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-   -   Footing for 12 inch retaining wall (http://www.diychatroom.com/f19/footing-12-inch-retaining-wall-116636/)

tibetie 09-08-2011 03:42 PM

Footing for 12 inch retaining wall
 
Hi-
I'm currently collecting quotes for a 12 inch high concrete retaining wall with fence post brackets next to a concrete pad on my side yard. The length of the retaining wall will be around 25 feet. I plan to have another contractor install a fence on top of the retaining wall. I'm confused because one concrete contractor told that the footing for the retaining wall should be 2 feet below ground. He proposed digging a continuous trench 6 inches below my concrete pad and installing piers 2 feet below ground (every 5 feet) to support the retaining wall. Another contractor told me that he'd dig a continuous trench 12 inches below ground to (with rebar) to support the retaining wall. What are your thoughts? Is 12 inches too shallow? Thanks.

jankencanada 09-08-2011 04:26 PM

Walls
 
Think that you will have to tell people.
What part of the country you live in?
How far the frost goes down?

Bud Cline 09-08-2011 04:31 PM

Think that you will have to tell people.
What part of the country you live in?
How far the frost goes down?

What will the fence be made of?
How tall is the fence to be?
Will it be a privacy fence that will gather a wind load?

There's all kinds of things to consider before you can expect any reasonable responses.:)

tibetie 09-08-2011 04:33 PM

Hi-
I live in Northern California (30 minutes outside of San Francisco). I don't know the frost level...we rarely dip below 30 degrees at night. The redwood fence will be 5 feet tall with 8 inch wide boards on the retaining wall. Hope that helps.

Bud Cline 09-08-2011 04:39 PM

There ya go...now we're getting somewhere.

I would say if the fence posts are metal pipe and also buried in the retaining wall then the guy wanting to install the piers is the way to go.

There is more than one suitable method.

You must consider soil type and rain and wind.:)

tibetie 09-08-2011 04:57 PM

Thanks for your quick response. The fence posts are going to be 4 x 4 pressure treated wood and will be placed not directly in the concrete but on concrete brackets. We have clay soil, around 20 inches of rain a year, and gusts of wind that don't seem to exceed 15 mph. Do you think that the 2 foot piers is better than the 12 inch continuous trench? Thanks.

Bud Cline 09-08-2011 05:05 PM

Quote:

The fence posts are going to be 4 x 4 pressure treated wood and will be placed not directly in the concrete but on concrete brackets.
Well okay but would you consider rethinking that concept?

Quote:

Do you think that the 2 foot piers is better than the 12 inch continuous trench?
I do.

tibetie 09-08-2011 05:15 PM

Should I reconsider the concept of the pressure treated posts or placing them in metal brackets? If one or both, what are the cons? I currently have metal brackets holding my fence posts in a retaining wall along the back of my yard and haven't encountered any issues yet. Thanks.

Bud Cline 09-08-2011 05:20 PM

I just worry about wind loads on privacy fences and with wood posts mounted in cheap metal post anchors I worry more.

I also wouldn't mix redwood rails and pickets with treated posts but that just me.:)

If you are happy with that method and your weather is mild enough to be compatible with that technique then go for it. I live in tornado alley so I get concerned.:)

tibetie 09-08-2011 05:34 PM

The only issue I've seen with the metal brackets is that the pressure treated wood shrinks in the summer, so there's a slight wiggle to a couple of the posts on my retaining wall on the hill, but I've been told to just tighten the bolts. There's not much wiggle, though. It can get windy, but not enough for the fence to sway. Do you definitely think that 12 inches for the footing of a retaining wall is way too shallow? Thanks for your responses.

kwikfishron 09-08-2011 05:37 PM

I’ve never met a wood fence installed on brackets that I’ve liked.

Bud Cline 09-08-2011 05:39 PM

Quote:

Do you definitely think that 12 inches for the footing of a retaining wall is way too shallow?
Don't know. I would also consider the clay soil. When it dries out it can shrink unbelievably. Over time if the continuous footing develops cracks and becomes segmented and the soil has shrunk away from the footing then what. I just see leaners as a possibility. I personally think the piers monolithic with the base are a better deal.:)

tibetie 09-08-2011 05:52 PM

Do you think the retaining wall should be tied into my existing concrete slab? I have one contractor that says that it needs to be and another contractor that says that it shouldn't be.

tibetie 09-19-2011 02:09 PM

Hi-

I just wanted to check again if there would be an issues with the new retaining wall being dowelled to my existing concrete slab. I have one contractor who wants to do that and another that says that musn't happen. Any thoughts on that? Thanks.

Bud Cline 09-19-2011 02:37 PM

I don't think it matters either way but I guess I would want it independent.:)


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