My 11-foot by 38-foot tandem garage is under the house. Rain and snowmelt drip off our cars and the water travels to the walls, damaging the drywall and anything on the floor. The drain is near the garage door, but the floor has no slope so I have to push water toward it with a snow shovel. A wet-dry vac would remove the water, but that is labor intensive and not the best solution. Can this problem be solved for $300 to $500?

First, determine how high the concrete foundation rises above the floor—it should be about 6 inches. Hammer a nail into the drywall to see if you hit concrete, and move the nail up until you hit the wooden plate.

Once you determine the height of the concrete on all four sides, snap a chalk line around the perimeter about 4 inches above the floor. Score the chalk lines with a utility knife until you cut through the drywall and can remove the bottom pieces. This will prevent it from wicking up water from the floor.

If the wall between the garage and home sits on the concrete floor, then only remove the bottom 1 1/2 inches of drywall (which leaves enough drywall in place to keep your fire-rated wall in compliance) and replace it with treated plywood. Apply marine caulk where the bottom plate meets the floor, out the thickness of the treated plywood, and between the plywood butt joints. Install the plywood with construction adhesive, not fasteners. Finally, paint the plywood with a premium grade oil paint.

Consider replacing the floor drain with a sand trap, which can take water from pipes below the floor or trenches in the floor.

Basically, a sand trap is a rectangular floor opening a minimum 18 inches wide by 36 inches long. Any inlets (pipes or drain troughs) need to be above the minimum 3-inch ABS plastic drainpipe that would enter the sand trap's side at least 6 inches above the bottom of the sand trap.

The drain will extend into a 45-degree elbow extending up to a 3-inch wye fitting which continues the drain to the sewer. On the other side of the wye, install a long-sweep 90-degree elbow and extend a cleanout to the floor surface. A 2-inch vent is required for the sand trap.

I recommend that you build a custom sand trap in place although you can purchase them pre-made. Install it over the existing drain and construct troughs, about 6 inches wide and almost the full width of the garage, on each side that slope into the sand trap.

An expanded traffic metal grate flush with the floor will allow you to drive and walk over the sand trap and troughs. It may be less expensive to size the overall system to correspond with the length and width of pre-made grates. In a residential area, you might be able to install a smaller sand trap and a 2-inch drainpipe. Check with the building department on this and to see if a permit will be required.

The concrete floor will require cuts, so contact a concrete cutting contractor for this phase. You will also need a plumber for the drain, a concrete contractor for the sand trap, and possibly a metal fabrication shop for the traffic grate. Unfortunately, this project cannot be done for $500.

Purchase a floor squeegee to help direct water to the troughs. The only other solution would be to remove the entire garage floor and install a new sloped floor to better direct water to the original drain.

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C.R.S., Inc. · Spokane, Washington · USA