DIY Doctor

Replacing a retaining wall and fence where posts have rotted

Postby stonky » Sat May 02, 2020 12:10 pm

Hi. Looking for some advice please.

Some of my boundary fence posts have rotted and need replacing. The issue is that there’s a difference in height of about 50-60cm between my ground and my neighbour’s ground. The original “retaining wall” from when the house was built (in 2004) consisted of a series of 10cm thick wooden posts. These are now also rotting and need to be replaced.

The existing fence posts are set in concrete on the low side. The plan is to replace the fence these with 3m concrete posts. The fence panels are 1.8m.

I would really appreciate thoughts on how substantial the retaining wall needs to be. For example simply using gravel boards, with the first board set into concrete at the base, should be stronger than the posts that were there originally. But is that sufficient?

For anyone recommending an impermeable wall, would I need to consider drainage for that height? The area is not fully enclosed; the ground level decreases towards the front of the property. But there is approximately 11m of wall.

There is also the wind load on the fence to consider. As you can see in the drawing the majority of the fence is well sheltered from the houses. Despite the nature of the existing construction It is only the posts becoming rotten after 15 years that have caused an issue.

Plan drawing and photos attached, high side is on the right. The fence between C and D has no retaining wall; the ground is sloping away here.

Many thanks
Attachments
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boundary-fence.jpg
stonky
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Postby stoneyboy » Mon May 04, 2020 9:32 pm

Hi stonky
Point 1. Not all concrete posts are equal and for what you propose you will need some good quality ones.
Point 2. I assume you will use concrete gravel boards (again good quality ones) so you will need 4 of these where your neighbours land is highest. It's probably good insurance to fit a concrete spur at the mid point for extra support.
Drainage will occur along the horizontal joins in the gravel boards.
Regards S
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Postby stonky » Tue May 05, 2020 10:24 am

Hi @stoneyboy

Thanks - that was useful.

I'm assuming first off from your reply that you think posts and gravel boards are a good enough solution (as long as the quality is good) for this size wall - I have had it suggested that a block wall might be needed but it seems overkill compared to what's there already.

Re quality ... to me a post is a post. What do I look for in posts and gravel boards that will tell me they're of good quality - is there a particular 'type' or standard?

Cheers
stonky
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Postby stoneyboy » Tue May 05, 2020 9:43 pm

Hi stonky
A proper retaining wall would be the best solution but expensive. If timber posts have been adequate in the past I agree with you that concrete gravel boards are a good replacement.
As far as the quality of fencing components is concerned go and see what is on offer from the sheds and from national builders merchants - the heavier they are the better.
Regards S
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Postby stonky » Thu May 07, 2020 5:51 pm

@stoneyboy

Thanks again. Yep looks like we're going with gravel boards and a centre support; with one more GB and 5' fence panels instead of 6'. Fingers crossed.
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