Wednesday, January 22, 2014


Steel takes an edge.  For centuries it was the material of tools and weapons: carpentry, warfare & agriculture.

I grew up in South Yorkshire while it was still a land of coal and steel. For most of my twenties I lived in Sheffield, birthplace of crucible steel, and later the of the Bessemer process.  By 1850 steel had become the material of bridges, machines, railways.  Cast iron predated steel for structural use in buildings, notably in "fire-proof" factory construction.  Cast iron columns carried beams similar to railway lines in section, with brick jack-arches spanning between the beam

5 or 6 years ago I photographed some of the famous cast-iron facades in Soho, New York.  These were an early example of prefabrication: modular facades created in the factory and assembled on site.  It's interesting to note that behind the decorative/structural cast iron there are often timber sliding-sash windows. 

One of the best known examples is the Singer building.  It seems to me though that much of this is not cast iron, but steel: heated and bent, riveted together.  Even the window frames seem to be steel. We are approaching an era when steel seemed to be the ideal material for window frames, and glazing of all types.

Charles Rennie Mackintosh got in there early, using steel windows in 2 school buildings in Glasgow (Scotland Road & the School of Art)  Is he a modernist or a traditionalist ? abstract geometrist or arts & crafts flower person ?  Nobody seems to be quite sure.

Just over a decade later Peter Behrens and his former employee Walter Gropius designed buildings that have become famous for their steel-framed glazing.  Technically I think this is very similar to Mackintosh, but they did without his subtle decorative flourishes and projected the glazing in front of the masonry.  So everyone is quite cetain that they are modernists.

Mass-produced steel windows in standard sizes, ("off-the-shelf") became very popular in the 20s and 30s, rapidly replacing the wooden sliding sash.  But the heyday of steel windows in Europe lasted barely 50 years.  Disruptive innovation or blip on the screen?  By the 1970s it was clear that condensation related corrosion was a serious problem, and U values were becoming important.

So when I moved to Southern Africa in 1981, I thought of steel windows as an anachronism, an outmoded technology.  But in a dryer and warmer climate, where neither central heating nor air conditioning are needed in the average house, steel windows dominated the market.

I spend my first decade in Africa as a teacher & curriculum developer, returning to architecture as I approached 40.  As an architect, I used steel frames most of the time.  They are the ideal solution for the Zimbabwean climate and economy.  (We used to have an economy in the first 80s & 90s)

So this is the next installment in my "window technology" series, standard steel windows: the Crittall Hope variety.  I should explain once more what I am doing.  For BIM to really succeed it must become second nature to all participants in the Construction Industry.  We should use it as naturally as picking up a pencil, or sketching a detail in chalk, on the wall inside a building site.  So my focus is not to track the latest devices and software tools.  Others do that much better than I could.  I am trying to use Revit like a pencil: a tool with which to explore ideas, clarify my thoughts, make sense of what I have learnt over the years; in short, an aid to visual thinking.

I am using BIM techniques to explore how buildings work, how they have varied in time and place, the processes and trades involved in making them.  I am NOT making families for everyday use in projects.  That is a separate exercise.
Typically, an experts advice on making families will start with an injunction to plan ahead, to sit down with pencil and paper to plan out the parameters and reference planes you will need.  That is not what I am about here.  Revit IS my pencil, my planning tool.  I am using it to work something out.  In the case of the brass handles and stays, or the steel hinges, there are elements that belong to the sash and elements that belong to the outer frame; elements that move in space and elements that stay where they are.  There are pivot points and angular movements.  Ultimately it would be nice to articulate all that, to make it parametric and represent top-hung or side-hung lights with the sashes in different positions by punching numbers into dialogue boxes.

 But first I need to understand how these things work.  I have to get the sizes and shapes right.  That is an exploratory process.  I don't have any steel windows to hand.  I can't just fly back to Zimbabwe and measure the ones in my house there.  I have to work from grainy photographs and internet downloads, plus my memories of fiddling with windows that didn't close properly or had loose handles.

Let's take the handle for a side-hung sash.  A door handle sits in a horizontal position when at rest, but you don't want the window handle to spoil your view, so it hangs down when the window is closed.

In making this handle, I wanted it to look fairly convincing, without getting sidetracked by Revit technicalities.  The goal was to understand the main points of the design: how it works and why it is shaped like that.  So  I haven't rounded off all the sharp edges and I haven't gone to the trouble of using conceptual massing to capture the complex curves.  I made do with an extrusion cut by a couple of voids.  Building components should be "fit for purpose", not under-designed or over-designed.  The same goes for drawings: be they pencil sketches or BIM models.  (I could have said "BIMs" but I think that would have been both clumsier and less clear)  So my aim here is to do just enough to capture the essence of how these fittings work. 

But let's look at the window itself.  If you look in text books, you can find all kinds of refined details, with weather stripping and aluminium glazing beads.  Steel windows been reborn in a higher-tech form.  But this post is staying low-tech, the basic window that I know from my time in Zimbabwe.  Standard "Z" section, putty glazed.  The same "Z" section serves for outer frame and for hinged sash.

 Notice the little heel on the back of the "Z".  This forms a groove to channel water around the sides. In case of driving rain, you might get some water that needs to be directed in this way to the bottom and out again.  The same groove it the outer frame helps to key the frame into the internal render.  Internal plastering in Zimbabwe uses a sand-cement mix, not the lightweight gypsum base coat that I was used to in the UK.  Again it has to do with climate and the economics of material production.

I'm going to break off there and post this.  I've been far too quiet this last 2 months, got to get something out there.  Part 2 will follow shortly.



  1. Nice topic Andy. Steel section windows are still popular in most of the Asian countries like in India. I think profiles for steel section windows should be available on Autodesk Seek. Go ahead.

  2. Andy,

    Thanks for sharing this post, I grew up with the same kind of steel windows in Hong Kong when I was a kid. Your handles reminds me of how they work, and they leak when there was a typhoon. Many of these windows gradually got replaced with aluminium frame window in the 90s.

  3. Thanks guys. Interesting to know where else steel windows have been popular. I can imagine that they would struggle with a typhoon though.

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