{"id":5517,"date":"2025-06-16T15:41:58","date_gmt":"2025-06-16T10:41:58","guid":{"rendered":"https:\/\/marcoreparationdefondation.com\/?p=5517"},"modified":"2026-10-05T21:42:07","modified_gmt":"2026-10-05T16:42:07","slug":"understanding-the-different-types-of-foundation-cracks-a-visual-guide-for-montreal-homeowners","status":"publish","type":"post","link":"https:\/\/marcoreparationdefondation.com\/en\/understanding-the-different-types-of-foundation-cracks-a-visual-guide-for-montreal-homeowners\/","title":{"rendered":"How Do You Recognize Each Type of Foundation Crack in Quebec?"},"content":{"rendered":"

You recognize a type of foundation crack by four clues: its direction (vertical, diagonal, horizontal or stair-step), its width, its edge (closed, or open with an offset) and the material of the wall (poured concrete, concrete block or brick).<\/strong> A thin, closed crack of constant width is almost always concrete shrinkage; a horizontal crack, or one that follows the joints of a block wall in a stair-step pattern, points to foundation movement.<\/p>\n

These benchmarks come from three Quebec sources: the APCHQ Performance Guide<\/a> (which sets tolerances for each building element; edition consulted: 2006, in French), the building engineers at Onesta B\u00e2timent Conseil<\/a> and the inspection platform Mon Inspecteur Certifi\u00e9<\/a> (both in French). The diagram below shows the five cases this article teaches you to tell apart. To find out whether a crack is serious and what to do about it, continue with our article When Is a Foundation Crack Serious in Quebec?<\/a><\/p>\n

\"Diagram<\/p>\n

Simplified diagram, not to scale.<\/em> Key: 1. shrinkage crack; 2. settlement crack, which widens; 3. horizontal crack, with a bowing wall (the dashed line shows the original position); 4. stair-step crack in a block wall; 5. slab crack.<\/p>\n

How Do You Recognize a Shrinkage Crack (1)?<\/h2>\n

A shrinkage crack is thin, nearly vertical and the same width along its whole length. According to Mon Inspecteur Certifi\u00e9, a vertical or slightly diagonal crack (under 30 degrees) that is under 3 mm and constant in width is almost always caused by the normal shrinkage of concrete as it hardens.<\/p>\n

The engineers at Onesta B\u00e2timent Conseil add that it is thin, vertical and not open, meaning closed. The APCHQ considers it acceptable as long as it doesn’t exceed 1\/8 in. (3 mm) and doesn’t let water in. It is the most common and least worrying kind of crack, but a shrinkage crack that seeps after rain should still be sealed.<\/p>\n

How Do You Recognize a Settlement Crack (2)?<\/h2>\n

A settlement crack is vertical or diagonal, open and often wider at one end, sometimes with an offset between its two sides. Onesta B\u00e2timent Conseil describes these cracks as vertical and open, with a visible offset on either side at times.<\/p>\n

They often start at the corner of a window or door, where stresses concentrate, and are sometimes accompanied by sticking doors. The simplest test: run your hand along the crack. If one edge sits proud of the other, the wall has moved. Our article beyond the basement<\/a> describes the signs that show up in the rest of the house, and our guide on soil type<\/a> explains why some lots settle more than others.<\/p>\n

How Do You Recognize a Horizontal Crack (3)?<\/h2>\n

A horizontal crack runs along the wall, often at mid-height, sometimes with a wall bowing inward. According to Onesta, it is caused by the lateral thrust of the soil, which increases considerably in frost-susceptible soil such as clay, especially without proper drainage behind the walls.<\/p>\n

To check whether the wall is bowing, hold an 8-foot (2.4 m) level or a straight board against it. The APCHQ allows a bow of at most 1 in. (25 mm) over 8 ft (2.5 m) for a new poured-concrete basement wall, measured from the base to the top of the wall: a larger gap exceeds that benchmark. Concrete block walls resist this thrust less well than poured concrete walls. To understand where it comes from, read our articles on hydrostatic pressure<\/a> and on the 4 kinds of water damage that threaten a foundation<\/a>.<\/p>\n

How Do You Recognize a Stair-Step Crack (4)?<\/h2>\n

A stair-step crack follows the mortar joints of a block or brick wall on a diagonal, like the steps of a staircase. According to Mon Inspecteur Certifi\u00e9, it is typical of concrete block foundations: thin and stable, it may come from minor, normal settling; widened or offset, it signals differential settlement of the foundation.<\/p>\n

It follows the mortar rather than cutting through the blocks, because the joints are the wall’s weak point. Measure it and recheck it like any crack: its evolution is what decides. Be careful with exterior brick, which also cracks for normal reasons: the APCHQ accepts a certain amount of shrinkage and thermal-expansion cracking, see the table below.<\/p>\n

How Do You Recognize a Basement Slab Crack (5)?<\/h2>\n

A slab crack is most often concrete shrinkage. The APCHQ considers normal-shrinkage cracks in a slab acceptable as long as their width doesn’t exceed 1\/8 in. (3 mm), and requires repair of those that let water in, by epoxy injection, flexible-product injection or a membrane.<\/p>\n

A slab that sinks, heaves or sounds hollow is a different problem: the APCHQ guide treats out-of-level slabs and voids under the slab separately, and they call for an assessment. If the slab crack meets a wall crack, photograph them together: it is a valuable clue for the professional.<\/p>\n

