The first step in correcting foundation drainage issues is to determine if the soil around your home has the proper slope. Fortunately this is fairly easy to check. Obtain a nice straight 2x4 that is 10 feet long and a carpenters level. The ground should slope away from the house at least 6 inches over 10 feet - see the picture below.
Check the ground slope all around home about every 3 feet. Note the slopes on the drainage sketch you make for Step 2.
Some areas with insufficient slope can be corrected by moving soil from the areas 10 feet from your home back towards the foundation wall and smoothing it out to the proper slope. In other cases soil may need to be imported to the yard.
If your yard is very flat and the foundation wall is not tall enough to allow soil to be added, you may want to explore adding an underground slope as explained in the last 1/2 of this linked article. The concept is shown in the picture below. Basically it creates a relatively dry area of soil next to the foundation, and allows you to dig your deep French drains some distance away from the foundation where it is safer for the structure and easier to dig.
Now that you have determined your foundation slope and your plan to correct any slope problems, it is time to figure out how to correct any downspout drainage issues. Or as we called them in Step 1, figure out how to avoid having a Lake Downspout. Correcting downspout drainage issues is a matter of getting the water away from the house and spread out over an area of yard that can absorb it.
If you have too much roof area draining through a single downspout, or two down spouts very close together, you will want to consider altering your gutter and downspout arrangement to add more downspouts or rearrange the ones you have.
Once the downspout drains onto the ground it is best to move that water at least 3' away from the house as quickly as possible. See the pictures below for some ideas of how to accomplish this.
If you connect to your downspout to your French drain be sure to use leaf seperators (shown above) to keep leaves and twigs from clogging your French drain. They are available in either plain or fancy versions.
Another option is to use a rain barrel to collect the surge of water when it rains and then slowly drain the barrel over the next day by having it hooked to a hose leading to a garden or flower bed. The hose should have an inexpensive ball valve at the end that is opened enough to allow a steady trickle of water. Open the valve fully occasionally when the rainbarrel is full to clean out the hose and valve. Be sure to install an overflow pipe on your rain barrel for those very rainy days. The fact that the barrel self drains each time prevents mosquito problems too.
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