Saturday, December 13, 2014

Chain Link Fencing Basics - Part 2: Framework

Framework is the tubular steel pipe that makes up the posts and rails of a chain link fence; it is available in a wide array of diameters and wall thicknesses.

When talking about the diameter of a fence post, there are a few important things to know.  First , similar to dimensional wood products, steel posts and fittings are usually labeled in nominal sizes; so, for example, a fence post listed as 2” is actually 1 7/8” O.D., and a fitting listed as 2" is meant to fit a 1 7/8" O.D. pipe.  Second, fence pipe is measured in outside diameter (O.D.); so, if you see that a post is 1 7/8”, it means that the diameter of the outer wall of the post is 1 7/8”, unless stated otherwise.

The strength of a tubular steel fence post is primarily a function of its wall thickness. There are a wide number of residential, commercial, and industrial grade pipe choices available. Different manufacturers have different brand designations for their pipe. For example, Allied Tube & Conduit designates its fence pipe as follows:

SS15 – Residential, Light Commercial – Wall Thickness on a 1 7/8” Pipe = .072”
SS20 – Commercial – Wall Thickness on a 1 7/8” Pipe = .090”
SS40 – Commercial/Industrial – Wall Thickness on a 1 7/8” Pipe = .120”

Also common in industrial fence applications is Schedule 40, also known as Standard Weight, pipe, which is a national standard size and has a wall thickness of .145”

Chain Link Posts


The size of the fence post that you use will be determined by a number of factors, including: the height of the fence, the gauge of the fabric, and the primary use of the fence. For example, a 4’ or 5’ residential fence with 11 gauge wire can usually be installed with 1 5/8” diameter line posts and 2” terminals. On the other hand, an 8’ commercial grade fence with 9 gauge wire will require line posts that are at least 2 ½” in diameter and terminal posts that are at least 3”. A general rule of thumb is that your terminal posts should be at least 1 size larger than your line posts.

Another factor to consider in choosing your posts is whether you will be using some type of privacy screening on the fence, either now or in the future. Privacy screening, slats, and fence weave products all add surface area to the fence, thereby increasing the wind load on the fence. You will typically have to increase your post sizes when using such products. So, on the 8’ commercial fence in the example above, you may need to switch to 3” line posts and 4” terminal posts. Depending on the estimated wind load on your fence, you may also have to adjust your posts wall thickness, spacing, and footer size/depth. A thorough discussion of wind load is beyond the scope of this introductory article. For more comprehensive information, view the Chain Link Fence Manufacturer’s Institute’s Wind Load Guide.

Chain Link Rails


Almost all permanent chain link fences have a top rail to support the weight of the chain link fabric and keep it from sagging over time. The fabric is tied to the rail using wire ties, which keeps the fence tight and prevents the fabric from being pushed down for easy ingress onto the property – either by an animal or trespasser.

Top rails are typically sold in 21’ sections (though they may be cut shorter for transportation purposes), and are either swedged* end or are sold with sleeves that can be used to splice the rails into one continuous rail. The top rail attaches to the terminal (end or corner) posts via rail ends, and runs through loop caps on the line posts.

*A swedged rail is tapered at one end so that it fits into the unswedged end of another rail, enabling you to create one long continuous rail.

A bottom rail serves the same purpose as the top rail – preventing the fabric from being pushed inward, thereby allowing easy access. Unlike top rail, however, bottom rail does not run in a continuous line; it must be cut down to fit between each section of fence. It attaches to the terminal post with an end cap, and line posts with line rail clamps. Many homeowners / fence installers choose to forgo the bottom rail in favor of bottom tension wire, which serves the same purpose, but is a less expensive alternative.

Often, chain link fences taller than 6’ also have a mid-brace rail, at least on each section between a terminal post and line post. The mid-brace rail provides support for the terminal post against the tension of the stretched wire fabric. In other words, it helps to keep the terminal post from being pulled over due to the high tension needed to keep the stretched fabric taut.

The typical diameters for top rail are 1 3/8” O.D. for residential installations and 1 5/8” O.D. for commercial installations, and most fittings are available for both sizes.

No comments:

Post a Comment