I strongly suggest a diagonal brace, this will stop the gate sagging. Either add another piece of wood from the bottom hinge to the top corner (compression), or a metal strip from the top hinge to the bottom corner (tension). There are lots of illustrations on how to brace a gate on the Internet.

Like Trevor, my first thought was to add a brace. They'll never repeal the Law of Gravity, so the gate will want to fall. The hinges prevent that side from moving down, so the outer edge will will want to rotate down. By bracing from the upper, outer corner to the lower, hinge-side corner, that tendency to rotate will be opposed.

You'll notice that even though he didn't mention it in the text, Mark did add a horizontal brace across the middle of the door. He came to the same conclusion both of you mentioned after trying out several of these extremely light weight doors over the last year --- they do tend to sag a little if they're not braced. We'll see if his simple brace works or whether he needs to add a diagonal.

I agree, with the other commenters you need some sort of diagonal brace for furring strips. Otherwise your gate will lean terribly in a year or two. Even those little metal angle brackets put in several of the corners would help a lot. Horizontal bracing just will not cut it.

If you look at framework constructions you will see triangles everywhere. The reason for that is that a triangle is a stable structure even if the beams are just pinned together.

To make a rectangular structure resist shear deformation you have two choises; either you add a diagonal brace to convert it into a combination of two triangles, or you nail triangular plates to the corner so that the corner can withstand shear deformation.

As Trevor noted, if you add a diagonal brace from the top hinge to the opposite bottom corner (the side of the door with the latch and opposite the hinges will tend to sag), this brace is only loaded in tension and thus self-straightening and can be as simple as a steel wire.

Thanks for all the shoring up ideas. I agree the gate will sag over time, and I guess I'm going to let it sag and then see if I need to implement one of the upgrades at that point.

Rebecca-Those little metal corner brackets sound like one of the easier ways to shore up the design, which I might do in the future when it starts sagging.

Roland-That steel wire idea is what I was thinking yesterday with the addition of one of those turnbuckle dohickeys that allow one to tighten the tension.

I'm with everyone else here, and agree with Roland's explanation. A horizontal brace will do very little if anything to keep the gate from sagging. You really need to form a triangle of some sort to keep the gate from sagging, and when using light lumber (including 2x4s) that triangle needs to support the entire gate. With 2x4s corner bracing is usually not enough. However, just some bailing wire (not aluminum, preferably steel) from the top hinge down to the far corner will suffice.

Hey Shannon,

Thanks for adding your voice to this thread....I'm still curious to hear how your search for a gravity wave is fairing?

I agree with you about using steel wire, it's just that I don't have any turnbuckle things handy and it would require a trip to the hardware store, but the main reason I'm putting it off for the future is the 100 other things pressing on the honey-do list. Right now I'm just going to focus on finishing the fence for that pasture, installing a 5 gallon bucket waterer, and fixing the gaps near the ground, and then moving on to whatever is next on the list.

Sometimes you can use the wire mesh as a structural component, if it's not stretchy on the diagonal (e.g. welded mesh), to avoid the need for diagonal bracing. Probably more useful on ornamental gates than chicken pasture gates :-).

Well, gravity wave searches are on hold while we do upgrades. We'll be searching again come 2014 or so...

As for no turnbuckles being handy... there's an old fence trick you can use. Take two strands of steel wire between the upper hinge and the bottom corner. Screw them to the wood, or just twist them into place. It helps if you install them so that there is a gap between them, maybe to the opposite outside edges of the wood. Then, you take a sturdy stick, place between the two strands of steel wire, and start twisting. Once it is tight enough to resist sag, you tie off one end of the stick.

Kind of like this:

http://4.bp.blogspot.com/-pXvn6nuqmtM/Tb6h003tp9I/AAAAAAAAAjs/ekU35ifQhGE/s1600/DSC_0947.JPG

or this:

http://www.trublufence.com/images/hbrace.jpg

The stick is apparently known as a twitch stick, which I didn't know before tonight. http://www.ehow.com/how_8565101_secure-twitch-stick.html

I've been thinking about everyone's comments, and I think there are two points you're all missing. First, if used like a screen door, a very thin-framed door will sag really fast, but this isn't quite the same. The latch on one side holds that edge up to match the hinge side, which is probably why Mark's furring strip door with absolutely no cross-bars at all isn't sagging all that much 18 months later.

Second, remember this is for a chicken pasture. We're not building the Taj Mahal. If the doors last without sagging for two years and then I have to ask Mark to add a cross-brace, they've done their job well!

I'm surprised that you used treated wood. A lot of the chemicals used for treating wood are copper (and in the case of CCA also chrome and arsenic) based and quite toxic to soil organisms.

I am with Mark, keep it simple and see what happens. I have to build a gate and put up a fencend in area this weekend and plan to do what he has done as far as the gate goes. I am a bit puzzled about the depth of the 8' post, however, at only 19 inches did you cement them in???

Roland --- Excellent point. At the moment, we're willing to use treated wood in areas far from the garden like this, figuring it's no more harmful to the environment than the alternative (which, belowground, means using concrete, which has a lot of energy costs to produce, and aboveground would presumably mean painting repeatedly, which again has potentially environmental problems.) Cedar posts would be a good alternative (although I wonder whether the antifungal compounds that keep the wood from rotting also hurt soil microorganisms --- I'm not sure anyone has studied that.) My experiments with cedar posts, though, show that we have to use the relatively large trees since only the heartwood is rot resistant, which seems wasteful for a project like this.

John --- Mark's gate frame has quite a bit of structural integrity due to the cross-piece at the top and then the fencing wire on each side. Sure, it might move a bit if the ground freezes and thaws, but we haven't had trouble with other gate frames like this moving out of true. What Mark neglected to mention, though, is that he compacts the earth around each post when he backfills it with extreme vigor. He's a pro with what he calls a spud bar and what other people call, I believe, a tamping bar. By the time he's got a post in, it's in.

Remember that correct post depth is dependant on location. the depth for mid-southern virginia is only 18 inches because the ground does not freeze very deep. in md it is 30" and ct is 3-4 ft. So 19" without any thing other than earth tamping is fine in VA.

Good point, Rebecca, although southern Virginia actually has very variable frost depths depending on whether you're in the mountains or not.  Our part of Virginia is equivalent to eastern Maryland.  The map below should be helpful for the general idea of which areas have deeper frost penetration than others.  (I've seen maps that give the frost depth as twice that shown below, but no matter which numbers you use, the relative frost depths stay the same.)