Why does a CMU wall need control joints?

Concrete masonry shrinks slightly as it cures and dries — without planned weak points (control joints) to accommodate that shrinkage, unpredictable random cracking can occur elsewhere in the wall.

Should control joints always be placed at the maximum spacing?

No — control joints should also be placed at natural stress concentration points: changes in wall height or thickness, near the ends of openings, at wall intersections, and at abrupt changes in wall foundation support, even if that means closer-than-maximum spacing in places.

Does this apply to brick veneer too?

Brick behaves differently — clay brick actually expands slightly over time (moisture expansion) rather than shrinking, so brick veneer uses EXPANSION joints on a different spacing logic, not the same shrinkage-based control joint spacing used for CMU.

Can I set out joints on a loadbearing or fire-rated wall from this number?

No. This page has two inputs, height and length, so it knows nothing about how the wall is reinforced, how firmly the base and top restrain it, or what the wall is being asked to do. A control joint is a deliberate vertical break in the masonry: where the wall forms part of the lateral system, where a bond beam or lintel has to run across that line, or where the wall is a fire separation and the joint has to be detailed so it does not become a hole in the rating, the position of every break is a design decision and not the output of a spacing ratio. Published concrete masonry guidance also commonly allows longer panels where more horizontal crack-control reinforcement is built in, and this page takes no reinforcement input at all. Use the count to budget joints on a straight run of ordinary CMU, and take the layout itself from whoever designed the wall.

What should go in Wall Length, and why does a taller wall stop changing the answer?

Wall Length means one straight, uninterrupted run, corner to corner — enter a building's whole perimeter and you get a joint count for a wall that does not exist, so run each elevation separately. Wall Height is the height of the masonry on that run; where the height steps along it, entering the lower height is the cautious choice, because the spacing here is twice the height and a shorter wall therefore gets closer joints. Height also stops mattering above roughly 3.8 m (12 ft 6 in): beyond that, twice the height is past the 7.6 m ceiling this page holds, so a 4 m wall and a 6 m wall of the same length come back with the same joint count. That ceiling is a 25 ft figure carried in metric, so whenever it is the one binding the imperial breakdown line reads 24.93 ft rather than a round 25.

The answer is a count — how do I set the joints out and build them?

Divide the run by the joint count plus one, not by the maximum spacing. Five joints on a 40 m run 4.5 m high give six panels of 6.67 m, inside the ceiling rather than at it, which beats marking maximum-length bays off one end and leaving a stub at the other. That even division is a first-pass layout and not a setting-out drawing — the stress points above pull lines off it. Then shift each line onto the nearest block module: the joint is a continuous head joint running the full height of the wall, so it lands where the units break, not where the tape says. The rest is detailing, and that is where these go wrong. The joint is commonly formed with sash or shear-key units, or a preformed rubber or PVC key, so the panels still transfer out-of-plane load across the line while being free to move in plane, with the mortar raked back and the gap sealed over backer rod on the exposed faces. Horizontal joint reinforcement is normally stopped either side rather than carried through. A joint buttered solid with mortar or grouted through is a line on a drawing, and the wall will crack somewhere nobody chose.

Materials & Quantities

Masonry Control Joint Spacing Calculator

Estimate the number of vertical control joints needed in a CMU wall, using a common simplified spacing guideline.

Answers as you typeNo submit button
Every formula citedNamed published standards
Calculated in your browserNo account, nothing uploaded

SettingsSettings for this calculationUS

Market

Imperial · sales tax

Wall Height

The wall height.

This is the number that sets the spacing, not merely the area. The common rule takes the LESSER of twice the wall height or 7.6 m, so below about 3.8 m the height governs and every 300 mm of error moves every joint by 600 mm. Measure the full height of the masonry from its bearing to the top course, parapet included — a parapet shrinks with the rest of the wall and cracks first if the joint stops below it.

Wall Length

The total length of the wall run.

