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Crawl Space Dehumidification

Basement provides some extract space in the house, while crawlspaces are built to raise the level of the house to avoid flooding. This is why today, more than 35% of new houses are built on a crawlspace, and in some states like south Carolina and most coastal area, the number is over 80%.

Basements and crawlspace have a lot of advantages, however since most are either fully or partial underground, these space have lots of humidity issues. Most home owners spend thousands of dollars every year to repair humidity related damages.





Sign of high humidity in the basement or crawlspace.

  • Damp and humid air.
  • Condensed water trickling out of the walls.
  • Puddles of water standing on the floor.
  • Mold and mildew growth on the item in the space or on the walls and floor.
  • Rot and decay of wood.
  • Water stains on the walls.
  • Musty smell /Odor from the decay of items.
  • Increased condensation especially in the summer.
  • Damp carpets.

In our over 30 years in water damage and restoration, we have realized that the most common mistake most home owners make is investing in repairs caused by humidity without fixing the cause of increased humidity in the house. It is important to control the sources of humidity.

What are the sources of humidity in basement and crawlspace?

There are three main sources of moisture in the basement :

      1.Interior moisture sources – most home owners do not know that basic household activities like showering, cooking, laundry among other can produce over 5 litres of moisture a day. Since the warm moist air is more dense and heavier it easily finds its ways to the lower level room.

        Other indoor sources of moisture are :

        Moisture in concrete after construction.

        House plants – watering the plants can produce over 2 litres of moisture

Problems with the plumbering – leaking pipes, drains and taps can produce over 3 litres of moisture everyday.

      2.Exterior humidity – the humidity levels outside changes with the seasons, if this humid air can easily get into the basement. This moisture will condense on the cold basement walls and floors. This is one of the reasons some basements feel damp in some month while it dry for the rest of the year.

        The basement or crawlspace should become air seal all the vents should be maintained to ensure the outside moist air remains outside.

     3.Rain/ground water – if all the rain water is deposited just next to the house foundation, it will saturate the soil around the basement. this water will find its water into the basement or crawlspace walls and floor hence increasing the humidity levels.

        It is, therefore, important to ensure most of the rain water is collected and directed away from the house foundation.

You implement the following :

  • Install a rain gutter system – gutter will collect all the rain water from the roof direct it to the down spouts that will direct the water to safe place estimated to 5 tp 10 feet away from the house. If the rain gutter system is installed well all the rain water from the roof should collect. You should also clean the gutters and downspouts often to ensure the efficiency of the system.
  • Slope grading along your house. – as the house settles in the area it is built some of the spots will it grading hence rain water will collect. You should ensure the soil around the house is graded to maintain a slopy landscape that will direct the rain water further all from the home’s foundation.
  • Dig a trench – if too much water is still settling around the house, especially after heavy rains, you can dig a trench to direct the rain water away from the house.
  • Add foundation drain tile – this applies to new home builder foundation drain tiles are added to the foundation. They protect the foundation from rain water. adding a foundation drain tile to an existing house can be costly.

 Am sure after hearing for some of these sources of humidity, you must be wondering how exactly the moisture moves into the basement or crawlspace.

Humidity movement into the basement or the crawlspace

Our water damage and restoration expert will tell you the only reason most homeowners will always have humidity issues in their basement or crawlspace is that these spaces are not well built and even those that are constructed well – they are still not built for handle any water drainage issues. Drainage and air circulation are the two most common of high humidity in the basement or crawlspace.

Moisture use four main mechanisms to get into your basement or crawlspace.

      1.Moisture diffusion in to the foundation – diffusion is easily described as the movement of a substance from any area of high concentration to an area of low concentration(refer to Wikipedia). If the soil along the foundation is highly saturated with water, the foundation walls will automatically absorb this water via diffusion. Once the wall is saturated the water will be eminate into the basement or crawlspace as water vapor increasing the relative humidity levels.

        This process is, however, dependant on a few elements :

    • Pressure diferential of the different surface.
    • The foundation walls have to be made of a substance like concrete which absorbs water and not polyethylene or any other waterproofing. These will slow down this process.

      2.Capillary suction – this refers to the movement of water through porous materials. Water can be drawn into the basement or crawlspace walls and floor. This effect causes dampness in the basement or crawlspace. Capillary suction is a  real problem especially for homes built in the place where the water table is high.

         If not controlled capillary suction can lead the destruction of the home foundation.

     3.Air movement – in the summer most home owners open the basement or crawlspace windows and vents to allow fresh air circulation. While this may remove the dampness for a short period it will create more problems in the long term. Opening windows allows humid air to get into the basement, the humid will condense on the cold walls and floor. This is usually the cause for water droplets to drip on walls, most home owners mistake this for wall leakage.

The stack effect.

In reference to the air movement as a mechanism of humidity movement, the stack effect is the reason you can not ignore the high humidity in the basement or crawlspace.

The stack effect occurs when warm air rises and exists the house from the upper rooms, this creates a negeative pressure in the basement or crawlspace. This pressure force humid outside air into the basement or crawlspace through the vent, open sump pits and cracks. All sumps should be closed tightly.

Effects of the stack effect :

        The increased humidity in the basement or crawlspace is spread out throughout the house.

        The odor in the basement or crawlspace will be spread throughout the entire house.

        Mold spores will spread from the basement or crawlspace. Mold spore is known allergens that can cause respiratory problems.

        Increased humidity in the house lead increase in damage and cost of repairs and home maintenance will go up!

Once you have identified the source of humidity your should implement the following control measures:

       Reseal your concrete – seal any cracks in the foundation.

       Seal all cracks in the walls.

       Seal all the vents.

Add gutter, downspouts and grade the soil around your home. This will easy any drainage issues around your foundation.

Install a dehumidifier – a dehumidifier is an electric appliance that extracts all the excess moisture in the air.

Choose a basement or crawlspace dehumidifier that has a capacity capable of lowering the humidity level depending on the size of your basement or crawlspace and the level of humidity.

A basement or crawlspace dehumidifier will maintain the relative humdifty levels below 50%, hence your space will remain dry and mold free.