Exterior waterproofing - digging up a house you live in

What is exterior waterproofing?

Exterior waterproofing on an existing home means excavating the soil away from the foundation, all the way down to the footing, exposing the outside of the wall so it can be cleaned, treated and drained, and then putting everything back. It is the most durable approach available, because it stops water entering the wall rather than collecting it after it has. It is also a construction project rather than a service call: machinery needs to reach the wall, utilities have to be located, whatever sits in the excavation zone comes out, and the backfill will settle for years afterwards. The interior alternative is cheaper, faster and far less disruptive - and it manages water instead of excluding it. That is the trade, stated plainly.

Signs you need exterior waterproofing

• Interior drainage has already been installed and water is still arriving through the wall above it
• Seepage is coming through the middle of a wall or through a specific crack, not at the floor-wall joint
• The basement is finished or you intend to finish it, and you do not want a drain channel around the perimeter
• The wall is deteriorating from the outside - block face spalling, mortar joints eroding, coating visibly failed
• You need the space to be genuinely dry rather than reliably drained - a wine cellar, an archive, a workshop with tools
• The soil against one wall is a known problem: heavy clay, a hillside above you, a neighbour's runoff arriving
• You are already digging for another reason - an addition, a new patio, replacing a buried service line
• You intend to stay in the house a long time and want to buy the fix once rather than maintain a system

Seeing something not on this list? Browse waterproofing problems by symptom →

How exterior waterproofing actually works

1. 1

   Access is assessed before anything else - including whether it is possible

   A machine has to get to the wall and spoil has to go somewhere. A zero-lot-line house, a wall against a neighbour's property, a wall behind an attached garage, or a slope with no route for equipment can make full excavation impractical or impossible on part of the perimeter.

   Watch forA quote for the full perimeter without anyone assessing how equipment reaches the tight side of the house. Hand-digging a section is legitimate and much more expensive; it should be in the number from the start.

2. 2

   Utility locates, private lines and the things no locate service marks

   Public utility locating covers the incoming services. What it does not cover is your own buried lines - irrigation, landscape lighting, a gas line to a grill, a septic run, an old oil tank line, the electrical feed to the garage. Those need to be identified by you and the contractor together before a bucket moves.

   Watch forLocates treated as a formality. The trench runs directly along the wall where every service enters the house, so this is the highest-risk digging on any residential property.

3. 3

   Everything in the excavation zone comes out

   Shrubs and mature plantings, decks and stairs, patios, walkways, air-conditioning condensers, a section of driveway, fencing. Some can be lifted and reinstated; some are consumed by the job. This is where the difference between quotes usually lives, and it is frequently under-described.

   Watch forLandscaping and hardscape covered by the word "restoration" with no specifics. Get an explicit list of what comes out, what comes back, what is replaced with new, and what is simply gone.

4. 4

   The trench is opened to the footing, safely

   Digging a deep trench along a foundation is regulated work with real collapse risk, and the depth is not negotiable - the treatment has to reach the bottom of the wall to be worth doing. Spoil is stockpiled away from the trench edge, and the wall is not left unsupported longer than it should be.

   Watch forA deep, vertical, unsloped trench with spoil piled at the lip and crew working in it. Trench collapse is the serious hazard on this job, and a contractor casual about it is telling you something about the rest of their work.

5. 5

   The wall is cleaned, repaired and treated

   Decades of soil come off, old failed coating is removed, cracks and deteriorated mortar are repaired, and then the wall receives its membrane, drainage layer and footing drain. The assembly itself is the same one specified on new construction - that is a different page, and it is worth reading before you choose products.

   Watch forA fresh coating rolled over a dirty or damp wall to save a day. Adhesion is the whole basis of an exterior membrane and there is no second chance once the trench is closed.

6. 6

   Backfill, in lifts, with material chosen deliberately

   How the trench is refilled determines two things: whether water drains down to the new footing drain instead of ponding against the wall, and how much your ground drops over the next few years. Free-draining granular fill placed and compacted in layers does both jobs. Dumping the excavated clay back in one go does neither.

   Watch forThe trench refilled in a single pass with the spoil pile. It compacts under its own weight for years, leaving a settled trough beside the house that collects surface water and directs it at the wall you just paid to seal.

7. 7

   Settlement, grading and the year after the job

   Even well-compacted backfill settles. The finished grade should be built up so that when it does settle it is still running away from the house, and you should expect to add soil once or twice in the following seasons. Hardscape reinstated over fresh backfill can move.

   Watch forA perfectly flat finished grade on day one and no conversation about settlement. Ask who returns to top up the grade, and whether reinstated paving is warranted against movement.

8. 8

   The wall gets documented before it is buried again

   Photographs of the cleaned wall, the repairs, the membrane, the drainage layer, the footing drain and its outlet. This is the one and only time anybody will see the outside of your foundation, and you paid a great deal for the view.

   Watch forNo photographic record and no walk-around before backfill. Ask to be on site the day the trench is open - it is the only inspection that will ever be available to you.

What does exterior waterproofing cost?

Full exterior excavation is typically the most expensive option in this industry, usually several times an interior system on the same wall, and the spread between quotes is driven less by the waterproofing than by access, depth, and what has to be removed and reinstated above ground.

See the full exterior waterproofing cost guide - by material, size and region →

If the number is the problem, here are the ways people pay for it →