Category: Interior Drainage

A sump pit (or sump basin) is the collection point for your basement waterproofing system. Without a properly sized, correctly installed pit, even the best sump pump will underperform. This guide covers how to install a sump pit yourself and what it costs to have a contractor do it.

What Is a Sump Pit?

A sump pit is a hole dug into the lowest point of your basement floor, typically 18–24 inches in diameter and 24–36 inches deep. It collects water that drains in through your interior perimeter drain or seeps up through the floor. The sump pump sits inside the pit and ejects water out through a discharge pipe.

Sump Pit Sizing Guide

Basement Size	Pit Diameter	Pit Depth	Recommended Liner
Up to 800 sq ft	18 inches	24 inches	18″ round plastic liner
800–1,500 sq ft	24 inches	30 inches	24″ round plastic liner
1,500–2,500 sq ft	24–30 inches	30–36 inches	Large basin with drainage holes
Over 2,500 sq ft or high water	30+ inches	36+ inches	Contractor-installed concrete

DIY Sump Pit Installation

Tools and Materials

• Rotary hammer drill with concrete chisel bit
• Jackhammer (rental: $50–$100/day) or sledgehammer
• Shovel and bucket for soil removal
• Plastic sump basin with pre-drilled holes ($30–$80)
• Gravel (pea gravel, 1/2 bag minimum)
• Concrete mix for patching around the basin
• Level

Step 1: Choose the Location

The sump pit must be at the lowest point in the basement, typically in a corner. It needs to be at least 8 inches from any wall to accommodate the basin and pump. Avoid placing it near electrical panels or water heaters. Check for underground utilities before digging.

Step 2: Break the Concrete

Use a rotary hammer or rented jackhammer to break through the concrete slab. Most basement slabs are 4 inches thick. Mark a circle 2–3 inches larger than your basin diameter to allow for gravel backfill and leveling. Remove concrete chunks and set aside.

Step 3: Dig the Hole

Dig down 6 inches deeper than your basin height to allow for a gravel base. The soil beneath most basements is dense and may require a digging bar. Remove soil and dispose of it — do not dump it near the foundation. Add 6 inches of pea gravel to the bottom of the hole.

Step 4: Set and Level the Basin

Lower the plastic basin into the hole. Check level in both directions. The top of the basin should sit flush with or slightly below the finished floor surface. Backfill around the basin with gravel, then compact lightly. Fill gravel holes in the basin sides if your basin didn’t come pre-drilled — drill 1/2-inch holes every 4–6 inches around the lower 2/3 of the basin.

Step 5: Pour Concrete and Finish

Mix concrete and pour it around the basin rim, feathering it smooth to meet the existing floor. Allow 24 hours to cure before setting the pump. Install a tight-fitting lid on the basin (required by many building codes and important for radon mitigation).

Contractor Costs for Sump Pit Installation

Service	Cost Range	Notes
Sump pit only (no pump)	$300–$700	Includes excavation, basin, concrete patching
Pit + submersible pump installation	$600–$1,500	Most common installation
Pit + battery backup system	$900–$2,500	Recommended for flood-prone areas
Full interior drainage + pit + pump	$4,000–$12,000	Complete system installation

Once your sump pit is installed, choosing the right pump is the next step. See our sump pump buyer’s guide for 2026 recommendations, or learn about interior drainage systems that feed into the pit.

When your basement takes on water, you face a fundamental choice: manage water on the inside or stop it at the source outside. Both approaches work, but they solve different problems at very different price points. This guide breaks down exactly when each is the right call.

The Short Answer

• Interior waterproofing is the practical, cost-effective solution for most homeowners. It manages water that enters by redirecting it to a sump pump. Cost: $5,000–$15,000.
• Exterior waterproofing stops water at the source by excavating around the foundation and applying a waterproof membrane. It is more comprehensive but also more expensive and disruptive. Cost: $15,000–$50,000+.

How Interior Waterproofing Works

Interior waterproofing does not prevent water from entering the wall — it intercepts water after it enters and drains it safely away before it reaches your floor. The system works like this:

• A channel is cut into the perimeter of your basement floor
• A perforated drain pipe (French drain) is installed in the channel
• Gravel is packed around the pipe
• Concrete is poured over the channel, leaving the pipe accessible
• Water that seeps through walls or up through the floor drains to a sump pit
• A sump pump ejects the water outside

Interior Waterproofing Advantages

• Lower cost (typically 1/3 to 1/5 the cost of exterior)
• No excavation — work is done inside, no landscaping or deck removal
• Work can be completed in 1–3 days
• Highly effective for managing high water table situations
• Can be installed year-round (no frozen ground concerns)

Interior Waterproofing Limitations

• Does not stop water from entering the wall or soil contact side of foundation
• Walls may still show efflorescence or minor staining
• Dependent on sump pump function (power outages are a risk without a battery backup)
• Does not address exterior soil drainage issues

How Exterior Waterproofing Works

Exterior waterproofing gets to the root of the problem by creating a barrier between the soil and your foundation. The process involves:

• Excavating around the entire perimeter of the foundation (down to the footing)
• Cleaning and repairing the foundation wall surface
• Applying a waterproof membrane (asphalt-based, rubber, or crystalline)
• Installing a drainage board or dimple mat to direct water downward
• Installing an exterior footing drain (also called a footer drain or tile drain)
• Backfilling with gravel, then soil

Exterior Waterproofing Advantages

• Stops water before it contacts the foundation
• Addresses root cause — damaged exterior waterproofing membrane or failed footing drains
• Can also correct grading issues during backfill
• Best long-term solution for foundations in areas with high rainfall or poor drainage

Exterior Waterproofing Limitations

• Requires excavating to the footing — 8–12 feet deep in many homes
• Destroys landscaping, patios, decks, and driveways next to the foundation
• Takes 3–10 days depending on house size
• Cost is 3–5x higher than interior systems
• Difficult or impossible on some properties (attached homes, tight lots, underground utilities)

Cost Comparison

Factor	Interior System	Exterior Waterproofing
Average cost (full perimeter)	$5,000–$15,000	$15,000–$50,000+
Installation time	1–3 days	3–10 days
Excavation required	No	Yes (down to footing)
Landscaping impact	None	Significant
Effective for high water table	Yes (with sump pump)	Partially
Stops wall moisture/staining	Partially	Yes

Which Should You Choose?

Choose interior waterproofing if:

• Your primary goal is keeping the floor dry
• You have a high water table (water comes up through the floor or cove joint)
• Budget is a concern
• You cannot lose landscaping or hardscaping
• You need the work done quickly

Choose exterior waterproofing if:

• Your original exterior membrane has failed (home is 20–30+ years old)
• You are doing major renovation work that already requires excavation
• You want the walls completely dry, not just the floor
• You are finishing the basement to living space and need absolute waterproofing
• A structural engineer has recommended exterior work

For most homeowners with a leaking basement, an interior French drain system with a quality sump pump delivers 90% of the protection at 30% of the cost. See our full cost guide for regional pricing data.

Interior French drains (also called interior perimeter drain systems or footing drains) are the most common professional solution for chronic basement water problems. Costs vary widely — and knowing what drives the price helps you evaluate quotes intelligently.

Average Cost of Interior French Drain Installation

Scope	Low	Mid	High
Partial perimeter (1 wall, ~25 ft)	$2,500	$3,800	$5,500
Full perimeter (~100 ft)	$6,000	$10,000	$16,000
Full perimeter + sump pump	$7,500	$12,000	$20,000
Full perimeter + battery backup	$8,500	$14,000	$22,000

Estimates based on U.S. national averages, 2026. Regional variation ±30%. Get 3 local quotes.

What’s Included in a French Drain Installation

A professional interior perimeter drain system includes:

• Sawcutting the concrete floor around the perimeter (typically 12–18 inches from the wall)
• Excavating the trench to footing depth (usually 8–18 inches)
• Installing perforated drain pipe surrounded by drainage stone
• Wall dimple mat or drainage board — channels water running down the wall into the drain
• Sump pit installation — a liner (crock) installed in the floor with a sump pump
• New concrete poured over the trench
• Discharge pipe running from the sump pump to outside the house

Factors That Raise the Price

Basement Size and Perimeter Length

Most contractors price per linear foot of drain installed, typically $50–$150/linear foot. A 1,200 sq ft basement with a 140-foot perimeter costs more than a 600 sq ft basement with an 80-foot perimeter.

Concrete Thickness

Older homes often have 4-inch slabs. Newer construction may have 5–6 inch slabs. Thicker concrete = more cutting time and labor.

Access Challenges

A finished basement requiring demo first, or a basement with limited access for equipment, adds $1,000–$3,000 to typical quotes.

Number of Sump Pits

Large or irregularly shaped basements may need 2 sump pits. Each pit and pump adds $800–$1,500 to the project cost.

Battery Backup Systems

A battery backup sump pump ($300–$600 in parts) ensures your basement stays dry during power outages — which often coincide with the storms causing the water problem. Always worth adding if you’re investing in a full system.

Warranties: What to Ask For

Reputable waterproofing contractors offer transferable lifetime warranties on their drainage systems. This is important — it protects you when you sell the house. Get the warranty terms in writing before signing anything, and verify:

• Does the warranty transfer to new owners?
• What does it cover — just the drain, or also the sump pump?
• Is there an annual maintenance requirement to keep the warranty valid?
• What does the company’s history look like — have they been in business long enough to honor a lifetime warranty?

French Drain vs. Exterior Waterproofing: Which Is Worth It?

Factor	Interior French Drain	Exterior Waterproofing
Average cost	$8,000–$15,000	$15,000–$45,000
How it works	Manages water after it enters	Stops water before it enters
Disruption	Interior only, 2–3 days	Major excavation, landscaping destroyed
Best for	Most residential situations	New construction, severe cases
Effectiveness	Very high if properly installed	Highest, but rarely worth the cost difference

For most homeowners dealing with chronic wet basements, an interior French drain with a quality sump pump is the most cost-effective permanent solution. See our sump pump guide for help choosing the right pump for your system.