How do I get the garage floor level with the house floor for a conversion in Moncton?

Most garage floors in Moncton sit 4 to 8 inches below the main house floor level, and bringing the garage floor up to match the house floor is one of the most common challenges in a garage conversion. There are several approaches depending on the height difference, your budget, and whether plumbing work is also needed — ranging from building up the floor with a sleeper and subfloor system to pouring a new concrete topping slab.

The most common and cost-effective approach for height differences of 4 to 6 inches is a built-up sleeper floor system. This involves laying pressure-treated 2x4 or 2x6 sleepers flat on the existing concrete slab, shimmed to level, with rigid foam insulation fitted between the sleepers, and 3/4-inch tongue-and-groove plywood screwed to the top of the sleepers. A 2x4 laid flat provides 1.5 inches of height, and a 2x6 laid flat provides 5.5 inches — either can be combined with varying thicknesses of rigid foam insulation and plywood to reach the exact height needed to match the house floor. This system also provides floor insulation and creates a cavity for routing electrical wiring if needed. Budget approximately $6 to $12 per square foot for a complete sleeper floor system including moisture barrier, sleepers, insulation, and plywood subfloor.

Before building up the floor, install a moisture barrier on the existing slab. A dimpled polyethylene membrane (such as Delta-FL) laid dimple-side-down creates an air gap that allows moisture migrating through the concrete to escape without contacting the wood framing above. This is essential in Moncton's Maritime climate, where ground moisture and seasonal water table fluctuations make slab moisture an ongoing concern. Do not skip this step — without it, the pressure-treated sleepers and plywood subfloor will eventually develop mould and rot from below.

For height differences of 6 to 8 inches or more, you have two additional options. The first is a conventional framed floor using 2x6 or 2x8 joists on edge, which provides both the height needed and ample space for insulation (R-20 to R-28 between the joists). This creates a floor system similar to a standard house floor and can span the entire garage without being fastened to the slab at every point, though the joists should be anchored at the perimeter. The downside is that an 8-inch framed floor on top of a 4-inch-thick slab and frost walls consumes height from below, and you must verify that the resulting ceiling height still meets the NB Building Code minimum of 2.3 metres (7 feet 6 inches) in the finished space.

The second option for larger height differences is pouring a new concrete topping slab on top of the existing slab. This is practical for height differences of 2 to 4 inches — a self-levelling concrete overlay can be poured at 2 to 4 inches thick to bring the floor up. For larger pours, the existing slab must be structurally capable of supporting the additional weight, and proper bonding agents or mechanical anchors are needed to prevent the new layer from delaminating. This approach costs $8 to $15 per square foot and is typically done when the homeowner wants to maintain a concrete floor (for example, with a polished or epoxy-coated finish) rather than installing a wood subfloor system. If plumbing is being added for a bathroom, the slab will be cut for drains anyway — this is the ideal time to pour a new topping slab at the correct height.

The transition point between the garage floor and the house floor is critical. Even if you bring the garage floor to the same height as the house floor, the connection must be smooth and code-compliant. Remove the old garage-to-house door and threshold, and frame the opening to match the new floor heights on both sides. If a small step remains (1 inch or less), a bevelled transition strip handles it safely. Any step greater than 1 inch should be eliminated or converted to a proper ramp if the space is intended to be accessible.

One important consideration in Moncton: if your attached garage has a slab that slopes toward the overhead door for drainage (most do, with a 1 to 2 percent slope), the floor will not only be lower than the house floor but also unlevel from front to back. The sleeper system handles this easily — sleepers are shimmed to level before the subfloor is installed. A self-levelling concrete pour also corrects this slope but requires more material at the high end.

The floor levelling work itself is within the capability of experienced DIYers — laying a moisture barrier, shimming sleepers, cutting insulation, and screwing down plywood are straightforward tasks. However, if the project involves cutting the slab for plumbing, pouring new concrete, or modifying the structural connection between the garage and the house, hire a professional. Get matched with experienced contractors through New Brunswick Garages — a free service through the New Brunswick Construction Network.