Does a deck built over a concrete patio still need footings under the BC Building Code?

Yes, a deck built over a concrete patio still requires proper footings under the BC Building Code if the deck is more than 600mm (approximately 2 feet) above grade. The existing concrete patio does not eliminate the need for code-compliant structural support for the deck above.

The concrete patio and the deck are considered separate structural systems under the BC Building Code. Even though you have a solid concrete surface below, the deck posts must still bear on footings that extend below the frost line and are properly sized for the deck loads. You cannot simply place deck posts directly on the concrete patio surface, as this creates several structural and code compliance issues.

Proper footing installation over concrete requires either drilling through the existing patio to install footings in the soil below, or using engineered concrete footings that are properly attached to the existing slab. The first option is more common and typically more cost-effective. Contractors use concrete coring equipment to cut precise holes through the patio, then dig down to install standard concrete footings or helical piles in the undisturbed soil beneath. The holes are then backfilled around the footings.

Why the code requires this approach: The existing concrete patio was designed and engineered for its original purpose — typically to support pedestrian loads and patio furniture. It was not engineered to support the concentrated loads from deck posts, especially when you factor in live loads (people, furniture, snow), dead loads (the deck structure itself), and potential additional loads like hot tubs or planters. A 300 square foot deck can impose thousands of pounds of load on each post location.

Metro Vancouver considerations make proper footings even more critical. Our marine climate means the deck will be subjected to constant moisture, and any structural movement or settling can compromise waterproofing membranes if you're building a waterproof deck over the patio. Additionally, BC's seismic requirements mean deck posts must be properly anchored to resist lateral forces during an earthquake — surface-mounted posts on a concrete slab cannot provide this resistance.

The engineering reality is that most concrete patios are only 4-6 inches thick and were poured over a gravel base, not engineered as structural slabs. They can crack, settle, or shift over time, especially in areas with clay-heavy soils like Surrey, Richmond, and Delta. If your deck posts are bearing on the patio surface and the patio settles or cracks, your entire deck structure moves with it.

When to hire a professional: Any deck over 600mm above grade requires a building permit and professional construction, and drilling through concrete adds complexity that makes this definitely not a DIY project. You'll need contractors with concrete coring equipment, and depending on your municipality, you may need engineered drawings showing how the new footings integrate with the existing patio structure. The permit process will require showing proper footing depth and bearing capacity regardless of what's underneath.

The bottom line is that the concrete patio doesn't eliminate structural requirements — it just changes how you meet them. Proper footings ensure your deck is safe, code-compliant, and will last for decades in Metro Vancouver's challenging climate.