Seeking assistance with fenceposts for gate.

Sandyclay · 6 Oct 2008

It seems I can't dig deep enough for the front gate I want to build. I've been told I should have 1/3 of my fencepost underground, I've hit some roadblocks, and am not sure which way to go.

The holes: I've dug each down 2'1". In one hole, I've hit a large rock I can't get past. I'm pretty well at my limit due to arm length anyhow. I've not had much luck with the digging scoop, as the soil at that depth is sand and rocks, and just falls through the hold in the scoop. Power tools are out as my locate says I'm digging close to power. I've pretty well accepted that these holes are as deep as their gonna get, unless someone has any other ideas.

The posts: I want to have a 6'6" clearance, and on top of that a 6" Arbor, which I believe should give the frame some support. This doesn't seem doable given the shallowness of my holes. I've already bough 4x6x10' posts for this.

Can I get away with sticking my posts in these holes, or is this completely stupid? Is there something else I can do to make this work, or should I change my plans and just go for 4 foot aboveground posts for the gate, and forget the arbor?

Thank you in advance,
Sandy.

JohnD · 6 Oct 2008

you say gates, and you say fenceposts, and you say arbour

What exactly is it that you want to build?

Sandyclay · 6 Oct 2008

JohnD said:
you say gates, and you say fenceposts, and you say arbour

What exactly is it that you want to build?

I'm building a front gate, bordered by two gateposts roughly 3 feet apart. For now I am just putting in the gateposts. The gate will be roughly 4'high. I have been told that by attching the posts at the top with an arbor, the gateposts will be more solid.

(sorry if I confused things by saying fencepost instead of gatepost)

JohnD · 6 Oct 2008

Is the arbour a single lintel, or a rectangular structure like a pergola frame or gazebo?

Of the four posts, how many will be attached to each other?

Sandyclay · 6 Oct 2008

JohnD said:
Is the arbour a single lintel, or a rectangular structure like a pergola frame or gazebo?

Of the four posts, how many will be attached to each other?

I wish I could intelligently answer your questions, but I lack the terminology. I looked up pictures of your terms, but they didn't look like what I'm doing. I will simplify:

the design is two 4x6 posts, 3 feet apart, sticking 7' out of the ground. The tops of the posts will be joined by a 2x6 affixed to the vertical faces of the post, leaving a clearance of 6'6".

Perhaps the discussion of the arbordesign is distracting from the original questions:

1) Is 2'2" dept sufficient to support 2 posts that will be 7' aboveground?

2) Can anyone suggest any workarounds to get my holes deeper? I am limited on one hole by the length of my arms, the the other hole by a football sized rock I can't dig out (holes are 1' diameter at top). Soil composition is hampering scooping, and proximity to underground power prohibits power tools.

JohnD · 6 Oct 2008

Sandyclay said:
the design is two 4x6 posts, 3 feet apart, sticking 7' out of the ground. The tops of the posts will be joined by a 2x6 affixed to the vertical faces of the post, leaving a clearance of 6'6".

So this is like a doorframe, with a head connecting the two uprights. this will tend to prevent the posts tipping towards each other from the weight of the gates (this is something that gateposts tend to do)

You mentioned another two posts. If these are in a row with the first two, they will not contribute much because they are already bracing each other in that direction.

However, if the other two posts are set back from the first two, so that the posts are in a rectangular shape, and you join the extra pair to the front pair, then the extra posts will brace them against the load of the gates when they are open (their weight will tend to pull the posts over backwards)

In this case it will be like the frame of a wooden building, and it will be very strong, and the posts will not be under much strain.

It is relevant that the gates you have in mind are only 4' gates, so (1) they are not very heavy (2) they will not have a lot of wind load. If the gates are of open structure, like palings, rather than being solid, they will have even less wind load.

For a 4' gate, a 2' hole would be enough. If you are setting the posts in concrete, it is worth casting a concrete "doorstep" joining the two concrete pits. this will brace them together, adding strength and preventing them from leaning. it does not need to be as deep as the post holes, and can be made an attractive feature.

Sandyclay · 6 Oct 2008

JohnD said:
So this is like a doorframe, with a head connecting the two uprights. this will tend to prevent the posts tipping towards each other from the weight of the gates (this is something that gateposts tend to do)

This is exactly it!

JohnD said:
You mentioned another two posts. If these are in a row with the first two, they will not contribute much because they are already bracing each other in that direction.

Sorry for the confusion... It's just two posts, in a doorframe configuration as you've mentioned, above.

