Minimum Retaining Wall Height below which Design is not Required 1

[CWEngineer]

I am trying find some guidance stating minimum heights below which a design is not required for a retaining wall. For example, if a wall height is 3 in, 6 in, 9 in, etc. is a design required for a retaining wall? Appreciate your advice.

Thanks

 

[Canuck65]

In Ontario(Canada), any retaining walls under 1.0m in height (39.4") are not considered a designated structure under the building code, therefore a design is not required.

 

[hokie66]

It varies a lot with jurisdiction. Where I am, the last time I looked, it was 1.2 metres. You see a lot of walls lean and some fall over, but if it is less than 1.2 metres, it normally won't kill you.

 

[kmart30]

I believe anything 4 feet or higher is the magic number but I haven't checked in a while.

 

[WARose]

Under the IBC 2012, I don't think any wall is exempt from design (regardless of height). However that particular code does exempt walls that are not over 4' in height (measured from the bottom of the footing to the top of the wall) from requiring a permit (if they are not supporting a surcharge or retaining certain liquids).

 

[hokie66]

Measuring to the bottom of the footing is strange. After the fact, how is an inspector to know?

 

[WARose]

Measuring to the bottom of the footing is strange. After the fact, how is an inspector to know?

Get out the shovel I reckon. (Or guess.)

Wouldn't be that much different from a lot of other "inspections" I've seen.

 

[msquared48]

Here - 4 feet of finish grade difference.

Footings are a luxury.

Mike McCann, PE, SE (WA)

 

[hokie66]

But Mike, aren't you in IBC territory like WARose?

 

[JStephen]

Whether it needs permits- see above.
Whether it needs PE seal- would depend on the project it was on, not just on the wall.
Whether it needs design calculations- judgment issue, if in doubt, make up a spreadsheet with your typical or minimum dimensions/ reinforcement, and then see how high you can go before those don't work.
It is appropriate to say "Based on prior experience, design loads will not govern the dimensions or details" or however you care to word it.

Around here, I've seen a few low retaining walls that won't kill anybody, but long-term poor performance may mess up the foundation of the house that they are next to, so there could be some low liability even if there's no danger to life.

 

[msquared48]

Yes Hokie, but he was talking permit, not engineering. Some jurisdictions have their own pre approved standard details. Fall out of that scope, and you need engineering.

Mike McCann, PE, SE (WA)

 

[XR250]

Here (central NC), the inspectors use 4 ft. I have no idea where they measure that from.

 

[RPMG]

IBC tables 1807.1.6 provides prescriptive design

 

[Shotzie]

@Canuck65, can you provide the code references? I'd like to read it

 

[JoelTXCive]

I'm not sure of your layout and where the wall is going, but could you change the name on your sheets to 'oversize curb' versus 'retaining wall'? That might attract less scrutiny by building officials.

 

[Canuck65]

@Shotzie,

OBC, Division A, Part 1 (Compliance and General), cl. 1.1.2.2(2)c states (paraphrased):

Parts 3, 4, 5 and 6 apply to (c) a retaining wall exceeding 1000mm in exposed height adjacent to, (i) public property, (ii) access to a building, or (iii) private property to which the public is admitted.

 

[Canuck65]

@Shotzie,

Also repeated in Division A, Part 1, 1.3.1.1 - Designated Structures

 

[Shotzie]

@Canuck65, Very useful! Thanks for the references.