Calculate how many weep holes you need for brick veneer or a retaining wall from the wall length and spacing, with typical code spacings built in.
Weep Hole Formula
For a brick or masonry veneer wall, the number of weep holes along one line of flashing is the wall length divided by the maximum spacing, rounded up, with one added so a weep sits near each end:
N = ceil(L / S) + 1
The even on-center spacing that this count actually produces is the wall length divided by the number of gaps between weeps:
OC = L / (N - 1)
Each equal-width opening run is modeled separately at its lintel flashing, with a weep at each endpoint. This layout convention gives at least two per positive run; it is not a drainage-capacity calculation:
For a retaining wall the weeps form a grid. The count across one row and the grid total are:
Variables:
- N is the number of weep holes along the wall run
- L is the length of wall above the flashing
- S is the maximum on-center spacing you allow
- OC is the even spacing between weeps that the count produces
- W is the width of a window or door opening
- Cols is the number of weeps in one horizontal row of a retaining wall
- Rows is the number of horizontal rows of weeps
Choose what the wall is at the top of the calculator. In brick or masonry veneer mode you enter the wall length and pick a spacing standard, and the tool returns the number of weep holes plus the even spacing to mark out. Turning on the openings option adds weep holes above each window and door. In retaining wall mode you enter the length, a horizontal spacing, and the number of rows, and the tool returns the grid total and, if height is entered, geometric wall face area. No generic one-per-20-square-feet drainage rule is applied. The two-endpoint convention keeps calculated gaps at or below your selected maximum, but does not establish drainage capacity or code approval. Unit selectors reinterpret entered measurements rather than converting their numeric values.
Weep Hole Spacing Standards Compared
Spacing depends on the weep type and the code you build to. This table lines up the common standards so you can see how the choice changes the count. The last column is the number of weep holes for a single 40-foot wall run.
| Spacing standard | Max on-center | Common weep type | Weeps for a 40 ft wall |
|---|---|---|---|
| 2024 IRC R703.8.6 maximum | 33 in (838 mm) | Open head joint | 16 |
| BIA recommended | 24 in (610 mm) | Open head joint | 21 |
| BIA recommended | 16 in (406 mm) | Wick or rope; tubes not recommended by BIA TN7 | 31 |
The code maximum and the recommended spacing are not the same number. The 2024 IRC model code specifies a 33-inch maximum and a 3/16-inch minimum diameter immediately above flashing. Confirm the locally adopted code and amendments. BIA Technical Note 7 (2017) prefers open head joints at no more than 24 inches and recommends no more than 16 inches for wick weeps; it does not recommend weep tubes. This next table gives the weep count at each of those spacings for common wall lengths.
| Wall length | 16 in spacing | 24 in spacing | 33 in spacing |
|---|---|---|---|
| 10 ft | 9 | 6 | 5 |
| 20 ft | 16 | 11 | 9 |
| 30 ft | 24 | 16 | 12 |
| 40 ft | 31 | 21 | 16 |
| 50 ft | 39 | 26 | 20 |
Example Problems
Example 1: Weep holes for a veneer wall.
You have a 40-foot brick veneer wall and build to the IRC maximum of 33 inches. Convert the length to 480 inches and divide by 33 to get 14.5, round up to 15, then add one:
N = ceil(480 / 33) + 1 = 15 + 1 = 16 weep holes. The even spacing is 480 / 15 = 32 inches on center, which stays under the 33-inch limit.
Example 2: Weep holes for a retaining wall.
For an illustrative 30-foot run with one design-specified row and a 6-foot maximum spacing, the two-endpoint count is ceil(30 / 6) + 1 = 6 weep holes. At a 6-foot height, its face area is 180 square feet. Those dimensions alone cannot establish adequate drainage, required rows, or outlet size; use the project drainage design.
Frequently Asked Questions
How far apart should weep holes be?
For the referenced 2024 IRC masonry-veneer provision, the maximum is 33 inches on center. BIA TN7 prefers no more than 24 inches for open head joints and recommends no more than 16 inches for wick weeps. These veneer references do not size retaining-wall drainage. Confirm the assembly, product instructions, and local project requirements.
Where do weep holes go on a wall?
Place weep holes in the first course of brick immediately above the through-wall flashing. That means at the base of the wall above the foundation, above the lintels over windows and doors, and above any shelf angles. Water travels down the back of the veneer, collects on the flashing, and needs an opening right at that level to escape.
What size does a weep hole need to be?
The referenced 2024 IRC provision sets a minimum diameter of 3/16 inch immediately above flashing. An open head joint is an unfilled vertical mortar joint. BIA TN7 prefers open head joints, gives separate wick-spacing guidance, and does not recommend tubes. Size and detailing must match the applicable assembly and approved drainage design.
