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Interior vs. Extrerior Drain Tile

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  • Interior vs. Extrerior Drain Tile

    This topic seems to stir a lot of passion among experts, so I thought I'd try to ask a thoughtful question. Interior drain tile seems to get bashed so often by plumbers and waterproofing contractors who insist that exterior systems are the only solution. Some of the passion seems to stem from the fact that many waterproofing companies suggest interior french drains for every situation when often there are less complex solutions available. I'll concede that there seem to be a fair amount of disreputable companies out there. However, done properly, shouldn't an interior system be just as effective, if not more effective, than an exterior system?

    I have both in my house. I have an older, higher basement that was part of the original house, and a new lower basement that clearly sits very close to the level of the water table. The old basement had no drain tile or sump pump when I moved in - and every time it rained (even moderately heavy rains), I got seepage on the floor - something the seller neglected to mention. My choices were to excavate aound my entire house, tearing up sidewalks and landscaping, or install an interior system. I did the latter and the results have been good. My company used 4" PVC in a trench dug around the perimeter of the basement.

    For my addition, I had the black pipe laid as drain tile around the outside of the foundation. I had no idea what I was doing and unforutnately didn't insist on the job being done properly - as a result, I'm sure it wasn't done properly and was likely either laid too high or not sufficiently covered with stone and drainage fabric. In any event, I get seepage at the floor/wall joints - even on the interior wall where the new basement meets the old basement - despite a pretty active sump pit during rains. My choices are to dig up around the new basement - which would entail taking the deck off of the back of my house and probably spending $10,000-$15,000 - or to install an interior system to supplement the exterior system for thousands less.

    I realize that exterior systems, installed properly, are ideal in that they stop the water before it gets in. But don't they have several disadvantages? They're very hard to service, if they are even servicable, they can clog over time, and when intalled in existing homes can cause considerable disruption and be a tremendous expense.

    Those who bash interior systems seem to imply that they don't work - and that can't be true or they would never be sold or approved by municipal code. I see criticisms that state they're not waterproofing, they're water managment. OK, so what's wrong with that? If you are managing the water so that it gets pumped out to the sewer or far away from the property before it gets into the living area, is that such a bad thing?

    Other criticisms can also be addressed - sump pumps can fail, so it would be wise to have a backup (I have a water powered backup that would last infinitely in the event of a power outage). I've seen comments about "letting the water in increases humidity..." I have a $200 dehumidifier that keeps my basement humidity at 50% in the summer and 30% or less in the winter - my basement is also air conditioned.

    I live on 5,000 square feet of land - there are only so many options I have with respect to my property. I would imagine there are thousands of people with similar properties, where no matter how much grading you do, living 10 feet from your neighbors limits what you can really accomplish. Are we really wasting our money on systems that don't work, or is the only acceptable option to some folks to spend 4 to 5 times as much and have their property disrupted even more?

    Looking forward to some reasoned discussion.

  • #2
    Re: Interior vs. Extrerior Drain Tile

    I don't have much experience with these. I generally only see them when they are not working. I think an exterior system is preferable, and if it is new construction, why wouldn't you? The main problems I see with these are that
    - not a lot of care is taken in their installation with regard to proper grade, backfill, daylighting them appropriately, and leaving access should they ever need service.
    - they often get compromised during later stages of construction; equipment gets driven over the area and crushes the flexy corrugated pref, or it gets whacked right through when they ditch in utilities.

    The main problem I see with interior systems is poor pump installations; pits too shallow so no room to set the pump up on a block away from mud and debris and pump has to cycle so often it burns itself out, poor float arrangements, no provision to remove and service pump, etc.

    as a retrofit to dry an existiing building, I think you get what you pay for. I'd think the water seeping in can't be doing any good in terms of structural stability, and you've got this pump pit that will need service once in a while, and your space, while dryer, probably isn't really finishable living space, suitable mostly for storage or workshop, and I'd still store anything I didn't want wet off the floor.

    Not may area of expertise, but there's my $.02 for what it's worth.
    This is my reminder to myself that no good will ever come from discussing politics or religion with anyone, ever.