25th Foundations
Illustration: Ian Worpole
A proper foundation does more than just hold a house above ground. It also keeps out moisture, insulates against the cold, and resists movement of the earth around it. Oh, and one more thing: It should last forever. No wonder builders like This Old House general contractor Tom Silva take foundations seriously. "Without a good one," he says, "you're sunk."

For Tom, "good" means steel-reinforced foundation walls and footings made of poured concrete. By comparison, all the laboriously assembled foundations of stone, brick, and mortar that have supported buildings for centuries—even the walls of concrete block that most builders were using when This Old House was launched 25 years ago—are just crack- and leak-prone dinosaurs.

But a good foundation requires a lot more than digging a hole and pouring some concrete into forms. It must be tailored to its site like a custom suit, taking into account soil conditions, water tables, even the quality of the backfill. And as with a custom suit, every detail must be perfect: the base properly compacted, the formwork set up right, the concrete free of voids. Neglect even one of these, and the most carefully poured foundation can fail. Until a better method comes along, here's how Tom builds a foundation that lasts.

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