Henri De Marne - About the house with Henri de Marne : how to maintain, repair, upgrade, and enjoy your home

Foundations take many forms, including full basements, piers, slabs, and crawl spaces. They need to be strong enough to hold up the structure, built on solid ground to avoid sinking or shifting, and protected from frost, soil and water pressure. They should be constructed in ways that help keep the house comfortable, and, when possible, provide extra space for living and for storage.

Much can go wrong with a foundation. But as you read through this chapter, youll see that similar problems keep repeating themselves: the foundation backfill is improperly done; the soil around a foundation is not properly graded or drained; the concrete is not properly cured; incorrect methods and materials are used for insulating, painting, and other finish work. Repetition is necessary because these problems manifest themselves in many ways.

Foundations for New Houses and Additions

The best time to avoid problems with foundations is while they are built. Its much easier and less expensive to avoid moisture problems, in particular, with proper design than it is to fix them later. And if mistakes are made, its probably easiest to fix them (and perhaps to hold the contractor accountable) when the house is new. The most common serious mistakes are improper backfilling of the excavation, including provisions for a working and long-lasting drainage system and grading of the soilwhich should always slope away from the house. There are also unique problems with new foundations. They include taking precautions for proper curing of poured concrete walls or choosing the right size concrete blocks for the depth of the excavation (too often, 8-inch blocks are used for foundation walls deeper than 5 feet). Once built, other problems are related to moisture in the concrete walls and floor of a basement, which may take as much as two years to dry and can cause considerable moisture problems in the living quarters.

Design of a walk-out basement

Q. I am building a house this summer. It will have a walk-out basement, which will be finished with living space. Do both sides of the concrete foundation need to be insulated? Should footing drains be on the inside and outside of the footings? What is the sequence of materials for the drain: Does the fabric go down, then the stones, the drain pipe and sand? What kind of fill do I need to backfill with to make sure my concrete walls dont crack? What is the ideal distance from the top of the concrete wall to grade? Do I need at least 4 feet of concrete below grade?

A. Lets start at the beginning. Frost walls should be below the frost line of the area where you are building. The recommended practice in your climate (Northeastern U.S.) is to have frost walls a minimum of 4 feet deep below grade. It is best to have about 1 foot of the foundation above final grade but you must plan for the final grade to slope away from the house by 2 inches per horizontal foot. Concrete walls can be insulated from the outside or the inside; there is no need to do both.

Drain pipe should be installed next to the footings and not on top of them. The best procedure is to lay a 4-foot-wide band of geotextile (filter) fabric against the excavation wall (pin it with 16-penny nails) and place 2 inches of egg-size stones in the bottom of the trench. (If stones are expensive or hard to get in your area and recycled rubber tire chunks are available, they are a better alternative anyway.)

Now lay perforated pipe, holes down, over the stones; place at least another foot (preferably 18" or more) of stones over the pipe; fold the fabric over the stones bringing it up against the foundation walls and tape it to them to hold it in place until further backfilling.

Complete the backfilling with coarse sand or bank-run gravel to within a foot of what has been determined as the finish grade to ensure good drainage and protection against frost pressure. Complete the grading with topsoil. The only time it is advisable to install footing drains inside the foundation as well is if there is a seasonal high water table or very heavy soil.