The construction of a garage for a car often begins not with the construction of walls, but with a decision on the type of foundation, and for light frame structures the optimal choice becomes columnar foundation. This type of support allows for significant savings in concrete and excavation costs while maintaining the high load-bearing capacity required to support a lightweight frame. Unlike a massive tape or slab, pillars minimize contact with heaving soils, which is critical for regions with harsh winter periods.
Self-production of such a base requires accurate calculation of loads and adherence to installation technology, but this is a completely feasible task for a car owner who wants to reduce the cost. Frame garage, being lightweight, does not require burial below the freezing depth if the support points are correctly distributed. Next, we will analyze all the stages of creating a reliable base for your vehicle, eliminating common mistakes of beginners.
Advantages of the columnar type for lightweight structures
The choice in favor of a columnar structure is due to a number of technical and economic factors that make this option the only option for projects with a limited budget. The main advantage is the reduction in the volume of materials used: instead of pouring concrete all over the perimeter, you use it only at points of maximum load. This is especially true when building frame garage, where the main weight falls on the corners and intersections of the walls.
In addition to savings, it is worth noting the speed of construction. While the neighbors are waiting for the massive slab to gain strength, you can already install the bottom trim. The technology allows work to be carried out even in areas with difficult terrain, since the height of each pillar can be adjusted individually. This eliminates the need to level the site with heavy equipment.
Use asbestos-cement or plastic pipes as permanent formwork - this will speed up the process and improve the geometry of the pillars.
It is important to understand that such a foundation is not suitable for heavy brick or block buildings, but it is ideal for wood and metal. Load capacity the soil is used as efficiently as possible, since the pressure is transmitted pointwise. With the correct calculation of the cross-section of the supports, the structure will last for decades without distortions or cracks.
Geological surveys and parameter calculations
Before purchasing materials, it is necessary to determine the type of soil on your site, since the depth and cross-section of the supports depend on this. If you plan to store a heavy SUV or truck, the requirements for foundation are increasing. The simplest way to check is to dig a hole in the proposed construction site and evaluate the moisture and density of the soil.
The number of pillars is calculated based on the total weight of the structure along with snow and wind load. For a standard 6x4 meter garage, it is usually sufficient to install supports at the corners and at the intersections of internal walls. The step between the pillars should not exceed 2–2.5 meters to avoid sagging of the bottom frame beams.
The depth of installation is determined by the level of soil freezing in your region, but for light frame buildings shallow options are often used. In this case foundation base located below the fertile layer, but above the freezing depth, provided that a sand cushion is used to compensate for heaving. Accurate data on freezing depth can be found in the building codes for your region.
Required tools and materials
For high-quality implementation of the project, you will need to prepare a complete set of tools so as not to interrupt the work process halfway. The basis will be a concrete mixer or a powerful drill with a mixer, since the volume of concrete, even for pillars, is impressive. Don't forget about personal protective equipment, especially when working with cement and rebar.
The list of basic materials includes cement grade M400 or M500, sand, crushed stone and reinforcing bars with a diameter of 10–12 mm. Pipes or blocks are often used to form the body of the column, and bitumen mastic or roofing felt is required for waterproofing. Quality reinforcement cage directly affects the durability of the entire structure.
☑️ List of tools
Pay special attention to waterproofing materials, since concrete tends to absorb moisture from the soil. Usage roofing felt or modern bitumen-polymer membranes will protect the structure from capillary rise of water. This will prevent the concrete from collapsing when moisture freezes inside the pores.
Site marking and excavation work
Construction begins with careful marking of the perimeter, where pegs and a stretched cord are used. Accuracy at this stage is critical, since an error of a few centimeters can lead to misalignment of the entire frame in the future. Check the diagonals of the rectangle - they must be absolutely equal.
After fixing the contours, they begin to dig holes or drill holes for the pillars. If pipes are used, the diameter of the hole should be 5–10 cm larger than the diameter of the pipe for ease of installation and filling of the sinuses. When manually digging holes, their dimensions are made slightly larger than the planned cross-section of the support for installing the formwork.
