3" fence posts or 4" fence posts?

[Al-W]

Hi, oh learned ones!

I need to construct a fence that will be subject to some strong winds. It i s only 5.7 meters long and will have 5 posts, two of which will be bolted t o buildings. The three intermediate posts will be held by galvanized fence post holders (concreted in). My big question is: Is there any point in stre tching to 4" posts and hardware, or will the 3" versions be perfectly adequ ate? I find it hard to imagine a 3" fence post snapping in even the stronge st winds - but I could be wrong.

Any insights or advice on this matter?

Many thanks

Al-W

[Andrew Mawson]

Depends how high it is !

3" tall no issue

3 Metre tall might be a problem!

Sheltered location - probably no issue

Cliff top in outer Hebrides - problems ensue !

All parameters needed :)

Andrew

[Al-W]

is only 5.7 meters long and will have 5 posts, two of which will be bolted to buildings. The three intermediate posts will be held by galvanized fenc e post holders (concreted in). My big question is: Is there any point in st retching to 4" posts and hardware, or will the 3" versions be perfectly ade quate? I find it hard to imagine a 3" fence post snapping in even the stron gest winds - but I could be wrong.

PS.. I forgot to mention that the fence will be 2 meters tall and all timbe r.

Al-W

[Chris Green]

'All timber'? Is it panelled, if so I'm not sure if 3" posts will be enopugh, even 4" might be marginal.

[The Natural Philosopher]

Use 4" concrete posts set in cement, with concrete gravel boards

Then the things won't rot

[Tim+]

3" definitely not enough! 4" minimum unless you enjoy replacing broken posts. ;-)

Tim

[The Other Mike]

Concrete posts, set in concrete (postfix/postcrete) and then clad in rough sawn wood if someone objects to the bare concrete look.

[Brian Gaff]

In my fence it was the arris rails that broke due to wind loading first, then the wood near the base where it rotted. Depends very much on the type of fence panels and how strong the actual structure is.

Brian

[Brian Gaff]

Its not the posts that I find are the first casualties its the panels themselves. Also whether metal concreted or wood directly concreted, after a time the post shrinks and swells and water gets down into the bottom of the post hole in the concrete, it cannot get away, rusts the sockets and rots the wood and the break occurs at ground level usually. make damned sure the wood is well protected al the way down and if possible impregnated as cheapo posts tent to break. Can you run to concrete posts? Brian

[Davidm]

I have a 6ft high close boarded fence with 6" square posts bolted to concrete studs down one side of the garden. A couple of months back the strong winds actually snapped one fence post AND it's concrete stud at ground level. It was a pig of a job to dig it all out!

[newshound]

And just what you mean by "strong winds"; which very much depends on where you live, and how exposed the area is. Between two buildings should give some protection, unless it leads to a tunnel concentration.

ISTR there is geographical data in BS6399.

Googling "wind loading" gives lots of hits.

[Al-W]

Chris, thanks for the input. I plan to use 6" x 1" vertical boards, nailed alternately, each side of the fence, in order to allow some wind through, a nd thus reduce wind resistance.·

Al

[Al-W]

It is only 5.7 meters long and will have 5 posts, two of which will be bolt ed to buildings. The three intermediate posts will be held by galvanized fe nce post holders (concreted in). My big question is: Is there any point in stretching to 4" posts and hardware, or will the 3" versions be perfectly a dequate? I find it hard to imagine a 3" fence post snapping in even the str ongest winds - but I could be wrong.

Thanks for the suggestion. Unfortunately, I need the fence to be temporaril y removable without too much aggro. Hence my use of metal post holders. Oth erwise, I would probably have used concrete posts.

Al

[Al-W]

It is only 5.7 meters long and will have 5 posts, two of which will be bol ted to buildings. The three intermediate posts will be held by galvanized f ence post holders (concreted in). My big question is: Is there any point in stretching to 4" posts and hardware, or will the 3" versions be perfectly adequate? I find it hard to imagine a 3" fence post snapping in even the st rongest winds - but I could be wrong.

That sounds like a great idea. Unfortunately, I need the posts to be remova ble easily.

Al

[Al-W]

It is only 5.7 meters long and will have 5 posts, two of which will be bol ted to buildings. The three intermediate posts will be held by galvanized f ence post holders (concreted in). My big question is: Is there any point in stretching to 4" posts and hardware, or will the 3" versions be perfectly adequate? I find it hard to imagine a 3" fence post snapping in even the st rongest winds - but I could be wrong.

Wow - that's relevant information; thanks! I think I will have to choose my 4" wooden posts carefully then. Also, I plan on making for less wind-resis tance by staggering the vertical boards alternately on each side of the hor izontal pieces - allowing some wind to pass through.

Al

[Al-W]

Yes, there are buildings and a high wall on three sides but not to the south or southeast. Gales are not uncommon here in winter on the south coast, but of course a hurricane (though not yet experienced) is not impossible. Thanks for the suggestions.

Al

[Robin]

ITYM "removable easily except by the wind" :)

Do you need to be able to remove the posts down to ground level or would you be able to get away with concrete spurs to which you bolt the posts? (They can be sunk lower than usual at the risk of earlier rot of the posts.)

IMLE "concrete in" metal posts holders are a bit weedy for 2m panels but there may be stronger ones out there.

[Robin]

I'd be interested if anyone knows of evidence of how much (or little) that reduces wind resistance. I've seen "up to 15%" quoted but (a) "up to" makes me wonder if that is in ideal wind speed and direction and (b) it surprised me given the wind load even for chain link fencing can be

25 to 50% of the wind load of a solid fence.

[Al-W]

s. It is only 5.7 meters long and will have 5 posts, two of which will be b olted to buildings. The three intermediate posts will be held by galvanized fence post holders (concreted in). My big question is: Is there any point in stretching to 4" posts and hardware, or will the 3" versions be perfectl y adequate? I find it hard to imagine a 3" fence post snapping in even the strongest winds - but I could be wrong.

movable easily.

Thanks very much for that suggestion. Unfortunately, I need the posts to be removeable to possibly allow a vehicle through, which has to drive though at a 45 degree angle, so unless those spurs were about 10ft apart, those c oncrete spurs are not really an option, unfortunately. Yes, I am a little c oncerned that the metal post holders will be the weak point in the fence, b ut I don't know of any other option that'll allow a vehicle to drive throug h when the posts are removed. Unless anyone herehas another suggestion.

Al

[Al-W]

led alternately, each side of the fence, in order to allow some wind throug h, and thus reduce wind resistance.·

Hmmm... That's a little worrying.

Al