CRAWLSPACES IN NORTHEAST FLORIDA

CRAWLSPACES IN NORTHEAST FLORIDA

Crawlspaces in the Jacksonville area are normal in homes built prior to the 1960’s.  The Jacksonville area is a pretty unique community with planned streets and lots with good draining yards to neighborhoods where the lots are poorly draining resulting in damp to wet crawlspaces and the resulting issues.

CRAWLSPACE FOUNDATION TYPES

Vented (traditional) crawl space: a crawl space with a continuous perimeter foundation wall (typically masonry) with ventilation openings to the outdoors intended to control crawlspace humidity. This is a typical foundation type we will normally see in our area.  

Open crawlspace: a crawlspace where individual piers (typically wood, masonry, or concrete) at the building perimeter support beams and floor joists. This type of foundation is usually found in homes that pre-date the 1930’s.

Unvented (sealed, closed, or conditioned) crawlspace: a crawlspace with a continuous perimeter foundation wall that is sealed (no wall vents) to improve energy and moisture performance. Insulation is installed on foundation walls or in floors above. Humidity is controlled by a dehumidifier, exhaust venting, or HVAC system. Relatively rare in our area but can be found in newer construction and on homes that have had past moisture issues.

A crawlspace beneath your home should be a dry and clean space.  Moisture in a crawlspace creates a multitude of issues that can be difficult and expensive to cure. Let’s look at causes to poor crawlspace conditions.

In older homes the crawlspace soil elevation maybe lower that the finished grade of the yard. This can allow roof rain water runoff to directly enter the crawlspace.  This water then needs to evaporate or percolate into the ground. 

In some cases, the lot is so flat the rainwater runoff has no place to go and the yard and crawlspace remains damp, mucky and even wet for long periods after a steady rain.

Whenever you have a damp to wet crawlspace the accumulated moisture has to go somewhere.  This moisture will be driven from warm to cooler/drier spaces as it evaporates (moisture vapor will rise through the house). 

Have you ever walked into an older house and observed a musty/musky/earth odor?  Are the wooden floors cupping? Is there powdery mildew in the corners near the ceiling on outside walls and inside closets? If yes, we probably have a wet crawlspace.

1.       Floors above vented and open crawl spaces in hot-humid climates are susceptible to moisture accumulation that could lead to mold, mildew, and decay within the floor assembly.

2.       Water vapor generally migrates from areas of higher temperature and relative humidity to areas of lower temperature and relative humidity (vapor drive). In a humid climate, during the cooling season, the vapor drive is from the crawlspace to the relatively cool and dry indoors through the floor assembly.

3.       A vapor impermeable floor covering can trap moisture in the wood subfloor Conditions within the crawl space can lead to condensation and high wood moisture content.  We call this a microclimate and it can lead to devastating results in the crawlspace.

   

MOISTURE MOVES FOR MANY REASONS

Moisture migration: water can enter the crawlspace as liquid (rain or groundwater) or water vapor. Water vapor can migrate from the crawlspace into the house due to air leakage and diffusion.

Water vapor migration due to air leakage: the transport of water vapor carried within moving air through air leaks in the floor assembly. Can be controlled with effective air barriers and air sealing.

Water vapor migration due to vapor diffusion: the migration of water vapor through permeable building materials. Can be managed using vapor retarders.

Vapor permeance: a measure of the rate of water vapor diffusion through materials. A lower “perm” rating indicates the material is less vapor permeable.

Relative humidity (RH): the amount of water vapor in air relative to the maximum amount air can hold at the same temperature. RH increases if air gets colder without losing moisture because warm air can hold more moisture than cold air.

Dew Point (DP): the temperature at which water vapor condenses into a liquid on surfaces (100% RH).

Moisture content (MC): the weight of moisture contained in wood expressed as a percentage of the wood’s dry weight.  The end result is that moisture must be controlled in our buildings. Left unchecked moisture migration can lead to wood decay and fungi in the structural framings, wood subflooring, and high indoor relative humidity resulting in our cooling system working extra hard to lower the humidity and temperature in the summer and excessive condensation on cold surfaces in the winter months.

WHAT ARE THE SOLUTIONS

We recommend that our clients take a systematic approach to problem solving.

•       Install the largest gutter you can afford, but certainly nothing less than 5” and best would be, 6”K style gutters with sufficient downspouts to move water away from the foundation edge.
•             Ensure the home has a at least a 1-2% slope away from the foundation walls. This will ensure that you have positive drainage away from the home.
•       If the home has soils in the crawlspace that is lower than finished grade you may need to install vent or window wells. These are manufactured assemblies that let air in but keep water out
•       Install a good quality vapor barrier over 90% of the crawlspace. Tape all overlaps in the plastic barrier.
•            Seal all holes through the floor system (plumbing and electrical penetrations).
•            Low flat lots may need specialist to determine low spots in the crawlspace to regrade and install sump pumps to mechanically extract and move water to the curb.
•             Perimeter drains and mechanical pumps may be required if the lower cost solutions above will or don’t work.
•             Finally, the most expensive method is call a sealed crawlspace. This is an expensive process where the crawlspace is sealed from the exterior. This involves the use of open and or closed cell foams, ridged insulation, heavy duty vapor barriers, and de-humidification. It may also require re-grading the crawlspace and installation of sump pumps in low areas to extract water from beneath the vapor barrier or if surface moisture is detected.   

SOME THINGS TO DO AND NOT DO

Do keep your crawlspace dry and clean.

Do keep you gutters clear of debris and extended away from foundation walls.

Do keep your crawlspace well vented (if a vented crawlspace).

Do keep your access cover closed (keeps out those stray cats and other critters).

Do install a vapor barrier over at least 90% of the exposed soils.

Do maintain a positive 1-2% slope at exterior walls.

Do an annual inspection of your crawlspace (look for termites and moisture issues).

Do install foundation well vents if soils in crawlspace are lower than finished grade.

Don’t place heating and cooling ducting in crawlspace unless it is absolutely dry year round.

Don’t insulate your crawlspace unless it is absolutely dry year round.

Don’t install porcelain tiles or other non-permeable floor finishes in the home.

Don’t allow soils to wood contact (keeps those termites out).

Don’t do interior improvements until you have corrected all crawlspace deficiencies.