JohnD said:
It is relevant that the gates you have in mind are only 4' gates, so (1) they are not very heavy (2) they will not have a lot of wind load. If the gates are of open structure, like palings, rather than being solid, they will have even less wind load.

That's great advice... I will ensure the gates are of an open structure type.

JohnD said:
For a 4' gate, a 2' hole would be enough. If you are setting the posts in concrete, it is worth casting a concrete "doorstep" joining the two concrete pits. this will brace them together, adding strength and preventing them from leaning. it does not need to be as deep as the post holes, and can be made an attractive feature.

That sounds like a great idea, although a bit tricky in my circumstances... there is already a sidewalk poured between the two posts, so I'd have to dig under the sidewalk, which would be pretty effort intensive. I will consider it, although it would be a last resort.

If I make the gate open as described, do you think 2' deep underground posts would support my 7' aboveground doorframe, or would I be absolutely insane to try? Do you have any other ideas that could help make this work?

JohnD · 6 Oct 2008

It's really a 4' gatepost (the rest of the post height is just ornamental ) so the 2' depth will be enough. The problem with gateposts is that they lean inwards with the weight of the gate. If you have a concrete path there you can probably get the concrete post pits to join up with the path. It will not have tensile strength unless you drill some holes and put steel wire or bolts in the old before casting the new, but you can prevent the posts leaning towards the centre by casting them tight to the path.

As you have a big block of concrete under each post, you will not want to be replacing rotten posts in a few years, so get pressure-treated or stand them in a bucket of preservative for a few days before placing. they are most prone to rot at about ground level where there is moisture (from below) and air (from above. If you mould the concrete up in shoulders round the base of the posts it will help water run off rather than penetrating round the posts (there will always be a gap as they will expand and contract with the weather)

One way to make these shoulders look neat is to put a plastic ring or square, such as an ice-cream or margarine tub with the bottom cut out, round the post on top of the main body of concrete, and fill it with a large spoon, then smooth it off. Do it before the rest of the concrete has set. Cover it with polythene to keep the concrete moist for a couple of weeks so it hardens well.

Sandyclay · 7 Oct 2008

Thanks a lot JohnD..... I understand this better.

I'm going to try to get those holes deeper, but at least I know what to do if I can't.

Thanks again.

Symptoms · 7 Oct 2008

Sandy - you must also 'undercut' your holes (so the base of the hole is wider than the top, sort of cone shaped). Why, I hear you ask ... well, in chilly Canada the ground freezes in those winters of yours; the frozen ground expands and can/will push a parallel plug of concrete out of the ground, a tapered plug won't lift.

libby lou lou · 7 Oct 2008

Sandyclay said:
Thanks a lot JohnD..... I understand this better.

I'm going to try to get those holes deeper, but at least I know what to do if I can't.

Thanks again.

No chance you could go wider? a bigger mass whateverever shape should help

Sandyclay · 8 Oct 2008

Libby and Symtoms,

I can definitely go wider at the bottom. I'm digging around a cotoneaster hedge, so my entry hole is pretty small: 1'.... but it does widen out as it goes down.

If I can get deeper, I'll ensure I go wider.

Thankyou.

Sandyclay · 14 Oct 2008

Well, I made it down to 2'8" on either side, and widened out at the bottom as per the advice given... I got my posts in, levelled, and braced - All that's left is the concreting.

Thanks to everyone for their help so far - It's really made a difference.

I have a remaining question:

Since it's getting cold here at nights, I'll need to cover the cement as it sets - Is it acceptable to do this by covering the concrete with 4" of dirt?

JohnD · 15 Oct 2008

you don't want it to freeze. Cold is OK. Put some plastic sheet over it first to prevent the fresh concrete being scratched or soiled. Prevent it drying out for a couple of weeks as it will continue hardening and gaining strength until it becomes dry. The plastic sheeting will protect it from drying out.

Sandyclay · 15 Oct 2008

JohnD said:
you don't want it to freeze. Cold is OK. Put some plastic sheet over it first to prevent the fresh concrete being scratched or soiled. Prevent it drying out for a couple of weeks as it will continue hardening and gaining strength until it becomes dry. The plastic sheeting will protect it from drying out.

Hi JohnD,

From my amateur perspective, it seems that covering with dirt would serve the same purpose, and would be less overhead for me. Would this not also serve to insulate the concrete and prevent it from drying? Getting soil on the top of the concrete is not a concern for me.

What do you think?

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Seeking assistance with fenceposts for gate.

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