Sometimes homeowners aren’t fully aware of the exact design of their septic tanks. Especially, if the property has been built several years back, and a lot of remodeling has taken place in it since.
Other times, building a garage requires using the spot on top of the septic tank as a driveway. Or even using it as a parking place. But the owners need to know if it would hold the weight.
We’ve all heard about dump trucks that fall into a septic pit that’s caved in under the weight. But is that the only weight that could crush a septic tank? Would a lawnmower be alright?
The question of loading is legitimate, so how much weight can drive over a septic tank?
It’s recommended not to drive or park any heavy machinery, equipment, vehicles, or RVs over the area to avoid damage or collapse of the septic system.
For the maintenance of mound septic systems, when mowing, use a hand mower rather than a riding mower. In general, it’s best to reduce the amount of foot traffic or other activity to protect the mound from losing soil to erosion.
Is It Possible to Design a Sturdy Septic Tank Covering?
If you ask any engineer if doing any task is possible, the answer would always be a quick yes! See, engineers believe they can make anything work. However, out of honesty and integrity, they’ll list all the problems that could come with the solution.
The case of the septic tank covering is no different. A concrete slab could be laid on top of the septic tank. In addition to that, properly fortified trenches could contain the whole pipeline from the house to the tank.
This should give the area on top of the septic tank some muscle power. But does that provide a full guarantee that a regular car could drive over it? Not really. Other issues should be considered as well. This is what we’ll talk about next.
Why We Don’t Recommend Using Fortified Lids
Here are some of the reasons why we don’t recommend using concrete slabs, stainless steel lids, or other structures on top of the septic tank.
Limited Accessibility
Septic tanks require routine maintenance and periodic inspection. Repairs are also likely from time to time. That’s why installing a heavy, fortified lid, on top of the tank is not recommended.
It would simply deter these interventions, and make them more labor-intensive. This naturally means a higher cost.
Extra Loading
Septic tanks are designed to carry the usual load of the soil covering them. A fortified lid might not crash the tank once it’s installed, but the constant loading could end up in micro cracks and material fatigue.
These mini failures occur over long periods of time, and they often go unnoticed in visual inspection. The real risk is that sudden failure becomes possible.
The odds are even worse if the area experiences rainy weather frequently. The soggy ground is much heavier than dry land. And there’s even more: imagine driving over a septic tank with the added weight of a vehicle. These things add up to sizable figures.
Extra loads usually end up in leaks, breaks, or dislocation. So if the tank somehow dodges the bullet of material failure, its position could shift under the consistent loading. This would lead to several problems down the line. The first signs would appear in the form of damaged pipes.
Soil Stability
The septic system is often designed as an integrated structure. The weight of the tanks is taken into account along with the nature of the soil. This takes extensive testing, to layout the correct supports, and choose the right tank material for the site at hand.
If the ground is too porous, it’s best to use a lightweight polyethylene or fiberglass tank. If it is too rocky, a concrete tank might be better, and so on. Putting a heavy lid, concrete slab, or other structures, on top of the tank constitutes a load that was not included in the original design.
This often affects the way the soil responds to the weight on top of it. Incremental compaction could lead to the ground falling in under the tank. This could have detrimental consequences if there’s a vehicle driving or parking on top of the septic tank area.
Gas Buildup
Septic tanks occasionally experience a build-up of methane and other gases. If the tank isn’t too deep into the ground, these gases often vent-out. A heavy lid, concrete slab surface, or wooden surface could lead to the trapping and build-up of such gases.
A crack could give off an obnoxious leak, and in a rather rare scenario, the gases could explode and damage the tank. However, when it comes to safety, every possibility should be taken into consideration, and the right measures put in place to counter them.
Is It Worth the Trouble?
Homeowners often feel that the area on top of the septic tank, as well as the area surrounding it, and the drain field, are completely wasted. As you might have noticed, clever people are often trying to make the best uses of their resources, and these lands often fall inside their radars.
Using the land on top of the septic tank as a parking spot, or a driveway to a garage is a frequent occurrence. Unfortunately, it doesn’t end well.
There’s also the possibility that this land is landscaped, and becomes part of the lawn. It’s not unlikely then that the lawnmower finds its way to that vulnerable spot. It’s also quite possible that the few rounds would be uneventful.
As we mentioned earlier, cracks buildup over time. And three times of lawnmower activity going well is no guarantee the fourth time would be more of the same. Actually, we know of instances where the lid of the septic tank caved, and the mower fell off in that fourth round.
The lawnmower weighs a fraction of what a car weighs, even if it’s a mini convertible car, the difference in mass is still significant. So you can do the math.
Final Thoughts
The costs of replacing a septic system could go north of $15,000. This is hardly a figure to trifle with, and so, practicing caution would be highly recommended.
Parking on top of a septic tank, or using this area as a driveway, might seem like a good idea. It’s certainly economic and clever to use every inch of the property. However, risks should be assessed.
This might sound a bit like a cliche, but it’s one we really believe in. Better safe than sorry! So if you’re wondering how much weight can drive over a septic tank? We’d say that of a wheelbarrow, or a small push mower.