A private home’s decision to add a basement should be well-considered and balanced. On the one hand, it makes sense to locate technical and utility spaces, like a billiard room or workshop, in the basement. A car garage, a sauna, a bathhouse, and a gym are frequently located beneath the house. However, accurate calculations, large financial outlays for the building of subterranean spaces, and dependable leak protection are needed.
The following actions are involved in building a basement foundation for a home:
- Preparatory work – cleaning, leveling the site, cutting and transferring the fertile soil layer to a dump for composting, moving communications, purchasing and storing materials.
- Marking the house plan on the ground, laying out axes, installing cast-offs.
- Excavation work – digging a pit, transporting earth, backfilling.
- Construction work – laying out a base for a basement, erecting walls, installing floors.
- Drainage device.
- Waterproofing.
- Insulation, vapor barrier.
- Laying of communications, ventilation device.
- Interior finishing, staircase installation.
- External cladding, blind area.
Building a basement beneath a house requires the same amount of labor and money as building a foundation with an above-ground floor. It may be under the whole structure or just a portion of it.
Excavation and drainage
They mark the foundation and then start excavating a pit. This is typically done mechanically using a front loader or excavator. It takes a lot of labor to dig up and remove large amounts of soil by hand.
If at all possible, the excavation process and the foundation’s subsequent construction should proceed without a brief pause to prevent surface water from seeping into the pit. Rain or snowmelt causes the soil to become saturated, the pit’s walls to erode, and the reinforcement frame that has already been installed to flood. In order to prevent rainwater from draining from the surrounding area, a continuous border of earth, 30 to 50 cm high, is formed around the perimeter.
Drill absorption wells and a 6-7 m long drainage channel as well as an acceptance volume, if at all feasible. This will assist in keeping the base dry.
The pit is excavated to a depth of -1.2 or -1.5 meters, in addition to the thickness of the reinforced concrete base and sand or sand-gravel cushion. Check the bottom’s horizontality with a level.
Following excavation, it is compacted and covered with a moistened layer of 20–25 cm thick sand and gravel.
Install retaining walls if needed to stop soil collapse.
Drainage
Water on the approach to the foundation is intended to be drained by the external drainage system. This is particularly crucial if the site has clayey soil, ponds are close by, the house is sloping, or the foundation is buried 1.3 meters below ground level.
If the foundation width and wall thickness are not sufficient, lateral impact may cause deformations, base shift and tilt, and soil subsidence beneath the supporting portion. This will cause the structure to lose stability and eventually collapse.
The "Manual for the Design of Buildings and Structures," which offers examples of an algorithm for figuring out ideal dimensions and reinforcement schemes for basement structures, goes into great detail about how to calculate a house’s foundation. In the absence of geological research, a large margin of error is applied to the computed soil resistance. As a result, the elements will have an excess of material consumption in addition to a sizable strength reserve. When the supporting portion is larger than the foundation wall, it makes sense to solve the problem.
Construction works
Slab and strip foundations with basements are most frequently used in private construction. Bricks and blocks, or monolithic concrete, are prefabricated components used to build walls.
Construction projects consist of:
- Construction of a reinforced monolithic slab or tape.
- Walling.
- Installation of floors made of wooden beams or reinforced concrete panels.
One or two rows of mesh are used to reinforce the slab, and frames are used to reinforce the tape in accordance with calculations. M200 grade concrete or higher is used. Vertical steel rods are used to reinforce monolithic walls, while horizontal wire or reinforcement is positioned every 300–400 mm in block or brick walls. In order to absorb multidirectional stresses, L- and U-shaped metal elements are installed in corners and joints.
Two opposing walls support reinforced concrete slabs down to a depth of 70–120 mm. Using overhead components, wooden floor beams are installed in "sockets" or end-to-end. Antiseptics are applied to wood to stop it from rotting.
Small cellars can be built with strip and pile foundations. In this instance, the subterranean chamber is situated beneath the dwelling at a reasonable distance from the supports to prevent foundation distortion or collapse due to the thinning of the soil and the weight of the walls.
Waterproofing
The most crucial aspect of the work done during basement construction is moisture protection. Expanding tapes and specific solutions are used to seal the joints between slabs and walls.
Both the interior and exterior of the room can be thermally insulated. Materials resistant to moisture are used for external insulation:
- extruded polystyrene foam in slabs;
- Styrofoam;
- thermal panels;
- plaster mixture with vermiculite or expanded polystyrene;
- spray polyurethane foam.
The installation of a blind area is part of the foundation’s external insulation. It keeps cold air from penetrating the soil layer and water from seeping into the wall space.
If performing this operation from the outside is not feasible, the basement floor is insulated from the interior. The room will still be heated, but the walls won’t be shielded from the outside air. When the temperature drops, water that has seeped into the pores and capillaries freezes and gradually destroys the material.
The same materials used for external insulation are used for internal thermal insulation, with decorative finishing coming last.
Basement ventilation
The basement is consistently humid. Furthermore, soil radon rises to the surface and builds up in the room’s lower level. It is more difficult to remove by basic ventilation through vents or transoms because it is heavier than air.
To ensure stability and durability, the foundation of a house with a basement must be built using exact construction methods and meticulous calculations. This entails measuring dimensions precisely, choosing the appropriate foundation type based on the makeup of the soil, and excavating, reinforcing, and waterproofing the structure in accordance with best practices. In order to ensure that the basement stays a sturdy, dry, and essential component of the house, proper planning and execution are crucial in preventing problems like settling, cracking, or water damage.
When building a foundation with a basement, careful application of insulation and waterproofing, as well as calculations that unbiasedly consider the structure’s operating circumstances, are necessary. The cost of building the base and upper floors is the same as that of building the basement level.
