The Craft of Architecture

What material should I use?

There are a few standard types of sheets used for perforation:

• galvanized steel,
• untreated steel,
• stainless steel, and
• aluminum.

In terms of price, aluminum and stainless are more costly while untreated and galvanized are the least expensive. For exterior use, all 4 types can be used, however, the untreated steel must be painted, and rust will most likely occur at points of connection over time even if painted. Galvanized steel won’t rust on the surface, but the galvanizing happens before the holes are punched, so there is still some chance that rust will form in an exterior application. I’ve been told that the rust is negligible, though. So your best bet for exterior use is the stainless or the aluminum, and both are the best looking as well as the most expensive.

What perforation pattern should I use?

There are all types of perforations such as squares and slots, but the most common perforations are circles. I’ll focus on the circles. There are several items that must be specified when choosing the circle pattern: diameter of circle, distance between circles from center to center, straight or staggered pattern, angle of staggered pattern, and finally percentage open. Let’s look at each one:

• diameter of circle: the diameter can range from tiny to several inches. When choosing a hole size, you have to consider 2 main factors: safety and visual effect. Safety really only comes up if you are using the perforations in a fence, guardrail or gate. In these locations, consider keeping the holes small so nothing can easily pass through the perforations such as a hand trying to open a door or a baby’s arm. For visual effect, there are two camps: those more concerned about seeing the circles and those who want the circles to fade away. The latter would use a smaller hole while people that would like to see the holes should consider a minimum hole of ¾” diameter for every 50 feet you will be away from the building. So, if you like to see the holes from the ground, but you have the perforated metal at the top of a high-rise, then use really big perforations.
• Circle Diameter, circle distance, and percentage open: These three items are related, and the one that is most important behind the circle diameter is the percentage open. This simple rule is if the perforated sheet is open 40% or less it will look a lot more like a solid panel. If the perforated sheet is open 50% or more then it will look more like a transparent panel. Look for these numbers rather than worrying about the distance between centerlines.
• Staggered versus Straight and angle of stagger: This should be obvious what the difference is between these two. They are normally written like this STR and STG. Straight will have a much lower percentage opening tan the staggered always, so I personally prefer staggered at a 6o degree stagger. Your choices of staggering is normally 45 degrees or 60 degrees. The only real difference is purely visual.

Small Perforations

Large Perforations

What thickness should I use?

Thickness depends on so many factors that I suggest consulting your fabricator. In general you would want to ask yourself: will the piece be curved or straight? Will the piece be within human contact? How frequently will the piece be attached to structure, every 1 foot or every 4 feet or more? My own personal preference is that I would not use anything thinner than 20 gauge and would prefer to use 16 gauge.

How wide will I make each piece?

There are only two standard widths which are 3 feet and 4 feet. Anything wider or narrower that need to have a solid border will need to be a custom sheet.

Should I use custom perforations or stock perforations?

With stock perforations, the choices are slim. From what I’ve found, if you decide to have more than 8 sheets on a project then the cost is negligible.

How should the perforated sheet be connected to the structure?

I really don’t want to speak too much about this because there are so many personal preferences. The only thing I would want to keep in mind are these questions:

• Will the connection be susceptible to rust?
• Will the connection retain water?
• Will the connection created stress on the panel? and
• Will the various materials react will together (i.e. aluminum and steel react badly when touching).

Here are some links to useful resources:

• Diamond Perforation
•  McNichols
• Hendrick Manufacturing

This entry was posted on Friday, November 2nd, 2007 at 12:58 am and is filed under Materials. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.