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Proper Post installation for heavy driveway gate  RSS feed

 
pollinator
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I'm building a solid wood double gate for my driveway that is two 6-foot wide panels, with a curved top edge  that will be 5 ft high at the outsides and 6 ft in the center.   I don't know how much it will weigh but figure 2x4 frames with 3/4" solid pickets on the face - (I can just barely lift them).   I've looked at a number of how-to's for details but am not sure about the posts.     I already did a quick and dirty trial with the existing picket fence posts that are 4x4x6 and buried 2 feet deep - hahahahaha! I can laugh with you - I really didn't expect them to be strong enough but it served the purpose for the summer.

If I use 6 x 6 x 8 posts (square, from Home Depot),  and bury them 3 feet deep in solid red clay, how much concrete should I use to keep them from leaning without using tension wires.   Should I make the holes extra wide at the bottom for extra resistance?

Would  2@ 40-lb bags in each hole do the trick ?  Should I use 2 or 3 hinges on the 5 foot tall post/gate.  I like the idea of overkill - don't want to deal with a sagging gate when I get old(er)

thks for any advice!
 
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2 posts per gate. The second post stabilizes the first

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Posts: 339
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I like to over- engineer things too - never have to revisit them again. So, avoid placing timber in contact with soil e.g. Swapping out timber for steel. But acknowledge the cost and aesthetics issues.

Fencing and gate installation can be a real PITA!

As Wayne suggested, the top option is probably the most aesthetically appealing once pickets are attached. A cross brace between the posts, and importantly, on each gate panel will reduce the likelihood of sagging.

Three hinges to take the weight.

Also, general rule is to put 1/3 of the posts into the ground, with the holes 3 to 4 times the diameter of the posts.

Obviously, allow the posts to settle/concrete to cure before attaching the gates. And, support on blocks when attaching 'em.
 
Susan Pruitt
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Oookaaaay - both of you ignored my request to not do tension wires so I'll be a good girl and beef up the fence posts with the angled cross braces.    And wow - hole 3 to 4 times diameter of the post ???   Would you fill that to the surface with concrete or just the bottom foot or two?  

I've been putting this off for 5 years but since I'm expanding the free range area for the chicks, and occasionally have neighbor dogs wander in - it's time.   I can't do metal - no skills, no tools, no money, no strength, but stubborn enough to git 'er done by wiggling those wood posts around :)     I'll probably only live another 20 years so pressure treated 6x6's should last that long don't ya think?

Big thanks for swift responses :)
 
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If anyone has clay soil that expands and contracts with the seasons, hard tamping 3/4" rock around a post that is set well below freezing level works well.  Tamp it  every 2"-3" with a heavy, skinny, flat-ended rod.  Concrete in clay can end up acting like a buoy in air once the clay contracts from around it, or gophers tunnel up to it and give the chunk of cement room to lean.  And if rodents tunnel next to the rock and it falls into the tunnel, it's easy enough to tamp it down and add more.   But there is very little room for the rock to be effective next to floating cement.   I have probably close to 30 4x4s and 6x6 wooden posts set in expansive clay with 3/4" gravel, with gates and grapevine wires with a lot of weight on the wires, and they are all holding steady.

And you'll save yourself a lot of extra work if you use treated wood.  I went through an inner struggle about that, but where I am, in my soil, the insects have untreated wood weakened in just a few years, and it's not worth it, especially in 100-foot rows of grapevines.

 
Susan Pruitt
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Thanks Cristo.   I don't know if I have "expansive" clay.  I installed about 350 linear feet of 6 ft privacy fence with 4x4 posts and half bag of concrete each, and backfilled with tamped clay, about 6 yrs ago and I don't see any indication of heaving or leaning or shifting.   We have virtually no freeze/frost depth here, 18" is code for house and deck footers,   so I'm guessing the same method will work for my heavy gates.   And oh yes, pressure treated only.  I did another "quick and dirty" garden gate 2 summers ago,  with salvaged interior door frame lumber and it collapsed in 18 months.  Rot is more of a problem here.   We get lots of moisture about 9 mths of the year.   So this is my year of permanent installations!
 
wayne fajkus
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My concern is not the hole, its the post bending. The full weight of the gate is gonna try to bend the post toward the gate until the end of the gate is setting on the ground.

Here's another option. A header over the 2 posts.
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F Agricola
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RE: ‘I'll probably only live another 20 years so pressure treated 6x6's should last that long don't ya think?’

