We know nothing about basements. This is going to be our first experience with a basement. Our previous homes were all on slab. So we're really nervous about basement leaks. I read a lot of horror stories out there.

Please educate me. Thanks.

1. The natural water table. Groundwater levels vary seasonally and from year to year. It is important to build the basement floor level higher than the highest level of the water table. If this is not possible, an inside sump and dewatering system is essential. Water will inevitably enter the basement if the surrounding ground water table rises above the floor level. It is VERY important to learn about the natural groundwater table before you do anything else.

2. Perimeter drains and waterproofing. French drains around the perimeter of the foundation must be built properly with perforated pipe, porous granular drain rock, and geotextile fabric, to collect liquid water while filtering sediments. Additionally, the exterior of the foundation must be coated with multiple layers of asphaltic emulsion to make a waterproof membrane.

3. Surface drainage- the grade outside the home should slope away from the foundation on all sides. The downspouts from the roof shall be diverted into the storm drain system, or into solid pipes discharging at least several feet away from the foundation.

If research indicates the groundwater table is ever at or above the level of your basement floor, you need to design a dewatering system for INSIDE the basement walls. A perforated pipe around the inside perimeter of the foundation, under the slab, some weep holes, a sump pit in one corner, might be a necessary secondary drainage system, if the water table is high.

Sprayed waterproofing can be used alone or in conjunction with membranes. Photo: Heather Joy Investments Ltd.

If the groundwater is well below the level of the basement, there are a number of typical waterproofing methods, such as the combination of an elastomeric coating and glass fibre /rock wool insulating/drainage boards mentioned by threeapples above.

Peel and stick membrane used for waterproofing.

Roxul Drainboard used in conjunction with spray-applied
coating. The high-density rockwool with a thermal value
of R4 both drains and insulates. Photo: Energy Source Builder

Other common methods include: applying a bubble plastic membrane, such as Platon, which may also be used in conjunction with an elastomeric coating; roll or spray applied crystalline waterproofing, such as Kryton Krystal, also in conjunction with a plastic membrane; and adhesive applied membranes.

Photo: Armtec
Here a foundation is wrapped in Platon brand plastic bubble membrane.

If the native soil is high-content clay, a free-flowing backfill may also be used. In most, but not all conditions, an external drain covered in at least two feet of freeflowing gravel is recommended or mandated.

Any competent builder should know of the appropriate solutions used in your area.

A porous board is usually placed over the membrane to allow water to drain to the footing drain system, to protect the membrane from damage from backfill and to provide thermal insulation. That material can be anything from rigid fiberglass (Warm-N-Dri from Owens Corning or Barrier Board by Tremco) to rigid plastic foam with grooves to plastic waffle sheets or a combination of materials.

Tremco makes a drainage board (Drain Star Z-Drain) that solves the problem of drainage over the edge of the footing. They also make a perimeter drain system (DrainStar Stripdrain) that eliminates the need for gravel and filter fabric.

Don't confuse "waterproofing" systems with "dampproofing" systems. Damproofing will do little or nothing to keep a basement dry.

Be very careful about using imitation products. The TUFF-N-DRI Basement Waterproofing System is installed only by contractors trained by Tremco.

Tremco acquired the TUFF-N-DRI system when it bought Koch Waterproofing Solutions in 2003.