Which colour of trapezoidal steel sheet should you choose and what should you check beyond the swatch?
Steel sheets and roofs
The colour of trapezoidal steel sheet should be chosen together with the coating, texture and the way the building is used. The RAL number helps to indicate the shade but does not describe the gloss level or the resistance of the surface. A matt graphite may look different from a gloss graphite, even though both have the same number. Before ordering, check a real sample, the compatibility of flashings and the availability of the whole batch. On a roof, the behaviour of the coating in a specific environment also matters. The shade number makes communication between the investor, the seller and the contractor easier. It does not constitute a full specification of the surface. Two steel sheets of the same colour may differ in texture, degree of gloss and type of paint. The difference is often particularly visible on adjacent sheets or flashings.
What does the RAL number mean and what does it not say?
The shade number makes communication between the client, the seller and the contractor easier. It does not constitute a full specification of the surface. Two steel sheets in the same colour may differ in texture, degree of gloss and type of coating. The difference is often particularly visible on adjacent sheets or flashings.
For the order, therefore, enter the colour and the name of the finish type specified in the offer documentation. In a public description it is enough to speak of matt, gloss or texture, but the order requires the supplier’s unambiguous designation. Keep the batch label and the sample. For later extension they will help to better match the material. They do not, however, guarantee that a new and a years-old coating will look identical.
How to match the shade to the roof and façade?
First choose the element that is to dominate. The roof can harmonise with the joinery and fencing or be a calm background for the façade. Graphites, browns and reds are widely available, but the catalogue itself is not a popularity ranking. More important is the match to the building form, the surroundings and the other materials.
The trapezoidal profile creates a rhythm of light and shadow. T35 gives a deeper pattern than T18, which is why the shade will not be perceived identically on both profiles. On the façade, the direction of laying also matters. Vertical and horizontal ribs can emphasise the building’s proportions differently. View the sample in a position close to the final one. A swatch lying flat will not show the full effect.
Does dark steel sheet heat up more?
Dark surfaces may heat up more strongly in the sun than light ones with comparable properties. The actual result also depends, however, on the type of coating and the exposure. A specific temperature under all conditions should not be attributed to a single RAL number. What matters is the season, the inclination and the weather conditions.
Temperature changes cause the sheet to move. The sheet lengths and fixings should correspond to the adopted system. This does not mean that a dark roof is by principle the wrong choice. In a heated house, the comfort of the attic depends above all on the entire building envelope, ventilation and glazing. A lighter colour alone does not replace insulation. It can be one element of a considered design.
How to choose a coating for the environment?
Colour does not determine corrosion resistance. What matters is the metallic protection and the organic coating as well as the approved conditions of use. Proximity to the sea, an industrial plant or an aggressive internal environment requires a separate assessment. The same aesthetic may be available in several protection variants.
Check the coating parameters and the scope of the warranty. Separate corrosion resistance from colour stability under sunlight. Long protection against perforation does not have to mean an identical period of aesthetic warranty. Do not select the material solely by paint thickness. Its properties, the substrate and the documented scope of application are important. The supplier should confirm the suitability of the chosen variant for the location.
Why is a sample better than a screen alone?
A monitor and a phone display colours depending on settings and lighting. A product photo is often additionally taken under studio conditions. It does not allow all changes in light reflection to be assessed. Examine the sample outdoors, in sun and shade. Compare it with the joinery, render or material that will actually be next to it.
For a larger order, establish batch consistency and how the sheets are to be laid. Coatings with a metallic effect may require maintaining a direction in line with the markings. Rotating a single element can change how its surface is perceived. Such a requirement should be checked for the specific coating. It does not occur automatically in every steel sheet, but it is worth clarifying before installation.
How can you avoid differences after delivery?
Compare the packs, markings and accessories before starting work. If the coatings differ clearly, clarify this before installing the sheets next to each other. Also check the colour on the underside if it will be visible under a canopy or at an open eaves. A decorative finish on the top surface does not mean the same appearance on the inner side.
During use, keep it clean. Dirt, deposits and uneven shading can change the perception of colour. The coating is cleaned in accordance with the instructions, without aggressive agents and random scrubbing. Touch-up paint is applied where needed. Extensive painting over of a small scratch can leave a more visible mark than the local damage itself. Colour selection therefore also includes subsequent care.
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