Ditto Wayne – only issue with that option is the likelihood of the fence leaning ‘forward’ or ‘backwards’ because of the top rail weight and longer posts. To reduce that you’d need to put more of the post in the ground to compensate i.e. +1/3 the length of the posts in the ground.

I hate treated pine and generally believe it to be a shit product. Besides it being very nasty from an environmental viewpoint, it just doesn’t seem to hold up in our coastal Temperate to Subtropical climate. Don’t know if UV has a significant role?

Anyway, from experience, I have red reactive clay (expands and contracts with moisture levels), when a treated pine post is installed, it only lasts a few years because the hole acts like a tub holding water = rot.

We’re blessed with a large selection of native timber, some of which is fungal and insect resistant, so I prefer to use one of those. A similar timber may be available in your locale.

Suggest you have a chat with a ‘real’ timber merchant, that is, not some well-meaning employee at a glorified hardware store. Find out what species alternatives are available for in-ground durability. (They may suggest treated pine in the end, but it’s worth checking. There is also treated hardwood but it’s not that commonly available e.g. structural timber, some used as marine piers, etc) … that could be overkill, but at least the gates won’t fall over just as you enter dotage!

Hardwood: more expensive but durable ~ 20-60+ years in ground depending on climate
Treated Pine: cheap, not durable but good enough for pickets ~ 5-10 years in ground depending on climate

Also, you may be able to purchase ready-made steel gate frames with/without hinges attached that you can simply screw timber pickets onto = very strong, self-bracing, easy-peasy.

There’s all sorts of bracing techniques for timber gates, in Google Images search for ‘Gate Brace’ and you’ll see what I mean.

Have we over-complicated this very simple request? If so, mission accomplished!
 
Susan Pruitt
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" Have we over-complicated this very simple request? If so, mission accomplished! "

Haha!   I asked for it didn't I?   Actually I am an over-thinker myself so I was hoping someone here would clarify and provide the definitive expert answer but I do love the extra thought because I like to "leave no stone unturned".  So this is good   The biggest challenge is, of course, the budget so I'm stuck with pressure treated pine which I do believe is okay in my climate and I really like the header idea as I've already been thinking about an arbor over it.   With a 10 foot post I'd be close to the 1/3 rule, and I can plant some sort of 'block' to rest the ends of the gate on when it's open to minimize amount of time under gravity.
 
pollinator
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Susan

I don't think concrete is the best way to set posts. It doesn't seem to do wood any good at all. About 10 years ago I made a point of getting a good cedar post, 8" at the bottom, 5" at the top, about 8' long. I had it set in concrete and in 4 years I started seeing rot around the post where it emerged from the concrete. I had mounded the concrete above grade and caulked that joint, but nevertheless... Now, that post is at the point of failure, this year, the next - soon in any case.

Drainage helps anything in contact with the ground if there is any way you can possible facilitate it. Concrete does the opposite - it wicks water and holds it against the wood to say nothing of water running down the post and seeping down into the joint at the concrete.

Since then I do posts by digging the post hole (1/3 in the ground) with at least 4" clear all around the post. Dig a little extra deep and arrange several bricks down there; or put in 6" of 1-1/4"+ sharp gravel and tamp it a little. This is to provide a footing for the post so it won't settle much once it's carrying a load. Use sharp gravel, not pea gravel because with sharp gravel, the pointy ends/edges interlock and form an almost solid mass. We want that because it makes it like the post is sitting on one big wide solid rock down there. Except the "rock" has huge pores in it and does not support capillary action and, to the extent the soil allows, drains water away. Then I add another 4"-6" of sharp gravel around the bottom of the post and tamp a little to settle it. This interlocks and secures the bottom of the post horizontally; it does the same job as concrete because the sharp gravel interlocks and forms a solid mass around the bottom of the post - except it's _not_ concrete and it drains and does not hold water against the post. Then I fill up the hole with concrete sand (that is a type of  sand which is like sharp gravel - lots of pointy ends and sharp edges; it's used to make concrete) to about 8" below grade, tamping hard every 3". To tamp use a 6' or 8' steel dirt bar with a 3"  flat anvil on one end to pound down in the hole and, when you have tamped each 3" "lift" properly, the feel of the bar when it hits the bottom will change - it will almost ring in your hands the sand will be so hard. Concrete sand provides the best drainage of any sand. In the top 8" at grade, I again place sharp gravel and tamp a little. Sharp gravel does not really tamp much at all; it's more like you're vibrating it a little to joggle the edges into their interlock. You place sharp gravel at the bottom around the post and the top of the hole at grade because when a force tries to tip the post (ie. the weight of the gate) these are _the_ two places that hold the post steady - most especially the gravel (or concrete if you absolutely must, for some reason) at grade. This works because sharp gravel locks together and becomes effectively one solid piece; since we made the hole at least 4" larger than the post on all sides, there is now a large wide solid thing (the interlocked gravel) set in the ground and holding the post steady at ground level. If you want to make it stronger, make the hole bigger around at ground level and down about 6" so the gravel "block" will be larger and thus be able to resist more sideways forces.

