Landscape Drainage

by Matt

This is a question about landscape drainage.


I have a landscaping drainage issue. I know this is short notice but if you could get back to me as soon as possible I would greatly appreciate it! I really enjoy your site and you
have helped me tremendously!

I am closing on a house on Friday morning. It is a brand new construction, but the back yard slopes down
toward the concrete patio, which is 15X20. The patio is connected to the house. The slope
is about a foot high measuring about 25-30 feet from end of patio to end of property.

Is this sufficient for landscape drainage? The builders say it is up to code but I do not believe them...

Thank you so much.

Matt

ANSWER

Congratulations on your new home! I am glad my site has been helpful.

I am not sure I understand what you mean when you say that the slope is a foot high. Do you mean that when you reach the end of the property to the rear, the land is one foot higher than the grade at the patio...or
something else entirely?

Could you please explain this and I would be
happy to give you my opinion on your lawn drainage possible problem.

Susan


From Matt

Sorry I really didn't know how to explain it but how you stated it is correct. I went again last night to measure and it's 14" higher in the
back yard than the back door at a 30ft distance from back door to end of back yard... I hope this helps you better understand.

Thank you so much for all your knowledge!

ANSWER

Hi Matt,
Ok. The way I understand it now is that your rear yard is sloping from the rear property line towards the patio. It is one foot higher at the rear property line than the patio elevation. I'll assume this is
correct.

A couple of things...
Land should not slope towards the house without taking into consideration the landscaping drainage, where the water will go and allowing or designing for it. However, if your land also slopes to the side and is graded to take the water away from the patio, this would be acceptable. If not, in my opinion, a couple of things should have been done or should be done now.

1. A drainage swale can be created. Land is graded away from your patio for a distance of about 4 or five feet. Since the land is already slope towards the patio, a "ditch" is created which runs parallel to your patio. It should decrease in elevation from one point to the next, so that the water is directed elsewhere to a lower area on your property.

2. A drainage pipe can be installed along the patio perimeter. This would be a perforated pipe with holes in the top. It would be wrapped in filter fabric to keep any dirt from getting in and a decorative stone should be laid on top. The pipe should be sloped and lead to a lower elevation on your property.It might connect to a solid pipe and be led underground to this lower area.

3. Land can be graded to a lawn drain which would connect to a solid pipe, leading the water elsewhere.

If you do not have a lower area, a drainage pit can be installed. This is akin to a large drum with holes in the sides so that water can percolate out.

All that being said, your slope is at about 3% which is not so terrible.
However, I would still have the builder divert the water elsewhere for proper lawn drainage.

I hope this was helpful and good luck. If you have further questions,
let me know.

Susan



Comments for Landscape Drainage

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Inexpensive Drainage To Combat Other Drainage Obstacles
by: JP

Two problems I encountered when dealing with a very similar drainage problem in northern Virginia.

1. The soil is heavy yellow clay. It does not absorb water very well. The rain water seeps into the clay soil and at several different levels in the ground, it glides/slides toward the patio at the back of the house and at the basement walls.

When we have a heavy rain storm, this clay cannot and will not absorb the water. Thus, the intensified streams of water sliding toward the house caused basement flooding through the walls and upward from underneath the basement floor where the floor meets the walls.

2. My back yard has 10 large oak trees, six of which are 70- to 80-feet tall. Tree roots run near the surface of the soil and the tops of some large roots stick out of the soil. I could not put in submerged drainage piping of any kind without destroying the roots, and eventually the large shade trees.

Storm rain water drained toward the house/patio from a 12-inch high at the back of the yard. This is a north-south direction. As a last resort, I dug drainage ditches laterally (in an east-west direction) a few feet out from the patio and the back of the house. I disguised the trenches by planting small root azaleas and other small plants around the patio and the back of the house on slightly raised beds that drain away from the patio and the house into the trenches. These ditches or trenches resemble the trenching gardeners do to separate flower/plant beds from grass to make mowing and trimming grass easier. I mulched the beds. The trenches look neat and a part of the formal landscaping.

