Planning patio drainage is just a little more complicated than making sure that the patio is built with a drainage slope in the right direction. Building drainage into an existing patio has advantages because you already know where the water on the patio goes.
Step 1: Draining to Where?
As well as draining your patio, the system has to take the drained water and remove it from your property. Locate a suitable point to which rain water can be directed. This will probably be the nearest sewer or area drain.
Step 2: Plan How to Get the Water There
You don’t really want water simply flowing freely over the yard so you will have to plan a route for the water to take. Once you know the route you will have to decide if you will use a pipe or a channel to carry the water. Pipe or channel you will have to decide on dimensions that will handle the volume of water that you expect to flow down it.
Step 3: How to Drain the Patio
There are several ways to drain your patio. The simplest is just to let the water soak away but this is unreliable and a lot of water could take a lot of time to disappear. French drains could be installed under the patio feeding in to the main drain planned in Step 2. More simply, the patio can be designed with a channel running around all four sides. This channel will be the drain and will catch all the water that falls on to the patio. The channel will be covered with metal grills which will simply look like part of the design of the floor. Using expert help the channel can be laid so that the patio drainage slope leads to the end of the main drain already decided on.
Step 4: Connecting the Patio Drain to the Main Drain
The patio system can be connected to the main drain in a closed vault buried in the soil or in the foundations of the patio. For an existing patio the connection will have to be designed so that as little extra building work as possible is necessary. The simplest way will be to have the main drain installed so that it has an opening under the drainage point for the patio drain. This way the patio water will simply pour off the patio into the drain.
Step 5: Wait for a Really Rainy Day
Although what you have designed should work perfectly well, only seeing how the rain water actually gets dispersed now will confirm it. Make note of any areas where water lies unexpectedly on the surface. This won’t create a problem for the patio drainage but could give an opportunity to improve the drainage of that area by incorporating it into the system.
Once you have your drainage system planned out and the theory tested you should not have any problems once it is installed.