The uninterrupted run of masonry between the things that already relieve it: a corner, a pilaster, a movement joint in the structure behind, a full-height opening. A 30 m elevation broken by a corner at 12 m is two runs of 12 and 18, not one of 30 — working it as one puts joints where the corner already does the job and leaves the long leg short of them.

Control joints needed

4 control joints

Low confidence

This is a simplified general guideline, not a substitute for a project-specific control joint layout — actual spacing should also account for changes in wall height/thickness, openings, wall intersections, and the specific unit's documented shrinkage characteristics (NCMA TEK 10-2 or your local equivalent).

Maximum spacing used: 20 ft
Wall panels between the joints: 5
Panel length, as set out: 19.6 ft

Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

A commonly-used simplified guideline for CMU control joint spacing: maximum spacing = the lesser of 2x the wall height or 7.6m (25 ft) — actual project requirements vary by wall restraint, panel geometry, and the specific unit/mortar shrinkage properties, per NCMA TEK guidance

Inputs used

Wall Height: 10 ft
Wall Length: 98 ft

Intermediate steps

Maximum spacing used: 20 ft
Wall panels between the joints: 5
Panel length, as set out: 19.6 ft

Final result4 control joints

Confidence note: This is a simplified general guideline, not a substitute for a project-specific control joint layout — actual spacing should also account for changes in wall height/thickness, openings, wall intersections, and the specific unit's documented shrinkage characteristics (NCMA TEK 10-2 or your local equivalent).

What this calculation does not cover

The spacing comes from one simplified ratio - twice the wall height, capped at 7.6 m (25 ft) - with no input for horizontal joint reinforcement, unit shrinkage properties, mortar, or how firmly the wall is restrained at its base, ends and top. Published concrete masonry guidance ties the allowable panel length to the crack-control reinforcement built into the wall, and this page takes none.
The number is interior joints on one straight, uninterrupted run at even spacing. It adds nothing for the joints that stress concentrations demand - at openings, wall intersections and corners, pilasters, changes in wall height or thickness, and changes in foundation support - so a real layout normally needs more joints than this, and in places closer together.
This is not a structural or fire-rating design. Where the wall is loadbearing, forms part of the lateral system, carries a bond beam or lintel across the joint line, or acts as a fire separation, the position and detailing of every break in the masonry is a design decision, and nothing here takes reinforcement, restraint or a rating as an input.
Concrete masonry shrinkage only. Clay brick moves the other way, expanding with moisture over time and detailed with expansion joints on different rules, and stone, stucco and concrete slabs are all separate cases with their own spacing logic. Do not carry this count onto a brick veneer, a render, or a slab.
The ratio has no floor: halve the wall height and the spacing halves with it, so a low garden or planter wall comes back with joints roughly a metre apart or less. The output is also only a count - it says nothing about the joint itself, meaning sash or shear-key units, preformed keys, raked mortar, backer rod and sealant, and where horizontal joint reinforcement is stopped either side.

Estimated cost — your price

Price per control joint ($)

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Part of a bigger job

This trade is one line of a job takeoff. Run the whole job and every other trade comes back with it, off the same measurements.

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also measuresCavity Wall Weep Hole Spacing Brick Brick Veneer Anchor Spacing Brick Movement Joint Spacing

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-02 · in the site-wide review of 2026-09-06 · v1.0.1

Regulatory standards & verification citations1

A commonly-used simplified guideline for CMU control joint spacing: maximum spacing = the lesser of 2x the wall height or 7.6m (25 ft) — actual project requirements vary by wall restraint, panel geometry, and the specific unit/mortar shrinkage properties, per NCMA TEK guidance

Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Tools and safety for this job

To lay block. Generic types, no brands, no prices.

Protection this work requires

Cutting or grinding concrete, masonry, screed, tile or fibre-cement board releases respirable silica: cut wet or extract at the tool, and wear a P2/N95 respirator at minimum — a nuisance dust mask does not filter it.
Wet cement and lime burn skin and eyes painlessly until the damage is done: waterproof gloves to EN 374, safety glasses whenever the mix can splash, and never kneel in wet mix in permeable trousers.
Boards, blocks and bagged material cause most lasting back injuries on small sites: two people or a lifter for full sheets, and never a bag on one shoulder up a ladder.

