Many homeowners searching the internet for crawlspace repair information end up in home repair forums. While there is some good information out there, there are many examples of bad and outdated advice related to repairing crawlspaces. I have witnessed firsthand the results of unprofessional crawlspace repair and would like to set the record straight on what I consider to be the worst 5 crawlspace repairs I've seen.

1. Adding more foundation vents to the crawlspace - Old buiding codes and bad advice have resulted in homeowners adding more vents to their crawlspace in order to dry the high moisture content in their crawlspaces. The thinking behind ventilation was that air circulation would force the moisture in the crawl space air to end up outside. Through testing, it has been proven that warm, humid outdoor air brought into the crawl space through foundation vents in the summer can lead to increased moisture levels in the crawlspace. Also, the air movement in a home does not move side to side through the vents, but instead upwards (Stack Effect). This Stack Effect draws air inward from every crawl space vent and up into the living space of the home. A properly encapsulated crawlspace is the only solution to reduce high moisture levels in a crawlspace.

2. Spray Foam a wet or damp crawlspace foundation wall - In a dry below-grade crawlspace this method is the most energy efficient.  The problem is that in most below-grade crawlspaces, the foundation or ground floor of the crawlspace are NOT dry.  In fact, a majority of the crawlspaces I run across with spray foam have some form of dry rot in the structural components because the foam has trapped the moisture in the wood.  Sill plate repair is needed if they original plates are untreated. It is not uncommon to see the spray foam become separated from the wall from the moisture intrusion.  Unless the crawlspace has external footing drains, a foundation waterproofing membrane, a foundation sealant, positive grade, and downspout extensions, I cannot ever recommend this method of insulation. 

3. Staple a vapor barrier to the floor joists - I have not seen a single crawlspace repair mistake more responsible for wood rot and mold than when plastic is attached to the floor joist system. The thinking behind this is to stop moisture intrusion of the crawlspace air from entering the wood components. There are many problems with this; but the most important to know is that most crawlspaces are vented and the cooler surfaces such as duct work, pipes, and the floor will condensate in the summer. The plastic will trap the condensation up against the floor structure causing mold and wood rot to occur.  Floor joist repair is commonly needed after the joists are soaked with moisture.

4. Insulating a damp crawlspace with fiberglass insulation - This is another example of outdated advice resulting in mold growth. Paper faced insulation is "mold candy". The fiberglass will absorb the moisture from the air, become heavy, and fall to the ground.  Worse yet, if the insulation is stapled, it will hold moisture up against the wood components of the crawlspace.

5. Improper drainage system installations - Many crawlspaces have water standing on the ground floor after heavy rains. There are many reasons why water enters, and several solutions to prevent or remove the standing water. The worst solution is to ignore this recurring problem, or repair the problem with a stand alone pit and pump. A sump pump alone cannot pump all the water that pools around the perimeter or in the middle of the crawlspace. A perimeter drain is necessary to intercept the water and facilitate it to the pump.

6. Venting the Dryer into the Crawlspace - this is only considered a repair mistake because homeowners quit trying to replace the dryer duct in the crawlspace after it breaks or clogs. This will pump gallons of water into the crawlspace air causing it to move upward into the wood components because warm air rises.

7. Insulating Heat Ducts in a Crawlspace with Fiberglass - Ducts in a vented crawlspace will condensate and the fiberglass will soak up all of this excess water causing mold to grow around the duct in the fiberglass.

Additional Problems:


Improper Gutter and Downspout Maintenance - Gutters are designed to take roof water away from your home and foundation. Allowing clogged gutters to over pour water will result in more water entering the crawlspace. The biggest mistake of all is allowing the downspouts to drain the water right up against the foundation. The downspouts should be extended at least 10' to 15' away from the home to prevent roof water from entering the crawlspace.

Larry Ralph Jr.

Indiana Crawl Space Repair

Indianapolis Crawl Space Waterproofing

Views: 57236

Tags: crawl, crawlspace, mistakes, repair, space, venting

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Comment by tedkidd on April 5, 2012 at 10:01am

Hey Tom, 

Are you looking in the wrong place for problems?  Looking at the crawlspace and not seeing problems doesn't necessarily mean the crawl space doesn't represent huge problems.  It may just mean you don't have access to the correct tools to determine/diagnose health - in this case, the energy bill.  

Think you can get annual therm consumption if you call the utility?  Or possibly back into it if they'll only give you the gas budget?  (We can only get "monthly budget" for other people's homes from our utility).

Where I am I would say the home has an unrecognized problem - one that might be significantly attributable to that crawl space -  if they spend more than $1000 per year on gas (particularly with that occupancy).  But we are at $1.05 per therm and in a colder climate, two variables you'll need to adjust to.  

So, how close are they to 1000 therms? That gives a rough starting point.  

Comment by Tom Delconte on April 5, 2012 at 9:17am

Hello Ted,

It never has any difficulties associated at all with the crawlspace, except odor in the summer if the vents have not been opened! Has twin 120,000 btu/hr heaters with humidifiers to maintain 58F @ 35% RH in winter, when it's not being used. I do not have the utility bill file, as I am not the owner. This particular home is hardly used even in the summer, and never rented out, so the energy costs are not an issue. I believe it to be the largest ranch home in So. Jersey Shore.

Just recalled that 2 of the 20 homes in this neighborhood were built with full basements, even though the soil is sandy. Those owners tell me that they have no difficulties at all with water in their basements. Go figure!

Comment by tedkidd on April 5, 2012 at 8:59am

Hi Tom!

"It never has any difficulties at all." 

Is this a summer home, or an all season home?

If it's an all season home, what is the annual energy consumption?  

(Annual BTU per sf may tell a different story...)

Comment by Tom Delconte on April 5, 2012 at 8:52am

I help maintain a 5000 sq. ft. ranch home at the south Jersey shore. The crawlspace has many vents, which are opened spring through fall. It was apparently insulated correctly in the floor joists when built. It never has any difficulties at all. This picture was taken previously to being insulated.

Comment by Stacy Sand on April 5, 2012 at 8:27am

So how do you recommend insulating a crawl space, heating vents and wall in crawl spaces, while keeping the moisture away from the house?

Comment by tedkidd on April 5, 2012 at 7:56am

Nice post!  

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