Wall Base

What it is.

The lowest band of the exterior wall, where the siding stops and the ground, the slab, or the foundation begins. It is the strip you never look at, usually hidden behind planting or a row of pots.

Why it matters.

Fire on the ground burns upward into whatever it can reach. Embers and burning debris settle at the base of a wall and stay there, so this band takes a long, low, sustained exposure rather than a brief one. If the siding at that height is combustible, the wall is being attacked at its weakest point with the most contact time.

What good looks like.

At least six inches of noncombustible vertical clearance at the base of the wall, such as concrete, masonry, or metal flashing, kept clear of soil, mulch, and stored items.

How it is judged.

The wall assembly itself is tested under SFM 12-7A-1 or ASTM E2707. California insurers are required to account for the wall base under 2644.9(d)(1)(B)2.e, which calls for six inches of noncombustible vertical clearance.

What we will ask you.

"Look at the bottom of your exterior walls. In the lowest six inches, is the surface concrete, masonry, or metal, or is it siding?"

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