Hydrostatic pressure refers to the pressures caused by water pushing against slabs and foundations, particularly underground concrete block or poured concrete walls of foundation and crawlspaces. Water is dense and weighs about 60 lbs. per cubic foot of volume and is therefore capable of generating immense hydrostatic pressure on anything that restricts its natural movement or flow.

The weight and pressure of the dry soil may affect and crack a foundation. There is wet soil that can exert a force against a foundation.

Collar Ties

Collar ties span between and connect opposing rafters, and they are typically placed in the top third of the attic spaces. Collar ties hold the rafters down against the ridge board and, to an extent, help prevent rafter spread. Home inspectors should take note of attics without collar ties, especially where the rafters run perpendicular to the joists. Collar ties must be at least 1x4 (nominal) and spaced not more than 4 feet on center. A lack of collar ties may allow roof rafters to separate and cause sagging of the roof's ridge and structure.www.nachi.org