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lercher2001 02-12-2007 09:17 AM

Grading Concerns
We are in the process of building a home. The home site is relatively flat where the home is to be sited, but then slopes 10-15 ft. around the rear of the home, somewhat like a bowl. There is netting that has been placed on the steepest parts of the hill to avoid erosion. Our builder initially agreed that grading/terracing/modification was necessary in order to avoid potential water problems in the future; he has since come to the conclusion that the grade of the site will not be changed. We are very worried that we will incur drainage problems if something is not done to reduce the slope of the site. Any and all suggestions would be greatly appreciated!

concretemasonry 02-12-2007 09:53 AM

Hard to give a drainage suggestion without knowing the direction and amount of slopes. If there is any slope (no matter how steep), it will direct the flow of water.

If you will have a basement, you should definitely make sure you have drain tile and a sump pump. This would apply even if the lot is level or near a slope.

lercher2001 02-12-2007 11:39 AM

Pictures of Grading Concern
Here are a few pictures of the slope in question. Would love your opinion as to how to handle this...we are meeting with the Superintendent on the subdivision this afternoon. Thanks so much!

lercher2001 02-12-2007 12:06 PM

A few more pieces of additional information:

There is a 4x4x2 deep "infiltration trench" on the blueprints to the right of the lot (as you are looking at the pictures). The next lot, to the right of us, has a long driveway that runs beside our proposed home, and next to the infiltration trench. On the top of the hill the land is level. The back of the lot borders another home's driveway. The entire lot is 1.2 acres. We have suggested a french drain, and the sales agent thought that the builder might terrace the hill, but now they are telling us that the site is as is. What to do??? Thanks!!

concretemasonry 02-12-2007 12:33 PM

Based on the photos, you are going to collect a lot of water. Even the relatively "level" area of the yard between the slope and the proposed house will collect a lot of water.

Terracing and vegetation can reduce (but not eliminate) the amount of errosion, but does not decrease the amount of water collected and coming down the hill. Segmental retaining walls units to define the tiers could be designed to intercept and divert water to the right.

French drains if enough are installed properly can intercept the water coming down and ultimately carry it around your house. By looking at the lot and assuming what kind of rain you may have, you will have a lot of water to deal with. It would take a huge "french drain" to carry that much water. Surface drainage structures are not pretty, but they will carry much more water.

What is done depends on your concrens and what the contractor is obligated to do. If he is to guantee a dry basement, he probably would be more inclined to do more to divert the water.

lercher2001 02-12-2007 12:46 PM

Thanks for all of the great advice. We have a blueprint of the elevations...the hill rises at 2 ft increments for about 12 feet until it reaches the top. What should we expect the builder to do at this point? We must make this demand today, when we meet. They want us to take the contingency we have currently off the property asap, and until we get some sort of assurance from them that they will make sure there is no problem, we don't want to do that.

concretemasonry 02-12-2007 02:41 PM

Your builder is trying to pressure you into accepting something that has not been spelled out yet. The sales agent is just throwing out someting to "grease" the deal.

You should expect some sort of definite plan and guarantee from the builder without him just burying it onto the cost of the house.

You concerns are important and you should decide whether you are worried about slope errosion or the problems of having water flowing around your home (or both). There are general rules for the slope of the soil way from the home. Providing this slope at the rear and sides, will mean raising the house or lowering the grade behind the house. - It all depends on what elevation is established for the house.

Since this is a last minute thing, it will end up being between you and the contractor (if he has a definite plan).

handy man88 03-23-2007 12:22 PM

You need to look at the grade plan for your building site. On it, should be indications of elevation changes and the projected path of water runoff. If possible, meaning if there's enough of an elevation change, you will see a swale/surface drainage sketched out on your grade plan. What you see right now isn't what it will look like after the house is built. You're worried about water coming down the hill, but what about water coming from your gutters into that flat backward. Where is that water going?

Your backyard looks relatively flat, so water will definitely just sit and pool in the back. If you decide to terrace that sloped area, you will need to make sure the drain is installed during this time. There will most likely be a french drain around your house, but that water will be sent to your sump pit and sump pump, and as we all know, sump pumps fail at the wrong time. You'll need to get a battery powered back up sump pump installed for peace of mind.

As I said before, check your final grade plan. What you see now is not what you will see after the house is built.

Brik 03-23-2007 12:32 PM

I would be more concerned with the 'flat' area than the hill. I would insist that the flat area slopes away, toward the hill. A swale at the bottom of the hill to direct water left and right if possible out into swales on the sides of the house carrying the water to the street. That's at a minimum.

handy man88 03-23-2007 12:44 PM

I think the only way to get water away from the house is to regrade the backyard and have it slope away. With that though, they will need to terrace that back area to hold back the dirt as that back area will be lowered. Problem is if i is done this way, that back area may be lower than the street. Water does not move uphill but itself.

It's probably too late now, but I would have the builder put in several feet of fill dirt to raise the house as much as possible. This would allow better grading options.

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