Pier and beam properties and crawl space design

As a Homeowners we should all understand how a crawlspace of a pier and beam foundation affects the living space above. Every effort should be made to keep moisture out of the crawlspace. Most crawlspaces today are constructed as unconditioned and vented systems. Protecting wood products from moisture is an important factor in preventing fungal decay. Did you know that a moisture content of less than 20% in wood framing will not decay? You can see the importance of maintaining low moisture content.


Moisture Control


A raised floor foundation separates a structure from one of the biggest sources of moisture — the ground itself. With proper design, construction, and maintenance practices, a raised floor system can remain dry and free of moisture-related problems. Moisture can be controlled by:


Providing proper site and building drainage is critical to moisture control for any foundation system. Proper drainage is needed to keep the foundation and underfloor areas dry. For a raised floor system, it is especially important that standing water be kept out of the crawlspace. The ground beneath an open pier-and-beam foundation should be graded to provide drainage away from the structure. Controlling moisture requires effective control of rainwater and ground water. Managing rainwater drainage from the building's roof helps to keep the foundation and underfloor areas dry. Most important is the use of gutters, downspouts, and splash blocks or drainpipes to direct the water runoff away from the foundation. Also, floor areas of adjacent porches or patios should be sloped to drain rainfall away from the structure.


Whenever possible, the elevation of the crawlspace floor should be higher than the exterior grade. When that is not possible, perimeter drains should be included.


For open pier-and-beam foundations, positive drainage within the crawlspace is important. The ground should be graded to maintain a dry crawlspace and to drain water away from the structure. On a level site, this could involve slight crowning, centered beneath the raised floor. On a sloped site, the ground should be graded so the water exits through and away from the pier system.


For continuous wall foundations, drain installed around the entire footing perimeter can greatly reduce moisture within the crawlspace. The drain should lead to a storm drain, a sump with a pump, or other positive drain system that moves the water away from the structure.


The finish site grade should slope away from the structure to provide positive drainage away from foundation walls. This is important for keeping any type of foundation dry and trouble free. A minimum slope of 5% away from the structure is recommended. Typical site grading creates a fall of at least 6" over the first 10' away from a foundation. Drains or swales can also be provided to ensure drainage away from the structure.


Crawlspace Ventilation 


Building code requirements for ventilation openings through foundation walls are intended to reduce moisture levels in the crawlspace. Section 1203.3 of the 2003 International Building Code sets forth the underfloor ventilation openings and cross ventilation requirements for enclosed crawlspaces, such as within stem wall foundations. Open pier-and-beam foundations, commonly used with raised floor systems, already create a fully vented crawlspace.


Generally, building codes mandate that the minimum net area of ventilation openings required are not less than one square foot for each 150 square feet of crawlspace area. When an approved vapor retarder covers the underfloor ground, the minimum vent opening area can be decreased to one square foot for every 1500 square feet of crawlspace area. Vent openings are placed to provide cross ventilation of the underfloor space. These vent openings should be screened to inhibit pest entry into the crawlspace (see Pest Management). They also should not allow rain water or runoff to enter into the crawlspace.


Conditioned and Unvented Crawlspaces 


Conditioned and unvented crawlspaces are only recommended when mechanical systems distribute conditioned air within the underfloor area. A conditioned and unvented crawlspace typically has insulated walls and can be thought of as a short basement. This type of crawlspace is designed to communicate with the living space. It should be dry, temperate, and have good air quality. Conditioned air spaces should not be ventilated with outdoor air.


Conditioned and unvented crawlspace systems should have a continuous ground cover sealed to insulated perimeter walls and any supporting piers. Care should be taken with all air-sealing construction details. This is necessary to minimize the unintentional introduction of unconditioned air, reducing the possibility of condensation on cold surfaces. In addition, extra care should be taken to prevent moisture from being trapped in the crawlspace. Any moisture that does get into the crawlspace should be remediated immediately.