I don't know how much drainage your soil will support and the best gravel sand installation can't make the water go away any faster than the soil will allow it. But concrete actively soaks up water and holds it against the wood just about forever.

> [weight of gate]
Depending on what the gate is supposed to do - stop marauding jeeps or just look pretty - you might want to try, hard, to build the gate to be light weight. Light weight usually means less wear, less damage when it swings into something, easier maintenance, etc. For example, use 3/4" x4 for the frame and diagonal brace and, perhaps, wire fencing or, if you want it to look more solid, 1/2"- cedar pickets, for infill. The latch and, unless the gate will swing through both direction, the stop s/b located to contact the gate in the center (vs. high or low) so that when it swings home hard and hits the stop (or the wind pushes against it for hours) it doesn't tend to twist. Hmm. I recall you're using two gates, meeting at the center. Then a rod into the ground at the bottom and a bar across the top so top and bottom are secured equally.

Another reason for a light gate for me, in any case, is to allow it to be easily lifted off it's hinges if it was snow bound or I need it off for some other reason. There are large pin hinges readily available, but be aware of two points: 1) Try to find or make the pins to be different lengths because it makes it HUGELY easier to set the gate onto it's hinges - one pin at a time. 2) The pins are usually just 3/8" or 1/2" bar stock bent at 90degrees with one end threaded. They are bolted or lagged into the post and work well when they line up in the same line as the closed gate.  BUT, they will eternally try to twist when the gate hangs off them at 90degrees, like when it's open. I know of different ways to fix this, but they require some metal work, and probably a small welder. So I usually just live with this shortcoming because I _really_ want my gates to simply lift off. Otherwise a snow drift against the gate on the side it has to open makes things difficult. If you're installing security gate, though, well, that's clearly a whole different situation. Or if you don't have snow... <G>


Cheers,
Rufus

 
Susan Pruitt
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Rufus I truly appreciate you putting so much thought and time into this query!   Have you thought about becoming a Youtube "How to" sensation ? :)

You've given me more food for thought and first I should correct my original post description of the gate pickets - they are 3/8" not 3/4" thick but I agree that lightening it up more is a good idea.  I might get creative with spacing between the pickets or cutting some design into it.   I worry that a 6 foot length of 1x4 for the frame and brace would warp.  But then, I've bought lots of 2x4 lumber that twists and cups too.   I suppose it wouldn't be too hideous to reconstruct in a few years if necessary.    

The purpose of the gate is to keep chickens in, dogs out, and privacy.   I'm the little old lady who only drives my car a couple miles to the grocery store, Lowes, library,  and a couple other errands each week so the gate won't be stressed much but I figure it can't hurt to support the tips to take the weight off when I'm away for hours.    We have very little snow here - dustings occasionally and maybe once a year a "monumental" 6inches that shuts the city down (haha!) but is easy to shovel and melts as soon as the sun comes out.   Good questions for most people though.

I do have clay soil which is compacted at about 18" below grade and poor drainage at that point.   The first 12" drains rather quickly but 18-24" below can take overnight.     So I wonder if moisture at 3 feet deep will cause rot, even with the concrete sand.   I've seen advice for planting trees not to create a "bowl" for moisture to stand around the roots but to cut a drainage channel away from the low side of the tree.  The gate will be at the top of a sloped driveway, about 3 feet above the road which definitely runs off quickly but I'll do some tests,  dig the hole now, fill with water and monitor drain time

I would never have thought that any sand could be as solid as a block of concrete for ballast at the bottom of the post.  Are you referring to the common builder's sand made by Quikcrete?   That's all I see at my local retail stores as "angled" sand.   But nothing larger than that - I will check with a couple landscaping sand/mulch places.

