Ask Kingi

What factors affect the durability of a metal roof?

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

The durability of a metal roof is also affected by the quality of the roofing material’s coating. There are roofing materials of different levels on the market. The best roofing materials come with a 50-year perforation rust warranty. It is also not irrelevant what kind of roofing screws are used to fasten 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. During installation, scratches may form in the roofing, creating a corrosion risk. Scratches should therefore be painted with touch-up paint immediately after installation.

The durability of a metal roof is also affected by how well the roof is cared for. The roof should be cleaned regularly if dirt and organic matter (sap, tree leaves, lichen) accumulate on it. A well-designed and properly installed metal roof cleans itself if the arrival of snow is not obstructed by a matt 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 metal roof. For example, snow removal should be carried out carefully so that the roofing is not dented in the process.

What does the CE marking mean?

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

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

A product must bear the CE marking if it is covered by a harmonised (harmonised, hEN) standard. The manufacturer must draw up a declaration of performance for a CE-marked product, stating the product’s properties. The amusing (or sad) thing here is that the manufacturer only has to declare one important property, perhaps two important properties in Finland in the future, even though the standard requires 10 properties.

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 official regulations relating to the matter at all.” Everyone can draw their own conclusions about how this instruction can be interpreted and taken advantage of. However, most products have more than one important property.

Roofing screws do not have a harmonised standard according to which the screw would have to bear the CE marking. Some competitors have applied for a CE marking for their product through the ETA procedure, because the CE marking improves the perceived quality of the screw. For some reason, manufacturers have failed to take into account 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 it is written into every manufacturer’s ETA approval. According to these ETA approvals, all roofing screws currently bearing the CE marking have been approved for indoor use only.

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

What kind of installation socket is needed to install Kingi?

Because the KINGI^® roofing screw has a thicker layer of paint and a higher head than other screws in use, a custom-sized installation socket has been made for it. This ensures that the screw drills steadily without scratching the coating.

How much do KINGI® roofing screws cost?

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 as well as the roofing sheet. Tests have shown that only a KINGI^® roofing screw with a three-layer coating 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 consumers €14.90/100 pcs. A price up to half lower indicates a single-layer-painted screw that does 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 sheet metal roof that complies with regulations and lasts a long time, you should invest in screws suitable for outdoor use.

Why are KINGI® roofing screws not made of stainless steel?

Good steel construction requires that the fasteners use a material whose corrosion behaviour is as similar as possible to that of the material being fastened. This prevents the formation of a corrosion couple and surprises caused by rust.

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

The compatibility principle has been emphasized, among other places, in the standard concerning steel construction, SFS-EN 1090-2 + A1: Execution of steel structures and structures made of thin sheets. Part 2: Technical requirements for steel structures. In the guidelines of the standard, section 5.6.1 states that “the connectors, fasteners and sealing washers shall correspond in corrosion resistance to 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, quite 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 owner of the roof, 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 properly constructed roof structure if the head part of the screw is well coated and a high-quality washer is used. The unpainted part of the galvanized screw is protected from corrosive atmospheric conditions, in the roof structure beneath the sheet (see standard SFS-EN 1995-1-1). If the roof has been constructed incorrectly and the body of the screw is subject to actual corrosive stress, rusting of the screw is among the smallest of the problems. The actual problem then is moisture entering 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 durability-related problems. Its strength is lower than that of carbon steel, and thus 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 part may detach from the installed screw on the roof. Visual durability is also often reduced because paint adheres less well to stainless steel than to electro-galvanized and properly pre-treated carbon steel. Stainless steel also has a risk of stress corrosion in a chloride environment. A well-known example of this dates back approximately 10 years and concerns Spa Hotel Rauhalahti 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.

What should be used to replace the fastening nails on an old aluminium roof, which are aluminium and are beginning to come loose?

A typical problem with roofing nails is that, over time, they rise out of their base. When the roofing nails come loose, the condition of the battens must first be checked when planning 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 rot, 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 ridge of the profile, so a 25 mm long KINGI^® roofing screw is not suitable as a replacement; 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 roofing screws are just more difficult to find, because they are not widely available. The screw can 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 solution, a sufficiently long (4.8 mm) screw could be used instead of the roofing 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 method must not be used. The old hole must then be patched, for example using the Enkopur method: http://www.rooftech.fi/tuotteet/katto/enkopur-takuutiivistys/. The fastening can then be made from the base of the profile with a new KINGI^® roofing screw. Hard work. This is admittedly a makeshift solution, but there are not many good options available.

Hello, I live in Riihimäki and need to make a temporary repair to my roof by replacing the roofing screws. Which is the nearest retailer for Kingi screws to Riihimäki? Best regards, Anssi

Hello Anssi,

Replacing the screws can sometimes significantly extend the life of an old roof. However, you could still wait a little while, as a longer KINGI^® roofing screw (32 mm) will also go on sale at the end of April. It could be a better and more secure option for your roof when the new roofing screws are installed in place of the old ones.

The nearest place for you to purchase KINGI^® roofing screws is in Tuusula, where they are sold by Tuusulan Peltikeskus Oy http://www.tuusulanpeltikeskus.fi/cms/

You can also conveniently order KINGI^® roofing screws from the Promart online store, even from the comfort of your own sofa:  https://www.promart.fi/tuote/kateruuvi-kingi-48×25/10KAT-4.8x25RR32K/

Remember to purchase a KINGI^® installation socket at the same time, so the installation work goes quickly and efficiently. Enjoy repairing the roof!

I am interested in where Kingi screws are manufactured, that is, where the factory is, as I have not even heard of a domestic screw factory?

KINGI^® roofing screws are manufactured in Finland at Kingi Oy’s own factory located in Nurmijärvi. Most of the manufacturing of the KINGI^® roofing screw takes place in Nurmijärvi – only those semi-finished products and raw materials that cannot be sourced from Finland are procured from foreign suppliers. The KEY FLAG symbol has been awarded to the KINGI^® roofing screw.

You can read more about the manufacturing stages of Kingi here

I would replace the roofing screws, many of the screw holes have deteriorated. Do you have 6.3 mm thick roofing screws available? Yours sincerely, Pekka.

Hello Pekka,

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

I have found Kingin screws to be an extremely good and functional product when installing new roofing sheets! But since there are still many old corrugated sheet roofs in the region that were fastened by nailing through the crest of the corrugation, and these often have to be restored by replacing the nails with screws, as the roofing sheets themselves are often still in very good condition, the question is whether you have at any point considered also manufacturing considerably longer (that is, 65 and 80 mm) high-quality roofing screws? These screws could naturally be the stronger 6.3 mm versions… Or has the idea of manufacturing these slightly more marginal screw sizes already been completely buried? I was just wondering whether it is worth waiting for something good or whether, with regard to these longer screws, we will continue to have to make do with the lower-quality screws of competing manufacturers? Best regards, Ville

Hello Ville,

Thank you for your pleasant feedback.

We have received similar requests from others as well, and we are currently investigating the possibility of cost-effectively producing longer Kingi roofing screws as well. If a positive decision is made regarding longer roofing screws, in practice this would mean that they could be supplied towards the end of 2017. Happy New Year 2017!

Where can I get 2,000 brown replacement screws? The roof has already been renewed once, and the screws have risen up. The battening boards are 25 mm long. What is the diameter of these new replacement screws? Regards, Kari 

Hello Kari,

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

The old roofing screws are already partly rusty. Some have twisted open at the eaves and are 25 mm long. Can they be replaced with 32 mm ones? The batten is 32 mm thick. 

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