The only choice for long lasting rooflights
It is widely recognised that the best looking rooflights are manufactured from steel. Whilst steel has many aesthetic benefits over modern rooflights, that should not mean that all steel rooflights are equal and that they are not without their issues. That is why all our rooflights are manufactured in the UK using only Marine Grade 316 stainless steel.
To overcome the issue of rusting that commonly affects mild steel rooflights, all Stella rooflights are manufactured in Marine Grade 316 stainless steel.
Stainless steel stains less easily than other iron-based metals. As with standard steel, stainless can still be marked up by fingerprints and grease and develop discoloration but the difference is resilience. Stainless steel can withstand much more time and abuse before showing signs of wear.
All steels have the same basic iron and carbon composition, but stainless steel also contains a healthy dose of chromium which is the alloy that gives stainless steel its famous corrosion resistance. There are multiple grades of stainless steel, each with slightly different alloy composition, and therefore slightly different physical characteristics. Stainless steel must contain at least 10.5 percent chromium. Depending on the grade, it may contain much higher chromium levels, and additional alloying ingredients like molybdenum, nickel, titanium, aluminium, copper, nitrogen, phosphorous and selenium.
Marine Grade 316 stainless steel rooflights do not suffer uniform corrosion in the same way as mild steel (carbon steel) versions will, when exposed to wet environments. Unprotected carbon steel will readily rust when exposed to the combination of air and moisture. This results in an iron oxide surface layer (the rust) which is porous and fragile. Since iron oxide occupies a larger volume than the original steel this layer expands and tends to flake and fall away exposing the underlying steel to further attack leading to water ingress through the failing rooflight frame. In comparison, stainless steels contain sufficient chromium to undergo passivation, spontaneously forming a microscopically thin inert surface film of chromium oxide by reaction with the oxygen in air and even the small amount of dissolved oxygen in water. This passive film prevents further corrosion by blocking oxygen diffusion to the steel surface and thus prevents corrosion from spreading into the bulk of the metal.
The two most common stainless steel grades are 304 and 316. The key difference is the addition of molybdenum, an alloy which drastically enhances corrosion resistance, especially for more saline or chloride-exposed environments. Stella rooflights only use grade 316 stainless steel which contains molybdenum whereas grade 304 or mild steel does not.
For rooflights, stainless steel is an ideal corrosion-resistant material, but it will only withstand long-term exposure if the grade is appropriate for its environment. Grade 304 is an economical and practical choice for most environments, but it doesn’t have the chloride resistance of Grade 316. There is a slightly higher price premium for Marine Grade 316 but it is well worth it in areas with high chloride exposure, especially the coast and heavily salted roadways.
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