Adding onto a house or building up rather than out is one of the biggest projects a homeowner takes on, and it's also one of the easiest to get wrong. This category covers 15 Mississauga contractors who handle home additions and second-storey builds: rear and side extensions, second-floor additions over an existing bungalow, in-law suites, and the structural, permitting, and finishing work that comes with any project that changes your home's footprint or roofline.
What this work actually involves
A second-storey addition means removing or reinforcing the existing roof structure, building new exterior walls, tying new framing into the old structural system, and often upgrading the foundation to carry the extra load. A ground-floor addition involves new footings, foundation walls, framing, roofing, and full integration of siding, windows, and interior finishes with the existing house. Both require a building permit, engineered drawings for structural changes, and inspections at multiple stages (footings, framing, insulation, final). Mechanical trades usually need to extend HVAC, electrical, and plumbing into the new space, and in some cases upgrade the panel or furnace to handle the added square footage.
What to check before you sign a contract
Look for a contractor who pulls their own permits rather than asking you to, works with a licensed structural engineer for load-bearing changes, and gives you a written scope that separates allowances (kitchen, bath, flooring) from fixed costs. Ask how they handle unexpected conditions once walls or roofs are opened up, since additions almost always surface at least one surprise. Get references from a project of similar scale and age, not just recent kitchen jobs.
How we score these contractors
Our ranking weighs licensing and insurance, the quality and specificity of past addition and second-storey work (not general renovations), how clearly they communicate scope and pricing, and patterns in verified client feedback. The full breakdown of how we weight and verify each factor is on our methodology page. For the ranked list of all 15 firms with scores and reasoning, see our best renovation contractors in Mississauga guide.
