GC4I team, structural engineering firm in Montreal
An existing building was designed for certain loads and a certain use. As soon as they change, or an element is damaged, the question arises: is the structure still adequate, or does it need strengthening?
Strengthening means restoring to a load-bearing element, or giving it, the capacity needed for the loads it now has to carry. It always starts with a diagnosis: you can only strengthen well what you have first understood.
Situations that lead to strengthening
- Added loadMechanical equipment on the roof, a terrace, a library or heavy storage, a clawfoot tub: the load increases where the structure was not designed for it.
- Change of useA dwelling becomes a shop, an office becomes a warehouse: the loads set by the Code for the new use can be higher.
- Opening or removing an elementRemoving a load-bearing wall, enlarging an opening, cutting a stair opening: the load has to find a new path to the ground.
- Damage or deteriorationRot, corrosion, fire, old alterations made without calculations: the element no longer has the capacity it once had.
First, assess what’s there
Before proposing a solution, the engineer needs to know what is in place: dimensions and condition of the elements, materials, supports, foundations. When the original plans are missing, which is common in plexes and older buildings, a survey and targeted exploratory openings take their place.
Checks are made under the Quebec Construction Code in force and the CSA standards it references for wood, steel and concrete. The Building chapter incorporating the 2020 National Building Code has been in force since April 17, 2025, with a transition period ending on October 17, 2026.
The weakest link
A load travels from the roof to the ground through a series of elements. Strengthening a beam is pointless if the column that carries it, or the footing under that column, isn’t adequate. So the diagnosis follows the entire chain.
The main ways to strengthen a structure
| Approach | In practice | What to check |
|---|---|---|
| Add a load-bearing element | A new beam, column or girder that creates an additional load path. | The supports and the foundation under the new element. |
| Increase the section | Sistered joists, bolted steel plates, concrete jacketing. | The connection between old and new. |
| Bonded composites | Fibre-reinforced polymer strips or fabrics, mainly on concrete and masonry. | The condition of the substrate and fire protection. |
| Reduce or redistribute the load | Move a piece of equipment, spread the load over several elements. | That the new distribution remains valid over the long term. |
| Underpin the foundations | Widened footing, underpinning, piles. | Soil capacity and neighbouring buildings. |
Bonded composites are covered by their own Canadian standard, CSA S806. As with the other approaches, the choice depends on access, available headroom, how the building is occupied during the work and the durability sought.
What you receive
- an assessment report on the existing structure, with the relevant findings and calculations;
- signed and sealed strengthening plans and specifications, with connection details;
- where needed, temporary shoring requirements during the work;
- supervision visits at key stages, when included in the assignment.
Designing the structural elements of a building is an activity reserved for engineers, except for certain residential, commercial or business buildings designed using the Part 9 solutions of the Code. Strengthening generally calls for building-specific calculations that go beyond these standard solutions.
FAQ
Can you strengthen a structure without engineering plans?
For a load-bearing element, strengthening must be calculated: the solution depends on the loads, the span and the supports. The municipality generally requires signed and sealed plans before issuing the permit.
Is sistering the joists enough?
Sometimes, but not always. You have to check the span, the loads, how the members are connected and above all the supports at the ends. A sistered joist that rests on a support that’s too weak solves nothing.
Are carbon fibre strips suitable for every building?
They are mainly used on concrete and masonry. Their use depends on the condition of the substrate, exposure conditions and fire protection requirements; the engineer compares them with traditional solutions.
Does the building have to be vacated during the work?
Not necessarily. Temporary shoring often allows work to proceed in an occupied building. The conditions are set with the contractor before the work begins.
A project that adds a load or removes a support?
Tell us about the project and attach the plans or photos you have: we’ll send you a written service proposal for the assessment and the strengthening plans.
Scope of this guide. This content is general in nature. It does not replace a site visit or an engineer’s opinion on a specific building.
Sources
- Régie du bâtiment du Québec, “Chapitre Bâtiment du Code de construction du Québec incluant le CNB 2020” (in French)
- Ordre des ingénieurs du Québec, “La nouvelle Loi sur les ingénieurs : les bâtiments” (in French)
- CSA Group, standard S806, “Design and construction of building structures with fibre-reinforced polymers”