retaining wall drainage

**John Dirks Jr** · 07-25-2011, 08:26 PM

The pictured retaining wall is masonry stone with full mortared joints. It had no visible drain tubes or weeps. It was 34" high (at highest point), not including footer depth.

Is there any specific code language in IRC or other that would require a drainage system of sorts?

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**Randy Mayo** · 07-26-2011, 08:40 AM

John

IRC code exempts retaining walls for the permit process if less than 4' from the bottom of the footing to the top of the wall. One of the exceptions to this rule is if the retaining wall is supporting a surcharge, in this case it is since the soil is sloping down towards the retaining wall. Also many cities and counties that have building codes typically have a generic handout for common items like decks and retaining walls. I would check with them first if you area has codes. For weep holes to be effective you typically will need clean aggregate behind the wall and some filter cloth to protect the aggregate from silt. Seeing weep holes is no guarantee the wall was built or designed correctly. So be careful in commenting on retaining wall defects, usually limit comments to visible cracks, bowing or excessive leaning.

**Billy Stephens** · 07-26-2011, 08:46 AM

Some Drainage Systems do not use weeps. Retaining Wall Drains
.

**Harry Janssen** · 07-26-2011, 06:14 PM

Randy,drainage holes are no guarentee that the wall is built properly,but a lest some thought was given into the construction of the wall,most companies and suppliers have their own installation instructions

**Markus Keller** · 07-26-2011, 06:15 PM

I wouldn't comment on the wall being defective because I can't see what's behind it, whether there is some other sort of drainage system or who knows what.
I would however put a note in the report about drainage and footings. Additionally, with that much sloped earth behind the wall I would want to know if tie backs were installed for the wall.

James Duffin · 07-26-2011, 07:14 PM

It looks like a nice wall. I would think that there is drainage out the ends of the wall where the wall stops...

**Jerry Peck** · 07-26-2011, 07:15 PM

Originally Posted by Randy Mayo

IRC code exempts retaining walls for the permit process if less than 4' from the bottom of the footing to the top of the wall.

Which somewhat conflicts with this: (underlining and bold are mine)
- R404.5 Retaining walls. Retaining walls that are not laterally supported at the top and that retain in excess of 24 inches (610 mm) of unbalanced fill shall be designed to ensure stability against overturning, sliding, excessive foundation pressure and water uplift. Retaining walls shall be designed for a safety factor of 1.5 against lateral sliding and overturning.

"shall be designed"

Sure sounds like the code is telling one that a retaining wall of 24" in height and is not laterally supported at the top (most are not) needs a permit as how else is the code, or the AHJ, to know whether or not the wall was designed to ensure stability etc.

""shall be designed" almost seems to imply an engineer is to design it as a non-engineer would go 'Yep, this should work ... ' - which is different than 'designing one to work'.

**John Dirks Jr** · 07-26-2011, 09:16 PM

They say "measure from the bottom of the footing to the top of the wall".

Where exactly is the bottom of the footer? Isn't that the lowest point which is burried in the grade?

If so, the wall in my picture had 34" exposed, not including footer. Add a qualifing footer and it's over the 4' limit and requires a permit.

The way this thing curved around on the slopped lot, I don't see how it could drain out the ends. The low spot would still be in the middle. I wrote it up on the spot and would do it again a hundred times.

**Jerry Peck** · 07-27-2011, 02:31 PM

Originally Posted by John Dirks Jr

They say "measure from the bottom of the footing to the top of the wall".

Where exactly is the bottom of the footer? Isn't that the lowest point which is burried in the grade?

If so, the wall in my picture had 34" exposed, not including footer. Add a qualifing footer and it's over the 4' limit and requires a permit.

Correct.

And it is also supporting over 24" of unbalance fill, i.e., one side of the wall has more than 24" of fill behind it as compared to the other side of the wall.

Now, if that wall had tie-backs installed into the upslope fill ... unless the tie-backs were at the top of the wall ... that would not be considered as "laterally supported at the top" ... and the tie-backs are usually not "at the top".

Ted Menelly · 07-27-2011, 04:34 PM

Originally Posted by John Dirks Jr

The pictured retaining wall is masonry stone with full mortared joints. It had no visible drain tubes or weeps. It was 34" high (at highest point), not including footer depth.

Is there any specific code language in IRC or other that would require a drainage system of sorts?

Is this wall from a neighbor or is this wall your clients walls and you are looking at the neighbors side.

In any case you have absolutely no idea what the drainage is for the wall other than some weep holes (usually pvc pipe) out the bottom of the wall. If the wall is sound and not cracked then there is nothing to write up there. If there is no apparent drainage issue with the neighbors yard draining into you clients yard and there is improper drainage in you clients yard then write it up. If there is no drainage issue visible then there is nothing to write up there. If the neighbors yard constantly washes into your clients yard over the wall and that is obvious then write it up.

If everything has the visual look of "looks all good to me" then there is nothing to write up at all. You being at the inspection could be the only one to draw any of those conclusions. No rain in a very long time, just too little to get a good visual.

T o me it looks like a fine wall with the exception of the neighbors yard washing into your clients yard (the build up at the bottom of the wall). If that's the case write it up.

**BridgeMan** · 01-17-2012, 02:59 AM

Originally Posted by Randy Mayo

John

IRC code exempts retaining walls for the permit process if less than 4' from the bottom of the footing to the top of the wall. One of the exceptions to this rule is if the retaining wall is supporting a surcharge, in this case it is since the soil is sloping down towards the retaining wall. Also many cities and counties that have building codes typically have a generic handout for common items like decks and retaining walls. I would check with them first if you area has codes. For weep holes to be effective you typically will need clean aggregate behind the wall and some filter cloth to protect the aggregate from silt. Seeing weep holes is no guarantee the wall was built or designed correctly. So be careful in commenting on retaining wall defects, usually limit comments to visible cracks, bowing or excessive leaning.

Randy, I like the way you think. Maybe we should get together sometime for a beer or two.

Michael Kober, P.E.