How much of posts in ground for pergola

Hello all,

Haven't posted here or even lurked for more than a year, and my news server is showing over 300,000 unread messages! Good to see a few familiar names though.

Anyway, I am building a pergola using the designs on

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noticed that the posts are approximately

2.8m long, but only about 0.5m is in the ground. For fence posts I have always been told that a quarter of the post should be in the ground, and this is less than a fifth.

Do you think this is because there isn't as much lateral force on a pergola (due to wind) so it does not need as much to stop the post moving as with a fence? I guess with all the braces the pergola could be pretty much free-standing, so the main thing is to keep it in the same position in the ground.

Also, would it matter if the holes were tapered slightly so they get narrower at the bottom?

Also, I will probably use a post fix concrete like Hanson PostFix or Blue Circle Postcrete because I have too much money and not enough experience of mixing mortars. Do you have any views on whether either of these is a superior product?

Sorry for all the questions! Thanks in advance for any help you can offer.

Al Reynolds

Reply to
Al Reynolds
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Don't buy named concrete or mortar mixes, just use plain old cement at £3 a bag, for each 25kg bag you'll need 2 sand and four stone, you can mix it wet or dry, litterally no water at all and it will still set rock hard through natural absorption.

I should imagine 500mm is ample, it's not a swing / gatepost / fencepost after all and shouldn't be under too much stress.....I would be inclined to get as much preservative into the legs prior to concreting though...leave each one resting in a bucket of creosote overnight or something similar, also place a few inches of concrete at the bottom of each hole first so that the end grain isn't sitting in wet soil, then concrete almost level to the top of the hole, thus protecting almost all of the timber below ground.

Reply to
Phil L

It shows a 2.8m post burried to give a min height of 2.1m, so you have 700mm in the ground, more than enough for a pergols I would have thought. Don't think you will find 2.8m posts though, they tend to be 2.1, 2.4, 2.7. 3.0m.

Hire or buy (about £17) a post hole digger

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You wouldn't believe how effecitive & easy they are.

Sorry to disagree with Phil L, but these products are excellent & well worth the money. I use Wickes Postcrete

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one bag per post. Sets in 10 mins & gives a very strong fixing.

Reply to
The Medway Handyman

600mm in the ground is enough. Once fully constructed the pergola is very solid and the posts should not take too much strain. Accurate placement is the key to successful installation in my experience - you cannot measure too often. The rest of the job is then easy. Ensure there is drainage at the bottom and if you can slope the concrete at the top away from the post so water drains. We used 80% of a bag of Blue Circle postcrete on each post and a few old broken bricks as packing and it worked really well. The dry mix method would work too and probably be cheaper. At the risk of being a bit radical though, I am not totally persuaded that you will need to concrete the posts in given the minimum loading on them assuming tha you are building a double pergola.

It is important that cut surfaces are properly treated with preservative. We bought our pergola as a kit from Jacksons fencing - they are possibly expensive but worked well and they were helpful. Check pieces are straight though, and avoid the sell of too many bags of nails to fix it. We had six bays and used just over one bag of 3" and just over one bag of 4" nails to complete it.

HTH

Reply to
hzatph

Thanks for the advice people - all useful as ever.

Any thoughts on the hole being tapered? They're about 11" diameter at the top and 7" at the bottom at the moment.

Cheers, Al

Reply to
Al Reynolds

The message from "Al Reynolds" contains these words:

The other way up would be better.

Reply to
Guy King

Why?

Reply to
The Medway Handyman

Because digging the buggers is a problem.

No; a small taper will not hurt. But I am with the poster who thinks you don't need to bother too much. After all a shed isn't set in stone is it?

The biggest problem with using concrete is that after the legs eventually rot away, they will be a real pain to repair or replace. Double what you think is enough preservative and chuck a few bits of copper in the hole for the post to sit on.

Talking of setting posts:

An interesting foible on the new road junction through Stoke is the concrete fencing they put on one of the small "off" ramps there. The posts are RSJs set in concrete which is formed in those plastic inspection "pipes".

The fence abuts a canal some 7 feet down the other side and the whole lot is just made up with infill. (Spoil from the rest of the site(?) and some top soil.)

It looks like a small bump from a little old lady out for a drive one Sunday afternoon could send it all in the water.

I imagine they have done their sums right though. I wish I had a photo to show you. The fence is some 6 or 7 feet higher again, so there will be a lot of sail area to catch the winds. (Not a very windy place though, the Miglans.) So you are walking under a 14 foot virtual cliff if you take a stroll to the shops along the cut.

It doesn't look right at all.

Still, for 40-odd million quid, what do you expect these days? Landscape?

Reply to
Weatherlawyer

Post hole digger - damn near perfect tubula holes.

Reply to
The Medway Handyman

Substituting a foreskin for farsight will not make you see more than a prick.

Reply to
Weatherlawyer

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