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Basement Foundations

By HHI Staff

Many people build a house with a basement with plans to convert it into living space. Yet, much of the time basements remain unfinished and uninsulated with a high potential for mold growth and other contamination problems. Building a dry, warm, comfortable and healthy basement isn’t impossible, but it requires planning and will add some cost to building the house. 


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Easy conversion from unfinished basement to healthy living space requires insulation of basement walls, effective drainage, a heating and cooling system and measures to control contamination by moisture, radon and other pollutants.
Basements can be insulated on the exterior or interior of the foundation wall. Exterior insulation generally consists of sheets of foam boards; virtually any material can be used on the interior. Often, a 2x4 wall is constructed just inside the foundation wall and insulated just like the above-ground walls. When insulated and sealed with caulking and gaskets, basement walls will make the space, warm, energy-efficient and air-tight.

In new construction, concrete basement walls need a certain amount of time to dry out. If they are to be insulated on the interior, the work should be delayed to let the concrete dry before being covered.
A drainage system should be used on the outside of the basement walls to divert ground water away from the structure. If a sump pump is used, it should have a sealed cover. Floor drains can be run by gravity to the outdoors or to a sump pit.

A foundation coating will minimize capillary suction and diffusion of moisture through the walls. As with concrete slabs, some builders install plastic sheeting beneath or coatings on top of foundation footings to stop moisture from wicking by capillary action into the basement walls. Capillary action can be responsible for a significant amount of moisture entering a basement.

Radon-removal piping should be installed in the concrete slab of the basement floor in the event radon becomes a problem when construction is finished.
Termite Prevention
The upper row of a concrete block wall should be sealed to prevent termites and soil gases from passing into the hollow cores then into the basement. An additional metal termite shield on top may also be necessary. Unfortunately, methods of insulating a basement wall may create hidden pathways for termites to travel unnoticed between the soil and the wooden structure. 

Heating & Cooling

If a basement will be used for living space, a heating/cooling system should be designed to maintain a comfortable temperature and humidity year round. The air should also be exchanged regularly with a mechanical ventilation system.

If neither heated nor ventilated, a basement’s temperature will reach an equilibrium between the house temperature and that of the ground. Mold can become a problem during the various times of the year when the relative humidity is high. In severe cases, moisture can condense on cool walls or floors. Anything stored in a basement with high moisture levels will become food for mold. Old books, magazines, suitcases, and clothing are especially susceptible.

Little-used basements often contain a large amount of dust, some of which may find its way into the rest of the house and aggravate symptoms in people with allergies or sensitivity to dust.
Contamination Problems
Because many existing basements were not constructed with insulation or proper attention to moisture control, it can be difficult or impractical to treat them as part of the conditioned and ventilated living space.

If mold and/or radon are problems, it may make sense to seal the basement off from the rest of the house as much as possible. This is often easier said than done because there are typically many cracks and holes where air-pressure differences can push mold spores, moisture, radon and other soil gases through and between the basement and the upper floors.

There are a variety of ways to deal with radon in an existing basement; solutions generally must be tailored to the specific situation. One of the most effective methods to control radon is to connect a radon suction fan to a sealed sump pit; this depressurizes the area under the floor and the radon can then be blown outdoors.

Mold and moisture problems are extremely common in existing basements. In many cases, the only practical solution is to run one or more portable dehumidifiers or install a central dehumidifier. If moisture is a chronic issue, it’s best to find the source of the problem and take whatever appropriate remedial measures are necessary.



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Basement Foundations:  Created on May 8th, 2010.  Last Modified on May 17th, 2010


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