For any building to be long-lasting and comfortable, a backfill-filled strip foundation must have a solid floor. This procedure entails a number of crucial steps that guarantee the floor is insulated and well-supported, giving your house or other structure a strong foundation. Even if you’re doing the project yourself, knowing these procedures will help you finish it professionally.
Preparing the strip foundation, which serves as the foundation for your building, is the first step in this process. To guarantee that the foundation can support the weight of the entire structure, precise measurements and construction are required. Backfilling is the next step after laying a foundation; it stabilizes the foundation and keeps it from possibly shifting or settling over time.
To provide a stable floor surface, the soil must be properly compacted after backfilling. By taking this step, you can prevent future problems like cracks or unevenness and ensure that the floor will stay sturdy and level. Installing a vapor barrier is required after compaction to stop moisture from penetrating the floor and causing damage and deterioration.
Ultimately, to create a smooth and even surface, the actual floor-laying process requires selecting the appropriate materials and adhering to precise instructions. A successful floor installation requires careful planning and execution, regardless of the material you choose—concrete, wood, or another. You can confidently build a floor on a strip foundation with backfill that will endure over time by comprehending each step and its significance.
| Step | Description |
| 1. Prepare the Site | Level the ground and remove debris to create a clean, stable base. |
| 2. Install the Foundation | Construct the strip foundation according to your building plan. |
| 3. Add Backfill | Fill the area within the foundation with gravel or sand, compacting it thoroughly. |
| 4. Install a Vapor Barrier | Lay a plastic sheet over the compacted backfill to prevent moisture from rising. |
| 5. Place Reinforcement | Lay a steel mesh or rebar over the vapor barrier to reinforce the concrete. |
| 6. Pour Concrete | Pour the concrete over the reinforcement, leveling and smoothing it. |
| 7. Cure the Concrete | Allow the concrete to cure properly by keeping it moist and covered for several days. |
- Soil preparation and excavation work
- Insulation options
- Rough coating
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Soil preparation and excavation work
All of the work should be focused on the central portion of the future building plan after the formwork from the strip foundation has been removed and the exterior cavities have been backfilled. The primary objective is to eliminate the uppermost soil layers and replenish the internal space with a substance possessing specific qualities, such as low thermal conductivity, hygroscopicity, and sterility. It is necessary to finish this task while considering several factors.
First of all, you should be aware that, in terms of a building’s thermal protection, the floor area is not the most obvious thermal bridge (also known as a "cold bridge"). However, high density and consequently the heat capacity of the surrounding environment promote enhanced heat flow through the floor. Furthermore, since the house’s zero level is higher than the foundation and lower than the ground when a floor is installed on it, planning should be done with the installation of a vertical thermal protection belt in addition to a horizontal one.
Excavation of the foundation’s soil is the first step in the preparation process; this is done until a layer of dense clay is visible, free of foreign objects, or as close to it as possible. This is done to stop moisture from the outer soil layers from migrating into the backfill. Therefore, if a dense waterproof layer was not discovered when opening to the foundation’s depth, it was manually created using the clay method.
The foundation is then backfilled. A sand-gravel mixture can be used for this purpose when screeding the ground later on. It is poured to the top of the foundation in layers of 3-5 cm with intermittent dry compaction. Expanded clay, poured to a level 15 cm below the foundation level, is preferable if the floor is made of wood.
Insulation options
On a strip foundation, the interior space can only be effectively insulated from the soil and the concrete strip at the same time. The last and most crucial point is that concrete will still be noticeably cold even with external base insulation. Furthermore, even if the foundation doesn’t freeze, condensation may still form if the interior surface temperature drops below a certain point.
Three thermal protection belts must be installed in order to provide superior floor insulation.
The vertical internal one is up to 20 mm thick and composed of low-density extruded polystyrene foam. Before backfilling, the foundation needs to be insulated from the interior. Concrete needs to have insulation boards glued to it.
Installed concurrently with the blind area insulation, the vertical outer belt guards against frost heaving of the soil, which is caused by concrete freezing, rather than heat leaks from the house. It is crucial that the basement thermal protection system extends at least to level zero and not just to the foundation.
Heat transfer from the area beneath the floor to the earth is restricted by the main horizontal thermal protection belt. Two methods are possible for its construction:
- If the depth of soil freezing in the region is insignificant, or high-quality insulation of the blind area has been carried out, an expanded clay embankment can be used as thermal insulation. This option is most preferable when installing a wooden floor.
- If the subfloor is formed with a screed, and supercooling of the soil at the level of the foundation is not excluded, it is necessary to place EPS slabs up to 100 mm thick under the load-bearing layer.Supporting floor system
There are two possible configurations for the supporting system or subfloor on a strip foundation. Due to its capacity to self-regulate indoor humidity, wooden flooring on joists is thought to be ideal; however, from the perspective of energy efficiency, this is the least profitable option. Furthermore, there are extra challenges in getting the floor ready in areas where tile flooring is going to be installed.
