Picture the scenario; you’ve identified the perfect place in the yard for your new patio, but there’s a septic tank in the way. Can you just go ahead and build the patio over the top?
You can’t build a paver patio on top of a septic tank, and doing so could be against the planning laws of your state or local area. Septic tanks can take very little weight without getting damaged, and you’ll also need access to the tank in the future too. You shouldn’t build a deck on one either.
In this article we’re going to look at this subject in more detail, so you can stay on the right side of local planning regulations when it comes to building a patio on or near your septic tank…
Should I Ever Pave Over My Septic Tank?
Building over a septic tank is never recommended, and indeed, some counties will have regulations about this. If you know where your septic tank is, you’ll need to design your patio around it.
Why is this? Well firstly, why make life hard for yourself? You’ll need to be able to access your septic tank, ideally without having to lift slabs. Sometimes, you see paved areas over tanks that have an access hatch in between pavers. This will solve the accessibility problem, certainly, but it’s still far from ideal.
This is due to weight, and how heavy a load your tank is able to handle. We’ll take a look at the different types of tank and their weight-bearing capacities in just a moment.
Of course, sometimes folk build over their septic tanks because they don’t know where exactly it is, leading to all sorts of problems down the line. The moral of this tale is: find out where your tank is before you build anything.
Sometimes, there can be an old septic tank under the yard, but the house itself has switched to mains drainage. In this case, you’ll need to find out whether the old tank has been correctly in-filled. A “correctly abandoned” septic tank should have been crushed and filled in for safety. If you suspect you have an old tank somewhere on your lot, speak with an expert surveyor or engineer.
And finally, the million-dollar question: why would you want to site your patio on top of a septic tank? When the tank is due to be emptied, it can become, shall we say, a little unpleasant in the vicinity. When it has to be drained, you’d need to move all your nice furniture and pot plants, and be prepared for the smell to linger for a few days afterward. It’s not the nicest spot in the yard.
How Much Weight Can Go On Top of a Septic Tank?
With an old-style steel septic tank, the answer tends to be “very little”. More modern septic tanks tend to be made from concrete, so are much tougher. Some have a “traffic rating” and give axle weights.
However, most of the advice is never to park on or even drive across a septic tank. Collapse or partial collapse can lead to serious accidents, with the driver, the vehicle, the tank, and the property all coming out of it very badly.
If you’ve inherited a tank, get it checked out to find out what it’s made from and whether it’s in good condition. If you are installing a new one, invest in a robust concrete tank that meets all the requirements.
As well as the septic tank itself, you have two other septic system components: the drain field and the drain lines (the pipes). The drain field (also called a leach field) is the area that contains the drain lines that run from the tank, and you don’t want these to get damaged either.
Ideally, the septic tank and its drainage system should have nothing heavier on top of it than the earth it’s buried under. Mark off that area so nobody tries to park on it.
But don’t worry: you won’t be left with an ugly and unusable section of yard. We’ll take a look at what you can do to cover your septic tank area.
What Can You Put Over a Septic Tank? (Can You Cover Them At All?)
So, what can you do with this marked-off piece of land? Leave the hatch exposed for easy access (you can always put a lightweight plant pot over it). We’ve also heard of light statues and bird feeders over the cover (these are also a good way to remind people not to park cars or mowers directly over the tank).
You could even make a feature of the hatch itself with mosaic decorations or a painted design. There’s a surprising amount about this on Pinterest!
The good news is that there’s more you can do with the drain field area to make it feel more like part of your garden. Plant grass over the drain field, as it keeps the soil around the septic tank healthy.
To understand how grass can benefit a tank, let’s take a closer look at how your tank works. The septic tank works by separating the solid and liquid waste. The liquid flows into drain lines,which slowly penetrate the drain field around the tank and are filtered by the natural microbes in the soil in the drain field. The microbes are more effective in loose, well-drained soil.
Grass will help to prevent soil erosion and remove excess moisture, helping to keep the soil in the ideal condition for drainage.
Choose a native grass that will grow happily in your zone without need for fertilizers, as you want to keep the soil as natural as possible. A drought-resistant grass is good, as you won’t need to water it much and can simply leave it alone. Find out more about the different types of native grass in our recent article.
Don’t plant anything deep-rooted however, as this could interfere with the tank’s drain lines. Trees are a big no-no near a septic tank system. If you want to add interest, ornamental grasses are a good alternative to trees and shrubs. It should go without saying that a septic tank drain field is not a good place for your vegetable or herb garden.
Can you have a surface that floats above the septic tank, like a deck? It sounds like a good idea; however, it would be very difficult to construct a deck that remains load-bearing with a large unsupported area above the tank. Plus, we have heard that the effluent air can cause damage to the wood…
How Deep Should Septic Lines Be Buried?
Every drain field is different, because the soil and the water table differs between areas. If you’re installing new septic lines, speak with an expert (and as much as we love a DIY yard project, the whole septic tank thing is best handled by the professionals). However, the general rule seems to be at least six inches deep.
This seems pretty shallow to us, and a bit of research shows that the ideal depth is between 18 and 36 inches below the surface. This also gives you that decent bit of soil cover for your grass roots to safely grow without disturbing the lines.
Where Should Your Septic Tank Be Located?
The rules about septic tank placement vary from place to place, but the general rule seems to be at least ten feet away from your home.
As we’ve already discussed, you also need to pick a spot that won’t interfere with your driveway or parking, as something as heavy as a vehicle should not pass over the tank. As well as all this, you need an area for the septic tank’s drain field and lines that you don’t want to plant much on or build over.
This can make choosing a location for a septic tank quite a tricky task. Again, speak to an expert drainage engineer who can help you work out where best to locate the tank and drain lines.
In the final analysis, septic tanks are not load bearing so you can’t build a patio or deck over the top of them. You’ll also need constant access – so that’s another reason this is a bad idea.
Building a paver patio over your tank could be against state and local planning laws too – so the last thing you want is to be up to your neck in it with the local authorities – or literally up to your neck in it if your patio furniture falls through into your septic tank! 🙂