How to make a pit in a garage: from pit to finish

It is impossible to imagine setting up a full-fledged place for servicing a car without an inspection hole. This space below the floor level allows you to easily get to the bottom of the car, change the oil, check the suspension and carry out complex repairs of units. Many car owners are wondering how to make a hole in the garage so that it lasts for decades and does not turn into a collection of groundwater.

Well made viewing niche increases the liquidity of the garage and greatly simplifies the life of the owner. However, the process of its creation requires careful planning, compliance with building codes and an understanding of the geology of the site. Errors at the design stage can lead to wall collapse or permanent flooding, making operation impossible.

In this article we will analyze all stages of construction: from choosing a location and digging a pit to finishing the walls and installing lighting. You will learn what materials are best to use for waterproofing and how to properly organize ventilation so that carbon dioxide and moisture do not accumulate in the room.

Planning and choosing the optimal location

The first step is always to analyze the soil and groundwater level. If the water is too close to the surface, construction will require extensive and expensive waterproofing, and in some cases may not be economically feasible. The ideal option is dry sandy or sandy loam soil, which does not require enhanced protection from moisture.

It is necessary to accurately determine the dimensions of the future recess. The standard width is usually about 70-80 cm, which allows a person of average build to work comfortably. The length depends on the size of the car, but most often it is about 4-5 meters so that the car can be driven in completely or partially. The depth is calculated individually, based on the height of the master and the ground clearance of the car.

⚠️ Attention: When planning, be sure to take into account the thickness of the walls and floor cushions. If you dig a hole exactly the size of the car, after concreting there will be no place to work.

It is also important to consider the location of the pit relative to the entrance to the garage. It should not start immediately at the gate so that rainwater does not flow inside. The optimal distance from the entrance is about 1 meter. It is also worth leaving space for installing stairs or steps for descent.

Calculation of dimensions and marking of the pit

Accurate dimensions are the key to ease of use. A hole that is too narrow will restrict movement, while a hole that is too wide will create a risk of falling. The standard clear width (between the walls) is 75-80 cm. This is enough to turn around, but not so much that your legs get tired when walking at a leisurely pace.

The depth is calculated using the formula: human height + 10-15 cm of reserve. If your height is 175 cm, then the depth should be about 190 cm. This will allow you to work standing without slouching, even if there is a rug on the floor. The length depends on the garage, but usually they try to make it about 5 meters so that a long-wheelbase car can be inspected.

• 📏 Pit width = Pit width + (2 × Wall thickness) + Waterproofing.
• 📐 Pit depth = Pit depth + Pillow thickness + Floor thickness.
• 🚗 The length depends on the size of the car, but at least 4 meters clean.

When marking on the floor, use pegs and strong thread. It is important to leave at least 1 meter of clearance from the garage walls so as not to weaken the foundation of the main building. If the garage has already been built, you will have to dig manually, which significantly increases labor costs.

Excavation and foundation preparation

Digging a pit is the most labor-intensive stage. If the soil allows, they try to make the walls vertical. However, on loose sand or wet clay, it may be necessary to dig with slopes or immediately reinforce the walls with shields to avoid collapse during work. The excavated soil must be immediately removed from the garage so that it does not interfere with further work.

After reaching the design depth, it is necessary to prepare the foundation. The bottom of the pit is carefully 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 also needs to be spilled with water and compacted to create a hard cushion that will distribute the load and act as drainage.

A layer of sand 5-10 cm thick is laid on top of the crushed stone. The sand is spilled with water and leveled. At this stage, it is important to check the levelness of the bottom using a building level. Any distortions in the future can lead to uneven distribution of the load on the concrete floor and the appearance of cracks.

Scheme of base layers:
1. Soil (compacted)
2. Crushed stone (10-15 cm)
3. Sand (5-10 cm)
4. Waterproofing (film/roofing felt)
5. Concrete screed (10-15 cm)

If the groundwater level is high, it is at this stage that a pit for the pump may be required. A recess is made in one of the corners, where a container for collecting water with an automatic float pump is installed. This will allow you to pump out water as needed.

Waterproofing and moisture protection

The issue of waterproofing is critical. Concrete has a droplet structure and is able to draw moisture from the ground, creating dampness in the garage. Therefore, high-quality insulation is mandatory. Most often, dense polyethylene film with a thickness of at least 200 microns or special membranes are used.

The film is laid on the bottom and walls with an overlap of at least 15-20 cm. The joints must be taped or soldered. It is important that the waterproofing is a single contour. The edges of the film are brought up, beyond the boundaries of the future pit, so that they can then be rolled onto the concrete.

