Downsides to retrofitting old home with interior drain (vs. exterior)?
In a perfect world, an exterior footing drain and some sort of vapor barrier and/or gravel under the slab as well would be the solution to keeping a basement dry.
However, for those with older homes with neither… is an interior solution both sufficient and long term?
Obviously for surface water, grading and gutters is crucial but if you want to completely finish a basement, I expect it’s needed to manage the water effectively that does get to your foundation and footers. Heck, it seems important even if only for longevity of your foundation.
But is an interior solution enough? And what exactly is it intended to solve?
Are interior drains going to solve water on the outside of the foundation that manage their way from the surface soaking soil next to your foundation and even creating moisture/water within foundation (or even in your cinder blocks)? In that instance… wouldn’t the act of water pulling into your foundation, even if it is then kicked out via weep holes and a interior drain, deteriorate the foundation slowly?
Or is the above really not an issue if surface water is solved via gutters and grading?
Then interior drains are simply a solution for ground water rising up beneath the foundation both from outside and inside below slab. As this water rises, both an interior and exterior drain would do the same thing… no?
I really would like to understand the science behind these systems and what downsides I’m looking at with an interior system for older home. It just seems like disturbing the compacted soil around my home, landscaping, stoop, concrete path and driveway, etc… all is expensive, time consuming and might not be worth the extra effort.
But maybe it is… it’s hard to find the right information though.
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I think it will depend on site conditions - my house for example, is on a hill, with rocky soil that drains well. I had the hose blow off my jet pump, it pumped full force into the dirt crawlspace for several hours, and there was no evidence by the next day. My sister, on the other hand, has dual sump pumps because if one fails, they will have a flood.
You need to know the water table relative to your foundation ( all year. It will change) and how well the soil drains. If, for example, your house is sitting on a thick layer of gravel, a single point drain will make a lot more difference than if it is sitting on dense clay.
As to it damaging the foundation... I'm sure it's not ideal, but water against the foundation I don't think is a huge deal if it isn't freezing. Not any kind of an expert, though.
Edit: and happy new year! In my time zone, I'm the first post of the year!
J,
Q. "Is an interior solution enough?"
A. If you have an old house with water entry problems, finishing your basement is always risky. If you don't want to accept the risk, you should build an addition or a third story.
If you are willing to throw enough money at the problem, you can get close to a bulletproof solution -- but you might not like the resulting ceiling height, and there remains some risk to all approaches.
Redundancy can be provided by installing two sumps, each with its own sump pump (and battery backup for the sump pumps, of course).
You can install dimple mat on the floor and walls, to provide channels allowing water to reach your new interior French drains.
You can install a rubber membrane and a layer of rigid foam insulation on the interior side of the dimple mat.
All of these details are good details -- not cheap, but high quality.
As I said, there is still risk. Sometimes a basement is just a basement -- it's not destined to be a living room or a home theater.
Take a look a this GBA blog resource as well, particularly the Hammer & Hand approach:
https://www.greenbuildingadvisor.com/article/installing-basement-waterproofing-from-the-negative-side.