Ensuring Precision in Concrete Construction: Guidelines for Tolerances
When constructing buildings with cast-in-place concrete elements, it’s crucial to allow for certain variations in dimensions. These variations, known as construction tolerances, help control the alignment, size, length, and placement of concrete elements. Perfect alignment is unnecessary, but tolerances must be carefully established to maintain the strength of the concrete member.
ACI 117M-10: A Guide for Construction Tolerances
The American Concrete Institute (ACI) provides valuable guidance through ACI 117M-10, offering tolerances for cast-in-place concrete members in buildings. This guidance ensures that construction proceeds safely and satisfactorily without unnecessary and costly perfection.
1. Deviation from Plumb
Deviation from Plumb
| Building Element |
Height Limit (m) |
Tolerances |
| Lines, surfaces, corners, arrises, and elements |
≤ 25.4 |
Lesser of 0.003 times the height or ±25 mm |
| Outside corner of exposed corner columns, contraction joint grooves |
≤ 25.4 |
Lesser of 0.002 times the height or ±13 mm |
| Lines, surfaces, corners, arrises, and elements |
25.4-152.4 |
Lesser of 0.001 times the height or ±150 mm |
| Outside corner of exposed corner columns, contraction joint grooves |
25.4-152.4 |
Lesser of 0.0005 times the height or 75 mm |
| Vertical edges of openings |
> 0.3 |
±13 mm |
2. Horizontal Deviation from Location
Tolerances for Horizontal Deviations
| Building Elements |
Tolerances (mm) |
Notes |
| Vertical elements (columns, walls) |
±25 |
Measured at the top of the element foundation or lowest support level |
| Other elements |
±25 |
|
| Edge location of all openings |
±13 |
|
| Sawcuts, joints, and weakened plane embedments in slabs |
±20 |
|
3. Vertical Deviation from Location
Tolerances for Vertical Deviations
| Elements in Building |
Tolerances for Vertical Deviations |
| Elements |
±25 |
| Edge location of all openings |
±13 |
4. Deviation from Elevation
Tolerances for Deviation from Elevation
| Concrete Element |
Tolerances (mm) |
| Top surface of slabs-on-ground, formed suspended slabs |
±20 |
| Lintels, sills, parapets, horizontal grooves, and other lines |
±13 |
| Top of walls |
±20 |
| Fine grade of soil below slabs-on-ground |
±20 |
5. Deviation from Cross-sectional Dimensions
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 |
< 600 |
+75-13 |
| Horizontal deviation of unformed beams and walls cast against soil |
> 600 |
+150-13 |
6. Deviations from Formed Opening Width or Height
The deviation from formed opening width or height ranges 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.
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