The vast majority of homes have some amount of basement leakage at some point, and in most cases it's a result of exterior water management issues that weren't properly being addressed.
As a former home inspector, I continually sound like a broken record advising homeowners to do proper grading, ensure gutters and downspouts are working properly, and fix any cracks in the foundation wall and walkways surrounding the house.
These approaches are great, because they address the problem at the source, rather than trying to fix the issue after the fact.
Case in point - it's probably better to avoid that family sized cheese whiz nachos with extra jalapenos than to down a bottle of Pepto-bismol™ after the fact. But that's no fun.
Fortunately, enormous fun can be had when we stop the water leaking at the source, resulting in a dry basement space either for recreational use or as a second suite.
Sometimes We Have No Choice
As much as we'd like to save thousands (or even tens of thousands) of dollars by stopping water from the source, and not having to actually waterproof the foundation, sometimes it's unavoidable if you want to make use of that basement space.
These would include issues such as:
- Narrow lots
- Mortar based foundations (eg. from best to worse --> concrete block, brick, stone)
- High water table in soil
- Damaged or clogged weeping tiles causing water backup inside
Poured concrete foundations generally don't have issues as long as there's no water from below, any cracks are sealed, and above-ground water is well managed.
In cases where we cannot stop the water from the outside, waterproofing may be necessary.
Why Do You Want A Dry Basement?
Before we consider any drastic solutions, it's worth asking first why do we want a dry basement? It makes sense of course if you're finishing the space to make more room, or using it as an apartment.
But if the space is unfinished and not used, moisture and the occasional leaking is not a big deal. And it's probably not worth spending all that money to make a dry basement to store canned goods. In the old days, basement leakage was expected, and no one cared too much because the spaces weren't being used.
Basements are largely a northern North American phenomenon to address frost issues getting under the foundation and heaving the house. You won't find too many basements in Texas.
So let's assume we have a wet basement, need to get it dry, and we're limited in what we can do from the outside.
In this case, we can either waterproof it from the outside or the inside.
If you have to waterproof, exterior is the preferred method because even though you cannot stop the water penetrating the foundation, you can stop it from getting into the foundation wall, and having potential frost damage.
This involves excavating down to the footing, replacement or repair of the weeping tile, and adding on a few layers of materials to the wall (see diagram below).
Cost wise to do this properly, you're probably looking at about $150 to $200 per linear foot.
In some cases, exterior waterproofing is not possible. These would include situations where landscaping or utilities may inhibit proper excavation, or a very deep dig is required without much room to work with. This potentially turns in to a safety issue for the workers doing the excavation. In these cases, expensive shoring might be needed.
Some older foundation walls are also not suitable to have the adjacent earth disrupted. Think about that old compacted soil helping to support the foundation in place for 100+ years - and now it's being dug up.
These include century homes where cement was brought on site, and mixed with whatever stones or aggregate materials were found in the soil. I've been to inspections where I've scraped the foundation wall with a screwdriver and a chunk of the foundation came off - Yikes!
When outside is not possible, yet water and moisture is still entering the house, and you really want to finish the space, interior waterproofing may be a solution.
Keep in mind that the interior method is not actually "waterproofing" the foundation, since water is still being allowed to pass through the foundation wall. So it is still sort of a "band-aid" solution, but it's better than none at all in situations where you can't address the issue from the outside.
This is where you dig a small trench inside the foundation wall, place a weeping tile along the entire perimeter of the house and direct it into a sump pump, and then cover it with gravel and replace the cement. A drainage board is also placed on the interior side of the foundation wall.
Cost for this method is roughly $100 to $150 per linear foot.
Disruption To Structure
In addition to the significant costs, you also have to consider the fact that you are disrupting the structure, regardless of whether you're using the outside or the inside method.
We talked about compromising certain foundation walls when removing well-compacted soil. Although less disruptive, removing the basement slab can also affect the structure if done improperly.
This is precisely why you can't really "cheap out" on a project like this. Anyone you hire should have plenty of experience, and know the best approach, not one that's going to make them the most money. Ensure they have proper liability insurance as well as for personal safety and to cover damage.
As a reminder, most basement water issues, can be dealt with from the outside, but sometimes there's no way around it.
As mentioned earlier, it's always good to go after the cause, not the symptoms.