Building garage on a slope

[bosnip]

Just recently bounght a new (old) house and would like to build a 20x20 garage in back yard. My back yard has a slope as seen in picture and retaining wall.
Retaining wall is constructed of 4x6's for the posts and wall itself. It seems fairly sturdy, but im just wondering if it needs to be replaced with concrete retatining wall or would this wall suffice?

The wall itself is 35" tall and the fill is about 30" of compacted dirt from years ago. From the back wall of garage to the wall I would have about two feet of space left.

P.S.
there was a tree in the middle before, I removed it and now added another section of the wall that why its different color.

Thank you.
https://ibb.co/wBtHp2Z
Not sure how to add image here, sorry. hopefully you can see it.

 

[kaymccampbell]

Do you want the shop above or below the wall?

 

[bosnip]

I want the garage above that wall, where the cleared ground right now.

 

[kaymccampbell]

What's your frost line? How deep must your footings be in your locale?

 

[bosnip]

Im in alberta. Google tells me the frost line is 3 feet and footing is 1.2 m (3.9 ft)

 

[ddawg16]

Im in alberta. Google tells me the frost line is 3 feet and footing is 1.2 m (3.9 ft)

I'm confused....your profile says Texas? Texas doesn't have issues with frost lines. Sweat lines, yes, but not frost lines.

You're saying 'garage'....do you plan to put a car in it? Or do you really mean 'shop'?

If a garage, then the level of the garage floor will be determined by the driveway into it.

Don't sweat the retaining wall. That is an easy fix with concrete and $$. Actually, I don't see the retaining wall being that much $$....and there are some creative ways to make it look good after the fact.

 

[bosnip]

sorry, thats an old account. i havent updated my location.

I plan on parking there, I have a shop already in separate building.

I dont mind building a cocrete retaining wall at all, I guess Im trying to see if its worth it to do so. Or will the current wooden wall be more than enough?
I asked an engineer, but he couldnt tell me over the phone and wanted $600 dollars for his official opinion on paper. Id rather put that money on concrete retaining wall if thats the way i have to go here.

 

[72Camaro]

How will cars access that garage? From the retaining wall side or from the fence side?

 

[bosnip]

I will be removing the fence at the back and the cars will drive through back alley. So main garage door will be on the fence side.

 

[thayer]

A rail-road tie retaining wall like yours has a useful life of about 20 years max with just the lateral load of the earth pushing against it. In Alberta there will also be significant freeze / thaw cycles that will push and prod it. All of this will be exacerbated by the additional loads your garage will put on it which will likely be significant. I think you will get differential settling that you will not be happy with and will face an expensive repair in 5-10 years.

It seems like you have no issue with concrete, so I have no reservations strongly recommending that course of action. Get a footing installed 36” below the lower grade and then either pour a foundation wall or lay one in block. Be sure to include rebar in the footing (likely 4 #5 bars horizontally in a cage of #4 bars spaced evenly) and in the wall (2 #5 bars on 48” centers for concrete, vertical #5 bars in it CMU prior to grouting it solid.) These are guidelines and your local code will specify it exactly for you. You maybe know all this already.


Good luck!

 

[matt_i]

Is there any way to go larger.. 20' square seems tiny and while it may be limited by other rules, I'd try for a 24' square at minimum. Doesn't seem like a lot but I think it will be beneficial down the road.

 

[bosnip]

Hello, thanks for reply everyone.
Unfortunately the biggest i can go is 20x20 garage on that pad.

Thayer - just wondering when you say "Get a footing installed 36” below the lower grade" - that means I need to dig in 36" down from that lower level of the existing wall? I actuyally have gas line 3 feet down from the top of that lower level, and 5 feet down gas line from the top of that proposed garage site.

Thanks

 

[larry_g]

Im in alberta. Google tells me the frost line is 3 feet and footing is 1.2 m (3.9 ft)

It seems to me that if you put a footer 3.9' below the grade the retaining wall will become moot. You will be removing all the soil behind the wall to get the footers and stem wall in.

lg
no neat sig line

 

[bosnip]

about 2 feet down I have sand soil and 3 feet from the top I have gas line, so I cant really dig that deep down.

 

[egdede]

Welcome aboard thayer. Those issues have to be dealt with; a sleeve for the gas line if it perpendicular to the footing. Thayer is right because, if I am understanding your plan, the wall will retaining an increased load; the shop.

 

[bosnip]

Yes, the wall will be retaining and will be under load from garage a s well. Garage will sit about two feet away from the wall

 

[larry_g]

about 2 feet down I have sand soil and 3 feet from the top I have gas line, so I cant really dig that deep down.

So what are your foundation plans? The AHJ may have some rules in place that dictate what you can do.

lg
no neat sig line

 

[Daniel Dudley]

You don't need a retaining wall, you need a foundation wall for your garage. And you need a plan and an engineer. At the very least you need a concrete guy who knows what he is doing. I put a slab on compacted river gravel years ago, but I let the grade taper off. You would be better off putting your garage on a foundation, by the look of things, or else you will need a very formidable retaining wall.

Sometimes a good engineer will save you more than he will cost you by suggesting a more direct solution. If you are trying to hit a very low budget, maybe a pole barn with deep poles and a 4 inch slab on gravel could get you in with a lesser retaining wall.

 

[theoldwizard1]

I think you will get differential settling that you will not be happy with and will face an expensive repair in 5-10 years.

Concur !

It seems like you have no issue with concrete, so I have no reservations strongly recommending that course of action. Get a footing installed 36” below the lower grade and then either pour a foundation wall or lay one in block. Be sure to include rebar in the footing (likely 4 #5 bars horizontally in a cage of #4 bars spaced evenly) and in the wall (2 #5 bars on 48” centers for concrete, vertical #5 bars in it CMU prior to grouting it solid.) These are guidelines and your local code will specify it exactly for you. You maybe know all this already.

You missed the most important thing ! DRAINAGE behind the wall !

 

[rsanter]

Depends how close to the wall you are building.
If you are building farther from the wall than its height, then adds are you are ok.
Closer than that and I say it's an automatic no-go

 

[ConCretin]

No way I'd build a garage on a slab 2' from that wall. I'm not sure that wall will hold the weight of the soil behind it for any length of time nit to mention a new structure. If your retaining wall is 3' tall, you want to be at least 3' back from it to avoid placing any additional loads on the wall. More would be better.

As I see it you have three options; Replace the wall with one engineered to support the loads, install a foundation under the new structure with footings below frost level or remove the wall and construct a structural fill with a gradual taper. I suppose you could rebuild the wall closer to the toe of the slope so as not to lose as much flat yard.

You mention a gas line? This needs to me moved anyway before you build a structure over it.