Footing drainage needed on top of interior waterproofing system?
Hi all,
I’m in the middle of rebuilding a cabin that sits downhill from a decent slope. I already have a french drain to intercept surface water coming down from the slope, and I also have an interior waterproofing system in the basement floor that collects water from beneath the floor and pumps it out. But an engineer has recommended that I also install footing drainage on the outside of the footers that are closest to the slope. Is this necessary? Wouldn’t the interior waterproofing system ultimately move enough water to make the footing drainage unnecessary? I will say that the water table is quite high; when they redid the basement floor, it was a wet mess.
Any advice would be greatly appreicated.
Robert
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Replies
It's much better to have your primary footing drain on the exterior, where it can intercept most groundwater before it reaches your foundation. Interior drains are good as backup and to double as radon control loops, when attached to a riser.
Draining the exterior:
•Keeps water from finding and eroding pathways to the interior, whether under or over the footing.
•Keeps silt, carried by water, from accumulating on the interior, in what should be a layer of granular fill, where it will fill the pores.
•Keeps your foundation walls drier; concrete is porous and can move a lot of water via capillary action. Most people don't use the recommended capillary break(s) and end up with a damp foundation wall, which can lead to high interior humidity and/or water rising into your framing.
•Keeps hydrostatic pressure from slowly pushing your house downhill.
Will reduce the amount of time your sump pump needs to run, saving electricity and money.
In a case like yours, I would actually run two exterior drains, in case one fails and to handle higher amounts of drainage if necessary; storms are only getting stronger. I would use rigid, perforated pipe because I've seen too many flexible drains get crushed. I would have clean crushed stone on all sides of the pipes, and wrap a geo-fabric outside of the stone to keep fine sediment out, rather than using a sock system.
Have you considered moving the cabin to a dryer spot on the property?
Walta