What Tolerances Does the APCHQ Set for Each Element?<\/h2>\n

The APCHQ sets a benchmark of 3 mm (1\/8 in.) for most concrete cracks, with nuances depending on the element. These criteria describe the minimum expected performance of a new build: they are not a diagnosis for an older home, but they give a recognized point of comparison in Quebec.<\/p>\n\n\n\n\n\n\n\n\n\n
Element<\/th>\nAPCHQ benchmark (new construction)<\/th>\nIf the benchmark is exceeded<\/th>\n<\/tr>\n<\/thead>\n
Poured concrete foundation wall<\/td>\nShrinkage acceptable up to 1\/8 in. (3 mm); no crack may let water in or cause frost heave<\/td>\nRepair: epoxy injection, flexible-product injection or membrane<\/td>\n<\/tr>\n
Concrete footing<\/td>\nA crack wider than 1\/8 in. (3 mm) is considered excessive<\/td>\nRepair, with reinforcement if the situation requires it<\/td>\n<\/tr>\n
Concrete slab<\/td>\nShrinkage acceptable up to 1\/8 in. (3 mm)<\/td>\nRepair by injection or membrane<\/td>\n<\/tr>\n
Bowed basement wall<\/td>\nAt most 1 in. (25 mm) over 8 ft (2.5 m), from base to top of the wall<\/td>\nCorrection of the gap<\/td>\n<\/tr>\n
Exterior masonry (brick)<\/td>\nAt most 1\/8 in. (3 mm) per 33 ft (10 m) of wall; no crack visible from more than 20 ft (6 m) or wider than 1\/8 in. (3 mm)<\/td>\nRepair by the contractor<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

How Do You Document a Crack Before Calling a Specialist?<\/h2>\n

Measure, mark, photograph and recheck. These four steps take ten minutes and give the specialist exactly what is needed to tell a shrinkage crack from an active one.<\/p>\n

    \n
  1. Measure the width<\/strong> to the millimetre with a ruler or a crack gauge, at the widest point.<\/li>\n
  2. Draw a pencil mark<\/strong> at each end of the crack and write down the date.<\/li>\n
  3. Photograph it<\/strong> with a ruler in the frame, always from the same angle.<\/li>\n
  4. Recheck after every winter.<\/strong> The APCHQ recommends checking how cracks wider than 1\/8 in. evolve after a freeze-thaw cycle.<\/li>\n<\/ol>\n

    Marco R\u00e9paration de Fondation visits in person for every estimate and every job site inspection. The company holds a valid license from the R\u00e9gie du b\u00e2timent du Qu\u00e9bec (RBQ No. 5775-3246-01) and serves Montreal, Laval, the South Shore (including Longueuil and Brossard), the West Island and Salaberry-de-Valleyfield. See what to expect during an inspection<\/a>, or visit our crack repair<\/a> page and our polyurethane vs. epoxy<\/a> comparison.<\/p>\n

    Does your crack look like none of these?<\/strong> Contact Marco R\u00e9paration de Fondation<\/a> for a free inspection and an honest opinion on its cause.<\/p>\n

    Frequently Asked Questions<\/h2>\n

    Is a vertical crack always a shrinkage crack?<\/h3>\n

    No. A thin, closed vertical crack of constant width is almost always shrinkage. But an open vertical crack that is wider at one end, or has an offset between its two sides, points to settlement instead and deserves an assessment.<\/p>\n

    Is a crack in exterior brick a foundation crack?<\/h3>\n

    Not necessarily. The APCHQ notes that masonry shrinks while curing and expands and contracts with temperature, which causes cracks linked to the normal behaviour of materials, within the limits of the table above. However, a stair-step crack that keeps widening in the brick, especially with sticking doors, is a reason to have the foundation checked.<\/p>\n

    Is a photo enough to identify a crack?<\/h3>\n

    A photo documents the crack, but it doesn’t replace measuring its width, tracking how it changes over time, or a professional’s opinion. The same photo, taken from the same angle before and after a winter, is however an excellent point of comparison.<\/p>\n","protected":false},"excerpt":{"rendered":"

    You recognize a type of foundation crack by four clues: its direction (vertical, diagonal, horizontal or stair-step), its width, its edge (closed, or open with an offset) and the material of the wall (poured concrete, concrete block or brick). A thin, closed crack of constant width is almost always concrete shrinkage; a horizontal crack, or […]<\/p>\n","protected":false},"author":1,"featured_media":1016,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[82],"tags":[],"class_list":["post-5517","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-reparation-de-fissures"],"_links":{"self":[{"href":"https:\/\/marcoreparationdefondation.com\/en\/wp-json\/wp\/v2\/posts\/5517"}],"collection":[{"href":"https:\/\/marcoreparationdefondation.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/marcoreparationdefondation.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/marcoreparationdefondation.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/marcoreparationdefondation.com\/en\/wp-json\/wp\/v2\/comments?post=5517"}],"version-history":[{"count":4,"href":"https:\/\/marcoreparationdefondation.com\/en\/wp-json\/wp\/v2\/posts\/5517\/revisions"}],"predecessor-version":[{"id":6810,"href":"https:\/\/marcoreparationdefondation.com\/en\/wp-json\/wp\/v2\/posts\/5517\/revisions\/6810"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/marcoreparationdefondation.com\/en\/wp-json\/wp\/v2\/media\/1016"}],"wp:attachment":[{"href":"https:\/\/marcoreparationdefondation.com\/en\/wp-json\/wp\/v2\/media?parent=5517"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/marcoreparationdefondation.com\/en\/wp-json\/wp\/v2\/categories?post=5517"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/marcoreparationdefondation.com\/en\/wp-json\/wp\/v2\/tags?post=5517"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}