Retaining wall & fence & tree roots

[Invisible Man]

Our garden is about 3 feet above the level of the public footpath that runs the other side of our boundary.

The existing retaining wall is about 35 feet long, sliding off its foundations and leaning.

We would like a 3 feet retaining wall and a 6 feet fence on top of it rather than back from it.

To complicate matters half way along the wall is a gap in the wall filled by an ash tree about 18 metres high with a diameter near the ground of something over 2 feet. It is based on our ground and extends to the boundary. It is the subject of a TPO obtained by our next door neighbour and the roots cannot therefore be damaged.

I rather doubt whether it would be possible to build a wall to both withstand the weight of soil and the pressure of wind on a fence mounted in/on it. I have seen a fence in situ around a commercial site where the supports were back from a wall but the fence was built forward from the supports to be above the dwarf wall.

Anyone got any ideas what is possible or who to approach? I anticipate getting it done professionally but doubt whether the average builder or landscape gardener could handle it all. Any particular type of surveyor or other expert?

TIA for any ideas.

(The footpath behind is not part of a public highway and I understand that I can build a 6 feet fence above the natural level of my land)

[John Anderton]

All the planning officers I've spoken to would understand differently :-)

You earlier describe the footpath as a "public footpath" therefore it

*is* a public highway so 1m above ground level is as high as you can go.

Your local planning officer is the best person to tell you what "ground level" is in this case. It could be the level of your land, the level of the path or some point in between.

As an aside, I've encountered one planning officer who swore blind that a retaining wall was not covered by permitted development and tried to con me into applying for planning permission for a 1m retaining wall so don't take everything they say as gospel. They are not always right but they're (usually) better than the "man in the pub"

Cheers,

John

[John Anderton]

Sorry, just tracked down the relevant legislation and the definition is "highway used by vehicular traffic" so I suspect you're OK up to

2m. (See part 2 here : the above is based on my assumption that part 2 hasn't been amended since 1995. Part 1 was amended last year)

Cheers,

John

[Invisible Man]

Thanks John

The public footpath is not made up. It has a sign showing it as a public footpath. It is quite wide and allows vehicular access for people who have rights of way along it to their garages at the bottoms of their gardens. At the moment it has 2 ruts full of water. The land is jointly owned by one of my neighbours and 2 others.

The neighbours both sides have similar retaining walls with 6 feet fences immediately behind them as I have at present. Theirs are upright whereas mine was not maintained in the past and wall and fencing are now leaning.

[The Natural Philosopher]

Of course it is, but how much hassle do you want?

Civil engineer, but here is the general approach

1/. drain holes through the wall base to prevent uber soggy soil creeping.

2/ backfilled with somethng porous to staiblise and drain subsoul.

3/. wall has to retain pressure: both in tems on not splitting and not sliding. The first is solved with steel ties or inserts and the latter is solved with back braces.

This is how I would do it in principle.

Dig out the whole bank at least 6 feet back from the path, and lay a concrete foundation about 600mm deep into the path side.

Pile drive steel posts to take the fence into the subsoil.

Lay steel mesh back into the excavated bank. and put steel tie points into it and concrete up around those points. The rest of the mesh leave.

Start building the wall around the posts. I'd use concrete blocks with holes and lay vertical rebar in those, and then lay rebar along every course, tying it loosely to the verticals and the posts. Leave gaps at the base course for drainage. Fill the hose with strong scrap mortar.

Build a face layer of nice engineering brick and tie it into the concrete block layer with ties, ad backfill; the gap with scrap mortar.

When you get to finished ground level minus 6 inches, get some stainless cables and connect the posts to the points you connected in to the rebar mesh in the first place. use turnbuckles to pretension, and concrete over those to prevent corrosion.

Finish wall with a course of cappings or sideways bricks, and backfill with porous material up against the wall - Limestone MOT 1 is good - mixed with gravel and sand. That provides a stable drainable base. Or use hardcore from existing wall?

Replace topsoil and seed.

If you want a pretty fence rather than a steel mesh think, build brick pillars round the steel posts, and attach panels to them

Expect the ash to cause damage. It roots will be very extensive and about a meter below the surface if that. Chop what you need to to build from below that level.The roots are unlikely to go UNDER what you have built, but may well dry out what is adjacent. Hence the need to tie the lot together well. You WILL get swelling of the tree at its base BUT if te wll is strong, that will push the soil out, not the wall!

I've done a 2ft high wall somewhat like this..didn't brace it though, and only where I didn't TIE it together are there any signs of cracking.

he result. Not as big as yours..

You may not need the bracing cables, but with a fence on top, Id go for it.

[TheScullster]

"Invisible Man" wrote

snip....

I have just had to jump through hoops to erect a 2m fence alongside our boundary. Planning insisted on the fence being 500mm from the boundary with planting in front to soften the steet scene. Totally irrelevant to your question but hey ho.. In terms of what you could do...I'm not sure if I understand the situation exactly, but could you use tall slotted concrete posts with concrete gravel boards upto the height of the inside ground level? You could do 1 bay as a trial for a year or two to see if this would take the strain - all dependent on your time scale of course.

Phil

[Invisible Man]

Good idea. Will need to investigate long and very strong ones.