The trenches are only 6- to 8-inches wide and two- to four-inches deep. They can be dug to go around large roots and other obstacles. The trenches must continually slope downward away from the high point where water first enters. The trenches run the water off to the sides of my house, down the front lawn and driveway, and out to the street gutter.

In a nutshell, the system works. We have several heavy rain storms each year. However, since I installed the trenches 7 years ago, I have not had any water leak into my basement.

Each early spring I take care to run through the trenches with garden tools to remove accumulated leaf and twig debris. At least once a month during the summer I make sure the trenches are clear. A little work, but just a part of the annual garden cleanup.

It is a lot cheaper than repeatedly dealing with a flooded basement. My neighbors have spent thousands of dollars to install basement water control systems,including pumps, to deal with the same problem.

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Landscape Grading Near House

Because of the large amount of snow we had this past winter, we had water seep into the garage floor in areas. If I slope the earth away from the garage,would this solve the problem of leakage into the garage floor in the future?

Thank you.

PS. This is the first time it happened!

ANSWER

That is the first thing I would do. Land should always be graded away from the house at a minimum of 2%, or 1/4" per foot. For example, if the level of the land at your garage is at "x", the level 4 feet out should be 1" lower than "x". In addition, the distance to be graded outward should be a minimum of five feet.

The ground in that area should have some coverage. Either mulch, lawn or plantings is advantageous to help absorb the water.
Please visit my page on lawn drainage
Susan

Another Grading Near House Question

Question

Hi Susan,
My problem is that my house is on a hillside, next to a steep hill on the left side of my house. When it rains during a heavy thunderstorms, water will start running under part of my house that is built over a crawl space. After unsucessfully trying to cement up the vent windows on that side of the house. (And finding out that cement does not stop water), I am now engaged in putting in a drainage ditch about 2 foot deep allowing the water to escape down a drainage ditch that contours with my landscaping in the front of my house onto a concrete driveway that runs into the street. I hope this corrects my problem, however, I have to wait until the next rainstorm to find out. My question is, am I heading in the right direction my solution. By the way, I am a retired landscaper! We bought this house a few years ago without the knowledge of the problem, beforehand. Thank you.

Response From Susan

Hi George,
Where is the drainage ditch?
Is it on the left side of your house, and if so, how far away from the house is it.
Have you in essence created a type of swale parallel from your house which leads to the front yard?
Is it a grassy swale or have you installed perforated pipe?
Is the picth at least 1/4" per foot?

Let me know so that I have a better picture...thanks.

From George

Hi Susan,
Yes, its on the left side, and the drainage ditch is 15 inches deep about 4 foot from house and the yard sloped to the front of the house and everything goes downhill from there. The pitch is good on the side yard to the front and I of course put in a good pitch in the drainage ditch. I have been trying to catch it raining in the day time to check the perfomance, but its been at night so far.

I have tried perforated pipe before, but we have gullywashers and it proved ineffective. I plan to line the bottom of the ditch with river rock, (too heavy to wash down) when I am finished. When it rains heavy here, its like a river coming off the hillside. My studies have shown me that I must divert the water to solve the problem. The drainage ditch is at the edge of the landcaping of the house. (Only thing I have left is a Savannah Holly that I am trying to save, on that side of the house). The 3 foot beside my house, I intend to put in a steep bank to help deflect any water into the drainage ditch also.

My front yard is severly sloped to allow for natural drainage. The only flat spot is where my house sets....lol.

Hope this helps. Thank you.

Response From Susan

Hi George,
It sounds to me that you are doing the right thing. Slope from your house to the drainage ditch, have the drainage ditch pitch properly (minimum 1/4" per foot), leading all that water to an acceptable place.

Let me know how it works out. Your river rock idea is interesting. I myself have a swale off my patio...a grassy swale. It works great, although there is an area near the drain that stays rather wet. At times the drain accumulates leaves and this slows the drainage, but it still works. I have often thought of using river rock in that area. However, the reason I hesitate is because the purpose of a swale or drainage ditch is to lead water in a particular direction. It is possible that the water will not be led down the ditch, percolate through the stones, and accumulate there.

Susan

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Drainage Swale

by Cathy

We have a swale at the back of our yard that doesn't grow grass. It is rather "mucky" and very unattractive. Any suggestions to make it look nice would be appreciated.

