Wall No.2:
Wall No.3:
Wall No.4:
Wall No.5:
Enter an average finish weight. Finishes can vary by room, so the calculator uses average values and multiplies them by the calculated wall and floor areas.
| Areas and volume | ||
| External walls | m² | |
| Internal walls | m² | |
| Ceiling | m² | |
| Floor | m² | |
| Roof | m² | |
| Foundation bearing area | m² | |
| Foundation volume | m³ | |
| Mass and loads | t | kN |
| Foundation mass | ||
| Wall mass | ||
| Slab mass | ||
| Roof mass | ||
| Finishing mass | ||
| House mass | ||
| Imposed load | ||
| Snow load | ||
| Design house mass | ||
| Ultimate load per pile | ||
| Load per pile | ||
| Bearing pressure | ||
| Bearing pressure | kPa (kN/m²) | |
| Allowable pressure (maximum) | kPa (kN/m²) | |
About Structural Load on Foundation Calculation
This calculator assembles building actions and checks whether the chosen foundation bearing area is sufficient for the structural load on foundation for the selected soil type. The calculation accounts for the self-weight of walls, floors, roof, foundation, and finishes, as well as imposed (live) load and snow load. The result is intended for an initial assessment and early-stage foundation sizing.
Guidelines and recommendations
Standards and adopted approach
Actions and combinations. The calculation logic follows the European approach to actions and combinations in EN 1990 (Eurocode. Basis of structural design) and EN 1991-1-1 (Eurocode 1. Actions on structures. Densities, self-weight, imposed loads for buildings). Snow load as a variable action is considered in line with EN 1991-1-3 (Eurocode 1. Snow loads).
Ground and foundations. The bearing pressure check is performed in a simplified form, following the limit state principles for geotechnical design in EN 1997-1 (Eurocode 7. Geotechnical design. General rules).
Building geometry and volumes
Building footprint area. The floor and ceiling area is taken as Afloor = A · B · n, where A and B are in m, and n is the number of storeys.
Wall height. The total wall height used for mass is Hwalls = hstorey · n, where hstorey is in m.
Wall load
Wall volume. For each wall, its plan length is determined, then the volume is computed as V = L · t · H, where L is in m, t is thickness in m, and H is total height in m.
Wall mass. The mass of each wall is G = V · ρ, where ρ is the material density in kg/m3. The total wall weight is the sum over all included walls.
Floor actions
Unit weight of a floor. For each floor level, a unit load g in kg/m2 is used. For cast-in-place reinforced concrete it is calculated from thickness as g = ρ · t, where ρ = 2500 kg/m3 and t is in m.
Hollow-core slabs. For hollow-core slabs, the unit weight is selected by slab thickness via tabulated linear interpolation. Typical reference values, kg/m2: 150 mm → 250, 200 mm → 285, 220 mm → 310, 265 mm → 365, 320 mm → 430.
Total floor mass. The total floor mass is Gfloors = (Σ gi) · A · B, where A · B is the area in m2 and gi is in kg/m2.
Roof actions
Roof area. The roof slope area is calculated from the chosen roof geometry. Plan dimensions, rise H, and eaves overhangs are used. In essence, the rafter length is computed as a triangle hypotenuse, then each slope area is found and summed to obtain Aroof.
Roof self-weight. A constant component for the roof framing is taken as 80 kg/m2 plus the selected roof covering weight gcover. The total is Groof = (80 + gcover) · Aroof.
Finishes
Finish areas. Floor and ceiling areas are taken as A · B · n. The façade area is calculated from the building perimeter with an allowance for openings, using a factor of 0.9 as an average reduction.
Finish mass. Finish weight is calculated as unit weight (kg/m2) multiplied by the computed area. For internal walls and ceilings, an averaging factor of 0.85 is applied to avoid overestimation for mixed finish types.
Foundation load and bearing area
Foundation material. Foundation mass is computed from volume and material density ρ (kg/m3): Gfnd = Vfnd · ρ.
Strip foundation. The strip volume is the sum of external and internal strips. The bearing area is the plan area of the strip base, i.e., the sum of L · b over all strips.
Raft foundation. Vfnd = A · B · h, and the bearing area is Ab = A · B.
Pad (pier) foundation. The number of supports nsup is obtained from the total length of bearing lines and the chosen spacing, rounded up. The volume includes the grade beam and the individual pads. The bearing area is taken from the plan bearing area along the support lines.
Pile foundation. The check compares the load per pile with the design resistance of a single pile, considering both toe contribution (from cross-sectional area) and shaft contribution (from perimeter), divided by a soil factor of 1.4.
Imposed and snow load
Imposed (live) load. It is calculated over floor area: Q = q · A · B · n, where q is in kg/m2 or kN/m2.
Snow load. It is calculated over roof area: S = s · Aroof, where s is in kg/m2 or kN/m2.
Unit conversions. For input in kN/m2, the conversion 1 kN/m2 = 101.9716 kg/m2 is used. For converting from tonnes-force to kN, 1 t = 9.80665 kN is used.
Design load and soil check
Total permanent load. The permanent part is the sum of walls, floors, roof, finishes, and foundation masses.
Design combination. Partial factors are applied as follows: 1.2 for permanent load, 1.5 for imposed load, and 1.4 for snow load.
Nd = 1.2 · G + 1.5 · Q + 1.4 · S
Bearing pressure. The bearing pressure is p = Nd / Ab. For readability, it is also shown in kPa.
Comparison with soil. The allowable soil bearing pressure is taken from a built-in table by soil type. The acceptance criterion for strip, raft, and pad foundations is p ≤ pallow. For piles, the load per pile is compared to the pile design resistance.
Practical guidance. If the margin is small, common steps are to increase base width, reduce support spacing, select a stiffer foundation scheme, or refine the input loads and ground data. For an actual project, soil type and design parameters should be taken from a site investigation.
FAQs
Why is the design load higher than the sum of masses
The calculation uses a design combination with partial factors. Permanent load is multiplied by 1.2, imposed load by 1.5, and snow load by 1.4. This reflects the limit state concept to cover unfavorable deviations.
Why is snow applied to roof area but imposed load to floor area
Snow acts on the roof, so the slope area is used. Imposed load relates to occupancy and usage, so it is applied to floors. This follows the typical Eurocode 1 logic for variable actions.
What affects the result more, wall density or soil type
Wall density and thickness strongly affect the permanent load, especially for heavy materials. Soil type controls the allowable bearing pressure. In practice, heavy walls combined with weaker soils often govern and require a larger bearing area.
Why include finishes if their weight is small
Finishes act over large areas, so their total contribution can be noticeable. The calculator uses averaged areas and factors to avoid overestimation. If finishes are heavy, use unit weights closer to the actual build-up.
Can I use the result to finalize the foundation design
The result is suitable for an initial sizing and sanity check. Final design should be based on site investigation data and a geotechnical design per EN 1997-1, considering foundation depth, groundwater, and settlements. The calculator helps you estimate load levels and identify where larger bearing area or a different foundation scheme may be needed.