Patio Drainage – Don’t Forget The Pitch

Summary: In patio installation the pitch and layout on large patios or terraces installed by professionals are “laid out” with surveying instruments. Homeowners and the DIY’er in building a small patio usually do not have access to surveying instruments and must be done by hand. Find out how to stay on pitch!
A pitch of a patio that is too steep makes for tilting garden furniture, and the irritation of liquid spilling out of containers set on a sloping table top. The pitch in laying a patio or deck should not exceed two and one-half inches in ten feet.

I once allowed myself to be bullied by a mason into building a patio at the end of a small garden with a pitch of five inches in twelve feet. I protested, but he was experienced and very determined. He insisted “I know how to lay a patio!”

When the job was finished, I asked him why he had been so insistent. He replied with Latin excitement, “My patio, no one would see my patio!” I realized he was so proud of his work that he would have stood it on end if he could.

The slope of the table on the patio was not good, but still not impossible, and the slight exaggeration of the pitch did actually play up the area and increase the apparent size of the garden slightly.

Patio Drainage Solutions – The Purpose of Pitch

The purpose of the pitch, of course, is for patio drainage, allowing water to drain off smoothly and fairly rapidly.


In a big job, elevations are established by surveying instruments, but on small properties, simple, rule-of-thumb methods often suffice. An easy way when landscaping small backyards is by laying out the paved area in the following:

After staking out the terrace, dig a trench round the whole area, about three inches deep on the high side and a little deeper on the low side.

Sink a frame of two by four lumber into the trench. Use a mason’s or carpenter’s level to be sure that the sides of the frame are level.

Place a board (piece of rigid lumber) across the frame, from the high side of the terrace to the low side. (If the terrace is more than about twelve feet wide, it will be necessary to perform this operation in more than one step, and establish the grade at, say, ten-foot intervals.)

Place the level on the board and, resting one end of the board on the frame at the high side of the terrace, adjust the board until it is level. Prop it in this position, and adjust the low side of the frame to the required pitch.

If the pitch is to be two inches in ten feet, and the terrace is ten feet wide, the low side of the frame should be two inches below the high side; if the terrace is fifteen feet wide, the difference in level will be three inches and so on.


When the frame has been adjusted, make it firm by driving stakes into the ground. You now have a frame into which to fit the terrace.

Laying Flagstone

If the terrace is to be made of heavy flagstone, three or more inches thick, without a cushion of cinders and sand, prepare the soil within the frame by removing all stones near the surface and raking it smooth.

If it has been necessary to work it deeply, let it settle for a few days. In any case, tamp it. When it is thoroughly settled, begin putting the flagstone in place. Prepare the bed for each flagtone separately by raking lightly and mixing in a little sand if the soil is heavy.

Begin at the upper side of the terrace and place the first stone so that its upper edge is resting against the frame and level with it. Then take the piece of board and rest it across the frame and the flagstone.

It should touch squarely the surface of the stone and the top and bottom sides of the frame. Continue in this way, testing the position of each stone as it is placed, until the whole terrace has been laid.

Use your eye to decide on a pleasing pattern, and try to avoid joints that continue in a straight line from stone to stone.

When the stone varies in color and texture, stones lighter or darker than the majority, or coarser or finer in texture, should be scattered rather than laid all together. When all the stones are in place, test them again with the length of board and adjust or tamp any pieces that are out of position; then brush clean sand into the spaces between the flags.

If the paving material is to be laid on a bed of sand and cinders, excavate within the frame to the required depth to allow for a cushion of cinders or gravel (about six inches) and sand (about two inches). Both the cinder layer and the sand layer should be flooded and tamped.

Whatever material is used to pave the terrace, the frame of two by fours makes it easy to achieve a uniform grade and a smooth surface. If it is necessary to pitch in more than one direction, divide the frame with a center board.

If the terrace is raised above the surrounding level, it should be faced along the exposed sides. Even when the facing stones are heavy, they should be set in concrete.

To do this, dig a trench and pour in a footing of concrete. This will hold the facing stones in line. Place one-inch boards along the exposed sides of the terrace and hold them in place with stakes driven into the ground.

Put the facing stones in position in front of the board. Pour concrete into the cracks between the facing stones, leaving a few openings for drainage. When the concrete has set, remove the board and pour concrete into the space between the facing and the terrace.

Exposed concrete should be colored to match the stone.


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