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Stop crawl space water entry:
How to stop water from entering a building crawl space.
Here we explain the three basic approaches to stopping crawl space leaks & water entry. This article series describes the steps needed to get into, inspect, clean, and then dry out a building crawl space.
Stop water from entering the crawl space from outside sources
This means attend to roof gutters and downspouts - the most common cause of crawl space water entry or high moisture in most areas.
[Click to enlarge any image]
Our page top photo shows frozen water in a wet and cold crawl space below a condominium in Poughkeepsie, New York. The very wet masonry blocks along the rear wall of the crawl area and water stains higher on these walls tell us where the water is coming from.
The photo at left shows another crawl space with standing water.
If a building site is unusually wet or springs are adjacent to the building foundation, additional steps such as the installation of a drainage system and sump pump inside or exterior foundation drainage and waterproofing could be necessary.
But before pursuing those costly measures, be absolutely certain that roof runoff and surface runoff have been directed well away from the building.
Inspect the building exterior, from roof to ground, for sources of water that need to be directed away from the structure.
Watch out: by far the most common source of crawl space water entry is improper handling of roof runoff. Spilling water along the building foundation wall because gutters are clogged, leaky, or absent, concentrates water in that location, ultimately overwhelming any foundation drain system.
Don't assume that just because gutters and downspouts are installed that they are working properly. Look more closely for signs of gutter overflow, clogged or leaky downspouts, drip lines under the roof eaves and similar clues.
At GUTTERS & DOWNSPOUTS we include roof drainage system inspection & diagnosis details.
If you see water stains high on the crawl space foundation wall it's a good guess that water is entering from either roof spillage by the foundation or by in-slope grade directing surface water against the building.
See GRADING, DRAINAGE & SITE WORK.
see FOUNDATION WATERPROOFING that discuss various methods used to keep water and excessive moisture out of buildings or to get rid of water that has leaked into a building.
Stop water from entering the crawl space from inside sources
Inspect the building interior, attic to basement and crawl spaces, also looking for sources of leaks, moisture, improper venting, that could affect the structure. In the basement and crawl spaces, look for visual evidence of the pattern of water entry - where has water been entering the building?
Trace that water to its source and cause.
Inspect the crawl space itself for clues pointing to water entry sources. We list a number of these below, including actual wet conditions, condensation on pipes, under flooring, on foundation walls; foundation wall stains, presence of sump pumps or other drainage systems, odors, visible mold.
Watch out: as we detail at CRAWL SPACE SAFETY ADVICE, entering a wet crawl area is dangerous, involving shock hazards and possible chemical or sewage contaminants.
Repair any leaks in building drains over or in the crawl space.
Check below bathrooms, kitchens, and also check hot water heating lines or steam condensate return lines in the crawl space.
Watch out: sewage-contaminated crawl areas are unsafe to enter without protective gear unless the space has been properly cleaned and disinfected.
See CRAWL SPACE SEWAGE CLEANUP
Repair any leaks in supply piping in the crawl space.
Insulate cold water pipes in the crawl space to stop dripping of condensation that forms on the cold water lines in humid weather. It's a good idea to do this in the basement too.
See CONDENSATION or SWEATING PIPES, TANKS
Crawl space venting – this is a debated topic as in humid weather venting outside air into a cool crawl space might increase crawl space moisture.
We no longer recommend simple passive venting nor humidistat-controlled venting except in special circumstances.
When our onsite inspection indicates a long-standing moisture problem in such an area the best current advice is to stop venting the crawl space and to convert the crawl space to a dry, conditioned space.
That means we close off crawl space vents, dry out the area, and add some heat to it.
At CRAWL SPACE DEHUMIDIFICATION we explain the use of heat, dehumidifiers, or crawl space exhaust vents to try to improve the humidity level in crawlspaces.
Crawl space venting practices and building codes specifying crawl space vent areas also discussed
at CRAWL SPACE GROUND COVERS.
Watch out: in some conditions, dust containment, negative air, and more protective gear or help from professionals may be needed.
