Cutting into a bank....??

[scoutcub]

No, not the one with money in it....

Will be building a garage next to a house, and have to cut into a slope (bank) to put it in. Any ideas on how far back I should leave the bank behind the garage? 1'? 3'? Should I put a retaining wall up? Pros/Cons? This isn't my retirement home, and will be excavating the site with my TLB, and doing everything else I can to save $$$. All input welcome!

 

[mjncad]

We need more information (e.g. slope height, soil type, how long of a cut, how much space behind the garage is available for cutting back) before we can even begin to offer any suggestions.

 

[Gary Fowler]

If I understand your question, you want to dig into a slope below your house to start a garage. My house is in the building stage, but take a look at this photo and see if this fits. The wall is for my lower patio, but It could be the start of a building wall if you wanted. THe builder installed a french drain behind the wall to keep water drained out> It seems you could do something similar as long as you had no underground utilities. OF course, you would need to put up the retaining wall during dry conditions and immediately upon digging out. I am building the retaining wall to hold the slab for the house. Seems that you could do the same as long as the soil type will not slough off and allow you to dig straight vertical wall. Leave enough room to install drain tile behind the retaining wall, pour a good footer that goes below the frost line and at least 16" wide with embedded rebar to set inside each CMU block in at least every other hole, fill each block hole with grout and you should have a good retaining wall.

 

[Ken45101]

You are talking how much space between the garage and the hillside? How are you going to mow it? What kind of mower do you have? How high is the hillside going to be?

How much room for water drainage? (that's a function of how high the hillside is and what is above it.)

Myself, I'd leave about ten feet, plenty of room to get the mower through. It also leaves room for the hillside to slump some before it stabilizes (depends on your soil and weather conditions.)

Ken

 

[miramadar]

We need more info to be precise, but I would leave as much room as I could behind the garage for mowing and water drainage. Install a perforated drain pipe between the hill and your garage and run it to daylight. I would avoid the retaining wall and just try to slope the hillside if possible.

 

[powerpace]

Most slopes can handle a 30 degree angle. The problem even with that is slump once it starts to rain. Put a retaining wall in and allow for drainage no matter what you do.

 

[CurlyDave]

Get an engineer to design a retaining wall for you if it is over 4' high.

The required strength of a retaining wall increases as the cube of its height.

A 5' wall needs to be twice as strong as a 4' wall, a 6' wall needs to be over three times as strong. If the wall is not drained properly it can easily fail from that source also.

Designing a retaining wall by guess and by golly sometimes results in real life failures.

* * * * * *

My neighbor had a "professional" stack concrete blocks (2' x 2' x 4') four high to make a retaining wall. It fell down that winter. I calculated how much he needed to set each block back from the one below to get a good wall, but he just had the same guy stack them right on top of each other again. Fell down again the next winter. Then he stacked them with some setback and drain rock behind them and they are still standing 3 years later.

 

[scoutcub]

OK, some more info, and pics. I went back down this past weekend, and it is ROUGHLY a 6' rise in terrain per 30'. I really don't want the added expense of a retaining wall, unless it's absolutely necessary. I can cut the bank back farther if need be. But, I'm worried about water runoff. I will put a drain system around the back of the garage. Looking at conventional construction for the garage, approx 30X30. garage will be going between the two vehicles in the pics.
Fire away!

 

[Dutch445]

There is lots of good info here, but it looks to me like
the question has already been answered. Behind the
house is a beautiful retaining wall. Wouldn't you
would want something similar behind the garage? or
combine them into 1 long wall?


How tall is that retaining wall behind the house?

 

[Ken45101]

I wouldn't worry too much about it. We put in a pole barn for the RV last summer. I had to cut into a hillside like yours, but a bit steeper and higher. I cut back ten feet beyond the barn and then sloped the ground away from the barn, about one foot in the 10' distance. Water drains down the hill into the swale and away from the barn into the swale. The ten foot gives me plenty of room to mow between the barn and the bank.

I sloped the bank low enough that I can mow it.

I would not bother with a retaining wall or drain tile.

Ken

 

[fire72]

Soil type is a big factor here. When I cut into the hill for my barn, I had a roughly 4' to 5' vertical bank, with the idea that the back wall of the barn will be the retaining wall. The project stalled for financial reasons, so the cut has just been sitting there unsupported. It's been that way for nearly two years, with no slump. This is in a heavy clay/shale soil. There's no way that would still be standing in a silt/loam or loose gravel soil.

