Can I install a new patio over an existing one?

utting 100 mm of crushed stone on top of the old patio isn’t a great idea here, mainly because you also want to make it bigger. Why: Uneven settling. The old patio is a hard, stable base. The new area around it (to reach 5 m × 5 m) would sit on soil. The two areas will settle differently, so within a season or two you’d likely see dips or cracks along the line where old meets new. Drainage. Crushed stone doesn’t lock onto a smooth mortared surface. Water can soak through the gravel and sit on top of the old patio with nowhere to go. In freeze–thaw weather that causes heaving and shifting, and it can push water toward the house. Height at the house. Raising the patio can bring it too close to door sills, siding or the house’s drainage holes. Keep the finished surface well below them, and slope it about 1–2% away from the house. What I’d recommend: Lift the old patio. Keep the slabs if you want to reuse them; the existing sand base can often stay if it’s solid. Dig out the expansion area so the whole 5 × 5 m footprint is at the same depth. Lay landscape fabric, then build one even base across the whole area. For a walking patio that’s usually about 150 mm of crushed gravel, compacted in thin layers with a plate compactor. Add a thin sand bedding layer, then the pavers or slabs, with edge restraints around the outside. Before any digging, call BC 1 Call (bc1c.ca) to have buried lines marked. It’s free. It’s more work up front, but you’ll get a flat, solid patio that lasts. If you’re in the Fraser Valley and want a hand removing and hauling away the old patio, feel free to reach out. Zubir, S.H.M Moving Services