Moisture Control in Homes
Part 3 of 3. See May and June 2005 issues for parts 1 and 2.
Managing External Water
Neglecting moisture and water problems in and out around dwellings can produce conditions that support mildew within the house and wood-destroying fungus attack the structural members. Management of both surface water and moisture vapor can prevent the conditions required to support mold and fungi growth. Some of the most common external moisture problem areas and their suggested solutions follow.
Lot Drainage
The grading and landscaping plan for every dwelling should provide control of surface water on the lot. One minimum standard requires a two percent grade sloped away from the house in all directions for a minimum distance of 10 feet, or about 21/2-inch drop in 10 feet. This is intended to prevent surface water from collecting alongside and under the house.
It is not unusual for the lots of the houses about 25 years old and older to need a complete renovation of the landscaping and grading. Additions to the landscape plan, maturity of shrubbery and some soil erosion tend to change drainage patterns and direction and too often surface water meanders against a foundation wall.
The illustration below shows the most common drainage problem of a sloping lot. The uphill side of the house must have a drainage waterway (valley) to conduct the water around the house. This drainage valley should be at least 10 feet away from the house and sloped to conduct the accumulated water away from the dwelling efficiently.
Illustration A on the top right shows the ease of obtaining drainage away from the foundation when the house is on the crown of a hill. Unfortunately, most houses are located on lots that have drainage problems illustrated in “B” and “C” below.
Illustration B (right, middle) shows a typical drainage problem of a house on a sloping lot. Field studies indicate most speculative houses have some seepage of water collecting under the house due to water accumulating on the uphill side and seeping through a foundation wall that is not waterproofed in any manner; nor is a footing drain installed. When the soil is saturated, the hydrostatic pressure tends to release a significant amount of water into the crawl space through the masonry foundation wall.
Illustration C (bottom) shows a house on a “flat” lot. During construction, the topsoil is usually removed from the house site, making the finish grade around the house one or two feet above the soil level of the crawl space. “Flat” lots also tend to have high water tables, especially during long, rainy periods. Developers and builders would do the homeowner a lasting service if the soil in the crawl space was brought to a level equal to the outside finished grade. This, in turn, would require the foundation to be higher by a foot or so, but would permit effective footing drains with an outfall near the house.
Gutter Water Management
Two basic methods used to manage gutter water are illustrated in the two drawings.
The first drawing shows a masonry splash block, a precast concrete product designed to receive the gutter water from the downspout. Its function is to prevent erosion and rapidly conduct and release the water at least two feet from the foundation wall. Positive drainage away from the house prevents water from accumulating near the foundation wall. Some splash blocks are made of plastic, but lack the sturdiness and durability of masonry concrete.
Waterproofing
If the walls are in place without opportunity to dig around the foundation:
1) Be sure the lawn is well-graded away from the house. If the soil level close to the house is too low, apply top soil sufficient to have the lawn grade away from the house.
2) Mix a special cement-based, waterproof material to apply to the interior of the concrete wall. Pay particular attention to the crack between the wall and the concrete floor.<
Reprinted with permission from the University of Georgia, College of Family and Consumer Services
Dorman, D. (1997). Moisture Control in Homes. Athens, GA: University of Georgia, Cooperative Extension Service
To Read the Full Article
ASHI offers its members unparalleled resources to advance their careers. ASHI offers training for inspectors at all levels of knowledge and experience, including resources about all major home systems. Members benefit from a vast network of experienced professionals, providing a community for mentorship and knowledge sharing..
In this Issue
FIND A HOME
INSPECTOR
Professional Networking
Grow your professional network, find a mentor, network with the best, and best part of the community that’s making home inspection better every day.
