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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.

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I'm just not sure what the best way to achieve that would be.

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Given the image above. How should the cross brace be installed? Does it even make a difference?

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maths tell me you want the face of the diagonal to be perpendicular to the transferred force angle. So that eliminates #1 and 3. Also you want your release force side as close to perpendicular to the force angle you want to set. Since you want to exert force straight right to left then your face would look like #2. –  DMoore Apr 21 at 15:40
    
How well this works or if it does any good is really a reflection of the current gate system. If it were created with high quality metal that could withstand a few thousand pounds then there would be little to no deflection so no force could be transferred. If you have stock lumber a brace will matter a lot. Configuration helps transfer load but not sure if the way you put it in matters because what matters more than transferring load is the fact that it is stabilizing the other boards. –  DMoore Apr 21 at 15:44
    
What about flipping the cross brace horizontally? So it becomes, left side to bottom. –  Bjørn Bråthen Apr 21 at 22:48
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@BjørnBråthen Then it wouldn't transfer the load appropriately. You're suggesting using a piece of wood as a tension brace, instead of a compression brace. Wood is much stronger in compression than tension, so a wood tension brace would not likely work so well. –  Tester101 Apr 22 at 10:35
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Why not a double mitre on the brace so that it runs actually corner to corner. That appears to be quite common for panelled construction and looks nice. It also allows the brace to be directly fitted to both the top bar and the upright. Open frame gates often use an arrangement that looks like this from a distance but actually the brace doesn't sit within the frame. –  Chris H Apr 22 at 10:57

4 Answers 4

up vote 13 down vote accepted

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.

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Not saying this is bad advice at all but this does deflect some of the load downward. –  DMoore Apr 21 at 18:13
    
I think a key to this may be that all the boards are fixed to the brace not just the frame, hence the fixing between the brace and the frame is not that impertinent. –  Walker Apr 22 at 7:55
    
+1 - A bit of explanation. The tension brace is being pulled lengthwise which is what keeps the gate in check. If you use a turnbuckle as suggested you can adjust it when your gate starts to sag or the ground heaves, etc. If you put the brace in the way you've laid out in your drawing, it will put additional tension on the joints of the gate, pulling the top apart from the hinge side. Putting the brace in this way forces all the joints together instead of apart. –  GenericJam Apr 22 at 11:35

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.

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Personally what I did to combat wooden gate sag was

  1. use 7 inch cast iron shelf holders as corner braces on all 4 corners of my frame
  2. hung my square frame with normal heavy household door hinges
  3. screwed my picket to the frame while it was hanging
  4. added a full corner to corner brace on the front of the gate over the pickets

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.

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A few simple answers:-

  1. 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.

  2. All the drawings you have drawn are quite similar. They all have material going directly from corner to corner "through" the cross brace.

  3. 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.

  4. 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

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