Having your own workshop in the garage greatly simplifies the life of the car owner, allowing you to carry out diagnostics and repairs without queuing at a service station. However, full maintenance of the chassis or oil change is impossible without access to the underbody of the car. That's why inspection hole is a mandatory element of a permanent garage, increasing its functionality and market value.
The construction process requires careful preparation, since errors at the design stage can lead to permanent flooding or collapse of the walls. You will need not only physical strength, but also accurate calculations geometry structures, as well as an understanding of the principles of working with soil. In this article we will analyze all the nuances, from choosing a location to finishing.
Before starting work, it is important to realize that the quality of the result directly depends on compliance with the technology waterproofing. Ignoring this aspect will turn your hole into a well after the first rainstorm. Let's look at how to avoid common mistakes and create a durable structure.
Site selection and geological exploration of the site
The first step is always to analyze the soil and groundwater level. If you are planning to build a new garage, then the place for the pit is selected at the stage of laying the foundation. In an existing building, the floor will have to be opened, which requires additional labor. It is critical to know that The groundwater level must be at least 2.5 meters from the surface of the earth, otherwise the pit will constantly fill with water, despite powerful waterproofing.
To check the water level, you can drill a control well at the proposed digging location. If the water is high, you will have to choose: either make pits with a drainage pump (which is expensive and requires electricity), or abandon the idea of a pit in favor of a lift. Also worth considering soil structure: sandy soils require mandatory reinforcement of the walls, clay soils require good ventilation.
⚠️ Attention: Never start digging a hole in your garage unless you are sure there are no underground utilities (cables, water or gas pipes) under the floor. Damage to a gas pipe can lead to catastrophic consequences.
The optimal time for construction is considered to be summer, when the groundwater level is minimal. This will allow for high-quality concreting and waterproofing without the risk of washing out the fresh mortar. It is not recommended to carry out such work in winter due to the risk of soil freezing and disruption of hardening technology concrete.
Calculation of dimensions and preparation of drawings
The geometry of the inspection pit is a balance between ease of use and maintaining the strength of the garage floor. A pit that is too wide weakens the building structure, and a pit that is too narrow limits the maneuverability of the mechanic. The standard width is usually 70-80 cm, which allows you to move freely inside without touching the walls with your shoulders. The length depends on the dimensions of your car: it must be at least 1 meter less than the length of the car for safe entry.
The depth is calculated individually according to the height of the master. When standing on the bottom, you should be able to extend your arms freely and reach the bottom of the car without bending. Usually this value varies from 180 to 200 cm. If you plan to repair different cars in the garage, it is better to make the depth universal, and for convenience use coasters under feet or adjustable ladders.
Below is a table with recommended parameters for different types of cars:
| Vehicle type | Width(cm) | Length(cm) | Depth (cm) |
|---|---|---|---|
| Passenger car (sedan, hatchback) | 70-75 | 400-450 | 180-190 |
| SUV/Crossover | 80-90 | 450-500 | 200-210 |
| Minibus | 90-100 | 500-550 | 210-220 |
When drawing up the drawing, be sure to take into account niches for tools and lighting fixtures. They are made in the side walls at chest or waist level so as not to clutter the bottom. It is also important to provide pits to collect liquid if you suddenly have to drain oil or antifreeze, although it is better to use special containers for this.
Excavation and foundation preparation
The markings on the floor are completed, and the most labor-intensive stage begins - digging a pit. The soil should be removed carefully, trying not to disturb the density of the walls. If the garage has already been built, you will have to dig manually, since the equipment will not enter the premises. It is better to immediately remove the excavated soil in a wheelbarrow so that it does not interfere with the work and does not create additional load on the edges of the pit.
The bottom of the pit must be carefully leveled and compacted. Then a layer of crushed stone with a fraction of 20-40 mm and a thickness of about 10-15 cm is poured. The crushed stone serves as a drainage cushion and prevents the capillary rise of moisture to the concrete floor. A layer of sand (5 cm) is poured on top of the crushed stone, which is also spilled with water and compacted until it becomes a monolith.
- 🚜 To speed up the process, you can use a small-sized excavator if it is possible to bring equipment into the garage.
- 🧱 It is better to immediately strengthen the walls of the pit in loose soils with boards to avoid shedding during work.
- 💧 If water appears at the bottom, it is necessary to make a sump (pits) in the corners to pump out the water with a pump.
After preparing the pillow, a layer is laid on the bottom and walls (if space allows) waterproofing film or roofing felt. This will create the first barrier to moisture. The edges of the waterproofing should extend 15-20 cm beyond the pit so that they can later be connected to the waterproofing of the floor or walls.
Waterproofing and insulation of the structure
Moisture is the main enemy of concrete structures and metal elements of a car. High-quality waterproofing of the inspection pit is carried out in two stages: external (cut-off) and internal. For external protection, bitumen mastics and roll materials such as TechnoNIKOL or special membranes. Usually 2-3 layers of roofing felt are placed on the bottom with an overlap of 15 cm, coating the joints with bitumen.
