Another foundation drainage question: inside vs. outside
I know there is a recent article on foundation drainage with good discussion, but I don’t think this particular question was touched on.
I’m having a full basement constructed under the existing house. I’m located in Massachusetts. The foundation is being built for obvious structural reasons, but while I’m at it I figured I would take steps now that would make the basement high quality living space (some day). On the exterior is spray-on waterproofing membrane on the walls and the top of the footer. On top of that will be 2 layers of 1″ roxul drainboard. I also had several egress-size windows installed.
The egress windows are quite large, so there is the potential for water intrusion there, although I intend to use a clear cover on the wells. But my thinking is that these large wells necessitate a drainage system on the exterior of the foundation, as is typically done in new construction.
However, bot the GC as well as the drainage contractor want to install the drainage system on the interior of the basement, with a sump on the interior that will pump water back out of the house. Because this is a brand new foundation, and all excavation is still exposed, I was surprised at this recommendation.
For the window wells, the recommendation is to use solid PVC pipe to drain the window wells and pitch it back to the interior sump pump. This would be a safeguard in the unlikely event the natural drainage was insufficient. I say unlikely because this seems to be a pretty dry site. Puddles drain quickly from the surface, and even 10 feet down in the trenches, the large puddles from the recent heavy rain disappeared in a few hours. But this plan does seem to be different from what I’ve been reading about. It seems that interior perimeter drains is a retrofit measure to solving water problems, while exterior is a new construction method.
So I’m interested in hearing other’s opinions: Is an interior perimeter drain as effective as an exterior perimeter drain in addressing both ground water and water intrusion from the surface? (measures such as proper grading and downspout placement will be taken of course).
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