Make sure you’re free of moisture problems before you build that rec room

The idea that you can gain more living space by finishing your basement is seductive. For a growing family, or for a household that frequently accommodates overnight guests, it can be a sanity-saver to have separate areas. You might be motivated by the prospect of sending the kids downstairs to entertain themselves. Or if you dream of retreating to a private study or workshop, you may be inclined to start banging together some partitions and insulating every surface in sight.

Whatever your motivation, you may have an impulse to leap into the project, because a basement reno is the kind of job that lends itself well to the do-it-yourselfer’s weekend work blitz. But before taking hammer in hand—in fact, before even sketching plans for the rec room of your dreams—you should ask yourself a question, and you need to be honest. Do you have a wet basement?

Like any other form of unwanted dampness, architectural incontinence is something most people would prefer not to talk about. No reputable contractor would undertake to finish a basement knowing there are unresolved moisture issues, but the onus is on the homeowner to fess up. If you’re in denial, you could end up with thousands of dollars of damage to your new floors, drywall, and insulation—plus potential mold problems and painfully high cleanup costs.

The good news is that moisture problems can be fixed, and if you do it right you can finish that basement with peace of mind, knowing the increased living space will improve your quality of life and add value to your home.

Identifying the source of moisture is like troubleshooting a glitch with your car or your computer; it’s best to start with the easy stuff that you can remedy yourself. It’s possible that dampness in the basement is coming from within your house. Check the plumbing for leaks, and wrap insulation around any pipes or tanks that are prone to condensation. Make sure the bathroom exhaust fan and the dryer are properly vented to the outdoors. If the air in the basement seems damp, install a dehumidifier with sufficient capacity for the area in question.

Even if it becomes clear that moisture is coming in through the foundation, it’s worth trying some interventions on the low end of the cost scale. One of the common causes of a wet basement is a drainage problem around the exterior of the house. Make sure that water from your eavestrough downspouts is being directed some distance away from the foundation. If there is a place where runoff hits the ground close to the house, a pre-fab splash pad can make a big difference by deflecting the water to where it will drain away safely.

It’s essential that the ground around your foundation slopes away from the house, but modifying the grade does not necessarily involve heavy equipment. With a load of topsoil and a wheelbarrow, a reasonably sturdy person may be able to restore the slope. It’s grunt work, not rocket science. Eyeball the gradient on all sides of the house, especially where there’s evidence of water pooling near the foundation.

Remember to check behind stairs and under decks, where fill may be skimpy. A layer of decorative rock or mulch does not count as higher ground, because water flows right through. You need soil packed against the foundation and sloping away from the house.

Basement windows that are low to the ground should be protected by window wells so you can establish a good grade without having dirt close to the sill. But if you have a window well that is collecting water and causing basement leakage, it will have to be dug out to create a channel for that water to enter the drainage system.

If you live on a naturally wet site, improving the grade may not be sufficient. This is where the excavators come in. A contractor who specializes in this kind of work will dig down to expose the entire foundation wall. A bit of subterranean detective work may reveal a drainage system that is inadequate or somehow compromised. The perforated plastic pipe, or weeping tile, which is often used for water drainage near foundations, may have been crushed or clogged. Today these pipes are usually blanketed with a geotextile fabric to prevent siltation.

Installing a new drainage system involves digging a foot or two below the level of the basement floor, creating a trench around the foundation and away from the house in the direction of lower ground. (Note that a trench dug to two feet below the level of the footing must also be at least two feet out from the foundation-—at a 45 degree angle away from the foundation—to avoid undermining the footing.) The trench is filled with coarse gravel to allow water to flow through. If there is not enough natural gradient, it may be necessary to install a sump pump to get that water away from the house. While the foundation wall is exposed, it can be sealed with a special membrane to ensure that water runs down to the weeping tile instead of seeping into the basement.

On a serviced lot or a property with other houses in close proximity, it may be impractical or impossible to do all this digging. In such cases, basement walls can be professionally sealed from the inside. Still, the water has to go somewhere, so a sump pump can be installed below floor level.

Experts say it’s preferable to establish natural drainage so you’re not dependent on electricity—especially since heavy precipitation may coincide with power outages—but in some cases there’s no other way. If you have a sump pump, you should consider investing in a generator so a storm-related blackout does not result in a basement washout.

If you’ve spotted a crack on your basement wall that appears to be a source of leakage, you can hire a professional or purchase a kit to seal it. The procedure is kind of like large-scale dentistry, involving cleaning, drilling and the injection of a high-tech epoxy or polyurethane substance that fills the gap and cures to create an impermeable patch. It’s an effective remedy for one particular crack, but a foundation with one crack is likely to develop more. If the soil on the other side of that concrete is wet, there will be constant hydrostatic pressure (the pressure exerted by a liquid at rest) on the wall, and there’s a pretty good chance the water will eventually get through.

The point is, don’t start finishing the basement until you’re confident the moisture has been dealt with. It may be worth paying extra for moisture-resistant drywall and lumber and insulated sub-flooring products that provide air space over the concrete—but do not consider this an adequate defense. Any attempt to create comfortable living space underground means going against the laws of thermodynamics; you need every advantage you can get.