Retaining wall

[madge1]

Morning

Got a question about retaining walls for you all.

Moved into a new house, and the area behind the garage is a mess (obviously just left when the garage was dug out of the hill); it’s a big slope. A waste of space, and dangerous for the kids.

So a retaining wall. It’s about 1.5m between the two ground levels, and about 10m long (ie the 5m at the back of the garage, and 5m at the side of the garage).

I’m thinking a 1.5m solid wall wouldn’t look the best, and be more dangerous, and would cost exponentially more than a stepped wall – say two rows of 0.75m, with a 2ft bed in between the two. Something like this

Untitled

• madge1
• 29 Oct 2012
• 1

but with straight walls, not curved. And less high.

Would this route be substantially cheaper?

In addition to this we need to move the wall by the back door out another 2m; to allow a table on the patio. It’s about 12m long, about 60cm high. All the soil we’d dig out here could be used to back fill the other wall.

Is this feasible, and how much do you think it would be? Easy access to the garden, with chalk soil.

Reason I asked was we had a Structural Engineer out the other day to talk extensions; asked him about it, and he said it would 25-30k. Seemed a ridiculous amount for what is basically 3 walls of a similar height (although, don’t get me wrong, I appreciate you need more with retaining walls, but they’re not the highest walls). I was thinking more of the range of under 10k.

thanks

 

[Mursal]

Yes to get him to sign off on it, he's probably about right. Solicitors, Architects and Structural Engineers, don't yo just love them?

All you have said makes perfect sense, ensure you have adequate strength in the wall especially the base, and don't let water build up behind them. Drain through or to the sides, even add another "step", if it helps make things easier.

As for prices, get three quotes from people you have seem working/completed projects, customers. Or take a deep breath and DIY?

Good luck

 

[madge1]

Cheers, not entirely sure I understand though. Are you saying you think it should be about 25k?

 

[Mursal]

See my edits, sorry I tend to go back and add bits to my posts. A bit dyslexic

Bottom line, if you want him in the mix, you will have to take his advice, or he will throw it back at you if anything goes wrong

 

[madge1]

cool. thanks. Got someone coming around tomorrow actually to quote, but one builder we had round ages ago (and no quote) thought it would be dead easy, and take about a week, even with the correct drainage, steps etc etc

 

[r896neo]

this is not a big deal. A retaining wall 900mm or higher with a building or boundary nearby should be spec'd by an engineer.

General retaining walls above 1.2m should be spec'd by an engineer.

If you want to build it in the dry-laid interlocking block like the picture the first builder is right this is not a massive job. Once you have the base in they go up in a day or less if its a nice straight run.

A 1.5m wall would definately need an engineers input but the actual construction cost may be slightly less than 2 walls. The ammount of spoil to get rid of though will be much much more and therefore considerably more expensive. You need to weigh up the benefit of a level area though both in terms of usability and it being a major plus if you wanted to sell.

 

[madge1]

is that 1.2m specced by an engineer just for one solid wall or the total rise of a stepped wall?

And hopefully there won't be too much spoil, as we've the area to backfill, and even with a stepped wall we should be gaining about 400sq ft.

thanks

 

[r896neo]

no a 1.2 single wall.

You obviously can not have a 750mm wall then 3 feet of level space and then another 750 as the loading from the higher one will significantly affect the other.

As a very general guide draw a 30deg line from the front bottom corner of the higher footing and if it doesn;t intersect with the other wall then they will have little effect on each other.

That reads badly, see below diagram but change angle to 30
http://activerain.com/image_store/uploads/2/5/4/6/7/ar127094577576452.jpg