Can I build a deck over an existing concrete patio in Saint John NB?

Yes, you can build a deck over an existing concrete patio in Saint John, using either pressure-treated sleepers laid directly on the concrete or adjustable pedestal systems that create an elevated surface. This approach saves the cost and mess of demolishing the old patio while giving you a fresh, attractive outdoor surface.

The most common method uses pressure-treated sleepers, which are flat lumber pieces, typically two-by-fours or two-by-sixes, laid on their flat side directly on the concrete surface. The deck boards are then fastened across the sleepers perpendicular to their direction. This creates a low-profile deck that sits just a few inches above the existing patio. The sleepers can be shimmed to create a level surface even if the concrete has minor cracks, heaving, or settling, which is common in Saint John given the city's clay-heavy soils and significant freeze-thaw cycling.

The critical requirement with any over-concrete deck build is maintaining proper drainage slope. Your existing patio was originally poured with a slight slope away from the house, typically one-quarter inch per foot, to direct rainwater away from your foundation. Your new deck structure must not obstruct this drainage. Water needs to flow freely beneath the deck boards, across the concrete surface, and away from the house. This means avoiding any design that traps water against the foundation wall. Sleeper layouts should run perpendicular to the drainage direction so water can pass between them rather than being dammed.

Adjustable pedestal systems are the more modern alternative and work particularly well on concrete surfaces. These are plastic or rubber supports with threaded posts that allow you to fine-tune the height at each point. They create a uniform air gap beneath the deck surface that promotes excellent drainage and airflow. Pedestal systems are more expensive than sleepers but offer superior levelling capability, which is valuable if your Saint John patio has settled unevenly over the years. They also allow easy access beneath the deck for cleaning or inspection.

Before building over your patio, assess the condition of the existing concrete. Minor surface cracks and cosmetic wear are not a concern since the concrete is serving as a base, not a finished surface. However, if the slab has heaved significantly, broken into separate sections that have shifted, or is actively sinking, these structural issues should be addressed first. A slab that has heaved due to frost can continue to move and will push your deck out of level over time. In Saint John, where winter frost penetration is substantial, slabs poured without adequate gravel base are particularly prone to this movement.

You should also check whether a building permit is required. In Saint John, the permit requirements depend on the height of the finished deck surface above grade and its overall size. A low-profile deck built over an existing patio on sleepers is often below the threshold that triggers a permit, but confirming with the City of Saint John's building inspection department before starting is always wise. If the deck will include railings, stairs, or will be attached to the house with a ledger board, permit requirements are more likely to apply.

One advantage specific to building over concrete is that you avoid the cost of excavation and footing installation, which can represent 15 to 25 percent of a typical deck budget. The existing slab serves as your foundation, and the sleeper or pedestal system distributes the load across its surface. This makes over-concrete builds one of the more cost-effective ways to upgrade your outdoor space in Saint John.

---

Find a Deck Building Contractor

New Brunswick Decks connects you with experienced contractors through the https://newbrunswickconstructionnetwork.com:

• Hickory Dickory Decks Moncton ✓
• Duguay Construction ✓
• Larmondin Carpentry ✓