Material	Water resistance	Difficulty of installation	Durability
Polyethylene film	High	Low	Average
Ruberoid/Bitumen	Very high	Average	High
Penetrating insulation	High	High	Very high
Liquid rubber	Maximum	Average	High

For additional protection, you can use bitumen-based coating waterproofing, applying it over concrete walls after they have dried. This will create an additional barrier. In places where the risk of flooding is high, it is absolutely impossible to skimp on insulating materials.

What to do if the water comes in quickly?

If the water arrives faster than the pump works, it is necessary to make a caisson of metal or monolithic reinforced concrete with external waterproofing, which is much more expensive and more complex than a regular pit.

Construction of walls and reinforcement

The walls of the inspection pit are most often erected from brick, concrete blocks or filled with monolithic concrete. The monolithic option is considered the most reliable, since it has no seams through which water can leak. However, it requires the installation of formwork and hardening time.

For reinforcement, a metal mesh with a cell of 10x10 cm or 15x15 cm from a rod with a diameter of 6-8 mm is used. The mesh is installed vertically along the walls, 3-5 cm away from the edge of the waterproofing, so that the metal is inside the concrete and is not subject to corrosion. The reinforcement is tied with knitting wire.

• 🧱 Kirichnaya masonry: requires high-quality solution and subsequent plastering.
• 🏗️ Monolithic concrete: concrete grade not lower than M250 (B20) for strength and water resistance.
• 🚧 Blocks (FBS, foam block): foam block requires mandatory hydrophobization, as it strongly absorbs moisture.

When pouring concrete, it is important to use a vibrator or carefully tap the solution with a reinforcing rod to remove air voids. It is better to fill the walls entirely, without interruptions, to avoid the formation of “cold seams”, which are the weak point of the structure.

⚠️ Attention: When installing the formwork, make sure that it will not be crushed by concrete. Use reliable spacers and ties, otherwise the geometry of the pit will be disrupted.

Floor pouring and finishing

After the walls have dried (usually 2-3 weeks to gain strength), they begin pouring the floor. The thickness of the concrete floor slab must be at least 10-15 cm. The floor reinforcement is performed with a mesh with a larger cell, for example, 15x15 cm from an 8-10 mm rod.

Concrete for the floor must also be of high quality, with the addition of plasticizers for better fluidity and strength. The floor surface is carefully leveled according to the rule. You can make a slight slope to one side or towards the center (towards the pump pit) to make it easier to clean up the water.

The final finishing of the walls usually consists of plastering with cement-sand mortar. For ease of work, niches are often built into the walls for storing tools, lamps or cans of oil. Embedded parts for mounting lighting are also installed.

Ventilation and lighting

An inspection pit is a closed space where heavy gases (exhaust, gasoline vapors) and carbon dioxide can accumulate. Natural ventilation is not enough here. It is necessary to organize forced or good natural inflow and exhaust.

The ventilation pipe descends almost to the very bottom of the pit (to a height of 15-20 cm from the floor). The ventilation outlet must be above ground level. This will ensure a constant flow of air and the removal of harmful vapors, which are heavier than air and spread along the bottom.

Lighting in the pit must be safe. The use of 220 volts is prohibited by safety regulations due to humidity and cramped spaces. A transformer must be used to reduce the voltage to 12 Volts or 36 Volts. Lamps must be protected by sealed shades with a protection class of at least IP65.

Security and additional elements

To prevent falling into the pit, a fence is made along its perimeter at the level of the garage floor. Usually this is a wooden beam or a metal corner protruding 10-15 cm above the floor level. This side serves as insurance for the wheels of a car and a person’s legs.

It is also necessary to provide a cover for the pit. When it is not in use, it is better to cover the pit with boards or metal sheets. This will prevent moisture from evaporating into the garage, reducing the risk of accidental falls, and allowing the garage space to be used for storing other cargo.

The descent ladder must be reliable and non-slip. It is often made of metal with a corrugated surface of the steps. The ladder must be secured firmly so that it does not wobble under the weight of a person with a tool in his hands.

Do I need to waterproof if it's dry?

Yes, definitely. Groundwater can rise seasonally (in spring or autumn), and the lack of waterproofing will lead to rapid saturation of concrete with moisture, the appearance of mold and structural failure.

How thick should the walls be?

The optimal thickness of concrete walls is 15 cm. When using brick, the masonry is made in half a brick or brick with mandatory reinforcement and plastering.

Is it possible to use foam block?

You can use foam block, but it is very hygroscopic. Very high-quality external and internal waterproofing will be required, otherwise the block will become saturated with water and begin to collapse when frozen.

How to get rid of the smell in a pit?

The main reason for the smell is lack of ventilation and dampness. Check the draft in the ventilation pipe, use moisture absorbers and regularly ventilate the garage.

How long does it take to dry concrete before use?

Concrete gains full strength in 28 days. It is recommended to begin active use and place heavy loads after this period, although it sets in 3-7 days.