What is the structural process for installing a steel lintel when enlarging a basement window opening in a concrete block foundation in Moncton?

Installing a steel lintel when enlarging a basement window opening in a concrete block foundation is a structural alteration requiring a building permit, engineered drawings in most cases, and a licensed contractor — this is not a DIY project.

That said, understanding the process helps you ask the right questions and know what to expect when working with a contractor in Moncton.

Why Concrete Block Foundations Complicate This Work

Concrete block (CMU) foundations common in Moncton's 1960s-1980s housing stock are load-bearing assemblies — every block course above the opening carries the weight of the structure above, transferred down to the footing. When you enlarge an opening, you're removing blocks that are actively carrying that load. Without proper temporary shoring and a correctly sized lintel, you risk cracking the block courses above, shifting the sill plate, or in worst cases, compromising the foundation wall structurally.

Moncton's sandy and silty soils add another variable — foundations in this area can experience minor settlement movement, which means existing block mortar joints may already be stressed. A contractor needs to assess the wall condition before cutting begins.

The Structural Process, Step by Step

Temporary shoring comes first. Before any block is touched, the floor system above the opening must be supported. This means installing temporary shoring walls or posts on the interior, typically 600-900mm back from the foundation wall, to carry the floor load while the opening is open. Skipping this step is how structural damage happens.

Lintel sizing is determined by an engineer. The steel angle or built-up steel lintel must be sized based on the span (new opening width), the load above (floor system, any walls above grade, snow load), and the block wall thickness — typically 200mm (8-inch) or 300mm (12-inch) block in Moncton homes. A structural engineer calculates the required steel size. Common residential lintels are L3x3x1/4 or L4x4x5/16 steel angle for single-wythe block walls, but your engineer specifies this — not a rule of thumb.

Cutting the opening. A contractor uses a diamond blade saw or angle grinder to cut the block courses. This is done in stages — the top course first, then working down. Block dust and debris management matters here, especially in a finished or semi-finished basement.

Lintel installation. The steel lintel is set into the block courses on each side of the opening, with a minimum bearing of 150-200mm (6-8 inches) on each end — this is the critical bearing length that transfers the load back into the wall. The lintel sits in a mortar bed, and the blocks above are tuck-pointed and re-mortared tight against the steel.

Window well and drainage. Enlarging a below-grade opening in Moncton means cutting through the exterior and installing or enlarging a window well. Given Moncton's sandy soils, the well must have proper gravel drainage at the base — a minimum 150mm of clear stone — and ideally a drain connected to the weeping tile system or daylight. Without drainage, the well becomes a water collection point that drives directly against your new window frame.

Egress compliance. If this enlarged window is for a bedroom, it must meet NB Building Code egress minimums — 3.8 sq ft clear opening, maximum 1500mm sill height from the floor. Confirm this with your Moncton building permit office before finalizing the opening size.

Practical Tips

Get a building permit through the City of Moncton before work starts — processing typically takes 1-3 weeks. Require your contractor to provide engineered drawings for the lintel if the opening exceeds 900mm wide, or if there's any load-bearing wall above. Ask specifically whether temporary shoring is included in their scope — some quotes omit it. Budget $2,500-$5,000 for the full opening enlargement including lintel, window well, and new window, though structural complexity can push this higher.

New Brunswick Basements can match you with experienced Moncton contractors who handle concrete block foundation work — get matched for a free estimate through the New Brunswick Construction Network.