Interesting thing - when I bought this century old house 7 yrs ago there was a tall 5" round post for a clothesline that was about 2 feet in the ground with about a foot of concrete at the bottom.   I dug out the side to remove it.   No rot whatsoever on any of those posts - just some checking and dry rot above ground.   Another square post had been set in the ground with about 12" diameter concrete at grade.   I have not removed that one but the entire post seems to be in excellent condition!  I don't know what type of wood but in NC almost all construction was hard yellow pine back in the day.   They just don't make 'em like they used to...sigh
 
Rufus Laggren
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Susan

I do set light duty posts just in sand, but that is not what I was thinking here.

At the bottom and at the top of a post hole I use 3/4 and up sharp gravel; better, I should probably call it "crushed gravel" - I think that's the more common term. The idea is that stuff has sharp edges and points and that (the gravel) is what locks together forming an interlocked mass that to some extent mimics solid rock. Material availability is a very local issue and the names used can vary considerably. What you _don't_ want, at least for this application, is pea gravel of any size. The rounded shape just slips and slides over themselves and never even approaches solid. The drainage sand was just easy filler for the post hole between the structural part at the bottom and the top of the hole. You could likely just use all gravel, but I've never done that for some reason. Maybe cuz I can get good sand cheaper than gravel...

If you want drainage sand (concrete sand) I would strongly suggest you locate and befriend a local concrete plant. I'm urban, just outside Chicago, and yet the big corporate outfit with 20 plants in norther Illinois is still friendly and happy to sell me sand in half yard and greater loads - as long as I drive in with my truck or trailer (or both) they'll drop a bucket full in with their house-sized loader in about 30 seconds and charge me the princely sum of $20/yard. I get the right stuff at 1/10th the price (or less) than buying bags at HomeDepot. The key is to talk with the yard boss beforehand and do and go what and where they say - get in and get out smoothly and promptly because they will have dozens of trucks in and out every hour. The stuff at HomeDepot is better than nothing; use the general purpose sand, not the "playground" or "finishing" sand. "Torpedo" sand is general purpose sand sold by materials yards. Look up the weight of sand before you run off to get a load. I happily overload and abuse my vehicles in many reprehensible ways, but I do it _after_ I find out just how bad I'm being...

It sounds like you _really_ want to build light. Put in some good posts and then hang a gate that those posts will just laugh at. At the very least, you want it light so that  you can swing it easily. Latch the top _and_ bottom to reduce prisoner breakouts and also minimize twist. Make it stupidly light at first and next year make it a little heavier - IF you need to.

If the ground isn't level at the gate you will need to add something below the gate to keep the critters in. Best just to take the time/trouble to level a short distance each side of the gate.

You can use lighter hinges if you make the posts taller than the gate by about 3' and suspend the end of the gate from the top of the post.

If 1x4's sag, use 1x6. Small gates (3'x4') I have made with 1x4 Poplar frames, some with half-lap corners and some with pocket screws, have lasted 8 years and counting with no twist or sag. I always use a diagonal. Paint the gate well. Prime it, twice is better. Then two or three color coats of exterior paint. Follow instructions on the can. This is not just so the thing looks neat and sheds rain - a good paint job minimizes moisture movement in the wood and helps things remain straight all their life.

Pocket screw tools are very useful when you don't want to be a furniture maker, just put stuff together in wood. The box stores sell them now and I guess all in for a pretty good set of jigs it might come out at $50; you can go cheaper. You supply the power drill; a corded tool is recommended for power, but 18+volt cordless should work OK. The screws and replacement drill bits and misc consumables are $10 or so for three of four jobs - less, probably. I made a 7'x8' sliding wood door, probably weighs about 80-90# in 2004 using 5/4x6" decking material for the frame with four pocket screws each corner and on the vertical and horizontal dividers. It's hung outdoors ever since and gets horsed around once or twice a week. It's an easy life except for the weather, but still, it does it's job and remains tight and true in all dimensions.

Have fun,
Rufus
 
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My recommendation is to look at really old wooden gates that are still functioning (there are a lot of these in Japan and Europe). Copy a gate that is still in use after 400 years and you can bet that yours will lst as long.
 
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I have built and repaired many gates such as you speak of.
All the issues mentioned previuosly may occur, and I have found a good way to reduce trouble is to ensure when the gates are either open or closed,there is a block. under the gate in the middle in the case of being closed.
And if swung open, under the gate in the open position
That block enables the load to be taken from the post  and the gate itself and everything will last much longer.
 
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