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Inside vs outside basement waterproofing

What's generally a "greener" approach to old basement waterproofing, outside or inside?

Asked by Andrei Sosnovsky
Posted Aug 5, 2010 11:41 AM ET


3 Answers

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I don't know about greenness, but I do know about effectiveness.

Exterior waterproofing is far more effective than interior waterproofing. The best approach from the interior is to collect the moisture in a French drain, conduct it to a sump, and pump it out.

Answered by Martin Holladay
Posted Aug 5, 2010 2:46 PM ET


Thank you Martin. That's what I thought too. I recently met with "Clarke Basement Systems" repreentative who claimed that interior perimeter drain, sump pump and their special waterproofing membrane on the interior of the walls is much better. His reasoning was that no matter what you do exterior wheeping tile will get clogged with time. Interir - never.

Answered by Andrei Sosnovsky
Posted Aug 5, 2010 3:35 PM ET


"Green" is pretty meaningless here.

An appropriate solution would depend on type and depth of foundation, type of soil and topography, water source(s), frequency and volume, and whether the basement is living space, storage space or just utility space.

The best solution starts with eliminating or diverting the source(s). That could mean installing gutters and downspouts with long leaders or underground drains. It could mean regrading the lot and/or installing a French drain to intercept the groundwater before it reaches the basement.

For water that can't be eliminated or diverted, second best is to capture it at the outside perimeter of the foundation just below floor level and drain either to daylight or to a pumped sump. A properly installed perimeter drain will not clog. It should be bedded in and surrounded by washed crushed stone and stone and pipe wrapped like a burrito with filter fabric before backfilling. Holes in the plastic drain pipe should be facing downward (offset 30° on each side), and pipe should be either level or sloped ¼" per foot. Exterior of foundation can be waterproofed (and/or drainage board installed) at the same time.

Lest best is to waterproof and/or install drains on the interior. But this is less expensive and less disruptive, particularly with lots of shrubbery or adjacent patios or decks or walkways or other exterior obstructions.

Sometimes the least expensive, least complex and least disruptive option is the most "green", but only if it's effective.

Answered by Riversong
Posted Aug 5, 2010 5:53 PM ET

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