This article series describes the steps needed to get into, inspect, clean, and then dry out a building crawl space. We give a step by step crawl space entry, inspection, cleanout, dryout and keep dry guide explains how to get into or inspect a crawl space even if there is no ready access, how to assess crawl space conditions, how to stop water that is entering the crawl area, how to dry out the space, how to clean up and if necessary disinfect or sanitize the crawl space, and how to keep out crawl space water and moisture in the future.
Continue reading at CRAWL SPACE WATERPROOFING or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
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Frequently Asked Questions (FAQs)
Question: how much will it cost me to dry out my crawl space?
hey first off great site, very informative.
I have a 450 sq.ft. crawl space accessed directly from a living space basement. It is clean and dry with gravel and stuff all over the place. I just bought the place and I was thinking maybe I should just have someone put french drain system around the perimeter there and put a 20 mill poly, a sump pump and just pour concrete all over (saw that online and thought is a good idea)and last spray foam the walls and joists. My question is how much roughly would all that cost me and do you think it is a great idea to do so.
thank you so much for your advise. - Walden 11/1/2012
The cost to install an interior perimeter drain in your crawl space depends mostly on
- the area covered
- the ease of access - entry and headroom
- the condition of the surface - e.g. if it is not level or doesn't slope to a drain location
- ease of disposition - to where water has to be pumped
- extent of wiring done
- need for backup power
Figure anywhere from $500 to $5000 for an area I know nothing about
I think I would first look for the history of water entry, signs of moisture trouble, ease of fixing outside sources of water entry, and other crawl space moisture sources and weigh those against the cost for this insurance..
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Questions & answers or comments about how to dry out a wet crawl space & prevent future crawl space water entry.
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 Harriet Burge, Harvard School of Public Health, and EM Laboratory, a private mold and environmental testing lab - email to D.F. August, 2004. Dr. Burge is an educator, writer, and consultant in the field of indoor air quality and mold contamination.
 Product literature and MSDS sheets for the biocides and fungicidal sealants listed in this article.
 US Centers for Disease Control, CDC: www.cdc.gov/ncidod/diseases/hanta/hps/ describes the risks associated with hantavirus.
 International Residential Code, IRC Section R408, Under Floor Space, http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_4_sec008.htm, retrieved 3/2/2013
See IRC Section M1305.1.4 [PDF] Section M1305.1.4 for access requirements where mechanical equipment is located under floors.
 International Residential Code, IRC Section R406, Foundation Waterproofing and Dampproofing, http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_4_sec006.htm, retrieved 3/2/2013
Thanks to reader C. Brown for suggesting the need for detail about rapid dryout procedures for a wet crawl space
Fiberglass: Indoor Air Quality Investigations: Health Concerns About Airborne Fiberglass: Fiberglass in Indoor Air from HVAC ducts, and Building Insulation
Humidity: What indoor humidity should we maintain in order to avoid a mold problem?
Stuff that is not mold but is often mistaken for it - things you may not want to test. Also, not all "black mold" is toxic - here are examples of harmless black mold.
Mold-Resistant Building Practices, advice from an expert on how to prevent mold after a building flood and how to prevent mold growth in buildings by selection of building materials and by anti-mold construction details.
"Weather-Resistive Barriers [copy on file as /interiors/Weather_Resistant_Barriers_DOE.pdf ] - ", how to select and install housewrap and other types of weather resistive barriers, U.S. DOE
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Asbestos: How to find and recognize asbestos in buildings - visual inspection methods, list of common asbestos-containing materials
Asbestos products and their history and use in various building materials such as asphalt and vinyl flooring includes discussion which draws on ASBESTOS, ITS INDUSTRIAL APPLICATIONS, ROSATO 1959, D.V. Rosato, engineering consultant, Newton, MA, Reinhold Publishing, 1959 Library of Congress Catalog Card No.: 59-12535 (out of print).
Asbestos Identification and Testing References
Asbestos Identification, Walter C.McCrone, McCrone Research Institute, Chicago, IL.1987 ISBN 0-904962-11-3. Dr. McCrone literally "wrote the book" on asbestos identification procedures which formed
the basis for current work by asbestos identification laboratories.
Stanton, .F., et al., National Bureau of Standards Special Publication 506: 143-151
Pott, F., Staub-Reinhalf Luft 38, 486-490 (1978) cited by McCrone
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