I would like your suggestions/experience/opinions on designing steel windows+patio doors, using hollow sections (RHS as they call them) and angle sections. The window style I have in mind (but can not afford to buy and transport to my country) are the iconic Crittall windows.



(first image was taken from here, second image from here)

Alas! Crittall use a special steel section which they manufacture themselves and I can not find in the market here. So I have to use steel sections which I can find in my country: angles, tees and hollow sections:

enter image description here

As far as aesthetics are concerned, my main worry is "thin sight-line", i.e. the frame to be thin, maybe a width of 30mm.

I have solved (i think) life-expectancy and maintenance issues as I intend to bath-galvanise them and then (optionally) powder paint them to give them a nice gloss color and life expectancy (maintenance free) of 20 years at least, if not 50!

The welding will be undertaken by a professional.

My main problem is air-tightness. It is easy to design on paper but in practice I do not know how efficient it will be.

Basically I follow the rule that when closed, the frame of a window should 'kiss'/'push against' the steel case (screwed on the wall) at two different places. Thus air trying to get inside the house must by-pass two obstacles/seals/weatherstrips.

I also intend to 'glue' (somehow, or even screw) on the steel frame rubber/insulation foam/seals (weatherstrip they call it) - something which aluminium and crittall windows do very well because their sections have been designed to have a channel where the rubber seal goes in and stays there without need of glue or screw. Glueing on metal is probably a nightmare.

The basic idea can be seen from these crittall drawings: http://www.crittall-windows.co.uk/wp-content/uploads/HOMELIGHT-DG-WEB-DOWNLOAD-11-15.pdf

There will be two types.

1) Opening out, 'casement' windows, height 2m, width of each pane 0.6m. They will be hinged on the sides, top and bottom. Here is a drawing of the side-section (i hope it makes sense):

enter image description here

2) Swivel or vertical pivot type. The hinges will be at the middle of the window frame, top+bottom. Sorry no drawing for this.

My questions:

1) Do you have any comments/suggestions about the air-tightness of the design in the image attached?

2) Do you have any suggestions on how to implement the vertical pivot window type (using the same RHS, flat and angles as with the openout window) as far as air-tightness is concerned. Suggestions about the hinge?

3) From the drawing you can see a wooden frame at the inside of the window securing the glasspane against the exterior steel angle. This wood will be screwed onto the steel frame. What do you think as far as safety is concerned?

4) What is the best way to secure the weatherstrips/seals onto the metal frame?


1) glass will be double-glazed 5mm+18mm airgap+6mm, weighting about 30Kg/m2, so for a 2m x 0.6m window, the total weight will be 45Kg plus, say, 10Kg of steel=55Kg.

2) The windows will imitate the crittall look of horizontal splits every 30cm by using a one-piece glass pane and then welding on the outside thin pieces of metal horizontally.

I have given only an outline of the project, if you need clarification let me know.

thanking you in advance,


  • 3
    Hi. Although this is a cool question, it doesn't really seem like a good fit for our "home improvement" topic; it's more engineering and manufacturing than we usually cover. – Daniel Griscom Apr 21 '16 at 11:42
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    I'm voting to close this question as off-topic because it's very broad and not a DIY topic. – isherwood Nov 28 '17 at 14:55

The windows in the top photo are actually doors. They are aluminum, probably a custom extrusion.

You will have a VERY heavy window. Your opening mechanism will need to account for that, as well as the structure which supports the hinges.

The windows in the lower photo are actually made of steel T-section. Yes, they are welded. The glass is glazed in using traditional putty glazing (on the outside of the building, very impressive!) However I would use a quality silicone, and a great deal less of it.

You get sealing by designing for gravity and using rubber gaskets. Trying to do it with steel fitting tightly is going to create windows which bind, get stuck, and are sensitive to tram problems. You won't knock the window out of tram, but the window frame? You betcha.

I don't like the screw-in plywood. You are dealing with heavy windows and it will not hold unless you use a lot of screws. I would go with metal for that. Tolerances should be not too critical since you should glue in the windows with a quality silicone caulk. Caulk has no shelf life, it is garbage after a year or so, so don't use old stock.

Designing windows well is an iterative design. The best aren't good because they're smart. They're good because they've made mistakes, learned, made more, learned, repeat.

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  • well crittall claims they are steel doors. – bliako Apr 22 '16 at 23:22
  • Thanks for your comments. Many building from the 70's around here have windows and doors made of steel ala Crittall. Fair enough they use single-glaze glass. I have calculated that each window frame will have 17Kg of metal (frame not the casing screwed on the wall) and 36Kg of double-glaze glass. A total weight of 53Kg for each 1.2m x 0.6m window frame. And that will be on two hinges (top+bottom). I don't see a problem (in theory). The plywood was a design effect. I can do without. Crittall design is very impressive I agree - doesn't matter if I get cold.... Thanks. – bliako Apr 22 '16 at 23:38
  • I'll be darn. They really look aluminum. They must be new and the paint must be perfect. – Harper - Reinstate Monica Apr 23 '16 at 2:22

i have multiple questions, but first, where is this being done and what is your climate like.

i think you will have huge sealing, glazing and warpage problems trying to weld that out of steel. even if you get someone who has a harmonic resonator, the thin sections will twist enough to make glass mounting a problem.

why not use aluminum. its stiffer per unit mass, available in multiple profiles to suit your purposes, and is just as weldable as steel, but doesn't warp. you just need someone who can TIG or MIG with an aluminum gun and gas.

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  • it's being built in malta. the climate there is hot in summer, about 30-40 degrees C, and in winter rarely reaches freezing point. – bliako Apr 22 '16 at 21:22
  • okay, so that answers the question as to why your glass wont be in sealed thermal panels. if i were you, i would do it in aluminum - not steel. a little more cost, but no corrosion or warpage, and you can get profiles that will do the job in a single extrusion – personal privacy advocate Apr 22 '16 at 22:57
  • I will see what's on the market for alu profiles. A local alu-window assembly factory has shown me some very ugly sightlines costing a fortune. I doubt it will be cheaper than me DIY-ing it (dying too!:)). For steel, my calculation for cantilever-beam deflection (fixed on hinge) of RHS 40x20x3, assuming a uniform 70Kg (glass+metal) and length=0.6m is 4mm. Not bad I think given that the window rectangular frame as a whole will decrease the deflection. – bliako Apr 22 '16 at 23:21
  • Twisting is another problem but don't forget the steel bars welded horizontally. Anyway it's better to make one frame and test it in practice. will keep posted. thanks – bliako Apr 22 '16 at 23:21
  • you misunderstand - i am not talking about sagging or bowing. the warpage i am talking about is during welding. if everything doesnt stay flat and true, you will have all sorts of problems with sealing and heat related glass failure. you can still diy this if you want (its actually much easier to fabricate in aluminum than steel), you just need someone who knows how to weld aluminum properly (there are lots of monkeys who say they can but can't) – personal privacy advocate Apr 22 '16 at 23:33

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