Do I need a French drain?
I have a walkout finished basement in a new residential project, and I’m curious whether it even makes sense to include a corrugated French drain. The homesite is the crest of an old glacial moraine and it’s on a combination of soil, gravel and rock with very good natural drainage (per the septic perc test). French drains are not required by code and many builders here skip them.
Would it be wise to skip the French drain and just fill the foundation excavation a foot or so with sewer rock covered with fabric to keep the footings dry, then backfill with natural materials? Of course there’s no real downside to adding a French drain, but if there’s no real significant upside I’d rather put my time/money into just laying more sewer rock around the footings.
Location is Anchorage, Alaska. Photo of the current state of the project attached.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Paxson, a French drain is typically close to the surface, essentially a filled-in ditch. It sounds like you're talking about a footing drain? If you have freely draining soil and no fines in the surround soil to create clogs, it may not be necessary. But it's cheap insurance and will help ensure your foundation stays dry for a long time.
(A bit of fascinating history about the term "French drain": https://www.washingtonpost.com/local/ever-wonder-why-its-a-french-drain-its-got-nothing-to-do-with-france/2015/07/15/5b7f326c-2b15-11e5-bd33-395c05608059_story.html)
Thanks for the clarification Michael. It looks like the term "French drain" has become kind of a catchall for perforated drains that protect the foundation. I guess I'm referring to a "footing drain" specifically. I was also planning on adding a surface drain to keep bulk water away from the home since I'm just under the crest of the moraine.
Paxton,
You are looking at maybe $250 to run it along the high wall and sides. That's cheap insurance.