What is waterproofing in the construction industry?

Waterproofing is the work that keeps water out of a building. In construction it means the materials and systems that stop ground water, rain, and moisture from getting into a foundation, wall, roof, or floor. For a house, that usually comes down to managing the water around and under the basement so the living space below grade stays dry.

Here is the plain version. Soil holds water. After rain or snowmelt, that water builds up against the foundation and pushes to get in. Waterproofing is how a building fights back, either by blocking the water at the surface or by giving it a path to drain away before it ever reaches the inside.

There are two broad approaches the trade uses.

Exterior waterproofing seals or drains water on the outside of the foundation. On new construction, builders apply a coating or membrane to the outside of the wall before they backfill. On an existing home it means digging the foundation back out, which we do not do. In our field experience that exterior fix on a finished house tends to fail in about 2 to 3 years once the dig settles, so we steer homeowners to the interior route.

Interior waterproofing manages the water from the inside. This is what holds up over time for a lived-in home. A full-perimeter drain channel sits at the floor wall joint, catches the water as it enters, and carries it to a sump pump that lifts it out and away from the house.

That floor wall joint is the usual entry point. It is the seam where the slab meets the wall, and water under pressure finds it first.

Why basements take on water in the first place

When a house gets built, the crew digs a hole, pours the foundation, then pushes the dirt back in around it. That replaced soil is disturbed backfill. It is looser than the packed ground around it, so it drains slowly and holds water right up against your wall. Add a New England winter and frost heave pushes on those walls from the side. The water has somewhere to sit and pressure to push it in.

That is why a dry basement is rarely about one crack. It is about the whole water table working on the foundation.

How we handle it

For a basement we install the Forever Dry System. That is full-perimeter interior drainage, a sump pump sized at 1/2 hp for every 120 feet of drain, a 12-mil vapor barrier on the walls, and a dehumidifier to handle the air. It is 100% guaranteed to be dry for life! The warranty is transferable when the conditions are met.

A crawl space is a different animal, so it gets a different fix. We call that crawlspace encapsulation: a 12-mil wall vapor barrier, a 20-mil floor barrier, dimpled drainage matting under that floor barrier, spray-foam-sealed seams, a dehumidifier, and a sump. The Forever Dry System is for basements only, so we never put that label on crawl space work.

Cost depends on the size of the space, how the water is getting in, and which system the home actually needs. Basement waterproofing runs $3,000 to $30,000. Crawl space encapsulation runs $3,000 to $25,000. We give you the real number after a free inspection, not a guess over the phone.

One thing worth saying. Not every wet-looking basement needs a full system. Sometimes a single seeping crack just needs crack injection at $1,000 to $3,000, and you do not need the whole perimeter dug into. We will tell you that when we see it.

For backup, our sump systems use a battery, not a water-powered unit. A charged backup battery can pump roughly a residential pool’s worth of water, about 15,000 to 20,000 gallons, which is plenty to ride out a power outage during a storm.

How waterproofing fits the rest of foundation work

Waterproofing keeps water out. It does not hold up a wall that is already moving. If the foundation is cracking or bowing, that is structural work, a separate trade. See our structural and foundation repair options for carbon-fiber straps, a power brace, or helical piers. For damp-air comfort and finishing later, a dry basement is the first step. You can read the full warranty terms on the 603 guarantee.

If you want the deeper building-science background on moisture and foundations, the U.S. Department of Energy’s Building America program (basc.pnnl.gov) is a solid neutral resource. For water damage and insurance, the Insurance Information Institute (iii.org) covers what is and is not typically covered.

Ready for a dry basement?

Call us at 603-610-1770 or book your free inspection. We inspect for free, give you a free estimate, and get a quote back to you within 24 hours. Financing is available through Hearth, subject to approval, and we make nothing on it.

Related questions

Is interior or exterior waterproofing better for an existing home? For a finished, lived-in house we recommend interior drainage. Digging out the exterior of an existing foundation tends to fail within a couple of years once the backfill settles. Interior drainage to a sump is the durable fix. See basement waterproofing.

Does waterproofing fix a cracked or bowing wall? No. Waterproofing keeps water out. A moving wall is structural and needs straps, a power brace, or piers. That work starts at $850 each for carbon-fiber straps. See foundation repair.

Do I need to waterproof a crawl space the same way as a basement? No. A crawl space gets crawlspace encapsulation with wall and floor vapor barriers, not the Forever Dry System. Encapsulation runs $3,000 to $25,000.

Will waterproofing help with radon too? Sealing a foundation helps the space, but radon is its own job. A dirt or fieldstone crawl needs sub-membrane depressurization. See radon mitigation, which runs $900 to $6,000, and most homes land around $1,950 to $2,250.