How to build a sunken patio
Sunken patios are constructed the same as ordinary patios, with the except, as the name applies, they are below the level of the surrounding terrain.
The first thing you must determine is the location of the patio. The surrounding terrain should be on high ground, where runoff and excessive pooling will not affect the patio during rainy weather.
In most communities, before you dig anywhere in your yard, you need to contact your utilities. They will do a free inspection to determine that no gas, water, sewage, telephone or electric lines are within the proposed site.
The patio is constructed from digging down to the depth you want, plus an extra six to ten inches to accommodate the depth of the crushed stone, sand and the pavers themselves. You also need the extra depth for stone if you are pouring a solid concrete patio, or, one with a combination concrete and pavers.
As with any patio, you need to measure out the square footage of the patio area to get an idea of how many blocks or stones you need and how much sand and stone, or, how many cubic feet of concrete.
The major problem with a sunken patio is water retention. A rain storm can cause your patio to turn into a pond that may take days to dry out. Before you level down the soil on the patio floor, you might want to add a drainage system, especially if you are pouring a solid concrete patio. This can be as simple as a PVC pipe that is run under the soil off the patio area, where is comes out at a lower level down slope from the patio area. The pipe is connected with an elbow joint to a flat drain cover that is incorporated into the patio floor. Make sure that your elbow pipe is tall enough to reach to the top of the stone pavers, or, future concrete floor.
You can also put in a French drain by digging down several feet in the center of the patio, and filling the area with stone. This allows excess water to drain down into the stone and evaporate. The diameter of the drain pretty much depends on the size of the patio, but it is usually not very wide. As with the PVC drain, a drain cover is incorporated into the top floor.
After you level down the soil on the floor of the patio area, add the stone and tamp it down. Then, add two or three inches of sand, if you are laying pavers, and place the pavers around the center drain, so there is a slight slope toward the center for drainage. Add sand over the pavers, and sweep it into the cracks.
If you are making a solid concrete floor, pour the cement over the crushed stone, and around the center drain. Once again, level the concrete to slope gently toward the center of the patio.
On one side of the patio area, you may want to carve out ledges from the terrain, which can be covered with stone for steps to your new patio.