Thanks,
Cathy

ANSWER

Hi Cathy,
Swales generally are not mucky. They are just an area of the lawn that look like a channel but that are really not very noticeable. The purpose of a swale is to take water away. It sounds as if yours is not functioning properly. This often happens if there is not enough pitch to the swale. In other words, the elevation should get lower and lower.

Sometimes also a swale can be too deep and narrow and grass will not grow.

If I am on the right track, you have two options. The first would be to widen it , regrade so that it has the correct pitch (the water will then not sit there but keep moving to a destination), and re-seed the area.

The second option is to clean it up and fill it with decorative stone. This then changes its function from a swale to more of a drainage pit/ditch. The soil below should be porous enough to allow water to seep into the ground. Clay soil will defeat the purpose as it is difficult for water to permeate through this type of soil. The stone on top will also allow infiltration to below.

You can then choose to plant at the edges in whatever areas you like...or even all of it.

I hope this was helpful.
Susan

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Landscape Drainage Problems

by Jenny

My sister-in-law recently purchased her 1st house. The home inspector said there was some negative grading problems in the back of the house that need to be fixed. Also she had the under ground oil tank removed and put above ground.

Now there is water coming into her basement in that area. I am assuming because it also now needs to be graded properly.

Lastly the previous owner had changed the back door from the side of the house to the back. In doing so they left an open hole next to the house where the original stairs existed. We are hoping to be able to get some free fill dirt (no money left) and fill in the where the oil tank was replaced and fill in the hole where the stairs used to be.

The area on the side of the house is approximately 6 to 8 feet from the house to the neighbor's small stone wall.

How do we make sure this is graded properly away from the house to stop the water that is now coming in?

I was also thinking we might want to make a swale close to the stone wall to channel any water towards the front of the house that has a natural downward slope towards the street.

Any help would be greatly appreciated since we can not afford to hire someone and need to stop the water from coming in.

ANSWER

Hi Jenny,

All land must be graded away from the house, as you seem to understand. It should be at 1/4" per foot. So let's take the area on the side where there is 6 to 8 feet until you reach the wall. Let's make it 8 feet.

Mathematically, this means that the land at the edge of the wall should be 2" lower than the land at the house. It can be more, but should not be less. Now there is the situation of where does that water at the wall go? If I were designing it, (and of course this is theoretical since I do not know the lay of your land), I would put in a perforated pipe at the wall and pitch towards the front of your house. The pipe gets wrapped in filter fabric and covered with decorative stone.

Creating a swale is possibly another option. I am just concerned about the narrow depth of 6 to 8 feet. It might be able to be accomplished if done well.

In this case, land would pitch downwards towards the swale at the same 1/4" per foot. Then you create the swale. The land at the stone wall pitches towards the swale. The swale gets lower and lower as it moves towards the street.

If you had 8 feet, perhaps the swale could be about 18" to 24" wide. The swale should pitch also at 1/4" per foot. So you need to know the elevations at the start and end of the swale to see if this will work.

Eye levels are available to help get elevations. They are not too expensive.

I hope this was helpful.
Susan

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water runoff on north side slope next to house.

by Lonna Phelps
(Salem, Iowa)

grading and drainage

grading and drainage

We have a walkout basement. On the north side is a 12' long slope. We have built a retaining wall on the north side of the walkout basement. We build 3 tiers on the 12' foot slope with large tumbled belgian stones about 8 feet out from the cement foundation of the house. We used weed fabric and put rock between the large stones.

The first year (this was a new house)the ground settled and we had to rebuild about 3' out from the foundation. This year after heavy rains, the water ran under the fabric and stones and washed out an area under the stones and rock. (The dirt went into a gentle slope by the retaining wall). So of course the stones settled even more. We are not sure how to solve this problem. Would shrubs planted next to the foundation hold the dirt in place? We have considered putting a 2' deep area of cement at the top of the slope so that the water would go over the stones and rock and not under it. It appears that only about 3' out from the foundation is being affected. Any advise would be appreciated. Thanks.

