Getting The Levels Right on Your Patio
Getting the levels right on a patio is a time-consuming and pain-staking job, but putting effort into it will give you a patio that looks good and drains well. The alternative is a patio where the flags don't line up correctly, there are height differences at the gaps that get bigger over time, and water forms puddles when it rains.
As with many other aspects of driveway laying, getting this right is more about the preparation of the supporting surfaces than the actual Laying Of The Stones, flags or other surfaces. No specialist equipment is needed and, although it is now possible to buy cheap laser levels, that's over-kill for just one patio.
What Does Level Really Mean?There are three different elements to getting the patio levels right. The first is to make sure the area is flat; that is to say that there are no raised edges between stones to trip people up. The second is to make sure it is level, as in all the flags are lined up with each other in the horizontal plane.
And the third, although it seems contradictory, is to make sure the patio surface is not level. For Drainage Reasons you need to have a gradient, known in the trade as a 'fall', from one end of the patio to another. Usually this slope will go away from the house, so that water isn't encouraged to pool next to it and cause damp problems. But in order to be able to make a fall that is not level, you need to know where the level is.
Starting the Level from the HouseAssuming the patio site has already been excavated and the edges marked out with pegs, pick a level on the wall of the house that is below your Damp-Proof Course, but not so low as to make too big a step coming out of the house. If your ground is on a steep slope, particularly if it slopes toward the house, then you will have to get creative at this point and perhaps decking would be a better choice than a patio (see When, Where And How To Fit Decking on this site)..
Using reasonably straight edges, such as new timber battens, and the longest spirit level you can lay your hands on, mark that line on the brickwork of the house all the way along with chalk or another semi-permanent marker.
Calculating the Patio FallIt's now time to calculate the fall, which will encourage water away from the house, using the industry standard ratio of 1:80. This means that for every 80 units of distance along the patio, the level must drop by one unit. So if your patio is a rectangle 6 metres wide and runs 4 metres from the house, it will have to drop by 4m divided by 80, which is 5cm.
Now we know the patio has to drop by 5cm between the house and the end of the patio, but in a straight line. In order to measure this we need to transfer the level from the house to the 4m mark. This can be done by getting the longest straight edge piece of timber you have and attaching your spirit level to it. Set the end near the house on a pile of sand and a brick then do the same for the far end, tamping down the brick on the sand until the timber is level.
Taking the Level OutThe nearest peg can then be marked with a level and the 5cm drop. Continue this procedure along the wall of the house and then join the marks on the pegs with timber boards or lightweight string, perhaps edging boards tamped down into the soil, whichever method you prefer that suits the materials you will be laying. Use those markers as guides when you are laying the top surface of the patio, with straight edges to make sure the slabs line up in all the relevant directions.
This is a simple method which should deliver the goods for the average patio and doesn’t need any specialist equipment. With care it should be good enough to ensure a smooth surface without puddles which won't trip the unwary.