Buying Land- Site Prep and severe slope- Insight?

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Spent a good part of my life working on vacation homes on lots very similar to that one in different Rocky Mountain states. Be careful trusting engineers, excavators, etc. - many lots with uphill slopes and clay layers in the soil, even thin clay layers that don’t hardly register, will have significant water issues on the site. Water runs downhill. All the water, surface and subsurface, on that hillside will run downhill - a deep cut like that is asking for all the subsurface water that’s soaked into the ground to come to the surface and backup along the foundation.

The most deceptive are lots without a deep cut and that kind of upslope hillside, but rest assured a hillside above it with a nice gentle surface is likely sitting on mud and clay. Visit all lots like this after spring runoff and heavy rains and you’ll be able to see the soil’s ability to perk water first hand.

Water runs downhill.

One of our clients runs a successful engineering firm and hired us to build a house on a lot like that. The first week we stepped foot on the cut and moved our shipping container onto it, we knew there were clay layers and water coming down onto the lot from a sloped hillside because the flat area our container was on was constantly wet. The very smart engineer told us he looked at the soil tests and talked to the architect’s engineer so it will be fine. Well, it wasn’t fine. After the foundation was put in and began to fill with water, again we told him there is obviously a clay layer under the surface that is transporting water downhill and backing up against the foundation and it’s not going to fix itself. The very smart engineer hired an excavator to dig a drain trench uphill of the foundation and add perf pipe - I watched him dig it down to the clay layer - then watched him backfill the trench with the same dirt that came out of the trench (“fabric and crushed stone were too expensive and not needed,” said the very smart engineer. Problem wasn’t fixed. New soil test, showed a lot of sand and gravel - should perk great, so they ignored what we were seeing and saying. Fast forward 4 years and the lawsuits are still going on over who’s responsible. We could have saved everyone involved hundreds of thousands of dollars had they listened to us.

Water runs downhill.

Two years later on a different mountain the layout was identical, but the ground did perk better. Week one I predicted water issues because it’s a heavy snow area and no amount of perk will prevent spring runoff from causing problems - the soil test and very smart engineering firm said it would be ok - the excavator said it will be ok - the builder said it will be ok. Well, it wasn’t ok and the foundation filled up with water when 3’ of heavy snow began to melt.

Water runs downhill.

A different problem pops up when the soil way under the house is clay and moves when it gets wet - often moving the whole house downhill. Not every lot has had a soil test, so prevent this and get a soil test. The lot you showed had the clay/mud dug out of the hillside and used as the base the house would be built on. From 50 yards away it’s easy to see that’s a clay/muddy mess.

The only really smart engineers that understand soil moisture seem to be the ones doing remediation work on entire developments sliding down hill sides. They deal with this every day and know it inside and out. One of them used to swap stories on our job sites and has a side business buying up condemned houses moving downhill and doing the remediation work then flipping them. His preffered method was to pour a large, thick, reinforced “sled” under the house, so the entire structure can slowly work itself down the hill and not crack the drywall in the process. Crazy. Lol

If you ever have to pay for a soil test, look at where the test holes are - they won’t tell you squat about the area uphill of the house - residential soil tests focus on the area the foundation is set on, and surface and subsurface water flows are largely ignored.

 

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It’s also not limited to out of town lots - one job running new trim on a multimillion dollar McMansion for a trust fund baby and retired professional golfer couple in the ritziest part of the ritziest development had engineers all over it for water issues in the crawlspace - the entire exterior of the foundation was dug up and rewaterproofed and that didn’t solve the problem, so they dug up the crawlspace and installed something like 10 sump pumps and tens of thousands in a fancy vapor barrier system. The owners were told the engineers don’t know where the water is coming from, it’s a natural spring, and that’s all they can do. I brought the owners outside and described how clay layers are like a slip-n-slide and pointed up the hill 50 yards to the 4th green on the exclusive golf course in their gated community. It couldn’t have been more clear their water issue is simply subsurface water flowing downhill from the over watered golf greens and backing up against their foundation and flowing under it. A simple shovel hole dug with three scoops showed the subsurface water at the uphill edge of the property. A simple perf pipe covered with washed gravel would have solved the problem and been much less expensive.

Another surgeon’s house had crawlspace water issues and it was the same issue - the house was built on a big bench cut into the hillside - the house sat on engineered fill and was stable, but the big lawn uphill of the house covered the material taken out of the cut - enough clay to get saturated easily, then it flows down the hill and backs up against the foundation until it works under and pops up as liquid water in the crawl space.

Another US senator’s daughter’s house had crawlspace water issues the engineers were just suggesting sump pumps to fix. A quick look around and they had a very large koi pond slightly uphill of the foundation - it took 5 minutes to find the pond liner didn’t reach the top water level and water was right under the sod layer headed for the house - the water level in the pond was reduced a few inches and problem solved.

From the hiway our construction crew noticed a new house built into a gentle slope and knew there would be water issues, so out of curiosity we stopped in one day to say hello and take a tour. Not only was the uphill slope directly against the foundation, but they were using a wood foundation that was supposed to have a very robust drainage to keep the pressure treated wood dry. That foundation is most likely shot by now for a number of reasons.