Answers to Your Questions: Bracing a Gate

In e-mail recently, a question about cross-bracing (with links by me):

You said that the bottom of a tensioned cross-brace goes away from the hinge. What is a tensioned cross-brace, and when does the bottom go away from the hinge?

This is one of those things it's easier to explain in pictures, so here's my response.

First of all, a little elementary structures for those of us who are a bit rusty. We have two kinds of forces that a piece of a structure can exert: tension and compression. Tension is a force that is most like pulling, while compression is most like pushing. In addition, every time you have a force, you need to have another force in the opposite direction. This is not a building code requirement, but a law of physics.

So let's take a theoretical gate and set it on the ground. There are two forces at work here, in the simplest way of describing this world: gravity and the force of the ground pushing up against gravity. They balance each other out: if there was not enough of one or the other, the gate would sink into the ground (which happens in soil with insufficient bearing capacity and is called subsidence), or the gate would float away (which, um, is not often a problem with structures).

how a gate is supported on the ground

Things change a bit when you put the gate up on hinges. Now all the force holding the gate up is on the left side of the gate, where the hinges are. But gravity is still pushing down on the gate over its entire width.

a gate on hinges

Over time, gravity will push the gate down, usually until it touches the ground, at which point it will be partially supported by the ground as well as the hinges.

how a gate will sag over time

You can remove sag by transferring some of that gravity load over to the left side of the gate with a cross-brace. There are two kinds of cross-braces: compression and tension. A compression cross-brace takes weight from the top bar and transfers it by pushing down against the bottom hinge like so:

how a compression crossbrace works

A tension cross-brace takes weight from the bottom bar and pulls it upward to the top hinge like so:

how a tension crossbrace works

Either type of cross-brace is fine. The limits are based on your material (wood in this situation works best as a compression brace, while wire can only ever be in tension), your design (you may want a less obtrusive brace), and the application (you may want to avoid tensioned wires where children will be playing).

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posted by ayse on 07/08/08

7 Comments

This is something great to know. Thanks for the explanation with drawings. It makes it much simpler to remember!

I done it the wrong way with wood, and it seems to sag even worse, from the extra weight maybe. I bought these really heavy duty hinges for my latest gate, the straps are 36" long on them. I hate a sagging gate. That's interesting about the tension cross brace, although I guess dangerous with kids around using it like a harp.

Ow, yeah, Derek. If you do it the wrong way you actually make the sag worse, because the brace will be working to make the gate sag rather than stay up.

Wow. Thank you for this. Great explaination, nicely illustrated.

You know you could write a book with stuff like this.

Thanks, Jenn. I've actually been considering writing a book, but at the moment I don't really have enough material (time is another matter altogether).

Hi Ayse,

Thats how I thought the brace should work but could not explain it as well as you have.
Thanks for the help.

It's amazing that it took me 30 minutes of searching the 'net to find the answer to this question. Thanks! I'll be adding the "correct" bracing to my gate this week.

Note: We're getting pummeled with spam comments, so I've turned off the ability to use any HTML or include any links for the time being. Email with any issues.

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