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Two different climatic stresses affect the durability of a sheet metal roof. General climatic stress, for example rural, urban and industrial climates (climatic stress classes C1–C5), burdens the steel roofing, as does the microclimate created by, for example, the chimneys of nearby thermal power plants. For the roof of a detached house, the house’s own chimney can also pose a risk if fireplaces are used frequently.

The quality of the roofing material’s coating also affects the durability of a sheet metal roof. There are sheet metal roofing materials of different quality levels on the market. The best roofing materials are promised a 50-year perforation rust warranty. It is also not irrelevant what kind of roofing screws are used to attach the steel roofing. The roofing screw should withstand rusting for as long as the roofing sheet.

Even the best roofing sheets must be installed carefully. Scratches may occur in the roofing during installation, creating a corrosion risk. Scratches should therefore be painted with touch-up paint immediately after installation.

The care given to the roof also affects the durability of a sheet metal roof. The roof should be cleaned regularly if dirt and organic matter (sap, tree leaves, lichen) accumulate on it. A well-designed and properly implemented sheet metal roof cleans itself if the arrival of snow is not prevented by a matte coating, snow guards or other roof structures that prevent snow from falling (e.g. a valley, skylight).

On the other hand, possible maintenance work can also damage a sheet metal roof. For example, snow removal should be carried out carefully so that the roofing is not dented at the same time.

The CE mark is not an approval mark granted by an authority. Tukes, which supervises the use of the CE mark, emphasises that the CE mark is also not a general safety or quality mark. https://www.tukes.fi/Tiedostot/julkaisut/Tukes_CE_A4.pdf

The CE mark is the product manufacturer’s own declaration that the product is safe and complies with EU legislation, and that it can be sold on the market.

A product must bear the CE mark if it is covered by a harmonised (harmonized, hEN) standard. The manufacturer must prepare a declaration of performance for a CE-marked product, stating the product’s characteristics. The funny (or sad) thing about this is that the manufacturer only needs to declare one important characteristic, perhaps two important characteristics in Finland in the future, even though the standard requires 10 characteristics.

The Ministry of the Environment’s website states as follows: “The manufacturer must declare at least one performance related to the basic characteristics of the construction product that is relevant to the intended use in cases where the Member State has no relevant regulatory provisions at all.” Everyone can draw their own conclusions about how this guideline can be interpreted and exploited. However, most products have more than one important characteristic.

Roofing screws do not have a harmonised standard according to which the screw would have to bear the CE mark. Some competitors have applied for a CE marking for their product through the ETA procedure, because the CE mark improves the screw’s quality image. For some reason, manufacturers have failed to notice that the corrosion protection assessment in the ETA approval procedure is based on the EN 1993-1-3 standard (Table B.1: Material of fasteners taking into account the climatic exposure class related to corrosion), even though this is written into every manufacturer’s ETA approval. According to these ETA approvals, all roofing screws currently bearing the CE mark have been approved for indoor use only.

The fact that a product bears the CE mark does not remove the obligation of the party undertaking construction to determine the product’s actual suitability for the intended use. Finding the CE mark on the product or packaging does not yet reveal whether the product is suitable for the purpose for which it is sold.

Because KINGI^® roof screws have a thicker paint layer and a higher head than other screws in use, a mounting socket made to its dimensions has been produced. This ensures that the screw drills in steadily without scratching the coating.

A roofing screw that complies with regulations can also be identified by its price. In accordance with building regulations, a roofing screw must withstand corrosion just as well as the roofing sheet. Tests have shown that only the three-layer-coated KINGI^® roofing screw has corrosion resistance as good as that of the three-layer-coated roofing sheets currently in use. A three-layer-coated KINGI^® roofing screw costs the consumer €43.42/250 pcs. A price that is even half as low indicates a single-layer-painted screw that will not last as long.

When calculating the total costs of a sheet metal roof, for example, the price difference between single-layer-painted and three-layer-coated roofing screws for a 150-square-metre roof is around one hundred euros. It is a small price to pay for a long-lasting sheet metal roof that complies with regulations. The KINGI^® roofing screw has a long warranty. More information about warranties here

If you want a long-lasting sheet metal roof that complies with regulations, you should invest in screws suitable for outdoor use.

Good steel construction requires fasteners to use a material with corrosion behaviour as similar as possible to that of the material being fastened. This prevents the formation of a corrosion couple and unexpected rusting.

When talking about sheet metal roofs, the material being fastened is galvanised and paint-coated carbon steel, such as Ruukki’s Pural or SSAB’s Nova, just as Kingi is. Kingi’s coating system has performed at least as well in corrosion tests as, for example, Pural^®.

