Keeping weeds, overgrown shrubs and soil mounds away from a building's foundation provides many maintenance advantages. Better air flow, and improved access, viewing and moisture drainage all occur when the foundation is free of debris. Placing organic mulch or inorganic ground cover such as gravel around foundation diminishes weed growth and helps to make a building look tidy and well-maintained. Laying gravel around a building foundation has benefits and disadvantages, all depending on soil type and grade. Gravel beds around a foundation are safe as long as they do not impede water drainage or keep the adjacent soil too moist, which encourages termites.
Unlike ground covers such as organic mulch, gravel does not absorb moisture. Gravel particles shun precipitation, allowing moisture to move away from the building's foundation. A gravel layer that is 2 to 3 inches thick suffices, and too much gravel can impede water's movement. Gravel surrounding a foundation reflects more sunlight than some other ground covers. Exposed gravel also heats in sunlight more thoroughly than organic mulch, and then it radiates the heat at night. That process melts ice and snow more quickly than mulch. Gravel around a foundation is no guarantee that termites and other pests will not be problematic. All ground covers -- including gravel -- can keep the soil below them moist, a condition preferred by termites when developing a colony.
While water may drain through gravel placed atop soil around the building foundation, the underlying soil's profile determines overall soil drainage. Sandy soils drain well naturally, but compacted loam and clay soils tend to shun water initially then hold large amounts of water when fully moistened. Drainage is slower in fine-particle clay soils. Placing gravel around a foundation that has compacted or clay soil may slow the movement of rainwater. The gravel may hold and slow the movement of surface water runoff, too, allowing it to stand or soak in and make a dense-particle soil hold more water than desired. If the water table is close to the soil surface, poor drainage beside a foundation is a perennial issue and requires even more resources to resolve.
Soils with good drainage are the best kind to cover with decorative gravel around building foundations. The soil, however, always must slope away from the foundation to ensure proper drainage; a minimum of 6 inches of drop for the 10 feet adjacent to the building is necessary. Flat soil or back-angled grades prevent precipitation from draining away from the foundation, potentially leading to underground concrete cracking and/or wood rot. Do not lay gravel next to the foundation if the soil does not already slope away from the foundation. The gravel can act like a dam, preventing timely movement of water runoff and slow evaporation of water from the soil surface.
Small gravel, including construction- or road-grade gravel that contains clay, drains water away from foundation more slowly than clean, large-particle gravel. Sloping the topsoil away from the foundation is essential before laying down gravel because it ensures drainage occurs at the soil surface under the gravel. As with organic mulches, do not pile rock against foundation cracks or wood eaves. Exposure to air and sunlight increases water drainage and decreases the time necessary for all parts of the foundation to dry. Gravel can be useful in preventing soil from splattering onto siding and basement windows. It also can diminish erosion -- washout from a downspout or roof after rain falls -- around the base of a building.