is not structural and thus not acceptable for non-bearing sandwich panels.
The same standard determines the need to use galvanized steel with zinc content not less than 190 g/m2. In this case, the zinc coating thickness from the external side shall be at least 20 microns, while the polyester layer shall be at least 25 µm thick.
Under DSTU B EN 14509:2014, the sandwich panels external facing thickness can be from 0.4 to 0.7 mm. In this case, the thicker a steel sheet is, the smoother the façade surface will look and the less glitter it will have in sunny weather. The internal facing layer is usually within 0.4 to 0.6 mm and affects the long life and bearing capacity of sandwich panels.
Depending on the use and operation conditions of panels, several types of polymer coatings are distinguished, of which the most widespread are:
In special cases, for instance, when the atmosphere inside the building is very aggressive due to influence of washing and abrasive detergents, as well as in pharmaceutical and food industries, it is recommended to use sandwich panels facing from stainless steel. Such a solution is the most expensive however the only possible one in certain cases.
Bearing capacity of a sandwich panel is an important characteristic, because in the course of operation panels are exposed to influence of snow, wind, seismic activity etc. When designing building envelopes using sandwich panels, it is necessary to take account of the requirements of DBN V.1.2-2:2006 “Loads and Impacts”. For instance, for construction of the same building in various regions, the values of wind and snow loads can differ several times. It is also necessary to take account of the structural peculiarities, service loads, as well as the conditions of the building operation. For example, in addition to snow load, a roof has to withstand a person with a cleaning tool.
When wall sandwich panels are used in high-rise buildings, special attention can be paid to selection of fixings and number of fixing points.
In projects, where an explosive situation is possible, light removable structures need to be used. In such structures, sandwich panels with special types of fixings are applied, which ensure decompression of certain parts of the façade in case of internal pressure increase. This allows avoiding injuries to people, who are inside the premises and near the object, as well as damage to the building structures.
The necessary characteristics of sandwich panels are selected according to the bearing capacity tables and with the help of calculation software, therefore prior to purchasing, one should find out whether the supplier has such software.
The sandwich panel thickness is selected based on the heat engineering calculation and can be within 40 to 300 mm, and its width is from 1.0 to 1.2 m. The panel length can be from 2 to 13.5 m and is limited by transportation possibilities. Based on convenience of installation, 6-8 m long panels are the most widespread.
Sandwich panels can be supplied with flat or zig-zag lock. Flat locks can cause condensate and through freezing. In its turn, the mortice and tenon zig-zag lock is more air-tight and energy efficient.
It is important to consider that precise geometrical characteristics of sandwich panels substantially affect the air-tight matching of locks, as well as the timing and quality of installation. In spite of the broad range of sandwich panels brands at the Ukrainian market, only a few manufacturers can guarantee that during installation, deviation from geometrical dimensions will be within the tolerances specified in DSTU B EN 14509:2014. This is caused by the fact that manufacturing products with precise geometrical parameters requires high-quality automated equipment, which only leading European manufacturers have.
Prior to purchasing sandwich panels, it is necessary to check whether the seller has the list of the necessary certificates and test reports, which includes:
The above list of documents only partly confirms the quality of supplied products, therefore it is recommended to request from the supplier additional documents to confirm such characteristics of sandwich panels, as:
When using sandwich panels in construction of buildings in zones of increased seismic activity, it is recommended to request the seismic stability conclusion from the supplier. To be absolutely sure in the quality of supplied panels, it is also necessary to request separate certificates and reports for materials used in production of the particular batch of panels: steel and core.
Before buying sandwich panels, it is important to know that even the best products, when using low-quality accessories or improper installation, are unlikely to last the declared period by the manufacturer. The choice of fixings, seals, battens, and rails, like the choice of sandwich panels themselves, has to be based on qualitative characteristics of products, peculiarities of a specific type of panels, and the manufacturer’s recommendations.
In spite of the seeming ease, sandwich panels assembly is a rather complicated and responsible stage, which all subsequent operational costs and building useful life depend on. Therefore it is recommended to commission sandwich panels installation to experienced specialized construction companies, which are able to confirm their experience with the relevant warranty.
When storing mineral wool sandwich panels in the open air, the core can absorb moisture, as a result the thermal performance of the products can deteriorate significantly. To prevent the joint parts of sandwich panels from getting wet, the Finnish manufacturer Ruukki offers Rain Protect technology, which protects the insulation from rain during storage and maintains the panels quality.
Inexpensive sandwich panels with the lowest requirements to quality and long life, are represented in Ukraine by a broad list of brands, from which one can distinguish AluTherm, Arsenal, Asten, Pantech, Promstan, Cualimetal, Gor Stal, Izovol, Paneltech.
The medium price segment is filled with products by Adamietz, Arcelor, Balex, Isopan, Joris, Metecno, Pruszynski, USP, Isospan, Inteco, Systeminvest, Thermo-bud, TPK.
Sandwich panels of the highest quality in Ukraine, meeting the DSTU B EN 14509:2014 European quality standard, are represented by only two brands – Kingspan and Ruukki.
One should remember that the sandwich panels price means not only funds initially spent for manufacturing and installation. Purchasing better quality products, the building owner not only receives excellent appearance and safety of a building, but can recover the funds spent due to reduction of costs for heating and air conditioning, as well as due to absence of problems with operation of the roof and façades throughout the whole useful life of a building.