Maybe someone can answer this while I wait for a reply from my buddy (civil engineer)

I am looking to buy a house and so far I have seen 2 homes which are either at the top or bottom of steep slopes. Today I saw a house sitting on flat ground about 20 feet back from a 5' high cinder block retaining wall which was bulging, cracking, and had no visible drainage.

Below that was a 6 foot wide steppe which was very old and was aggregate rock / dirt, no concrete. Below that were varous smaller concrete caps which appear very old down to the flat.

The next door neighbors on both sides have either improved or replaced some or all of their retaining walls. My question is - what would it cost to install these walls (the lot is over 100 feet wide and maybe 30-50 feet from base to the top). I am guessing a minimum of 10k per wall.

Also there is a brand-new deck on the house which runs right to the edge of the upper retaining wall which I imagine would have to be ripped out to replace the wall.

Anyone ever have to build or replace a retaining wall?

Does it rain a lot where you are? You may want to reconsider a home at the top of a hill.

From just about a year ago:

http://www.ctv.ca/servlet/ArticleNews/story/CTVNews/1106138196440_194/?hub=TopStories

In the end, the city is buying all the houses at the top and bottom of this particular hill to avoid a repeat.

I'm in San Diego. It doesn't usually rain a lot. But last year it did, and a bunch of houses in La Jolla and Oceanside were destroyed in a landslide.

I built one about 30 feet long and 4 feet high in front of an area that is (at a rough guess) 20 feet deep with a drop of around 3 feet (so not incredibly steep but certainly noticeable), and I used a combination of steel rods, reclaimed wooden railway sleepers, and poured concrete. I dug a two foot deep trench about six inches in front of the slope, stuck steel rods in every couple of feet (to a depth of about 2 feet below the bottom of the trench) and then filled the tranch with concrete. I then drilled through the sleepers and slotted them over the rods, braced them from behind with a series of plates with 4 inch long rods (with a sort of lange affair on the free end) protruding from them, then filled the gap behind them with more concrete.

All in all it wasn't *too* expensive (although an exact figure is hard to give as I bought all the bits piecemeal and never kept a running total) and it was backbreaking work (I probably moved several tons of earth), but it'd take something pretty devastating to shift the thing...

hmm... My concern is that to rebuild the upper wall I would need to rebuild the lower wall since the concrete footing for the upper wall would be poured into the lower wall. The total height from the house to the flat of the canyon is 30-50 feet. The neighbors have wide steppes - their lower wall is 5 feet high with about 15-20 feet before the upper wall foundation. In my case the lower wall is only 5-6 feet from the base of the upper wall.

And regarding the CTV story above, the same area is on evacuation alert this year (after 26 days of continuous rain). It's a risk. You may want to consult with the municipal level of government in your area and see what the codes are, how/if they are enforced, any known issues in the area, etc.

Personally, I think I would avoid those houses. If you keep looking, you should find houses that don't have such disadvantages. Since houses are the kind of thing you don't tend to buy and sell on a whim, it would be worthwhile to spend time finding the right one before buying.

AC: how long have you lived in Vanouver (area?). I didn't even notice the amount of rain we've been having... Other than the Grey Cup and Junior Hockey Championships, the only article about Vancouver that I've seen recently in the National Post is one the other day about the rain.

I've lived in Vancouver for about 34 years.

"I didn't even notice the amount of rain we've been having"

I didn't think much of it either, but apparently we're on the verge of breaking some record of days of continuous rainfall. If we can get to 29 days (Monday) then we've beat the record from 1953. I know, it's weird, I would have thought the record for days of continuous rain in a year for Vancouver was 365! ;o)

Google for "Angle of Repose". Here's a decent link:

http://gpc.edu/~pgore/geology/geo101/masswasting.html

Each situation is different - I would suggest you contact a geologist or civil engineer for an opinion if you really like the house.

Sassy, google for "Slip Circle"

First hit:
http://fbe.uwe.ac.uk/public/geocal/SLOPES/SLOPSLID.HTM

Make sure you install a toe drain. Even in dry areas a retaining wall has to be provided with a toe drain behind the wall at the bottom to drain away groundwater. If there is no toe drain and the wall doesn't leak then the wall effectively becomes a dam subject to loading from the water that builds up behind it. Pressure is linearly proportional to height.

"but it'd take something pretty devastating to shift the thing..." Just so.