A crawlspace is a shallow and uninhabitable area, usually between the soil and the first floor of the home. Crawlspaces usually provide access to the electrical, plumbing and heating, ventilation and air conditioning (HVAC) systems located below the first floor. The following general guidelines are required in new homes:
- Minimum access opening is 18 inches by 24 inches.
- Minimum access opening if mechanical equipment (i.e. if an HVAC system is located in the crawlspace) is 30 inches by 30 inches.
- Minimum clearance between the soil and joists is 18 inches and 12 inches between the soil and beams.
- Minimum ventilation, every 150 square feet of floor space, requires a one square foot ventilation opening.
Water control and management in the crawlspace is essential for maintaining a house. The most common problem associated with wet crawlspaces is that moist conditions can lead to wood destroying fungus that deteriorates exposed framing. In addition, excessive moisture is a conducive condition that can lead to infestation of wood destroying insects, such as termites. In exceptional cases, water penetration into a crawlspace can lead to the undermining of the foundation. For more information on how to deal with wet crawlspaces, keep reading.
A basement is an area below the first floor with a minimum height of 6 feet 8 inches. Basements may be unfinished and used to store personal belongings and to house the mechanical systems such as the HVAC system, electrical panel, and main plumbing controls. Other basements may have portions that are finished and used as a living area. But finished or unfinished, it is estimated that 90 to 95 percent of all basements will experience a water penetration problem.
Generally, water penetration in a basement causes more damage to personal belongings and the mechanical systems in the basement than actual damage to structure. However, excessive moisture in the basement can lead to health concerns such as mold and mildew. In addition, excessive moisture can lead to the development of wood destroying fungus and create conducive conditions that can lead to infestation of wood destroying insects such as termites.
Water or excessive moisture in the crawlspace or basement primarily results from improperly controlled surface water from rain or snow entering through or below the foundation wall.
A less frequent culprit of moisture penetration is when the groundwater in the soil (water table) rises to or above the crawlspace floor or basement slab.
Dealing with Water Penetration
When considering the most appropriate form of prevention and/or management, several factors need to be considered.
- Identifying the source of the water or moisture (90% of the time it is surface water)
- Severity of the problem
- Frequency of water penetration
- Budgetary concerns
- Foundation type (basement or crawlspace)
- Foundation material (poured concrete, concrete block, stone, etc.)
- Determining need and feasibility for prevention or management or both.
Methods for Controlling Surface Water
The easiest method to prevent surface water from entering the home is to direct the water away from the home. The simplest method to properly divert water away from the property is to use a gutter and downspout system in conjunction with proper surface grading around the home.
If gutters, downspouts and grading cannot prevent the surface water from entering the basement (or crawlspace), an exterior perimeter drain is the last method for preventing water penetration. The exterior drain collects the water that accumulates next to the foundation and redirects the water away from the foundation.
In basements and crawlspaces where water penetration cannot be prevented, water management systems such as trenches and sump pumps are used to collect the water that enters the home and redirects the water out and away from the home.
Methods for Controlling Groundwater
Groundwater that enters the basement is best controlled with a sump pump and/or an interior perimeter drain. The sump pump and interior perimeter drain collect the groundwater that rises to the basement slab (or crawlspace floor) and redirects the water away from the foundation.
Method for Controlling Excessive Moisture Vapor
All foundation materials (such as dirt floor, concrete slab and walls, or block walls) are porous and allows some moisture vapor to pass through from the exterior. In addition, the cooler temperatures in crawlspaces and basements create a condition that actually draws in the moisture through condensation. In homes where excessive moisture vapor is present, some control method should be used to prevent problems with wood destroying insects and fungus. In basements, when moisture penetration is slow, the most common method for controlling moisture vapor is with a dehumidifier. In crawlspaces, moisture vapor penetration usually comes through the soil floor and is usually controlled with a vapor barrier and crawlspace vents.
Surface Water Control
Controlling the surface water around a home is an important but often overlooked step in maintaining a home. Surface water in this case refers to water introduced to the soil when it rains. The water, if not properly controlled, could lead to water penetration and result in damage to the structure, interior surfaces, and homeowners’ belongings. In addition, hydrostatic pressure that is created when water accumulates next to or below a foundation may cause structural damage to the foundation. The best methods for controlling the surface water are contingent upon local weather patterns, the type of soil and the type of foundation the home has. However, the simplest method to properly divert water away from the property is to use gutters and downspout systems, combined with proper surface grading around the home.
