terraced garden

We have a slope in our back garden that we want to terrace. The rise is a little over 8 ft, and the run is 20 feet. We're thinking 4 terraces, each about 5 feet wide, with walls about 3 ft to 3 ft 6.
First, what do you suggest to maintain overall stability? And how about drainage? We get quite a bit of rain, but currently erosion is a problem (hope terracing will help that!)
Second, do we need building permits to change the landscaping in our own back yard? And if we don't get permits, what might happen??
Thanks! :-)
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snipped-for-privacy@gmail.com wrote:

My math says 3 will do it.

I like these- http://versa-lock.com/
My wall is about 3' high & 25' long- hasn't moved a hair in 5 NY winters. It is serpentine & I think that adds to both appeal and strength.

My wall started with a ditch twice the width of the wall & 8"(?) deep. Tamp. . . tamp. . . tamp. . . lay the first course. Laid a 4" flexible perf-pipe in a sock behind that-- and carried on to the next course. Once the wall was done I backfilled with a bit of #2 stone protected with landscape cloth. BTW- 1/2 of the first course is below grade. The low side is a paver patio.

That depends entirely on where you live- and who your neighbors are. *Probably* you can do a 3' wall without a permit. [If it was me, and I was confident of my ability to engineer the thing- I'd do a 3 foot wall. Then another. . . ] OTOH- a call to the building dept. is free and you might get some valuable insight.
What happens if you act without a necessary permit & get caught? anything from make an apology and buy the permit- to tear it out and pay a fine.
Jim
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Thanks for your replies!!

Jim, that's good to know! I like the idea of serpentine walls too. I'm concerned, though, that building one wall above another will create additional issues over and above the construction of one wall--what do you think?
Norminn, the slope is away from the house and will stay that way. we have a flood plain easement on our land and in fact the neighbors' gardens drain into that so, I don't think it will be a problem. Also we're thinking of putting in a pipe from the lowest terrace to encourage water down to that area. What sort of plants did you use to control erosion? And how quickly do they establish a root system sufficient to have some effect?
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snipped-for-privacy@gmail.com wrote:

dark green grassy stuff and doesn't spread. I also used concrete edger with rock and landscape cloth behind it - the edger stops the water flow long enough for it to soak into the ground through rock and l. cloth.
The space we had to work is very small, as downspouts are next to patio and not far from hedges and walks. The hedges were dying because so much soil had washed away. Replaced soil. In some spots I used plastic trays that plants come in, doubled for strength, placed in ground and filled with rock. I don't like those concrete thingies for downspouts.
County extension service or a good nursery can surely give you tips about landscaping the area.
The condo next to ours is only about 10 years old and probably doesn't have 10% of the lot with permeable ground......huge concrete parking area and most of the drainage off the building goes into the lot and then into our yard. Didn't take note of that until we had seawall repairs and new erosion came right after repairs. Strange the things you study when hubby is the building manager :o)
Your terrace idea is probably fine, but plants can do a lot of work with the right choices. The grassy stuff we used, planted on a slope, would probably do a lot to slow the flow and hold the soil, as it is dense and has very strong, dense roots.
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On Thu, 13 Mar 2008 04:09:06 -0700 (PDT), snipped-for-privacy@gmail.com wrote:

In my part of the world- and in my yard- it wouldn't be a problem. I'd be more concerned if I lived across the street on a big clay hill- or in some place that gets a lot more rain than we do.
But that's where your local landscape guy, the building inspector, or the nursery & county extension folks that Norminn mentioned might be able to help.
Jim
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snipped-for-privacy@gmail.com wrote:

Our local codes address changes in drainage, removal of trees, using rock for mulch, etc. Whatever you plan, I would run it by the building code office. You can probably find code online.
Is slope AWAY from the house? Will the drainage still be downslope as it is now, or will it be diverted? That would be a major concern. You don't want the water in a neighbor's yard. Does water collect?
From work we had done on our seawall, and old problems with soil washing out from behind the wall, I would pay special attention to using weepholes, and using landscape cloth behind the wall to hold back soil when water drains. Tiebacks to hold wall in place also something to think about.
We live on relatively flat ground, but have very heavy rains in summer (Florida). Building design is such that downspouts pour a huge amount of water out along the building. We were able to cure a lot of the erosion that had occurred from that with landscaping. We planted stuff that is dense and has tight roots - holds soil AND diffuses the flow. You can also place stuff like rock or timbers across the slope to slow down the water.
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