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2011-02-28 14:38:29

Crawlspace Foundations & Environ

Crawlspace foundations can be found in all parts of the United States. This type of construction is more prevalent in homes that stretch from the Carolinas across the center of the United States to Washington and Oregon.  Typically, basements dominate the foundation type in homes north of this geographical line, primarily due deep frost.  Slab construction dominates the geographical area below this area.

Crawlspaces and basements are not different other than lower ceiling height in a crawlspace, yet there are different building codes for basements and crawlspaces.  The only reason to build a home with a dirt crawlspace is to save money.  A dirt crawlspace is cheaper than a concrete floor.  A home with a dirt crawlspace can be very dysfunctional.  This type of foundation construction was popular before the advent of ready mix concrete.  The foundation perimeter walls and interior piers could be installed by the craftsmen masons and or carpenters, followed by the installation of the wooden floor joists and sub flooring.

The advancement of time proved that newer building products, technologies, and greater awareness of the environmental issues that can affect housing, buildings, and its occupants became more evident.  Construction methods and technologies have evolved and it is important to eliminate moisture and water penetration into crawlspace areas, just as one would strive to keep their basements dry.  Anytime there is a below grade foundation water and moisture management can become challenges.  Common problems associated with crawlspace construction include mold and decay, elevated radon levels, and termite and other pest concerns.  Condensation forms on ductwork.  Mold grows on joists.  Termites and wood boring beetles cause damage.  Hardwood floors can cup.  The historic and current widely recommended solution to crawlspace moisture control is to increase or provide ventilation of the crawlspace.  In the early 1950’s crawlspace foundation vents were introduced to eliminate humidity in crawlspaces.

New research by the National Association of Home Builders, American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE), and other state and privates sources have developed new theories contrary to open ventilation systems.  Now building codes are changing to allow builders to construct conditioned crawlspaces without crawlspace foundation vents.  Conditioning the crawlspace is the practice of removing all components that cause moisture, i.e.:  leaking pipes, broken dryer vents, ground water entering through the foundation, etc.  A proper vapor barrier needs to be installed to prevent moisture from evaporating from the soil into the home.  All components of achieving a clean and conditioned space will result in a more energy efficient crawlspace.  There are studies performed and methods to meet these energy efficiency ratings pursuant to Energy Star evaluations.  Keep in mind these criteria are typically geared to new construction where crawlspace construction is predominant.  It would be very hard for older homes to conform to these new codes, unless the owners were interested in being compliant and absorbing the cost of rehab.
What can be done to older homes with crawlspaces and what type of criteria are mandated by HUD?
HUD has outlined General Requirements for crawlspaces in HUD Handbooks 4905.1 REV-1, 2-14 & 2-11 and 4150.2 Section 3-6A.11.  HUD requirements state that there are minimum conditions that the property should have to protect against deterioration to the building and seriously affect the marketability of the property, it should have these crawlspace requirements:

•    Adequate access to the crawlspace
•    Minimum height of a crawlspace to be 18 inches from the bottom of the floor joist
•    Clear of all debris
•    Adequately ventilated, providing positive airflow with no dead air space
•    A vapor barrier is not typically required; however, if moisture problems are evident, a vapor barrier should be required
•    Must not be excessively damp and must not have any water standing or ponding. Manufactured Homes that are seeking FHA Title II mortgage insured loans must have a Permanent Foundation which meets the requirements outlined in FHA/HUD Handbook 7584 “Permanent Foundations Guide for Manufactured Housing” dated September 1996 and HUD Handbook 4145.1, REV-2, Change1, Feb. 14, 1992 “Architectural Processing and Inspections for Home Mortgage Insurance.  Essentially states that the Foundation by definition must be constructed of durable materials, i.e. concrete, mortared masonry, or treated wood – and be site-built and anchored to stabilize the manufactured home to transfer all loads to the underlying soil and or bedrock.  Further stipulated that a licensed professional engineer shall structurally design the system vertical uplift and lateral stability.  HUD is typically requiring  poured-in-place reinforced concrete footings with steel reinforced masonry block piers.  Additionally, there is a minimum clearance of 18 inches from the ground to the bottom flange of the chassis beams.  The crawlspace  must have 1 square foot of venting for every 150 square feet of the enclosed skirted area.  The skirting shall also be impervious to rot and infestation.  Positive surface drainage away from the foundation is also mandatory.

The National Association of Home Builders (NAHB) estimates that approximately 20% of new homes in the United States (200,000 per year) are built on vented crawlspace foundations and there is an estimated 26 million existing homes that have vented crawlspace foundations.  Building codes and HUD requirements often require foundation vents to allow air exchange between the crawlspace and the outdoors in order to provide a drying mechanism for crawlspaces.  Research has indicated that in the southeastern United States, the moisture content of the outdoor air in the summer exceeds that of the crawlspace area and does not act as a drying mechanism when introduced into the crawlspace.  Research studies have demonstrated that there are pathways and driving forces sufficient to cause transmission of pollutants from the crawlspace to the occupied space.  Insulating a Ventilated Crawl Space

The following are some guidelines to follow for insulating a ventilated crawlspace:

1.    Seal any and all holes in the floor above (which is typically the underside of the subfloor) to prevent air from blowing up into the home.
2.    Insulate between the floor joists with rolled fiberglass.  Install tight against the subfloor.  The insulation should be supported with mechanical fasteners, so it does not fall out.
3.    Cover the insulation with a house wrap or face it with a vapor barrier.  The orientation of the vapor barrier depends upon the home’s geographic location and climate.  In areas with mild winters and hot summers, the vapor barrier should face downward.  In other regions the vapor barrier should face upward.

Install a polyethylene vapor retarder or equivalent material over the dirt floor.  All seams should be tapped and sealed.  A thin layer of sand or concrete to cover the polyethylene is advisable to protect it from damage.  If concrete is being added, make sure there is adequate headroom.  The addition of gravel could cut or make holes in the barrier. Addressing the moisture issues is the first priority in a crawlspace whether it is closed construction or open construction.  Exterior water must be directed away from the foundation with proper grading of the lot and proper handling of the roof runoff.  The crawlspace soil should be completely covered with a vapor barrier retarder.  Capillary moisture movement should be restricted at the crawlspace  floors, piers, and foundation walls using capillary breaks such as vapor barriers
 

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