Insulation is necessary if you plan to use the garage year-round and do not want the cold from the frozen ground to come through the floor. Most often used as insulation extruded polystyrene foam (penoplex), which does not absorb moisture and has high compressive strength. Sheets of insulation are laid on top of the waterproofing before pouring concrete.
Use extruded polystyrene foam with a density of at least 35 kg/m³. Regular polystyrene foam can become deformed under the weight of concrete and cars, causing the floor to sag.
⚠️ Attention: When laying waterproofing, ensure the integrity of the canvas. Even a small puncture or rupture will become the site of a leak, negating all efforts to drain the soil.
Modern penetrating waterproofing compounds can protect concrete from the inside. After the walls and floors have hardened, they can be treated with special impregnations that crystallize in the pores of the concrete, making it waterproof. This is especially true for regions with high rainfall.
Reinforcement and concreting of walls and floors
Concreting is a critical stage that determines the strength of the entire structure. For walls and floors, concrete of a grade no lower than M250 (B20). Before pouring, it is necessary to install the reinforcement cage. For the walls, a mesh made of rods with a diameter of 8-10 mm with a cell of 15x15 cm or 20x20 cm is used. The reinforcement is tied with knitting wire; welding is not recommended, as it weakens the metal in hot spots.
The process of filling walls is most conveniently carried out using formwork. First, the floor (bottom of the pit) is concreted, then the formwork for the walls is installed. If the soil is dense (clay), you can pour concrete directly into the earthen wall, using waterproofing as formwork, but for reliability it is still better to make a full-fledged concrete box. The thickness of the walls should be at least 15 cm, and the thickness of the floor - 20 cm.
☑️ Concreting control
When pouring it is important to use vibrator or bayonet the solution with a reinforcing rod to remove air bubbles. This will ensure the solidity and strength of the structure. Concrete gains full strength in 28 days, but formwork can be removed after 7-10 days at air temperatures above +15°C.
During the concreting process, sleeves are placed in the walls for electricity and ventilation. For this, plastic or metal pipes with a diameter of 50-100 mm are used. Pre-designed channels will eliminate the need to chisel the walls later.
Ventilation, lighting and finishing
Even with high-quality waterproofing, moisture and vapors of fuels and lubricants (fuels and lubricants) will accumulate in the inspection hole. Therefore, a ventilation system is mandatory. The simplest option is supply and exhaust ventilation. The supply hole is made at a level of 20-30 cm from the floor, and the exhaust hole is made under the ceiling of the pit. The pipes are led outside, providing natural air circulation.
Lighting in the pit must be safe. According to the rules of the PUE, in inspection pits it is allowed to use a voltage of no more than 36 Volts, and in damp rooms - no more than 12 Volts. Therefore it is necessary to install step down transformer. Luminaires must have a sealed housing (IP65 or higher) and a protective grille to prevent accidental damage.
- 💡 Use LED strips with moisture protection, fixed around the perimeter of the walls - this will give uniform light without shadows.
- 🔌 Sockets in the pit should only be low-voltage (36V) or absent altogether (use an extension cord with a transformer).
- 🧱 Ceramic tiles are often used to decorate walls, which makes it easier to clean from oil and dirt.
Is it necessary to make a caisson if water does come in?
A caisson is a sealed metal or plastic container that is installed in a pit. If groundwater comes very close, the concrete pit will get wet. In this case, a caisson is welded or inserted inside the concrete box, which is guaranteed to hold water. This is expensive, but the only solution for difficult hydrogeological conditions.
The final stage is the installation of a metal corner around the perimeter of the pit at floor level. This strengthens the edges and serves as support for the boards or metal plates that will cover the hole. The boards must be at least 40-50 mm thick to support the weight of a person and a fallen tool.
A high-quality inspection pit is not just excavated soil, but a complex engineering object that requires compliance with waterproofing, reinforcement and ventilation technologies. Saving on materials is unacceptable here.
Is it possible to make an inspection hole in an already built garage with a finished floor?
Yes, it is possible, but it is labor-intensive. You will have to dismantle part of the concrete floor, dig up the soil and perform all stages of construction again. The main obstacle is the groundwater level, which can be high in populated areas. Difficulties may also arise with removing soil through a narrow gate.
Which material is better for walls: brick or concrete?
Concrete (monolith or FBS blocks) is considered a more reliable and durable material, especially in heaving soils. Brickwork requires very high-quality waterproofing and armored belts. However, it is more convenient to use brick if you need to make complex niches or curves.
Is it necessary to make a water pit in the inspection hole?
Yes, a pit (sump) in the lowest corner of the pit is necessary. Even with good waterproofing, condensation or accidental leaks will flow there. It is easier to pump water out of a pit with a pump or scoop it up with a bucket than to remove it from the entire floor.