Ground Cover (Vapor/Gas Retarder) 


Draining storm water away from the foundation, preventing standing water beneath the crawlspace, and making provisions to remove excess moisture entering the crawlspace, are all important elements needed to provide a dry, trouble-free raised floor system. Control of ground moisture is also essential. One of the best ways to control this moisture is through the use of a ground-applied vapor retarder.


Exposed soil in crawlspaces and under porches and decks should be covered with an approved vapor retarder. A ground cover that retards transmission of water vapor from the soil into the crawlspace provides an effective way to prevent moisture and humidity problems. It should have a permeance of no more than 1.0 perm, complying with ASTM E1745, to resist alkali and other chemicals that can be contained in soils. It should also be rugged enough to withstand foot and knee traffic. The most commonly used ground cover material is a 6-mil (0.006 inch) polyethylene.


Before installation of the ground cover, the crawlspace floor should be smooth and free from sharp rocks and construction litter. Exact installation details will vary depending on the primary function of the ground cover (i.e. moisture control or radon gas control). For any crawlspace system, it is important to avoid standing water on top of the ground cover.


For unconditioned and vented crawlspaces, the edges of the cover should be overlapped 4" to 6". The cover does not need to extend up the face of the foundation wall, and no sealing is required. If the control of radon or other soil gases is not of primary importance, the ground cover may be cut in several low spots to provide drainage if needed.


Conditioned and unvented crawlspaces should have a continuous ground cover over all crawlspace soil. The ground cover should be sealed at the joints, as well as sealed to the perimeter wall and any piers. A thin layer of concrete added over the ground cover provides a better seal and further inhibits the entry of rodents.


Radon Gas


In areas where radon gas is a concern, care should be taken to vent radon away from the building. By its very nature, an open pier-and-beam foundation readily dissipates radon gas. In enclosed, continuous wall foundations, the components of a passive, sub-membrane depressurization system are readily installed during construction. The soil within the crawlspace should be covered with a continuous layer of 6-mil polyethylene (minimum) soil-gas retarder. In addition, enclosed crawlspaces should be provided with tightly sealed pipes vented to the exterior of the building in accordance with the code. For more details, see Radon Reduction in Wood Floor and Wood Foundation Systems from the American Wood Council at www.awc.org.

Are you aware of asbestos?

Why Do You Need to be Concerned About Asbestos?

Asbestos is a mineral fiber that has been used commonly in a variety of building construction materials for insulation and as a fire-retardant. Because of its fiber strength and heat resistant properties, asbestos has been used for a wide range of manufactured goods, mostly in building materials (roofing shingles, ceiling and floor tiles, paper products, and asbestos cement products), friction products (automobile clutch, brake, and transmission parts), heat-resistant fabrics, packaging, gaskets, and coatings.

When asbestos-containing materials are damaged or disturbed by repair, remodeling or demolition activities, microscopic fibers become airborne and can be inhaled into the lungs, where they can cause significant health problems.

Most Common Sources of Asbestos Exposure:

• Workplace exposure to people that work in industries that mine, make or use asbestos products and those living near these industries, including: 
• the construction industry (particularly building demolition and renovation activities),
• the manufacture of asbestos products (such as textiles, friction products, insulation, and other building materials), and
• during automotive brake and clutch repair work
• Deteriorating, damaged, or disturbed asbestos-containing products such as insulation, fireproofing, acoustical materials, and floor tiles.

What is asbestos?

Asbestos is the name given to a number of naturally occurring fibrous minerals with high tensile strength, the ability to be woven, and resistance to heat and most chemicals. Because of these properties, asbestos fibers have been used in a wide range of manufactured goods, including roofing shingles, ceiling and floor tiles, paper and cement products, textiles, coatings, and friction products such as automobile clutch, brake and transmission parts. The Toxic Substances Control Act defines asbestos as the asbestiform varieties of: chrysotile (serpentine); crocidolite (riebeckite); amosite (cummingtonite/grunerite); anthophyllite; tremolite; and actinolite.

