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I'm building a wooden gate for my deck, and I want to put in a cross brace to reduce sagging. I want to install the brace so that it transfers the load from the top unhinged corner, to the bottom hinged corner.
I'm just not sure what the best way to achieve that would be.
Given the image above. How should the cross brace be installed? Does it even make a difference?
You asked for optimal: Follow a few thousand years of practical experience and put in a tension brace (lower outside corner to top hinge-side corner - opposite what you are going for, which is a compression brace) Go with the past few hundred years and make it a turnbuckle.
The best form of compression brace "in plane" is none of the above, and has a point on the end that connects to both sides of each corner, with the midpoint of the brace hitting each corner. Call it corner to corner. That is inferior to an "out of plane" brace in the same position that overlaps the backside of the face frame and is glued and screwed to the face boards; both are inferior to the tension brace, though you can use both for the classic X brace scheme - but the tension side will do most of the work.
Over time a wooden gate will tend to sag. So you need a cross brace.
If you are building the cross brace using wood, the cross brace should be in compression. So the cross brace will go from the corner with the bottom hinge to the top corner on the other side. (Wood is much stronger in compression than it is in tension.) The sagging part of the gate will push down on the wood.
If you are using a turnbuckle, it will act as a tension brace. So it will go from the corner with the top hinge to the bottom corner on the other side. The turnbuckle will pull up the sagging part of the gate.
See poorly constructed diagram below:
At my house we had some very heavy gates made up by a professional builder and we didn't want it to move. The frame was made of galvanised steel and it was covered with heavy kwila riveted to the the steel frame. So far so good.
However another gate made of pine for the back of the house by the same builder started off perfect, but winter weather has caused it to sag slightly despite the diagonal brace. I can tell you with all certainty that the way you place the brace will make no difference.
You're splitting hairs. What you'll find is your gate will move even though you've braced it. We were told this by our builder and I know it to be true of all wood as I've done a fair amount of wood working.
The reason is, it's because it's made of wood. Wood expands and contracts with the weather and the seasons. So if you don't want it to move, make it out of metal.
If you want it to move less, make it out of a something like cedar. Down here in NZ we make a lot of gates and fencing out of treated pine. It moves and twists all over the place.
I'd start by making sure your wood is dry. A lot of the timber you get from the merchant is often stored outside and isn't nice and dry. You may need to dry your timber out for a month by stacking it nice and flat off the ground and out of the rain. Turn it, allow airflow through it. Then when it's dry you can start making your gate.
You've got a couple of options. Do any of the diagonal brace options you've already asked about. Or, us Ecnerwal's suggestion with a turn buckle. It's a sensible idea. The reason is you can adjust the tension to move the gate up or down as it moves... and it will move.
Also, to help slow down the uptake of moisture into and out of the wood causing it to move you can paint it or oil it.
Personally what I did to combat wooden gate sag was
In 2 years the post has begun to warp to the south from Lake Erie's winter winds but the gate is still fine. Of course I was just using what I had on hand. Home Depot has a gate framing kit that does the same thing.
A few simple answers:-
the direction of your cross brace is wrong. It should go instead from top left to bottom right.
The reason for part 1) Try and imagine that the load you have drawn will push down all the way to the bottom right corner. This is the part that will move most if not secured. This gives a key to which part you need to secure most.
All the drawings you have drawn are quite similar. They all have material going directly from corner to corner "through" the cross brace.
None of your drawings have the theoretical ideal. This involves an element going directly from corner point to corner point. However, because this is a small force over a small distance it really doesn't matter if you attach the cross brace in any of the ways you have shown. Indeed,you should do so, because it makes the fitting much easier for you. This way of attaching elements, not exactly to the corners, but offset, is/was commonly used in steel bridge construction among other things. It exposes the crossbracing element to some bending forces, but this is not really of any consequence here.
Almost any material and thickness that you use will be strong enough, unless you are insane and go for string. (which would work as long as there was no upward force applied!!) Simply choose something strong enoough not to break if it is hit side on by someones foot or some other accident. And secure it cleanly to avoid rotting, etc.
hope that helps
The gate starts out square, but will want to sag into a parallelogram. The diagonal running from top left to bottom right will want to stretch and lengthen, and the other diagonal will want to compress and shorten. In theory, either a tension brace on the first diagonal, or a compression brace on the second, will prevent the gate deforming into a parallelogram. It is essential to recognize which diagonal is which. Putting a tension cable on the compression diagonal is undesirable and will actually aggravate the problem. Similarly, putting a compression brace on the tension diagonal is not ideal, although it may help somewhat if well-connected.
Gates are often built with just a compression brace alone, since the wood is available as the gate is being built. But as the wood dries and shrinks, the compression may be lost and the gate may sag. The best thing to do is to add a tension brace in the form of a cable or rod, and turnbuckle, so if the gate eventually begins to sag it can easily be drawn back into square.
The answer is #2
If you eliminate the outside vertical and the bottom horizontal... Which of those designs would still stand on their own? :)
