Chimney Brick Example: One Stack Worked from Measurements to a Pack Order

One chimney stack, worked from its measurements to its order. The stack below has a main section 3 ft by 2 ft in plan and 9 ft high, plus a cap band 3.5 ft by 2.5 ft in plan and 1.5 ft high. In modular brick it needs 729 bricks net, 766 bricks at the 5 percent waste rule, and 2 example packs of 500 bricks, which deliver 1000 bricks. Every step below is shown, so the same steps work on a different stack.

What does this chimney example order?

The order is 2 packs of modular brick, delivering 1000 bricks. The net count is 729 bricks, and the waste step lifts it to 766 bricks. Pack rounding, not waste, creates most of the surplus here: 234 bricks over the order need.

The figures here are worked fixtures, not project quantities. The brick is modular, at the Brick Industry Association rate of 6.75 bricks per ft2 for a 3/8 in joint in running or stack bond. The 500 bricks per pack figure is an example supplier figure, not a standard.

What are the stack measurements?

Both bands are measured above the roofline, on the outside faces of the stack. The main band and the cap band have different plan sizes, so each band gets its own perimeter and its own area line.

The chimney brick measuring guide shows how each band height is taken, including stacks on a sloped roof where faces have different heights. This example uses one height per band, because both bands sit on a level roofline in the fixture.

How do the band areas add up?

Face area for a band is its perimeter times its height. Work each band separately, then add the two areas.

Band face area = 2 x (plan length + plan width) x band height

1. Main stack perimeter: 2 x (3 + 2) = 10 ft. Main stack area: 10 x 9 = 90 ft2.
2. Cap band perimeter: 2 x (3.5 + 2.5) = 12 ft. Cap band area: 12 x 1.5 = 18 ft2.
3. Total net face area: 90 + 18 = 108 ft2.

Then apply the coverage rate to the total area.

Net bricks = net face area x bricks per ft2

For this stack: 108 x 6.75 = 729 bricks. The result is exact here, so no rounding is needed at the net step. When a net count is fractional, round it up to a whole brick before the waste step, because a fraction of a brick cannot be laid.

How does waste change the order?

The Association states a general rule of at least 5 percent added to net brick quantities for breakage and waste. Its table rates exclude waste, so this step is separate from the coverage rate.

Order bricks = net bricks x (1 + waste / 100)

1. Convert 5 percent to a multiplier: 1 + 5 / 100 = 1.05.
2. Multiply the net count: 729 x 1.05 = 765.45 bricks.
3. Round up to a whole brick: 766 bricks.

The chimney brick ordering guide records the waste basis on the order record, beside the net count and the pack count. A percentage written without its basis cannot be checked later, and a higher percentage needs its own reason on the record.

How many packs does the order need?

Divide the order count by the supplier's bricks per pack, then round a positive remainder up to a whole pack. The example supplier states 500 bricks per pack.

Packs = order bricks / bricks per pack, rounded up

1. Divide: 766 / 500 = 1.532.
2. Round up: 2 packs.
3. Delivered bricks: 2 x 500 = 1000 bricks.
4. Surplus over the order need: 1000 minus 766 = 234 bricks.

How does the count check in metric units?

Convert the area, then apply the matching metric rate. The two routes must land on the same net count.

1. Convert the area: 108 x 0.09290304 = 10.0335 m2.
2. Convert the rate: 6.75 / 0.09290304 = 72.66 bricks per m2.
3. Multiply: 10.0335 x 72.66 = 729 bricks.

The metric route confirms the imperial route. If the two routes disagree, the conversion or the rate is wrong, and the order should wait until the mismatch is found.

What changes with standard brick?

Standard brick uses a different rate: 6.55 bricks per ft2 at the same 3/8 in joint. The stack measurements stay the same, and only the rate changes.

The pack count stays at 2 in both cases, but the surplus changes. A rate carried from the wrong brick size gives a wrong net count even when the pack count looks the same. Check sizes and rates with Brick Sizes and Coverage before running the count.

What goes wrong if the cap band uses the main perimeter?

The cap band is wider than the main stack, so it has its own perimeter of 12 ft. Using the main stack perimeter of 10 ft for the cap band understates the job.

1. Wrong cap area: 10 x 1.5 = 15 ft2, instead of 18 ft2.
2. Wrong total area: 90 + 15 = 105 ft2, instead of 108 ft2.
3. Wrong net count: 105 x 6.75 = 708.75, so 709 bricks, instead of 729 bricks.
4. Shortfall: 729 minus 709 = 20 bricks short at the net step, before waste.

That shortfall survives the waste step, because waste is applied to the wrong net count. The chimney brick mistakes guide lists the other measurement traps that change a count this way, including a height taken from the ground instead of the roofline and one height used for all faces on a sloped roof.

Does a smaller stack follow the same steps?

Yes. A single band 2 ft by 2 ft in plan and 6 ft high gives a perimeter of 8 ft and a face area of 48 ft2. At 6.75 bricks per ft2 the net count is 324 bricks. At 5 percent waste the order is 341 bricks, because 324 x 1.05 = 340.2, rounded up. At the same example 500 bricks per pack, that order needs 1 pack, delivering 500 bricks, a surplus of 159 bricks over the order need. The steps are the same; only the numbers change.

What this example does not decide

This example settles a quantity for one fixture stack. It does not choose the brick grade, type, or mortar. Those choices belong to Choosing Brick and Mortar for a Chimney Stack and to the project specification. It does not size a flue, set a chimney height, price the order, or set a mortar quantity, and it does not approve a rebuild or a repair. Those decisions rest with the project design team and owner, under the governing code and the project specification.

Work on a chimney stack needs safe access and fall protection. Do not climb onto a roof or lean over an edge to check a stack without the access and protection the job requires.