The high service life of reinforced screed is attributed to the nearly limitless amount of insulation that can be installed beneath it. Despite its drawbacks, which include higher labor costs and complexity, this design is thought to be the best for homes built on strip foundations, particularly when floor heating is intended.
Installing a joist system—massive beams held up by brick support pillars—is necessary for a wooden floor. The layer of material used to backfill the foundation is directly on top of the pillars. After accounting for the lag plus 20–30 mm, the height of the pillars is determined so that their tops are below the zero mark by the total thickness of the floor pie.
After laying roll waterproofing on the pillars in 2-3 layers, they are covered with caps of thick cement mortar of strength grade M400. After laying the logs on the mortar cap, they are recessed to the required height, thereby ensuring preliminary leveling with a tolerance of up to 3 mm/m. The pitch of the beams can be easily calculated using a construction calculator based on the thickness and permissible deflection of the boards. The section of the joists is determined taking into account the floor"s own weight and payload (150 kg/m2 permanent and 300 kg/m2 temporary) using the method of calculating the deflection of a wooden beam on fixed hinged supports. For example, with a lag pitch of 1 m when installing flooring from pine boards 32 mm thick, their sufficient cross-section is considered to be 150×100 mm (per edge) supported by support pillars every 120 cm.
Prior to screed installation, the foundation is backfilled using layer-by-layer compaction, which then serves as the primary load-bearing component. Layers of 40–50 mm thick quarry sand separate the bedding from the soil and screed when large crushed stone or expanded clay is used as a compactor.
Insulation is placed on the bedding after it has been firmly compacted; it is typically placed in two layers with the joints spaced apart. Subsequently, a hydrobarrier composed of fiberglass and polyethylene film is rolled out and adhered to provide temporary protection. A heating system and reinforcement mesh measuring 10 x 140 x 140 mm are then installed on 20 mm spacer plugs. A screed that is at least 60 mm thick is then poured.
A crucial characteristic shared by both kinds of load-bearing floor systems is that they are completely above the upper plane of the foundation, or they cover it from above. This is necessary to give the cake more load-bearing capacity as well as improved protection for the ends. For these reasons, the tape’s width needs to be selected so that an interior ledge measuring 60 to 80 mm will form after the box is erected.
Rough coating
There are various techniques to guarantee excellent load distribution and high stiffness of wooden flooring. This is crucial for finishing materials like linoleum, where it is not permitted for adjacent boards to deflect while in use. As a result, you should either lay down a tongue-and-groove board or cover the floor with sheets of 5 mm plywood or 6 mm laminated fiberboard. Although a fixed connection between the boards is not necessary when using laminate as a finishing floor covering, the flooring should be planned ahead of time to be transverse to the laminate boards.
Since the screed is essentially a finished subfloor, no further processing is needed. Light floor coverings, like laminate or linoleum, only require the upper, weaker layer to be sanded or primed for highly absorbent surfaces in order to remove any remaining dust. Before using a self-leveling screed to level the floor, a "Betonkontakt" type primer is applied to the rough surface. It would not be unnecessary to wipe the screed with a cement-polymer adhesive mixture if you intended to lay tiles.
Building a floor on a strip foundation with backfill is a useful and efficient way to guarantee a sturdy and steady foundation for your structure. With this method, the advantages of a solid foundation are combined with the extra support and insulation that backfill offers. You can create a floor that satisfies both your structural and aesthetic requirements by meticulously organizing and carrying out each step.
Making sure the strip foundation is level and properly cured is the first step in the procedure. After that, the backfill material is picked with care and compacted to give the floor a sturdy foundation. In order to keep your floor from settling in the future and to prolong its life, this step is essential.
The flooring material can be installed once the backfill has been placed. To get a smooth and even surface, regardless of the material you choose—concrete, wood, or another—it’scriticalto adhere to best practices during installation. To prevent moisture and increase energy efficiency, proper insulation and moisture barriers are also necessary.
All things considered, building a floor on a strip foundation with backfill is a dependable and effective method of producing a sturdy, long-lasting floor. You can guarantee a project’s success and long-term viability by paying close attention to the details and taking the proper actions.
Building a floor on a strip foundation with backfill is a simple, doable method that guarantees a sturdy, long-lasting foundation for your house. In order to achieve stability and appropriate drainage, this process entails preparing the strip foundation, adding the appropriate backfill material, and layering it correctly. You can construct a sturdy, level floor that will effectively support your structure and endure for many years by following these steps.
