Concrete Isolation-Joint Filler Takeoff
Isolation-joint filler around a slab where it abuts rigid elements, so it can move freely.
Example
You enter
- Slab length (ft) 40
- Slab width (ft) 30
- Columns / piers in the slab 6
- Perimeter per column (ft, 12 in sq = 4) 4
- Filler strip length (ft) 10
You get
- Filler (LF) 164
- Filler strips 17
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
ScopePre-molded isolation-joint filler (usually 1/2 in fiber or foam) around a slab-on-grade where it abuts rigid elements so it can move independently: filler = 2 x (length + width) + columns x column-perimeter, strips = ceil(filler / strip length). A 40 x 30 ft slab around six 12 in columns is 164 LF (140 perimeter + 24 columns), 17 ten-foot strips; a 50 x 40 ft slab with no interior columns is 180 LF. This is distinct from the sawn CONTROL joints, which relieve shrinkage within the slab. The structural and slab-on-grade details (ACI 302 / ACI 360) govern where the isolation joints go and the filler type.
Formula or tableslab_perimeter_ft = 2 x (slab_length_ft + slab_width_ft); column_isolation_ft = round(num_columns) x column_perimeter_ft; filler_lf = slab_perimeter_ft + column_isolation_ft; strips = ceil(filler_lf / strip_length_ft).
Source and editionACI 302 (Guide for Concrete Floor and Slab Construction) and ACI 360 (Design of Slabs-on-Ground) isolation-joint practice, by name; the structural detail governs the joint locations.
Free accessThe takeoff arithmetic is public first-principles (perimeter plus column perimeters over strip length); the joint locations and the 1/2 in filler type come from the ACI 302 / 360 slab-on-grade detail.
What governsEstimate. AHJ and licensed professional govern.
API field namesslab_length_ft, slab_width_ft, num_columns, column_perimeter_ft, strip_length_ft, filler_lf, strips
- Isolation locations slab perimeter at walls/footings plus the full perimeter of each column/pier/pad the slab surroundsACI 302 / ACI 360
- Distinct from control joints isolation separates restrained elements; control (sawn) joints relieve shrinkage within the fieldACI 302