When the project gets back on track, there will be drain tile along the base of the wall. The top of the bank will be sloped to drain to either end. With the stability of the soil, I'm not too concerned about the strength of the wall, although the final specs have yet to be determined.

 

[scoutcub]

There is lots of good info here, but it looks to me like
the question has already been answered. Behind the
house is a beautiful retaining wall. Wouldn't you
would want something similar behind the garage? or
combine them into 1 long wall?


How tall is that retaining wall behind the house?

Dutch -

They did put a very nice retaining wall up behind the house, it's a good 6' tall. I was planning on continuing the curve around to the garage, but not behind it......as you would never see that nice expensive block!
However, Not sure if I want to cut the bank 10' behind the back of the garage.....I was thinking more like 2-4'.......hmmmm.....

 

[2manyrocks]

If this is a garage for your cars, I remember reading a suggestion in a landscape planning book that it's good to layout the space requirements for cars using a garden hose. There were some dimensional requirements that got to be fairly large to turn around, etc.

My question is whether you have enough space to reslope what you have so you don't have to use a retaining wall and so you can still cut grass when you're done.

There comes a point in reshaping land when a dozer is the best tool. My neighbor did some work for me at $60.00 an hour, and it was the best bargain I've had in a long time.

 

[roamerr]

That is quite a bit of digging/grading. I would question if a poured rear wall and partial sides would be better and be part of the building.The nice thing about a garage partly underground is that it adds some heat in the winter. The bad thing is that you have to do the drainage right or you will have a wet garage. A few feet of french drain is rarely enough...

 

[Tim_in_IA]

That is quite a bit of digging/grading. I would question if a poured rear wall and partial sides would be better and be part of the building.The nice thing about a garage partly underground is that it adds some heat in the winter. The bad thing is that you have to do the drainage right or you will have a wet garage. A few feet of french drain is rarely enough...

I was thinking the same thing. instead of a retaining wall just have a higher curb wall on the back side of the garage.

 

[davygp38]

I wouldn't worry too much about it. We put in a pole barn for the RV last summer. I had to cut into a hillside like yours, but a bit steeper and higher. I cut back ten feet beyond the barn and then sloped the ground away from the barn, about one foot in the 10' distance. Water drains down the hill into the swale and away from the barn into the swale. The ten foot gives me plenty of room to mow between the barn and the bank.

I sloped the bank low enough that I can mow it.

I would not bother with a retaining wall or drain tile.

Ken

I have to agree. I Live in an area with nothing but this type of topography. The hillside, is graded back, the ground around the garage is sloped into the hillside, the swale that is formed between the two, is drained into the yard. The only problem I ever saw, is when the swale is to slight, and over time due to mowing, and regular maintenance, the swale got smoothed out, causing water collection. The biggest reason was that the guy who bought the house, did not realize the swale was there for a reason, and did not maintain it.

 

[radioman]

Wow- you got alot of dirt to move. Do you want to have the new garage at same level as the house ? I would- and this means alot of dirt to be moved. Hopefully you have a place to put it.

IMHO- Since this is on a deep hillside, runoff is not really a concern until you start putting up retaining walls. I would have a poured wall, with french drain at the top,behind of the wall and bottom, front of the wall. you have excellent slope for drainage anyways. Since you need a concrete floor, have the same contractor pour the floor and wall. You should have at least 10 ft or more between back wall of barn and finished retaining wall . the ground behind barn should be sloped in a Vfrom center for more drainage.

 

[scoutcub]

Looks like nearly 50/50 on retaining wall or not. I like the idea of backfilling against the garage for the added insulation. An open area behind the garage would interfere with a path I'd like to have to the left of the garage, going behind it along the treeline to the back of the property. My property goes up to the treeline. How about conventional construction with a block/poured back wall? I've seen garages like I want to install with a block back wall into a bank that's failing, the ground is pushing the wall in. Unsure of the drainage behind it... again, I'm trying to do it as inexpensive as possible.....

 

[schmism]

put me in the pour a reinforced concrete rear wall of the garage and be done with it.

less expensive than a retaining wall with less dirt to move.