The compatibility principle has been emphasised, among other things, in the standard concerning steel construction, SFS-EN 1090-2 + A1: Execution of steel and thin-walled structures. Part 2: Technical requirements for steel structures. In the guidelines of the standard, section 5.6.1 states that “the corrosion resistance of connectors, fasteners and sealing washers shall correspond to that of the assemblies being fastened”. In addition, section 10.4 of the same standard states that “unintentional contact between different metallic materials, for example stainless steel and aluminium or structural steel, shall be avoided”.

Screw manufacturers of course often recommend using stainless steel screws, because for them it is “safe” – when a corrosion couple forms, the sheet corrodes, not the screw. For the roof owner, however, corrosion of the sheet is often a bigger and more expensive problem than replacing the screw.

In practice, a corrosion couple does not form in a correctly constructed roof structure if the head section of the screw is well coated and a good-quality washer is used. The unpainted part of the galvanised screw is protected from corrosive atmospheric conditions, under the sheet in the roof structure (see standard SFS-EN 1995-1-1). If the roof has been constructed incorrectly and the screw shaft is subject to actual corrosion stress, rusting of the screw is one of the smallest problems. The real problem is then the ingress of moisture into the roof structures, causing the wooden roof structures to become damp and creating a favourable growth environment for moulds and fungi.

The use of stainless steel also involves other problems related to durability. Its strength is lower than that of carbon steel, and therefore the risk of breakage is greater. Hydrogen problems also occur more often in stainless steel than in carbon steel, in which case the entire head section of an installed screw may detach on the roof. Visual durability is also often reduced because paint adheres less well to stainless steel than to electro-galvanised and properly pre-treated carbon steel. Stainless steel also carries a risk of stress corrosion in a chloride environment. A publicised example of this can be found from about 10 years ago at Rauhalahti Spa Hotel in Kuopio. There, the suspended ceiling above the main pool of the pool area collapsed onto the swimmers when the stainless steel fasteners failed as a result of stress corrosion.

Although stainless steel is in many respects a weaker option than carbon steel, it is nevertheless significantly more expensive.

A typical problem with cover nails is that over time they rise out of their base. When cover nails come loose, the condition of the battens must first be checked when planning the repairs. If the nails have been raised, water has usually entered through the nail hole. If the battens have rotted, the only proper repair is to replace the entire roof.

If the battens are still in good condition and moisture has not caused them to decay, there are a couple of solutions that can extend the life of the existing roof. Since the previous fasteners are nails, they were probably fastened from the crest of the profile, so the 25 mm long KINGI^® roofing screw is not suitable as a replacement, and a longer screw is needed. The nail should be replaced with a longer and thicker roofing screw (thickness 5.5 – 6.5mm) with a good washer. Suitable cover roofing screws are just more difficult to find, because they are not widely available. The screw may be hot-dip galvanized or electro-galvanized. If the screw is electro-galvanized, it must be painted within a couple of years of fastening.

As a second trick, a suitably long (4.8 mm) screw could be used in place of the cover nail to plug the hole, if the screw holds in the batten. In this case, the fastening must be secured with another roofing screw of equal length, fastened close to the first screw, preferably above it in a spot without a hole. If the plug screw does not hold at all, this trick must not be used. In that case, the old hole must be patched, for example using the Enkopur method: https://rooftech.fi/enkopur/. The fastening can then be made from the base of the profile with a new KINGI^® roofing screw. Hard work. This is certainly a workaround, but there are not many good solutions available.

KINGI^® roofing screws are manufactured in Finland at Kingi Oy’s own factory in Nurmijärvi. Most of the manufacturing of KINGI^® roofing screws takes place in Nurmijärvi. Foreign suppliers are used only for those semi-finished products and raw materials that cannot be sourced from Finland. The KINGI^® roofing screw has been awarded the Key Flag Symbol.

You can read more about Kingi’s manufacturing stages here

Hi Pekka,

The threaded part of the KINGI^® Replacement screw has a diameter of 6.3 mm, while a regular roofing screw has a diameter of 4.8 mm. You can order a replacement screw here.

Hello Ville,

Thank you for your nice feedback.

We have received similar requests from others as well, and our current selection now includes a 65 mm long option for both cover screws and replacement screws in all stock colors.

Hello Kari,

The threaded part of the KINGI^® Replacemen screw has a diameter of 6.3 mm, whereas a standard roofing screw has a diameter of 4.8 mm. Here you can order replacement screws.

Kingi has a KINGI^® Replacement screw developed for this purpose. Here you can order replacement screws.