An attic feels like free square footage, particularly when the garage is full. The boxes look light one at a time. Their combined weight has a less casual opinion.
A ceiling structure is not automatically a storage floor
The Structural Building Components Association's load-path explanation explains how loads and bearing points belong to the truss design. Ask for the original design information and an assessment of the proposed storage area. The guide supplies background, not a capacity calculation for your Ontario house.
Count the practical losses too
Safe access, service routes, insulation depth, and attic ventilation can all restrict the usable area. Do not compress insulation to make a larger platform or treat the ceiling between members as a walking surface. Describe what you actually want to store; dense books are different from empty luggage.
Before the next step
- Retrieve the truss drawings where available.
- List the intended items and their approximate combined weight.
- Have access, insulation, and storage loading considered together.
The best storage plan has an honest limit. A smaller approved area is more useful than an entire attic whose capacity everybody is guessing.