Basement waterproofing cost calculator

There is no single price for waterproofing, because there are several different fixes. We read six cost guides (Fixr, Thumbtack, This Old House, Modernize, UseCalcPro and LatestCost) and combined their prices for each method. The low is the middle of their lows, the high the middle of their highs.

As whole jobs, the same guides put a typical interior system at $3,000 to $10,000 and a full exterior job at $8,000 to $20,000. Only two of the six guides give a per-foot price for exterior work, and both are smaller publishers, so treat that line with more caution than the others.

Water does not always show up as a puddle. These are the signs that water is getting in, from the least to the most serious:

• A musty smell that does not go away, even with the windows open.
• White, chalky powder on the walls (efflorescence). That is mineral salt left behind as water moves through the concrete and dries.
• Peeling paint, mold or mildew on the lower part of the walls, or on things stored against them.
• Damp spots or dark lines along the floor where it meets the wall, especially after rain.
• Water coming through a crack in the wall or floor.
• Standing water after storms or when snow melts.
• Cracks that are growing, walls that bow inward, or doors upstairs that start to stick. These point to pressure on the foundation and need an engineer, not only waterproofing.

A simple test tells you whether damp is coming through the wall or is condensation from humid air: tape a square of plastic wrap tightly to the wall and leave it for a day or two. Moisture under the plastic means it is coming through the wall. Moisture on top means the air is too humid, and a dehumidifier may be all you need.

• Damp walls, musty smell, no standing water. Start with gutters, downspout extensions and grading, then a dehumidifier. An interior coating can help with damp coming through block walls.
• Water along one crack after rain. Crack injection, often a few hundred dollars.
• Water where the wall meets the floor, in several places. That is water pushing up from under the slab or through the footing joint. Interior drain tile and a sump pump is the usual fix.
• Water through the walls in many places, or a finished basement you cannot open up. Exterior excavation and membrane stops the water before it reaches the wall. It is the most complete fix and the most disruptive.
• Walls bowing, leaning or cracking in a stair-step pattern. That is a structural problem first. Get a structural engineer before any waterproofing contractor.

Watch for high-pressure sales. A contractor who quotes a full system without showing you where the water comes in, or offers a large discount only if you sign today, is a reason to get another opinion. Two or three inspections cost nothing but time and often find a simpler fix.

• Length of wall. Drain tile and exterior work are priced by the foot. One wall is about 30 ft; the full perimeter of a typical basement is 120 to 160 ft.
• Depth. A full basement means digging 7 to 8 ft for exterior work. A crawlspace or a shallow foundation is far less digging. The calculator assumes half the exterior price is digging and backfill and scales that half with depth.
• What is in the way. Decks, patios, driveways and landscaping next to the wall all have to come up for exterior work, and go back afterwards.
• Finished walls. Drywall, flooring and built-ins come out for interior work.
• Soil. Clay holds water and pushes on walls. Sandy soil drains better.
• Labor in your area. Most of a waterproofing job is labor. Enter a ZIP to scale it to your state's wages.

The per-foot price for interior drain tile already includes breaking out a strip of the floor along the wall, laying pipe in gravel and pouring new concrete over it. On a typical job the crew also seals the wall with a plastic flange or dimple board so water running down the wall goes into the drain, not across the floor.

Exterior work has more variables. Every foot of wall means digging a trench down to the footing, cleaning the wall, sealing it with a membrane or coating, laying drain pipe at the footing, and backfilling with gravel and soil. A deck, porch, driveway or mature shrubs along that wall all have to come out first. That is why contractors visit before quoting outside work, and why the range is wide.

A homeowner sees water along the base of all four walls after heavy rain. The basement has about 120 ft of wall and is unfinished.

• Interior drain tile. 120 ft × $50 / $80 / $100 = $6,000 / $9,600 / $12,000.
• Sump pump. One at $600 / $1,550 / $2,500.
• Total. $6,600 to $14,500, with $11,150 as the typical price at the US average, or about $93 a foot of wall.

The same basement dug out and sealed from the outside, at the full 8 ft depth, would run $10,800 to $27,000 for the wall alone. That is why most wet basements get an interior system and a pump.

Smaller job: one wall and a crack. If water only comes in along one 30 ft wall, interior drain tile on that wall is 30 × $50 to $100 = $1,500 to $3,000, plus a sump pump at $600 to $2,500 if there is none. Add one crack injection at $275 to $900. That is $2,375 to $6,400, a fraction of the full-perimeter price, which is why it pays to find where the water actually comes in.

The calculator covers the main fixes. Depending on the house, a waterproofing job can also include:

• A battery backup pump. Storms knock out power at the moment the sump is needed most. UseCalcPro puts a backup at $300 to $800.
• A vapor barrier on the walls or crawlspace floor: $1,500 to $3,000 in three guides (Fixr's high end is $4,000).
• Gutters and downspouts. This Old House puts gutter installation at $650 to $1,750 for a typical job; Fixr gives $3 to $30 a foot depending on the material.
• Excavation priced by volume. This Old House lists $50 to $200 a cubic yard, which is how some contractors price deep or hard digging.
• Putting things back. Landscaping, walkways and patios dug up for exterior work, and drywall, paint and flooring removed for interior work, are usually not in a waterproofing quote.
• Mold cleanup if the water has been coming in for a long time.
• Permits where your town requires them for excavation or sump discharge.

Ask each contractor which of these are in the price, and get the warranty in writing. Many interior systems come with a transferable warranty, which helps when the house is sold.

Whatever system you choose, keep the sump discharge line running well away from the house and clear of ice in winter. Water pumped out next to the foundation simply comes back in.

If you do waterproofing, quote from the inspection, not from a per-foot table. Show the customer where the water comes in and why your fix stops it.

1. Measure the wall that needs it. Not every job is the full perimeter.
2. Price materials by the foot: pipe, gravel, wall flange or dimple board, concrete to patch the floor, the pump, pit, check valve and discharge line.
3. Price labor by the day: breaking and removing the floor, digging, hauling spoil, setting pipe, patching.
4. Add the disposal and any permits. Some towns require a permit for sump discharge or exterior excavation.
5. List the options separately: the main system, a battery backup pump, a dehumidifier, crack repair. Let the customer choose.
6. Check the margin with the profit margin calculator, and include the cost of the warranty you offer.

The "Save as an estimate" button carries each fix into Koira as its own line. You can send it as an estimate with good, better and best options, and take a deposit when the customer signs.