Exterior Perimeter Drain
Though mistakenly referred to as “French Drains,” exterior perimeter foundation drains are designed to collect the water that accumulates next to the foundation wall and divert the water away from the home. Clay drainage tiles in older homes or perforated plastic drainage tiles in new homes are placed next to the foundation footer and covered with a minimum of 6 inches of gravel or crushed stone. The surface water that enters the soil next to the foundation flows down the wall, then following the path of least resistance, flows through the gravel and into the drainage tile or pipe. The water is then directed to either a storm sewer, dry well or, if necessary, to a sump pump to be directed away from the home.
Generally, the system is only placed next to the one or two walls that experience the water penetration problems. However, in some severe cases, the system is placed around the entire perimeter. In addition, to help prevent sediment from entering and clogging the drain pipe or tile, a filter paper is placed around the pipe (especially the openings) or gravel.
Interior Perimeter Drain
Interior perimeter foundation drains are designed to collect the water that enters through the foundation wall or rises to the slab and divert the water away from the home. Perforated plastic drain tiles are placed on the interior side of the footer, below the slab. The pipe is covered with a minimum of 6 inches of gravel or crushed stone. The surface water that penetrates the foundation wall or groundwater that rises to the slab is directed to the interior drain below the slab where it is captures. The captured water is then directed to either a storm sewer, dry well or, if necessary, to a sump pump to be discharged away from the home.
Generally, the system is only placed next to the one or two walls that experience the water penetration problems. However, in some severe cases, the system is placed around the entire perimeter. In addition, to help prevent sediment from entering and clogging the drain tile, a filter paper is placed around the pipe (especially the openings) or gravel.
Interior perimeter drains are often connected to sump pumps that direct the water to the exterior.
Clay Drain Tiles
Clay drain tiles are orange or red clay pipe sections, usually 2 feet in length with an interior diameter of approximately 3 to 3 1/2 inches. The 2 foot clay drain tiles are laid in a gravel bed. A 1/4 to 1/2 inch gap between each drain tile is maintained to allow the water to enter. The opening is then covered with a filter paper to prevent sediment from entering the pipe Clay drain tiles were the original drain tile and were replaced by perforated plastic drain tiles in the 1970’s.
Perforated Perimeter Drain Tile
Modern drain tiles are usually a 4 inch black PVC or Polyethylene plastic pipe that is perforated on only one half or side. The perforated side is placed face down so that water enters from the bottom of the pipe. A filter paper is usually place over the pipe or around the gravel bed to prevent sediment from entering and clogging the pipe.
The sump pump system is designed to capture water that enters the basement or crawlspace and redirect it away from the home. The basic sump systems include a sump pit, a sump pump, float or switch and drain line. The sump pit extends below the slab and collects the surface water that enters the basement/crawlspace or groundwater that rises to the slab.
When the water in the sump pit rises to a preset level, a float rises or pressure switch activates the sump pump. The water is then pumped through a drain line to either a storm sewer, dry well or the exterior, away from the foundation.
Trenches and Troughs
Trenches and troughs are depressions in the foundation floor that collect and funnel water to a specific location and are sometimes used to direct water to a sump pump. In crawlspaces, trenches are usually dug into the dirt floor. In basements, perimeter drain troughs are created at the junction between the slab and foundation wall.
Vapor barriers are intended to prevent the moisture vapor entering crawlspaces area. The vapor barrier is usually comprised of sheets of 6 millimeter polyethylene (plastic). The sheets are laid in rows over the soil. The edges of the sheets are overlapped and tapped to form a continuous barrier that will trap the rising moisture. In most locations, the vapor barrier is placed only over the soil and secured with weights. In some regions, the vapor barrier is continuous over the foundation wall and secured to the sill plate.
Crawlspace vents prevent moisture vapor from accumulating in the crawlspace by providing opening for the moisture to pass to the exterior. Vents are required on new homes. The general requirement is one square foot of vent opening for 150 square feet of under-floor area.