What is the best slope for a concrete patio for drainage in New Brunswick?

The standard drainage slope for a concrete patio in New Brunswick is 1/8 to 1/4 inch of fall per foot of distance — a 1-2% grade that moves water efficiently off the surface without creating a noticeably tilted patio.

For a patio 12 feet deep (measuring from the house outward), a 1/8-inch-per-foot slope means the outer edge is 1.5 inches lower than the edge against the house. A 1/4-inch-per-foot slope drops the outer edge 3 inches over the same distance. In practice, 1/8 inch per foot (about 1%) is the minimum you should use for a concrete patio; 1/4 inch per foot (2%) is preferred and provides more reliable drainage, especially as the patio ages and any frost heave effects reduce the intended slope over years.

Why drainage slope matters so much in NB. New Brunswick receives significant precipitation year-round — average annual precipitation in Moncton is around 1,100 mm, with Fredericton and Saint John receiving similar amounts. Spring thaw brings saturated soil and heavy runoff. Summer thunderstorms can dump 50+ mm of rain in an afternoon. A patio with insufficient slope turns into a standing-water problem that accelerates freeze-thaw damage at the surface, creates icy patches in shoulder seasons, and pushes water toward your foundation where it causes much bigger problems.

The slope must move water away from the house — this is the most important directional requirement. Never slope a patio toward the foundation wall. Even a minimal slope toward the house concentrates water against your foundation over months and years of rain events, increasing hydrostatic pressure and the risk of basement moisture infiltration. In situations where the backyard grade makes it challenging to slope away from the house, a central drain or linear drain channel at the outer edge of the patio connected to a proper drainage system is a better solution than compromising on drainage direction.

Building the slope into the base. The drainage slope must be established in the compacted gravel sub-base, not created by varying concrete thickness. Varying the concrete thickness to create slope leads to thin spots in the slab that crack first under frost heave and load. Set the forms at the correct heights to create the proper slope across the entire surface, and pour the concrete to a uniform 4-inch thickness throughout.

For patios adjacent to retaining walls or in yards with complex drainage patterns — situations common on hilly sites in Fredericton and Saint John — consult with a local concrete contractor who can assess the site drainage and recommend additional measures like weeping tile or catch basins. New Brunswick Concrete can connect you with experienced patio contractors in your area.