ANSWER

Hi Lonna,

The right way to grade this area would be to slope the area away from the house. I realize that your land slopes downward along the house foundation, but it can still be graded so that the ground is higher at the foundation and gradually gets lower as it moves away from this area. (Sideways) This can be graded at a minimum of 5%, or 1/4 inch per foot. That means that at the area that is five feet away from your house should be a minimum (can be much more) of 1/4 inch lower. I say five feet because the land should be graded away for at least five feet.

I am not sure how your land is beyond what is shown in the picture. Does it slope, is it flat, etc. This would determine how the land is dealt with once it gets into this area. You might need to create a swale or have another solution so that all water flow properly.

As far as planting shrubs, that would also help. Once they get established, the roots will absorb a fair amount of the water.

Comments for water runoff on north side slope next to house.

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Foundation Grading and Soils
by: Susan

Hi Gina,
In situations where there won't be any plants, I would suggest a clay like soil. This type is very dense and makes it difficult for water to seep down. Actually this can be a problem if used for planted areas as the plants get little water and it can just pool.

However, if the land is sloped, clay is good. If you use a good soil, a sandy soil, rocks etc., the water will seep into the ground instead of flowing along the slope.

It's not too important in areas away from the house, but at foundations you want the water to grade away to make sure you don't have water problems in your house.

Susan

Additional details
by: Gina

Thanks so much for the advice.

No, I'm not planning any plantings. On one side is the property line and I will have to put a swale or ditch there to direct the water away (but that's okay, the land slopes that way anyway).

On the other side is the driveway so no foundation plantings there either.

The front already has some pavers over a rubber liner as there had been problems there in the past.

At the back is where the garden will be and I will use some good soil there but what could I use elsewhere?

Thanks again!




Grading at House Foundation
by: Susan

Hi Gina,
If you want to add plantings, you will want to use a good soil mixture.

As mentioned above, the land must be graded away at a minimum of 1/4 inch per foot. It can be as steep as you like.

Let's assume there is no slope at all and the area is flat. You can do either of two things:

1. Go out about five feet and lower that area.

2. Raise the grade at the foundation. This is easier if you are adding soil against a concrete foundation. If it will be against any siding, you may have to either remove it or waterproof it.

In both scenarios, it should be sloped for a minimum of five feet (at least). Now, once it gets to the bottom of the newly created slope, where does the water go? Is it flat and will it just sit there? Here is where you have to address the drainage in this area too.

If you like, you can let me know what your situation is (is it flat, does it slope in any particular direction?) and I can give you some ideas.

Susan

Grading problem plagues my place too
by: Gina

I have the same kind of problem and I want to re-grade the land next to the foundation, but I'm not sure how to do this.

Do I just buy a load of soil and shovel it next to the house until it slopes away enough? Some people say I should use gravel or fill instead and just a few inches of topsoil on top.

Any advice?

Thanks and congratulations on the fine site!

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Landscape Swale At Road

by Pat
(Oregon)


We have a landscape swale at the road... between the front yard and a private road. Mowing it is awkward due to the slope. Do you have any ideas for landscaping that will be low maintenance but nice looking?

I sure appreciate websites such as yours. I live in Oregon.

ANSWER

Hi Pat,
Swales at the road are a problem in Virginia also...hard to mow and
untidy looking.

It all depends on your particular landscape swale as to how to improve it. There
are solutions, but many create a lot more maintenance.

1. Create a dry river bed with decorative river rock and place low
maintenance plantings at the edgings.
2. If the grade allows, sometimes you can fill it slightly to make the
slope less severe.
3. Raise the grade and install a pipe underneath. This is a solution
that is more costly and complicated and will most likely require an
engineer.

I am working on a design where I created a walk from the street to the
front door. I designed a wooden bridge to go over the swale, and planted
along the sides with a combination of river rock and plants. It doesn't
eliminate the swale but I worked with it to foster an interesting
design.

I'm glad you are enjoying my site!


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"Susan,  what a pleasure it was to work with you.  You made me feel like I was your only client - responding late at night and always so quickly!  Your design is amazing and we only hope we can do justice to it when we plant.  You have such fantastic ideas and you are so open to suggestions and changes.  Loved working with you - now if you could only come to Canada and plant it!!!"
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