A hairline, dry, stable crack in an older King Township basement can usually be sealed cheaply. A crack that is horizontal, stair-stepped, wider than about a quarter inch, or still growing needs an engineer before anyone seals it.
Older homes around King City were often built long before modern footings and drainage, and many sit on rural lots with a well and a septic bed close to the house. That changes what a sensible crack repair looks like. Here is how to sort the cracks that can wait from the ones that cannot, and which approvals to check before anyone digs or seals.
Step one: read the crack before you fix it
Hairline cracks, about the width of a sewing thread, are common in concrete and are usually not structural. The ones to take seriously are horizontal cracks and diagonal or stair-step cracks that are getting bigger, which often point to soil or water pressure against the wall. A common rule of thumb is to look closer once a crack passes about a quarter inch or keeps lengthening. These thresholds come from general homeowner guidance, not a King Township rule, so treat them as a prompt to ask a professional, not a diagnosis.
A simple way to find out whether it moves: pencil a mark at each end of the crack, date it, and photograph it next to a tape measure. Check again after the spring thaw and after a wet fall. A crack that has not changed over a full year is a very different job from one that has.
Why a farmhouse-era wall is different
The walls in an older rural home may not be poured concrete at all. Stone or block walls with old mortar joints behave differently from a modern poured wall, and an injection product made for a single clean crack in poured concrete is not the right tool for a crumbling joint. Ask any contractor what the wall is actually made of, and why their method suits that material. If the answer is the same for every house, keep looking.
Permits and approvals to check first
- Building permit. King's March 2026 notice says general maintenance needs no building permit, while structural changes, excavations and new or altered plumbing do. Foundation repair is not named either way, so call the Building Division at 905-833-5321 before any structural repair or any digging against the wall.
- Septic and well. The same notice lists septic installation or repair as needing a permit. If the dig, a new sump or a drain could affect where water goes near your septic bed or well, ask before work starts rather than after.
- Heritage. King's heritage permit applies to individually designated properties and those inside a Heritage Conservation District. A property that is only listed on the register does not need a special heritage permit beyond any building permit. Confirm which applies to your house.
- Conservation authority. Part of King Township falls under the Lake Simcoe Region Conservation Authority, and other parts under other authorities. Since April 1, 2024, Ontario Regulation 41/24 governs work in regulated areas near watercourses, wetlands and steep slopes. LSRCA can be reached at 905-895-1281 or regulations@lsrca.on.ca to check a property.
Sealing and radon
Health Canada's radon guideline is 200 Bq/m³ in the living areas of a home, tested over about three months. Radon programs describe sealing cracks as helpful but less effective than a professionally installed mitigation system. So seal for water, and test for radon separately, ideally before and after the work.
What it typically costs
Canadian price guides put crack injection at roughly $500 to $1,500 per crack, with epoxy and polyurethane priced similarly and a lower per-crack rate when several are done together. That is a general national estimate, not a King Township price. Exterior excavation to reach a leaking wall costs far more. Get at least two written quotes that name the material and the method.
Quick answers
Can I seal a basement crack myself?
You can seal a narrow, dry, stable hairline crack yourself with a masonry or polyurethane product. Anything wider than about a quarter inch, wet, horizontal, or still growing should be looked at by a professional first.
How much does foundation crack injection cost in Ontario?
Canadian price guides put crack injection at roughly $500 to $1,500 per crack. Treat that as a general national estimate; length, access and whether it is leaking all move the price.
Does sealing a crack stop radon?
Not reliably. Health Canada's guideline is 200 Bq/m³, and radon programs describe sealing as less effective than a proper mitigation system. Test for three months, then decide.
Do I need a permit to seal a foundation crack in King Township?
A small surface seal is general maintenance, which King's building permit list says needs no permit. Structural repair or digging around the house is different, so call the Building Division first.
When should I call an engineer instead of a crack-sealing company?
Call an engineer if a crack is horizontal, stair-stepped, wider than about a quarter inch, or visibly growing. Sealing a moving wall only hides the problem.
Before you pay anyone to seal it
Find out whether the crack is moving, what the wall is made of, and which approvals apply. If you want a fixed price for the sealing itself, Rhodex can arrange one.
Related reading
- More home repair guides for King City
- All Rhodex services: get a fixed price
- Window and Door Resealing on an Older King Township Home
- Septic System Maintenance and Small Repairs in King Township
- How Do Building Permits Actually Work in York Region?
- Drywall and Plaster Repair in an Older King Township Home
Not sure what's actually going on?
Every home is different, and home repair or renovation problems don't always match the textbook case. Describe your specific situation to Rhodex's AI Advisor and get a straight, honest answer — free, no obligation.
Ask the AI Advisor about your home repair or renovation question →