Bowing & Leaning Wall Stabilization · Kitchener

Bowing Basement Wall Repair in Kitchener

A block basement wall that has bowed an inch will bow two. Clay does not get tired. The method that holds it depends on how far it has already come in, which is why the first thing that happens is a string line across the wall.

The horizontal crack a few courses below grade, with the wall above it leaning into the basement, is the most common structural foundation problem in Kitchener. It shows up in the concrete block foundations under the 1960s and 70s houses in Forest Heights, Stanley Park, Centreville, Rosemount and Country Hills, and in older block walls under the post-war houses off Ottawa Street and along the Conestoga Parkway. Poured walls can lean too, but block is where it happens most, because a block wall has no steel through it and every mortar joint is a hinge waiting to open.

Why Kitchener block walls bow

Most of the city is on clay. Wet clay swells and pushes sideways against the wall. Frozen clay pushes harder. Dry clay in August pulls back and lets the wall relax a fraction, and the next wet season pushes it in again. Over decades the wall walks inward at the joint where the pressure is highest, usually a third of the way down from grade. Anything that puts more water into the soil beside the wall — a downspout dumping at the corner, a driveway sloped toward the house, a flower bed that gets watered against the foundation — makes it faster. So does anything that adds weight to the soil, like a driveway or a parked trailer beside the wall, and so do large tree roots. The foundation contractor looks at all of that from outside before deciding how to hold the wall, because bracing a wall while the cause keeps loading it is a losing game.

Measuring the deflection

A string line or laser is run from the top of the wall to the bottom, and the gap at the widest point is the deflection. It is measured at several points along the wall, because a wall usually bows most in the middle of its length and least near the corners, which brace it. The measurement decides the method. As a rule of thumb — not a code rule — a wall that has come in a small amount and is still plumb at the top can be held with carbon fibre; a wall that has come in further, or is sheared at the horizontal crack, needs steel; a wall that has moved past what the engineer will sign off on bracing is rebuilt. The engineer sets the threshold, not the contractor.

Carbon fibre straps

For a wall with early, modest bowing, carbon fibre straps are the least invasive fix. The block face is ground clean in vertical strips, a structural epoxy is applied, and a strip of carbon fibre fabric is pressed into it and saturated. The straps are anchored at the top to the rim joist or sill and at the bottom to the slab so the wall cannot continue to hinge inward. They cure to a layer a few millimetres thick, they do not rust, and the wall can be drywalled over them afterward. They stop further movement. They do not push the wall back.

Steel I-beam bracing

For a wall that has moved further, steel I-beams are set vertically against the inside of the wall at intervals set by the engineer, bottomed into the slab or a footing and bolted to the floor joists above with a bracket that can be tightened. Beams take the load the wall can no longer carry and, over successive dry seasons when the clay pulls back, some systems can be tightened to bring the wall part of the way back toward plumb. Beams take up space against the wall and have to be planned into any basement finishing.

Wall anchors

Where the outside of the wall can be reached — no driveway, deck or neighbouring house in the way — wall anchors are an option. A steel plate is set in the soil well out from the wall, a rod runs through the wall to it, and a plate on the inside is tightened against the block. Anchors pull the wall outward rather than bracing it from inside, and they can be tightened over time. They need room on the lot, and they need Ontario One Call locates before the anchor holes go in. On the tight lots in older Kitchener neighbourhoods they are often not possible, and beams are used instead.

Rebuilding a wall

A wall that has sheared and slid at the crack, lost its bond over a long length, or bowed past the engineer's limit is taken down and rebuilt. The house is shored from inside on temporary beams and posts, the wall is removed in sections, and it is rebuilt in block with reinforced, grouted cores or in poured concrete. It is the largest and most disruptive option and it is only used when bracing will not do. It is also the point at which the exterior is open and a waterproofing contractor's work — membrane and drainage — is usually coordinated at the same time, as a separate trade.

Permits and engineering

Steel bracing, anchors and any rebuild are designed by a professional engineer and built under a building permit from the City of Kitchener. The engineer inspects and signs off. The quote includes both. Carbon fibre on a lightly bowed wall is sometimes done without a permit, but an engineer's letter is still worth having if you ever sell the house, because buyers' inspectors will find the crack and ask.

What is not on this page

The water that comes in at the horizontal crack is a separate problem from the wall moving. Sealing it, adding weeping tile or a sump, or waterproofing the outside of the wall is a waterproofing contractor's work. It is often worth doing at the same time, and the two contractors can coordinate, but it is not what this site does.

Frequently asked questions

Serving Kitchener and surrounding areas. Contact us for a no-obligation quote specific to your property.