Crawl Space Sump Pumps

Not every crawl space needs a sump pump—assess your specific water infiltration situation.

You Need a Sump Pump If:

• Standing water appears after rain or during wet seasons
• Soil remains consistently damp or muddy
• Water seeps through foundation walls or floor
• High water table visible during excavation
• Natural springs or groundwater sources present
• Perimeter drains cannot handle groundwater volume

You May NOT Need a Sump Pump If:

• Crawl space stays dry except during extreme weather
• Proper grading and gutters handle surface water
• No evidence of groundwater infiltration
• Soil remains dry between rain events

Critical Timing: Install sump pumps BEFORE vapor barriers. Trapped water under barriers creates hydrostatic pressure and causes barrier failure. Address drainage first, then encapsulate.

Signs of Groundwater vs. Surface Water:

• Groundwater: Water appears from below, soil stays wet, happens even without rain
• Surface water: Only during/after rain, tied to poor grading or gutter problems

Fix surface water issues with exterior grading. Address groundwater with sump pumps and drainage systems.

Float design significantly impacts performance in crawl space applications.

Vertical Float Pumps:

• Float rises straight up to activate switch
• Less water needed: Activates at lower water levels
• Less space required: Fits smaller crawl space basins
• Faster response: Immediate activation as water rises
• Fewer hang-ups: Less prone to debris or tight space interference
• Preferred for crawl spaces: Better suited to compact installations

Horizontal Float Pumps:

• Float swings outward to activate switch
• Requires more water volume to activate
• Needs wider basin for swing clearance
• Slower activation as water must rise higher
• More prone to binding in tight spaces
• Better for larger basement sumps

Why Vertical Works Better in Crawl Spaces:
Crawl space access limitations often require smaller basins (11-18" diameter). Vertical floats operate reliably in these compact spaces, while horizontal floats need 18-24" minimum diameter to function without binding.

Bottom Line: Choose vertical float pumps for crawl space installations. Horizontal floats work for large basement sumps with space constraints not an issue.

Basin size depends on water infiltration rate and pump capacity.

Standard Sizing:

• Light infiltration: 11-14" diameter adequate
• Moderate infiltration: 14-18" diameter recommended
• Heavy infiltration: 18-24" diameter required

Factors Affecting Size:

Water Volume:

• High infiltration rates need larger basins for temporary storage
• Prevents pump from short-cycling (turning on/off rapidly)
• Allows pump to run in longer, more efficient cycles

Float Clearance:

• Vertical floats: 11" minimum diameter
• Horizontal floats: 18" minimum diameter
• Ensure float moves freely without binding

Access Constraints:
Crawl space access doors limit what fits through. Standard one-piece basins up to 18" diameter fit through 20"×32" doors. Larger basins require:

• Bigger access doors, or
• Two-piece basin designs that assemble inside crawl space

Depth:

• Standard: 18-24" deep
• Provides adequate water storage between pump cycles
• Bottom sits below floor level for effective water collection

Pro Tip: Slightly oversized basins prevent short-cycling and extend pump life. Better to have extra capacity than insufficient storage.

Proper discharge location prevents water from returning to your crawl space.

Minimum Distance: 10-20 feet from foundation

Discharge Options:

1. Daylight Discharge (Most Common):

• Route to surface away from foundation
• Discharge onto sloped ground that drains away
• Use splash block or erosion control at outlet
• Never discharge toward neighboring properties

2. Yard Drainage System:

• Connect to existing yard drain network
• Route to swales or drainage ditches
• Ensure system capacity handles added volume

3. Storm Sewer (If Permitted):

• Check local codes—many prohibit this
• Some municipalities allow with proper permits
• Professional installation recommended

4. Dry Well:

• Underground gravel pit for water absorption
• Good for areas without surface drainage
• Size based on soil percolation rate

What NOT to Do:

• Never discharge into crawl space perimeter drains (overloads system)
• Never terminate near foundation (water returns)
• Never discharge into sanitary sewer (illegal most places)
• Never discharge uphill (water flows back)

Discharge Line Requirements:

• Slope away from pump (prevent backflow)
• Minimum 24 feet length for proper distance
• Check valve prevents water return
• Insulate if line runs through cold areas