Construction tolerances are allowed variations in a designated dimension of cast-in-place reinforced concrete elements. They are necessary means of controlling vertical element plumb, size, length, and location of various cast-in-place concrete elements in a building. This is because structures are not constructed exactly plumb, level, and straight and such perfection is unnecessary. Nonetheless, tolerances should be established carefully to ensure that they do not influence the strength of the concrete member.
ACI 117M- 10 provides tolerance for cast-in-place concrete members in buildings. Such guidance helps contractors construct cast-in-place buildings satisfactorily, especially in terms of safety, without needing unnecessary and costly perfection.
Construction Tolerances for Cast-in-Place Concrete Members in a Building
1. Deviation from Plumb
The maximum acceptable deviation from the plumb for various cast-in-place concrete members is presented in Table-1. The deviation is the departure from an established point, line, or surface measured perpendicular to the reference line or surface, ACI 117M-10, section 1.3.
Table-1: Deviation from Plumb for Different Cast-in-place Concrete Elements in Buildings
| Building Element | Height Limit, m | Tolerances |
| Lines, surfaces, corners, arrises, and elements | ≤ 25.4 | Lesser of 0.003 times the height above the top of foundations or lowest support level as shown on Project Drawings or ±25 mm, see Figure-1 |
| Outside corner of exposed corner columns and for contraction joint grooves in exposed concrete | ≤ 25.4 | Lesser of 0.002 times the height above the top of foundations or lowest support level as shown on Project Drawings or ±13 mm, see Figure-2 |
| Lines, surfaces, corners, arrises, and elements | 25.4-152.4 | Lesser of 0.001 times the height above the top of foundations or lowest support level as shown on Project Drawings or ±150 mm |
| Outside corner of an exposed corner, columns, and contraction joint grooves in concrete exposed to view | 25.4-152.4 | Lesser of 0.0005 times the height above the top of foundations or lowest support level as shown on Project Drawings or 75 mm |
| Vertical edges of openings, see Figure-3 | >0.3 | ±13 mm |
2. Horizontal Deviation from Location
The horizontal deviation is the departure from an established point, line, or surface measured normal to a vertical line through the point of interest, ACI 117M-10. Tolerances of horizontal deviation from a location for various concrete members in a building are presented in Table-2.Â
Table-2: Tolerances for Horizontal Deviations from a location for different Concrete Elements in a Building
| Building elements | Tolerances, mm | Notes |
| Vertical elements | ±25 | Vertical elements such as columns and walls, measured at the top of the element foundation or lowest support level, see Figure-4 |
| Other elements | ±25 | see Figure-4 |
| Edge location of all openings | ±13 | see Figure-4 |
| Sawcuts, joints, and weakened plane embedments in slabs | ±20 | see Figure-4 |
3. Vertical Deviation from Location
A vertical deviation from a location is the departure from an established point, line, or surface measured perpendicular to the horizontal line through the point of interest. Â
Table-3: Tolerances for Deviation from Location
| Elements in Building | Tolerances for Vertical Deviations |
| Elements | ±25 |
| Edge location of all openings | ±13 |
4. Deviation from Elevation
Table-4 presents tolerances for deviation from elevation for various elements in cast-in-place reinforced concrete elements in a structure.Â
Table-4: Tolerances for Deviation from Elevation
| Concrete element | Tolerances for deviations from elevation, mm |
| Top surface of slabs-on-ground, and formed suspended slabs before and after removal of supporting shores | ±20 |
| Lintels, sills, parapets, horizontal grooves, andother lines in exposed concrete | ±13 |
| Top of walls | ±20 |
| Fine grade of soil immediately below slabs-on-ground | ±20 |
5. Deviation from Cross-sectional Dimensions
Tolerances for deviation from cross-sectional dimension for different concrete members can be found in Table-5.
Table-5: Tolerances for Deviations from Cross-sectional Dimensions
| Concrete element | Cross-sectional dimensions, mm | Tolerances, mm |
| Thickness of elements except for slabs | ≤300 | +10-6 |
| Thickness of elements except for slabs | 300-900 | +13-10 |
| Thickness of elements except for slabs | >900 | +25-20 |
| Horizontal deviation of unformed beams and walls cast against soil from plan dimension | <600 | +75-13 |
| Horizontal deviation of unformed beams and walls cast against soil from plan dimension | >600 | +150-13 |
6. Deviations from Formed Opening Width or Height
The deviation from formed opening width or height falls between -13 mm and +25 mm.
- Deviation from Relative Elevations or Widths for Stairs
- The difference between the largest and smallest tread or riser in any flight shall not exceed 10 mm.
- The difference in the height of adjacent risers measured at the nose shall not exceed 5 mm.
- The difference in depth of adjacent treads shall not exceed 5 mm.
- Stair tread from back to nosing is ±6 mm
FAQs
Construction tolerances are allowed variations in a designated dimension of cast-in-place reinforced concrete elements. They are necessary means of controlling vertical element plumb, size, length, and location of various cast-in-place concrete elements in a building
1. Set up the ease of construction without the necessity for later modifications and changes.
2. Ensure the structure performs satisfactorily, especially in terms of safety.
3. Avoid unnecessary and expensive accuracy and perfection.
The horizontal deviation is the departure from an established point, line, or surface measured normal to a vertical line through the point of interest, ACI 117M-10.
A vertical deviation is a departure from an established point, line, or surface measured perpendicular to the horizontal line through the point of interest.Â
The maximum acceptable vertical deviation from a location for walls and columns is ±25 mm
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