Fencing advice on steel posts

[SallyL]

Looking at eventually fencing the front of the new build , contemporary style steel posts with horizontal infill boards.

Fence is approx 30m long 2m high. If i use steel box section for the posts what size would be sufficient in others opinions?

Infill with 6ft softwood boards treated and chamfered top and bottom to shed the water and allow some air through.

Is 80 x 80 5mm box section overkill or will another size do, most other sizes will be 3mm or 3.2 thickness though.

Fairly well protected site from direct wind but would rather be safe and overkill than have it bend/break/blow down.

Thoughts plse.

[Russell griffiths]

I have an 80 x80 x 8 holding up a 600kg beam with the entire house roof on top, I think this will be very overkill for a fence. 

I would start to look at galvanised steel box and see what sizes you can source at a reasonable cost. 

[Carrerahill]

2 hours ago, SallyL said:

Looking at eventually fencing the front of the new build , contemporary style steel posts with horizontal infill boards.

Fence is approx 30m long 2m high. If i use steel box section for the posts what size would be sufficient in others opinions?

Infill with 6ft softwood boards treated and chamfered top and bottom to shed the water and allow some air through.

Is 80 x 80 5mm box section overkill or will another size do, most other sizes will be 3mm or 3.2 thickness though.

Fairly well protected site from direct wind but would rather be safe and overkill than have it bend/break/blow down.

Thoughts plse.

2mm wall would be fine. 

 

If you actually go and see this steel you are talking about, stare it in the eye, you will see what I mean.

 

I recently did a project with 2.77mm wall steel tube - I needed it for cantilever strength in my situation but it was solid - like seriously solid. 

 

Compared to 4x4 timber a 80x80x2 would be stronger.

 

Get the posts capped with a welded plate on the top and galvanised and set them in stone for drainage with a ring of concrete around them further up. They must be allowed to fully breath right through - have a decent hole circa 20mm around 75-100mm above ground level and another about 100mm from the top. You need holes for galv anyway.

 

Alternatively - flange mount bolted to concrete. Pads with J bolts sticking out would work well. Same breather holes apply and make sure it can drain out at the base via the flange. 

 

 

 

 

 

 

 

Edited July 29, 2019 by Carrerahill

[SallyL]

Thanx guys appreciate the info, I can save a fair bit by going down in size and mm was just worried that the fence is basically a 60sqm sail and wind can exert a shjt load of pressure, the fence is a planning condition for perpetuity and so want it done once and outlasting me with minimum upkeep. 

I was going to sink the post  down 1m into concrete and if the bottom end was capped with slightly larger plate and the top was capped off would they still need breather holes?

Will have them either powder coated or hammerite/equivalent  painted.

So with the advice 80 x 40 x 2.5mm would be ok ? or 3mm or 3.2mm 

 

[Carrerahill]

On 29/07/2019 at 15:27, SallyL said:

Thanx guys appreciate the info, I can save a fair bit by going down in size and mm was just worried that the fence is basically a 60sqm sail and wind can exert a shjt load of pressure, the fence is a planning condition for perpetuity and so want it done once and outlasting me with minimum upkeep. 

I was going to sink the post  down 1m into concrete and if the bottom end was capped with slightly larger plate and the top was capped off would they still need breather holes?

Will have them either powder coated or hammerite/equivalent  painted.

So with the advice 80 x 40 x 2.5mm would be ok ? or 3mm or 3.2mm 

 

 

I think I would still use something like an 80x80 - 40mm is a little narrow. 2mm to 3.2mm wall thickness would do well. 

 

Being from a farming family I have seen fences come and go, from 3x3 stobs to 10x10" posts and telegraph pole strainers and there is a knack to installing a good fence that lasts. The best ones are well planned and prepared and can last 60 years. 

 

If you cap the post top and bottom it will sweat in the cold with nowhere for the moisture to go, let's say you welded the caps on today, humid, warm (read able to hold more moisture) summer air trapped in the tube, and let's even say you have the caps welded on to pressure vessel standard - by the time the cooler nights approach the moisture will fall out the air and condensate on the inside of your post - rot starts and this moisture will just cycle as the temperatures change - hot day it will rise to the top, then condensates at the top and runs down the tube, so the rot goes on and on. 

 

Now let's say the same scenario as above,  but the caps are welded on with gaps and pinholes through the welds that air can be sucked in through on a cold day it will do exactly the same as above, only difference is the moisture may drive out in the hotter months bringing in fresh cool air loaded with more moisture every night.

 

It is like our roofs and solumns and cavity's:  ventilate well and have plenty air movement.

 

So what you do is set the post on top of a decent layer of hardcore, this means that the moisture can drain out and have vent holes top and bottom - if you order the steel and do this yourself I would just take a stepped drill through them to make about a 20mm hole - personally I would have a fab shop make them up, weld and galvanise them.

 

Paint is fine if done well - but the inside walls always remain a weak point as they are difficult to coat. If you want to paint, then give them a really decent de-grease with thinners or pre-paint wipes, scotch the steel then degrease again before hitting it with a good primer, zinc chromate stuff (they use that on the subs) then I'd use a 2K sprayed paint or a single pack industrial paint, I have tins of shipping container paint which is really good stuff. Tough as nails. Powdercoat is OK but powdercoat forms a film over the metal it doesn't actually "stick" that well - a single scratch or knock and the whole coating is compromised. Chemically bonded paint is far better which is why cars a painted with a wet paint system. 

 

 

 

 

 

 

[scottishjohn]

800mm block  wall with 1200mm fence on top --no rot problem then and no weeds coming through ?

 

Edited July 31, 2019 by scottishjohn

[SallyL]

ty guys really helpful , answers it all i think