Moisture: The Root of all Maintenance

One of the primary issues in building science is the study of how moisture damages buildings and reduces the quality of life of its inhabitants. Moisture penetration can cause mold, rot, and interior damage. Serious moisture problems and their cure are often hard to solve as the physics of air flow, dew points, and vapor transmission can be complicated even with invasive inspections and the introduction of modern tools such as infrared scanning and moisture meters. As these more difficult problems will need a longer article to fully explore, let us focus instead on the more common problems faced by homeowner association and condo boards.

Leaking Foundations

Foundations are usually constructed with poured concrete or concrete block. Modern foundations are protected with a waterproof coating on the exterior surface and a foundation drain around the foundation perimeter at the base of the footing, often with an under-slab drainage system with an associated sump pump. With these operating properly, basements should be dry. If a modern foundation (less than 30 years old) experiences water infiltration, something is not working right and the source is probably surface water. If someone tells you it is due to rising ground water, be skeptical. Keep in mind the water table is the depth in the earth that is permanently saturated with water. According to the building code, modern foundation basement slabs are built above the water table. If the water table is too high, then the building will not have a basement but rather it will be built on a slab on grade. If you have any question about where the water table is, the municipal code officer or a local foundation excavating contractor can help.

Two-Step Approach

If your foundation is leaking, you need a two-step action plan. First, fix the wall problem allowing water to infiltrate into the basement and second, minimize surface water reaching the exterior of your foundation wall. As it will prove difficult and expensive to re-apply waterproofing to the exterior wall, the typical repair is a pressure injection of polyurethane or other type of foam product into cracks in the wall. The second step is just as important.

Surface water comes from a variety of sources. It can be rain or snow melting on the roof, rain falling on the soil near the foundation, or water from nearby sloping land. Roof gutters are supposed to divert water away from the building, but often they are the primary source of water to the ground around the foundation. Gutters are often poorly designed – either they are undersized in handling the flow of water off the roof area, do not have enough downspouts to handle the quantity of run-off water, or the gutter/downspout is broken or incorrectly placed.

If gutters are installed too low at the roof edge, steep roofs will create a velocity in the laminar flow of water to overshoot the gutter during heavy rain events. Downspouts often discharge their water near the foundation rather than diverting it away from the wall. I recommend adding a minimum six-feet extension to the end of the downspout. Furthermore, you should treat the drip edge area along the foundation wall as a ‘secondary’ roof. By this I mean, you should seal the drip edge from allowing water from the roof or other source to enter the soil near the foundation.

Keep in mind the soil has been cultivated and it absorbs water readily. Newer homes also have the problem of the soil along the foundation being backfill soil that is not compacted well, allowing easy water passage, in effect creating a short circuit from the roof to your basement. This soft soil also is susceptible to settlement, creating a place for water to pool or cause erosion allowing even more water to enter the soil.

To prevent this problem, you must first create a positive slope on the surface away from the foundation. A good rule of thumb is to create a slope dropping three inches over six feet. Once the proper slope is in place, cover it with 6 mil poly plastic approximately 18 inches wide along the foundation perimeter. This is your “secondary’ roof preventing water from entering the soil. Cover this waterproof barrier with stone or other suitable material to prevent the poly sheet from moving.

You may also have to slope the land nearby to prevent your neighbor’s land from contributing to your surface water. This can be done with shallow surface ditches called swales or buried ditches called French drains. This type of drain is a trench at the foot of a slope shedding water toward your home designed to intercept surface water from reaching your foundation wall. Buried in the trench is a perforated pipe to divert water. Your landscaper or property manager can provide details on available options. With a logical plan, you can have the dry basement you deserve.

Maintain proper drainage

A cost effective approach to basement waterproofing is to maintain with perimeter surface drainage conditions.  The importance of proper drainage and landscaping (mature trees) around a foundation cannot be over emphasized.  Poor drainage around the foundation is the most common cause of foundation problems and basement moisture problems.  Drainage and moisture control around the home include proper ground slopes away from the foundation.  It also includes keeping your gutters clean and the downspouts functional.  Not doing so, allows the water from the roof to overflow the gutters.  This water then runs along the foundation and in turn can cause basement seepage or foundation movement.

New Construction Basement Waterproofing

In new construction, cast-in-place concrete foundations are more resistant to water penetration than concrete block. Bituminous waterproofing should be used, at a minimum, to seal the outside of any foundation wall, however. An effective perimeter drain system should be installed to collect water from around the foundation and under the slab.

The National Association of Home Builder’s booklet on dry basements entitled, “Basement Water Leakage – Causes, Prevention, and Correction,” recommends perimeter drains on the inside and outside of the foundation. These drains should either flow downward to a gravity outlet (natural drainage) or to a sump where the water can be discharged with a sump pump.

A building built in a wet site should take advantage of additional waterproofing; a membrane system. One example of a membrane system consists of multiple layers of impervious material applied in a hot tar mopped system to the outside of the foundation. Special attention should be paid to the joint between the wall and the footing. The concrete floor and walls (whether block or concrete) should be reinforced to minimize cracking.

Existing Construction Basement Waterproofing

A water problem in an existing basement can only effectively be dealt with by:

• rewaterproofing the outside of the foundation walls and/or
• upgrading the exterior foundation drainage system

Both approaches require excavation around the outside of the foundation.

There are alternatives which will intercept the water using a channel-like system around the interior of the foundation wall to collect and guide the water into a sump and discharge it using a sump pump. These systems do not correct the water problem but they do control the water once it has entered the basement in a way that minimizes problems related to water entry. Such systems, while dealing more with the symptom than the cause, are typically less expensive because they can be accomplished from the inside.

Ultimately, when dealing with a basement water problem, the tried and true conventional methods working from the outside are still the most reliable.

Basement waterproofing and existing building, or rewaterproofing, the outside of a basement wall requires excavation to the full depth of the wall, careful cleaning of the wall surface and proper application of bituminous waterproofing. A multi-layered membrane system should be used if the surrounding water conditions are severe. At the same time, a perimeter drain system should be installed, similar to the recommendations noted above for a new foundation. If there are cracks in a wall, the cracks should be chipped out to form a V-groove along the length of the crack approximately one inch deep. The V-groove should then be sealed with a good quality epoxy or silicone caulking, filled with mortar and covered with bituminous waterproofing.

Epoxy injection

An effective, but sometimes expensive alternative, is epoxy injection into the crack. This can be done from the inside. The epoxy bonds with the concrete and creates a somewhat permanent seal against water penetration. The limitations to this system are cost and effectiveness, depending on the size of the crack. The smaller the crack, the less likely it is that full penetration injection is possible. However, before undertaking expensive excavation around the outside of a foundation, you may want to get proposals from local epoxy companies to compare the cost and potential effectiveness.

Basement water is controllable but there is no easy answer. Only the more complex and sometimes expensive approaches are truly reliable.

Peaceful Coexistence

Peaceful coexistence is sometimes an appropriate resolution to a basement water problem. While keeping water out of a basement may seem ideal, there are risks. Preventing water from entering an older stone or concrete block foundation can cause water to accumulate on the outside of the foundation walls increasing water pressure on the walls themselves. The result can and has been total failure of the foundation wall. Where the construction of the foundation wall is marginal or questionable, the better approach to water control is to permit the water to enter, collect it into an interior drainage system, guide it to a sump and pump it away.

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