Q. Are precast concrete foundation walls subject to the same dampproofing or waterproofing requirements as cast-in-place and block foundations? I've heard that because these walls are made of a high-strength concrete that's virtually nonporous and impervious to water, they don't require extra dampproofing or waterproofing. My building inspector disagrees.

A.Bill Palmer, former editor of Concrete Construction and president of Complete Construction Consultants in Lyons, Colo., responds: In general, concrete and masonry foundations need to be either dampproofed or waterproofed, depending on the soil conditions. Section R406.2 of the 2006 IRC requires waterproofing "in areas where a high water table or other severe soil-water conditions are known to exist" and defines several different acceptable waterproofing methods. But even normal soils contain a certain amount of water vapor, which can move through masonry and concrete, so section R406.1 requires acceptable dampproofing treatment even when walls don't need waterproofing. Most people use a black bituminous coating.

The same provisions apply to precast foundation walls — though that may change. Under conditions where waterproofing is required, precast walls need the same waterproofing treatment as cast-in-place concrete and concrete block foundations. But Greg Stutz, vice president of technical services at the National Precast Concrete Association, says the International Code Council is considering a proposal to exempt the walls from the current dampproofing requirements based on precast concrete's low permeability. "The problem right now," he says, "is really one of perception. Builders dampproof because owners and inspectors expect it — although we know that precast concrete is already dampproof."

Check with the manufacturer of your precast wall system. For example, testing performed by ICC Evaluation Service on precast foundation wall panels built by Superior Walls (800/452-9255, www.superiorwalls.com) resulted in ES Report ESR-1553 (issued in November 2006), which states that Superior Walls alone are an alternative means of dampproofing and "therefore, no additional dampproofing is required." Steve Glatfelter at Superior Walls says that this is due to the very dense concrete mix used to make the panels (5,000 pounds per square inch of compressive strength and a water-cement ratio of around 0.4) and the triple bead of polyurethane caulk used in the joints between them. With the ICC report in hand and the panel manufacturer's guarantee, both you and your inspector might be comfortable skipping the dampproofing.