⚠️ Attention: Do not leave dug holes open at night or waiting for rain - the walls may crumble and the work will have to be redone.
The bottom of each pit must be compacted and covered with a layer of sand 15–20 cm thick. The sand is spilled with water and compacted to a solid base, which creates a drainage cushion. A layer of crushed stone is placed on the sand, which prevents capillary suction of moisture into the concrete.
Support pole installation technology
There are several installation methods: using ready-made blocks, brickwork or pouring concrete into the formwork. The most reliable and common option for a garage is monolithic concrete in permanent pipe form. A pipe is lowered into the prepared hole, inside which a reinforcement cagetied with wire.
Concrete is poured in layers with mandatory jointing or using a deep vibrator to remove air bubbles. It is important that the reinforcement does not touch the pipe walls and is completely immersed in the concrete solution. The upper end of the post is leveled to ensure that the future framing is horizontal.
| Soil type | Laying depth (cm) | Pole diameter (cm) | Installation pitch (m) |
|---|---|---|---|
| Dense clay | 100–120 | 25–30 | 2.0 |
| Loam | 80–100 | 30–40 | 2.0 |
| Sand | 60–80 | 25–30 | 2.5 |
| Sandy loam | 80–100 | 30–35 | 2.0 |
Is it necessary to lay reinforcement below the frost line?
In the case of using a shallow foundation for light frame buildings, the reinforcement frame bends when the soil moves, so its length should be maximum, but laying below the freezing depth is not always necessary if a sand cushion is provided.
After pouring, concrete gains primary strength within 5–7 days, but full load can be given no earlier than after 28 days. In hot weather, the concrete surface must be periodically moistened and covered with film to avoid rapid drying and cracking. Strength gain - a chemical process that requires moisture.
Waterproofing and grillage installation
After dismantling the formwork (if it was removable) or cutting the pipes, the surface of the pillars is covered with bitumen mastic. This creates a barrier to groundwater and protects the structure from aggressive environmental influences. Particular attention is paid to the place where the pillar emerges from the ground - this is where waterproofing should be most thorough.
The next stage is the installation of the grillage, which combines the individual pillars into a single system. For a frame garage, a wooden beam with a cross-section of 150x150 mm or 200x200 mm, treated with an antiseptic, is most often used. The timber is laid on roofing felt laid on the ends of the pillars and fixed with anchor pins pre-filled in concrete.
⚠️ Attention: There must be a layer of waterproofing between the wooden grillage and the concrete pillar, otherwise the wood will begin to rot from contact with the moisture of the concrete.
The corner connections of the timber are made “half-wood” or using metal plates, which ensures the rigidity of the structure. Properly assembled grillage evenly distributes the load from the garage walls to all support points. After installing the piping, you can begin installing the floor and building the wall frame.
High-quality waterproofing and a rigid connection of pillars with a grillage are the main conditions for the durability of a frame garage on a columnar foundation.
Frequently asked questions (FAQ)
Is it possible to build a columnar foundation in winter?
Theoretically, this is possible by using special antifreeze additives in concrete and heating the structure, but for private construction this is impractical due to the high cost of work and risks. It is better to wait for a thaw or stable positive temperatures.
What is the service life of such a foundation?
If waterproofing technology is followed and loads are correctly calculated, concrete pillars will last 50 years or more. A wooden grillage may require replacement or repair after 20–25 years, depending on the quality of the antiseptic treatment.
Is it necessary to make an insulated blind area around the pillars?
For a columnar foundation, a classic blind area is not required, since there is often a ventilated space under the garage floor. However, if you plan to make an insulated floor, then insulating the perimeter from the outside will help reduce heat loss.
What to do if the site is on a slope?
A columnar foundation is ideal for slopes, since the height of each column can be varied. This allows you to bring the upper end of all supports to one horizontal level without carrying out expensive excavation work to level the site.