Any home inspector can tell you that most crawlspaces have moisture problems. There are two different types of crawlspace setups – vented and non-vented.
Vented crawlspaces have vents that allow for cross ventilation and the home’s sub floor is insulated along with the pipes in the crawlspace to prevent freezing. There is a vapor barrier on the ground and vents are closed in the winter time. A small heater or heat tape may also be used to help keep the pipes from freezing in addition to insulation on the pipes.
With non-vented crawlspaces, foundation walls are insulated, but the sub-floor is not. The vents are blocked off with insulation all year long, and a vapor barrier is in place on the ground. Air is conditioned with a dehumidifier. A small heater and pipe insulation may still be used.
Problems arise when there are inadequate or no rain gutters. Did you know the average roof lets go of 1,000 gallons of water during 1 inch of rain? You can keep water from falling along the foundation and finding your crawlspace by using solid rain gutter covers to cover the gutter opening. This allows water to come in by curling under the cap. Unfortunately, mesh and screen covers get clogged up or collapse.
Do downspouts end along your foundation? They need to let water run 6 feet or more away from your home.
Does your terrain slope toward your foundation? Water must be directed away from the home because water can cause serious foundation damage. If the terrain around your home slopes towards your foundation this can lead to serious water damage. If the terrain is flat it may still allow excess water to damage your foundation.
Do you remember to open the vents when weather warms up? The vents in a vented crawlspace need to be closed each winter but also opened again when the weather is above freezing. Your house needs to breathe. Low decks and shrubs can block vents and make them useless. Make sure that there is sufficient clearance in front of the vents to allow air into the vents. Your home’s crawlspace needs a minimum of 1 square foot of ventilation for every 150 square feet of crawlspace floor area. Vents should be within 3 feet of the corners allowing for cross ventilation.
Could your insulation be installed upside down? You may have insulation in the flooring. The paper side of the fiberglass insulation should face the heated living space and be placed against the sub flooring. Otherwise it will trap moisture between the sub floor and the paper and hide moisture damage. A properly set up non-vented crawlspace won’t need insulation.
Is your moisture (vapor) barrier damaged or loose? It should be a 6 mil thick poly vapor barrier on your crawlspace ground and should be overlapped and sealed around columns and walls. This keeps ground moisture vapors from rising up into your framing.
If you have a sump pump installed, make sure it is at the lowest point in the crawlspace. All areas should easily drain to it. Inspect your pump regularly. Does it work automatically? It should be in a plastic cylinder in the ground and eject water outside, away from the building and not into the septic or sewer system.
If your crawlspace is non-vented, you must have a dehumidifier, and the collected water should be piped to a sump pump or condensate pump. If you don’t do this, you’ll have to dump water daily, and who wants to do that? Incidentally, buy a good quality dehumidifier with an adjustable, automatic setting so it does not run all the time.
Is your crawlspace kept neat, clean and accessible? Inspect it often for signs of moisture or mildew. Check with the local code official for any repairs you might need. Don’t underestimate the importance of your crawlspace and what you can do to prevent that all too common moisture damage.