High Moisture In Crawlspaces
December 26, 2014
Finding high moisture in a crawlspace can lead to a homeowner's worst nightmare. When high moisture is found it usually is associated with molds, mildews, wood rot, termites, standing water, etc. Once it is found, then comes the decision on what to do about it. Install a sump pump, put in french drains, mold treatments, replace insulation, vapor barriers, dehumidifiers, seal the crawlspace? And the list can go on and on. Today I would like to address the problems that we see in Raleigh and other Triangle area houses on a day to day basis.
Just like most things in the crawlspace of a house, the homeowner may not know about or understand them, mostly because the homeowners are not under these areas on a regular basis. High moisture is very common in our area due to the amount of rainfall and high humidity we get every year. Anytime you have high moisture in an area where cellulose (wood) is found, problems can occur. When talking about moisture in the crawlspace I like to break it down into two separate problems: Liquid water (I know it sounds weird) and water vapor/humidity.
This problem occurs when water is penetrating into the crawlspace through the foundation wall. This will typically cause moisture staining on the foundation wall (dark, wet areas), efflorescence on block/brick foundations, standing water, and erosion. The fix for this type of moisture is considerably different than water vapor. If liquid water is the problem, you have to physically prevent the water from entering the home by:
- Installing gutters if none are present
- Diverting downspouts away from the foundation
- Regrading areas around the home to get proper drainage away from the foundation
- Installing exterior French drains (I prefer these to prevent water from ever entering the foundation) or
- Installing interior French drains with a sump pump or other crawlspace type drain to remove water when entering the crawlspace
Stopping liquid water from entering the foundation is the first priority. You can not skip this step and get proper results. Water entering your foundation over time can weaken the foundation wall and erode the footing. This can lead to very expensive repairs if foundation walls have to be repaired and/or replaced. If no standing water is present and it does not appear that liquid (ground) water is getting into the crawlspace you may have problems with:
Here in the Raleigh/Durham area, we have a lot of problems with high humidity. High humidity means an increase of water vapor available in the air for the wood in the crawlspace to absorb. High humidity is the number one problem that we encounter during our termite inspections and home inspections of crawlspaces in the Raleigh/Durham area. Some symptoms of high humidity in crawlspaces are:
- Moisture levels in wood members of the crawlspace >20% (as tested with a moisture meter)
- Stringing and fallen insulation
- Dark staining on the floor joists
- “Sweating” on wood and insulation
- Water droplets forming on heat/air ducts
- Water droplets on top of the vapor barrier
I have high moisture in my crawlspace, now what?
In the past, the recommendation was to keep all your foundation vents open during the hot summer months and to close them during the cold winter. Most of this research was done before it was common to have central air and now is the opposite of what current research is showing us. When we leave the foundation vents open during the hot humid months of summer, we are allowing air, laden with high moisture into the crawlspace which in turn is condensing on the cool wood, insulation, water pipes, and air ducts. This will quickly elevate the moisture content of the wood and increases the likelihood of mold growth and makes the wood more conducive to termite and insect attack. Moisture levels above 20% in the wood can also support mold growth. Moisture levels above 28% can lead to wood decay fungi which can literally rot the crawlspace out. Keeping your crawlspace free from this moisture can help keep your home sound for years to come. Here are the steps I would take to ensure your home is protected from the damage of moisture:
- If there is liquid water entering your foundation see tips above. If you can not determine the source of the water hire a professional waterproofing company to evaluate your situation and stop this problem first.
- A vapor barrier should be in place in the crawlspace. A vapor barrier is a plastic sheathing (6 mils or greater) that is laid on top of the ground in the crawlspace. The desired coverage is 100% of the crawlspace floor. After installing a vapor barrier don’t be surprised to see water droplets forming under the plastic. This is normal and means the vapor barrier is trapping the moisture and not allowing it to be absorbed into the air.
- Keep your vents closed during times of high humidity (above 60%). This can help dry out your crawlspace and prevents humid air condensing on the cool sub-floor.
After following these three tips, monitor the crawlspace between June-August and see what the moisture readings are. In some cases, this is enough to help reduce the moisture below the danger zone (above 18-20%) If through a summer cycle the moisture levels do not drop low enough further action should be taken.
- Install a dehumidifier. In almost all cases, installing a dehumidifier has solved moisture problems that we have dealt with over the years. It is the most economically feasible option after installing a vapor barrier. The dehumidifier is programmed to run on a humidistat which turns the machine on and off depending on the humidity available in the air. We have controlled extreme cases of moisture (like seen in the attached video) in a short amount of time.
- Seal the crawlspace. Many companies are installing sealed crawlspaces on new homes and converting older homes to a sealed crawlspace. This is a great option for the homeowner, however, the cost can be quite expensive and may be overkill in many instances. This includes permanently sealing all crawlspace vents and creating a “conditioned air” space under the home.
If you have high moisture in your crawlspace, some action should be taken. If nothing is done to correct these issues, serious damage to the structure of the crawlspace can develop and possible health-related issues with mold growth can occur. If you think you may have an issue with your crawlspace do not delay having it inspected by a professional.