Asbestos health effects

Exposure to asbestos increases your risk of developing lung disease. That risk is made worse by smoking. In general, the greater the exposure to asbestos, the greater the chance of developing harmful health effects. Disease symptoms may take several years to develop following exposure. If you are concerned about possible exposure, consult a physician who specializes in lung diseases (pulmonologist).

Exposure to airborne friable asbestos may result in a potential health risk because persons breathing the air may breathe in asbestos fibers. Continued exposure can increase the amount of fibers that remain in the lung. Fibers embedded in lung tissue over time may cause serious lung diseases including asbestosis, lung cancer, or mesothelioma. Smoking increases the risk of developing illness from asbestos exposure.

Three of the major health effects associated with asbestos exposure include:

Asbestosis -- Asbestosis is a serious, progressive, long-term non-cancer disease of the lungs. It is caused by inhaling asbestos fibers that irritate lung tissues and cause the tissues to scar. The scarring makes it hard for oxygen to get into the blood. Symptoms of asbestosis include shortness of breath and a dry, crackling sound in the lungs while inhaling. There is no effective treatment for asbestosis.

Lung Cancer -- Lung cancer causes the largest number of deaths related to asbestos exposure. People who work in the mining, milling, manufacturing of asbestos, and those who use asbestos and its products are more likely to develop lung cancer than the general population. The most common symptoms of lung cancer are coughing and a change in breathing. Other symptoms include shortness of breath, persistent chest pains, hoarseness, and anemia.

Mesothelioma -- Mesothelioma is a rare form of cancer that is found in the thin lining (membrane) of the lung, chest, abdomen, and heart and almost all cases are linked to exposure to asbestos. This disease may not show up until many years after asbestos exposure. This is why great efforts are being made to prevent school children from being exposed.

For more information on these and other health effects of asbestos exposure see the Agency for Toxic Substances and Disease Registry's Web site.

Where can asbestos be found?

Asbestos fibers are incredibly strong and have properties that make them resistant to heat. Many products are in use today that contain asbestos. Most of these are materials used in heat and acoustic insulation, fire proofing, and roofing and flooring. In 1989, EPA identified the following asbestos product categories. Many of these materials may still be in use.

asbestos-cement corrugated sheet	asbestos-cement flat sheet	asbestos-cement pipe	asbestos-cement shingle
roof coatings	flooring felt	pipeline wrap	roofing felt
asbestos clothing	non-roof coatings	vinyl/asbestos floor tile	automatic transmission components
clutch facings	disc brake pads	drum brake linings	brake blocks
commercial and industrial asbestos friction products	sheet and beater-add gaskets (except specialty industrial)	commercial, corrugated and specialty paper	millboard
rollboard

What if I have asbestos in my home?

The best thing to do is to leave asbestos-containing material that is in good condition alone. If unsure whether or not the material contains asbestos, you may consider hiring a professional asbestos inspector to sample and test the material for you. Before you have your house remodeled, you should find out whether asbestos-containing materials are present. If asbestos-containing material is becoming damaged (i.e., unraveling, frayed, breaking apart) you should immediately isolate the area (keep pets and children away from the area) and refrain from disturbing the material (either by touching it or walking on it). You should then immediately contact an asbestos professional for consultation. It is best to receive an assessment from one firm and any needed abatement from another firm to avoid any conflict of interest. In such a scenario as described above, asbestos-containing material does not necessarily need to be removed, but may rather be repaired by an asbestos professional via encapsulation or enclosure. Removal is often unnecessary.

Where can I find an accredited laboratory to test for asbestos?

The National Institute for Standards and Technology (NIST) maintains a listing of accredited asbestos laboratories under the National Voluntary Laboratory Accreditation Program (NVLAP). You may call NIST at (301) 975-4016.