Steel vs. Aluminum for windows and doors?

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Window wall | out-swing door | lake view | sun room | muntin grids | steel windows and doors
Interior view of a sun room with a wall of windows and a single out-swing door

Windows and doors were never made from aluminum until the mid 20th century.  Steel was the metal that dominated the market before then dating back to the 19th Century.  Cast iron storefronts can still be found in building of the late 1800’s, however, hot-rolled steel became the most popular option once it was discovered.

The mining of coal in the late 1700’s created a problem . . . it needed to be delivered . . . it was bulky and heavy.  Enter the railroad.  Railroad tracks were first made from cast iron, the technology of the day.  The problem with it is that cast iron is brittle and prone to crack and fall apart when “shocked”.  A new process was developed for rolling steel into continuous rail shapes while it was solid, not molten, but still red hot making it formable by a progressive series of shaped rollers that “push” it into its final form.  Railroad rails were first made from hot-rolled steel in 1859.  A synergy was formed out of this alliance between coal and steel via the railroad because coal needed railroads for transportation and the hot-rolled steel rails needed coke which comes from coal.

The ability to hot roll steel into any shape with the resultant sections being strong, accurate and inexpensive created an opportunity for window and door makers.  Up until the 1960’s hot-rolled steel windows and doors were shipped in standard sizes to warehouses in the US In box car loads.  Today, these windows are only available as custom order and none of the steel bars are manufactured in the US.  Most of the bars come from Switzerland and a small amount from India.

Aluminum became popular for making windows and doors in the 1960’s and 1970’s as an alternate to steel because processes were developed to make it cheaper and with product specific grooves that were convenient for the manufacturers.  The first shortcoming discovered was that aluminum transmitted 4 times more heat than steel does so aluminum doors in northern climates caused condensation on the inside that became ice.  Thermal breaks were added at additional cost.

There is no question that aluminum windows and doors are less expensive to produce, but the extrusion process creates a shape and size that is fixed unless a new die is built.  It is what it is.  Also, aluminum sections are joined in the four corners with screws or crimps mechanically, but NOT welded.  Mechanically joined corners weaken over time because of the dynamic forces like wind gusts and opening hinged leaves.  Sagging and leaking often result from this weakness.

Finally, there is the question of strength.  Steel is 3 times stronger than aluminum and 16 times stronger than wood when comparing identical sections.  Fatter, deeper sections are needed for doors made from aluminum or wood to have the same performance as steel sections.  Steel offers strength inherent is the material to reduce bending and the welding of the corners creates more strength of the frame assembly because the vertical and horizontal profiles become one, not held together with screws.  Strength is what steel is all about.

Steel is not without its issues, though.  Rusting and thermal performance need to be addressed.  Rusting can be prevented with careful applications of zinc often referred to as galvanizing before painting and there are several methods of making steel perform equal to or better than thermally broken aluminum.  More on this another time.

2Fold® is a door that derives its strength from steel and adds Accoya® to the inside to provide a superior thermal barrier.  2Fold® is thinner, stronger and longer lasting than any other folding door, and it’s “Made in America”.

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