Show the 6 tools this job needs

Essential

Brick trowel and jointer
Spirit level
String line and pins
Wheelbarrow

Recommended

Block splitter
Cement mixer

what each masonry tool is for, and the spec that decides which to buy where one does.

Now that you have the number

These guides cover the work this quantity is for — the first ones run this calculator inside the section that raises the question.

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Still deciding? Masonry Control Joints vs Joint Reinforcement — the factors that actually differ, with no invented prices.

Already gone wrong? The mortar is crumbling out of my brickwork

How to calculate masonry control joint spacing in 3 steps

Wall HeightThe wall height.
Wall LengthThe total length of the wall run.
Control joints neededThe tool computes the control joints needed from those figures and shows the formula, its sources, and a confidence rating alongside it.

Frequently asked questions

Why does a CMU wall need control joints?: Concrete masonry shrinks slightly as it cures and dries — without planned weak points (control joints) to accommodate that shrinkage, unpredictable random cracking can occur elsewhere in the wall.
Should control joints always be placed at the maximum spacing?: No — control joints should also be placed at natural stress concentration points: changes in wall height or thickness, near the ends of openings, at wall intersections, and at abrupt changes in wall foundation support, even if that means closer-than-maximum spacing in places.
Does this apply to brick veneer too?: Brick behaves differently — clay brick actually expands slightly over time (moisture expansion) rather than shrinking, so brick veneer uses EXPANSION joints on a different spacing logic, not the same shrinkage-based control joint spacing used for CMU.
Can I set out joints on a loadbearing or fire-rated wall from this number?: No. This page has two inputs, height and length, so it knows nothing about how the wall is reinforced, how firmly the base and top restrain it, or what the wall is being asked to do. A control joint is a deliberate vertical break in the masonry: where the wall forms part of the lateral system, where a bond beam or lintel has to run across that line, or where the wall is a fire separation and the joint has to be detailed so it does not become a hole in the rating, the position of every break is a design decision and not the output of a spacing ratio. Published concrete masonry guidance also commonly allows longer panels where more horizontal crack-control reinforcement is built in, and this page takes no reinforcement input at all. Use the count to budget joints on a straight run of ordinary CMU, and take the layout itself from whoever designed the wall.
What should go in Wall Length, and why does a taller wall stop changing the answer?: Wall Length means one straight, uninterrupted run, corner to corner — enter a building's whole perimeter and you get a joint count for a wall that does not exist, so run each elevation separately. Wall Height is the height of the masonry on that run; where the height steps along it, entering the lower height is the cautious choice, because the spacing here is twice the height and a shorter wall therefore gets closer joints. Height also stops mattering above roughly 3.8 m (12 ft 6 in): beyond that, twice the height is past the 7.6 m ceiling this page holds, so a 4 m wall and a 6 m wall of the same length come back with the same joint count. That ceiling is a 25 ft figure carried in metric, so whenever it is the one binding the imperial breakdown line reads 24.93 ft rather than a round 25.
The answer is a count — how do I set the joints out and build them?: Divide the run by the joint count plus one, not by the maximum spacing. Five joints on a 40 m run 4.5 m high give six panels of 6.67 m, inside the ceiling rather than at it, which beats marking maximum-length bays off one end and leaving a stub at the other. That even division is a first-pass layout and not a setting-out drawing — the stress points above pull lines off it. Then shift each line onto the nearest block module: the joint is a continuous head joint running the full height of the wall, so it lands where the units break, not where the tape says. The rest is detailing, and that is where these go wrong. The joint is commonly formed with sash or shear-key units, or a preformed rubber or PVC key, so the panels still transfer out-of-plane load across the line while being free to move in plane, with the mortar raked back and the gap sealed over backer rod on the exposed faces. Horizontal joint reinforcement is normally stopped either side rather than carried through. A joint buttered solid with mortar or grouted through is a line on a drawing, and the wall will crack somewhere nobody chose.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.