Do I need to replace the garage floor when converting to a living space in Ottawa?

Whether you need to replace the garage floor depends on the condition of the existing slab, how you plan to insulate, and how you want the finished room to feel. In many conversions the existing slab can stay with modifications, but sometimes removing it and pouring a new one is the better long-term choice.

Start by assessing the slab. Walk the whole floor and look for wide or displaced cracks, areas that have tilted or sunk, and signs of moisture such as staining or white mineral deposits. Clay and silt soils are frost-susceptible, and a slab on poorly drained ground can heave or settle over the years. Significant structural cracking or movement usually points toward replacement. Minor surface cracks and small level differences can often be handled with a levelling compound. Ask your contractor or an engineer to look at anything that worries you.

Moisture is the critical factor. Many garage slabs were poured without a vapour barrier underneath, so ground moisture can move up through the concrete. In a heated room that moisture can damage flooring and encourage mould. A simple check is to tape a square of clear plastic sheet tightly to the floor and leave it for a couple of days. If moisture appears under it, you have moisture coming through that needs to be dealt with before finished flooring goes down.

If you keep the slab, the usual approach is to lay rigid insulation over the concrete, add the vapour control your designer specifies, then a plywood subfloor and finished flooring. This raises the floor, which creates a step at doorways and may mean adjusting door frames. The insulation you can fit this way is limited by how much height you can give up, so ask your designer whether it meets the energy target for the project.

Replacing the slab means breaking out and removing the old concrete, excavating, placing drainage gravel, a vapour barrier and rigid insulation, and pouring a new slab. It costs more, but you keep the original floor height, get a fully insulated floor, and can embed in-floor heating, which makes a big difference to comfort through winters that regularly reach well below -20°C. Ask for itemized quotes on both approaches.

Do not forget the floor drain if your garage has one. When the space becomes living area, the drain has to be dealt with properly so sewer gas cannot get into the room, either by permanently sealing it or keeping it trapped and protected. Plumbing alterations are on the City's list of permit work, and plumbing is a compulsory trade. Your designer will confirm what the City requires.

Compare itemized quotes from renovation contractors in the Ottawa Construction Network directory.

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