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A thin layer of asphalt-based dampproofing is applied to nearly every foundation wall. Some people think this is a waterproof layer, but it isn’t designed to stop liquid water and won’t bridge cracks where water can enter.

The building code requires at least dampproofing on all foundations, and only on foundations that are exposed to pressure. All is fine when the foundation drainage system is working well. If the system doesn’t work or you get an inch of rain in one hour, all bets are off, and you may wish you had paid more for a waterproof foundation.


Most foundations have a thin layer of asphalt applied to them. The purpose of dampproofing is to stop the water from entering the house. If you backfill with a well-drained, granular material next to the foundation wall, or a drainage board that provides a capillary break, dampproofing will do a good job of keeping water from entering.

The small cracks that develop in concrete walls and slabs will not be fixed with dampproofing. It is not possible to prevent basement leakage or flooding with dampproofing.


If you plan to use the below-ground construction as living space, or want to provide that option in the future, then you should considerUpgrading from dampproof to a full basement waterproofing system. Most systems start with a heavy spray-on coating that can bridge cracks and keep water out of the system.

A common entry point for water is the joint between the foundation wall and the footing. Before applying the waterproof coating, it is important to clean the dirt out of the joint.

A layer of protective board over the coating of the system protects it from damage during backfill and settlement of the soil. A foam or insulation board can be used.

I am skeptical of the claims that some coating do not need a protective layer, and that some mats are marketed as complete waterproof systems. If it sounds too good to be true it probably is.

Drainage Boards & Mats

There are a number of products that provide a break against the wall. They are designed to eliminate the need for backfill. Some are used in conjunction with a spray-on coating, while others are not.

Some insulation products include foam made with vertical drainage grooves or insulation boards that provide both drainage through the open matrix of the fibers.

Foundation products have a hard life. Excavation contractors don’t always do their job well. The boards can be damaged during backfill, dragged down as the soil is attacked by insects, and damaged at grade level. The attachment details are important.

It is important to pay attention to the end at the top. Some are more secure than others and run the risk of being damaged or buried. The insulation on the exterior of the building continues up to the wood frame, so there is no reason to worry. It can be difficult to protect the exposed foam above grade.

Some of the more popular sheet products include:

The gap between the wall and the plastic sheets is about 12 inch. Platon Air-Gap is one of the widely available products basement waterproofing. It is important to choose a product that is strong enough to resist being crushed.

The filters are laminated to a layer of fabric to protect against clogging. Platon DoubleDrain, Delta-Drain and CCW Miradrai are products.

The air gap is formed by a tangle of plastic fibers. The best known is Enkadrain, a product that uses 40% to 50% post recycled material. This product has been around for a long time.

nsulating drainage panels provide both insulation and drainage. The foam that is used in the Insul-Drain is foam with grooves for drainage. Warm-N-Dri and Drain & Dry are both fiberglass panels that insulate and drain, but Warm-N-Dri is no longer available as a stand-alone product. The new kid is on the block. The mineral wool insulation board has good drainage characteristics. Mineral wool is impervious to water, insects, fire, and a lot more.

Some materials can be used as a drainage layer and insulation. The two I am familiar with are the Insul-Drain Drainage Board and the Roxul Drainboard. Rockwool is marketed as a commercial product and is not available in all areas. It is impervious to water and insects and has some advantages. A nice, warm home can be excavated by insects.

It is less important to use backfill when there is a drainage mat that can go over it to create a drainage space and capillary break. These products are marketed as the main waterproof material. This can work with the drain system. The drainage mat may not be enough if the footing can’t drain fast enough or the water can’t get to the foundation.

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