Swale used to control surface runoff (C) Carson Dunlop Associates How to Identify & Fix Exterior Sources of Foundation Leaks & Basement Water Entry

  • EXTERIOR WATER SOURCE ELIMINATION - CONTENTS: How to identify and fix outdoor sources of water that cause foundation leaks, wet basements, wet crawl spaces, rot, insect damage, and mold contamination in buildings. Steps to prevent a wet basement and offers a few simple cures for existing wet basements
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This article describes the common sources of foundation leaks and wet basement and how to find and fix them:

Sources of water outside and around buildings such as roof spillage, surface runoff, groundwater, mishandling of roof gutters and downspouts, and improper exterior foundation drains or footing drains.

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Eliminate Exterior Sources of Water that Cause Building Leaks, Water Entry, Flooding

Gutter defects (C) Daniel FriedmanBefore launching a costly repair or retrofit to dry out a wet basement or crawl space it makes sense to check these common sources of basement or crawl space leaks and water entry:

Our page top sketch of swale drainage construction is provided courtesy of Carson Dunlop Associates.

[Click to enlarge any image]

Roof Gutters, Downspouts, & Leaders: the most common source of foundation leaks and wet basements

Roof gutters and downspouts - check to see that roof runoff is effectively disposed of away from the building, and that it is actually working.

Most of the wet basements that we (DJF) have investigated were suffering from mishandling of roof drainage. Between gutter defects that spill large volumes of water close to the foundation and improper site grading, we estimate that 80 percent or more of basement water entry problems can be explained.

Do not tie the downspouts into the footing drains - you will simply overload the footing drain system and risk future basement water entry. We want to see gutters extended to release roof drainage no less than 10 feet from the home, more is better, and even more important, from the point at which water leaves the downspout end, it should continue to flow away from the building, not back towards it.

Add a splashblock to route surface runoff around a chimney whose side formed a water trap against the foundation wall

Improper Site Grading, In-Slope Grade May Send Roof Spillage or Surface Runoff into Building Basements or Crawl Areas

Inslope grade makes site drainage difficult (C) Daniel FriedmanSite grading and control of surface runoff - see Finish Grading.

Keep water away from the foundation.

As we detailed at BASEMENT WATER ENTRY PREVENTION, this means proper site drainage that assures that surface runoff and roof spillage are conducted away from the building.

Our photo (above left) shows a home with an in-slope grade facing the house wall. It would have been relatively easy to install a swale draining hillside water and roof spillage around the left side of the home in this picture.

Instead the owners suffered decades of wet basements until the wet conditions made the home sills so attractive to termites that major

Guide to Finish Grading Details to Prevent Foundation Leaks & Water Entry

Swale used to control surface runoff (C) Carson Dunlop Associates

At grade, the main object is to get water away from the foundation as quickly as possible. Finish grade should slope away from the building for at least 10 to 15 feet, and should not contain low spots that will make water ponds.

Swales: if one or more sides of the building face an upwards sloping hill, slope the finish grade away from the building for at least 10-15 feet, and then shape the finish grade at that point into a swale that itself continues to carry water around to the downhill side of the building.

A swale, illustrated by Carson Dunlop Associates' sketch at left, is a nice word for a "gentle ditch" - it does not have to be deep.

Details about proper surface grading to control runoff are found at SURFACE CONTOURING for DRAINAGE

Foundation ditches: Do not do what we have found at some flooding basements: an in-slope grade problem that was trapping surface and roof runoff against the house was "fixed" by digging a ditch right against the foundation wall in an attempt to carry water away. The ditch digger simply had built a water trap to guarantee that water would be sent against the foundation wall.

If a site absolutely has no room for a swale located 10-15 feet away from the foundation, you might make a workable drainage system by building a waterproof swale closer to the foundation wall by lining the swale or "ditch" with a heavy duty waterproof rubber or plastic membrane of the same material described at

Intercept drain at garage (C) Daniel Friedman

  • Add an intercept drain at the entry of garages into which a paved driveway is sending water whenever it rains.

    If you are planning to re-pave a driveway, that's a great time to go to the trouble of cutting in and installing a drain that prevents water from flowing into the garage.

    Connect the intercept drain to a storm drain or to a new buried drain line that slopes to daylight well away from the building.

    Don't connect the intercept drain to the building footing drain system - you may overload the footing drains and cause basement leaks.

Guide to Foundation Drainage Details to Avoid Foundation Leaks & Wet Basements

Footing drain to daylight (C) Daniel Friedman

Footing drains / foundation drains - check for presence of and check that water is flowing out of footing drains if water is in the basement. If the basement is wet and the footing drains are dry, they are not working.


Our photo (left) illustrates a foundation drain that is "brought to daylight" at a property.

But this foundation drain (or "footing drain" extension) raises some questions: the use of perforated pipe far from the building may be ok.

And it's proper to use perforated pipes around the foundation footings themselves, so that water can enter the drainage system for disposal.

But if the pipes carrying this drainage "away" from the building are in fact perforated and are leaking it back into soils close to the structure, we may be simply recycling water rather than disposing of it.

Clogged footing drain (C) Daniel Friedman Clogged footing drain (C) Daniel Friedman
  • Find the end of the footing drain system that used to drain to daylight - it may have become buried with mud or covered by backfill. Clear it open and check the end for water flow in wet weather. Our photo (above left) shows the footing drain that was excavated and removed at the home of a client whose house suffered recurrent flooding. The old footing drain was totally impacted with mud.

    The photo at above right shows the ends of three new footing drains that were installed and carried to daylight. We remained a little nervous about just what the builder used for backfill - notice that silty mud coming out of the new drains? They may not have a long life.
  • Find and un-clog the footing drains: excavate at a building corner, find the footing drains, cut open the drain to see how full it has become with silt, and have the drains cleaned using high pressure water or other methods.
  • Reroute a non-working footing drain to a drywell if you can't get it to daylight
  • Add missing foundation footing drain sections that were omitted, such as around a chimney or building addition

Other Outdoor Sources of Basement Leakage & Water Entry

  • Repair foundation holes and cracks - see Seal Cracks in Concrete, How To
  • Storm drains - nearby storm drains should be un-blocked and not backing up onto the property.
  • Sump pumps - also check that if they are installed, the sump pump(s) are working and that water is pumped to a location that does not drain back into the building. Some properties use an outdoor catch basin and sump pump to dispose of roof runoff or surface runoff.


Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

This article series discusses methods for preventing wet basements by attention to multiple best construction practices, including the basics of foundation d & roofing, poor site drainage, bentonite clay for basement waterproofing, foundation membranes to prevent leakage, foundation drain tiles, proper backfill, and proper finish grading.


Continue reading at GRADING, DRAINAGE & SITE WORK

Or see GUTTERS & DOWNSPOUTS or select a topic from the More Reading links shown below.

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EXTERIOR WATER SOURCE ELIMINATION at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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