Allergy Resistant Housing - Principles and Practice 

Subrato Chandra
David Beal
Andrew Downing

Florida Solar Energy Center
1679 Clearlake Road
Cocoa, FL 32922

 

Abstract

The importance of common residential allergens and irritants (tobacco smoke, dust mites, pollens, pet danders, cockroaches, fungi and molds, endotoxins, volatile organic compounds, odors, fine dust and radon) is reviewed. A systems oriented solution called DDAMPFIRM (Drainage and waterproofing, Dehumidification, Air tight construction, Material selection, Positive pressure ventilation, Insulation to avoid cold floors, Return air ducts or transfers, Maintenance) is discussed. Construction details and measured data on energy use and dust mite levels in allergy resistant and conventional houses are presented.

 

Acknowledgement

This work was sponsored by the U.S. Department of Energy, Office of Building Systems, Mr. George James, program manager whose support and goodwill is very much appreciated. The authors are grateful to the American Lung Association affiliates in Minneapolis, Central Florida and Washington who asked us to participate in the design and construction of demonstration Health (or Healthy) Houses^®. We thank the homeowners who allowed us to monitor their homes. The dust mite allergen analysis was conducted by Rosa Codina, Ph.D. at the laboratory located at the James A. Haley VA Hospital in Tampa. The laboratory is directed by Dr. Richard F. Lockey, MD, at the College of Medicine, University of South Florida. Recommendations on carpets and carpet pads come from Alfred T. Hodgson, Ph.D. of the Lawrence Berkeley National Laboratories.

 

Introduction

The increasing incidence of allergy and asthma, particularly among children, is a world wide concern. Since most of us stay indoors over 90% of the time, the indoor air quality in buildings is of paramount importance in maintaining respiratory health. A review of literature indicates that the common allergens and lung irritants in the home environment are:

• Environmental Tobacco Smoke
• Dust Mite Allergens
• Pollen Allergens
• Pet Dander Allergens from cats and dogs
• Fungi and Molds
• Cockroach allergens
• Endotoxins
• Volatile Organic Compounds and Odors(VOC's)
• Fine Dust
• Radon
  

Of course exceptions prove the rule. For the chemically hypersensitive a certain VOC might be lethal. Poorly maintained water systems can harbor deadly bacteria such as legionella. Excessive rodents, pesticides and malfunctioning combustion devices can be extremely hazardous. Recent studies point to the increasing importance of cockroach allergens to asthma in inner city housing causing asthma in up to 8.5% of the children (1), almost twice the national rate. Because of genetic factors, Native Americans have a low incidence of asthma and smoking related lung disease (2). To them tobacco smoking may be a lesser concern.

The above list is in probable descending order of importance in terms of health impacts on the general population. What is interesting about the list is the relatively low importance of VOCs and Radon as far as their adverse health effects are concerned. Yet substantial sums of money and effort has been expended in controlling these two irritants and not enough effort is expended on controlling the more important allergens.

Energy efficient buildings are sometimes thought of as harbingers of poor indoor air quality. Yet allergy resistant houses must begin by being airtight and well insulated. Unless the house is airtight, one cannot control and filter the ventilation air; nor can one maintain a positive pressure. Unless the house is uniformly well insulated, cold spots and cold floors may be present. The resultant high local relative humidity hastens the formation of molds on surfaces and is conducive to breeding and proliferation of dust mites. Thus energy efficient construction is a prerequisite for allergy resistant housing. However it is not sufficient. One must employ a systems strategy involving DDAMPFIRM (Drainage and waterproofing, Dehumidification, Air tight construction, Material selection, Positive pressure ventilation, Insulation to avoid cold floors, Return air ducts or transfers, Maintenance) to obtain an allergen free house.

 

Allergens and Irritants

Environmental Tobacco Smoke (ETS). About 25% of North American adults smoke today. In countries such as Japan and Poland, above 50% of the adult males smoke. The sidestream and exhaled smoke (i.e. ETS) is a major cause of respirable particles indoors as well as various carcinogens, odors and other toxic compounds (3). Some air filtering and purifying devices are reported to clear up ETS somewhat. High levels of localized ventilation may also help. However, the most practical solution seems to be banishing the smokers to the outside of the house. Building science is probably of limited help in alleviating ETS.

Dust Mite Allergens. About 20% of the general population suffer from allergies. About 5% suffer from asthma. Among children the percentages appear to be higher. The increasingly large percentage of people suffering from allergy and asthma appears to be a worldwide phenomena. In humid climates, dust mites appear to be a leading cause of asthma (4). In the hot, humid central Florida climate, approximately 60% of the patients complaining of respiratory problems tested positive to dust mite skin prick tests (5), rates two to three times greater than any other aero-allergen. In a study of North Carolina school children, 30% tested positive to house dust mites (6).

There are several dust mite species. Dust mites feed on human skin flakes and are about 300 mm (micrometers or microns) in size. There are two types of dust mite allergens -- type I and II. The dust mite fecal particles contain large amounts of the most common type I dust mite allergens, Der p I and Der f I. The fecal particles are about 10 mm in size and heavier than air. When airborne, they settle out in about five minutes. Dust mites live and breed on carpets, sofas, beds and other soft and fluffy furnishings. When a person lies down on a bed, they may release puffs of dust containing dust mite fecal particles. These are likely to be breathed in by the person before they get a chance to be filtered out by a room or a whole house air filter. Dust mites themselves also generate type II allergens from their body parts.

Washing clothes in hot (greater than 130° F) water, frequent vacuuming with a central vacuum cleaner or a good dust filter (pore size less than 1 micron) and covering mattresses and pillows with impermeable covers can reduce exposure to dust mite allergens. As will be discussed later, our research has documented that weekly vacuuming with a central vacuum cleaner may be an effective strategy as it removes the food source for dust mites. Another way to dehydrate and kill dust mites is through humidity control. Laboratory experiments (7) have shown that limiting relative humidity (RH) to about 50% kills the two most common species of dust mites. Our research indicates that it is difficult to maintain RH below 50% at the floor level in humid climates at all times, even if the average air RH level is maintained at or below 50% with whole house central dehumidifiers. However, we consider this is a very promising strategy and are continuing research in this area. Some results are presented later in this paper.

Pollen Allergens. Pollens from grasses, weeds and local trees are another frequent cause of allergy. In a study of North Carolina school children, 29% tested positive to grasses and weeds. Measurements in the Tucson area (8) indicate that between 10 to 25% of the outdoor pollen can come indoors. Pollen can come indoors by convective transport through open windows or cracks or can be carried indoors on clothes and footwear. Since most pollen grains are larger than 10 microns, efficient filtration should be effective if the pollen can be trapped before they are breathed in by humans. The practice of removing shoes and outerwear outside the house may be helpful in reducing the pollen inside homes. This could be encouraged by designing such a "mud room" space in the garage just before the garage entry door into the house as most North Americans enter the house through their garages rather than their front doors.

Pet Dander Allergens from cats and dogs. This is another important class of allergens. In the same North Carolina study, 25% of the school children tested positive to animal danders. Pet dander allergens are small, about 0.3 microns in size, and adhere to walls after being airborne. Frequent bathing of pets can reduce the allergens. However, like smokers, pets need to be outdoors to eliminate this allergen from the house.

Molds. Mold allergy is also quite common. 20% of the schoolchildren in the above study tested positive to molds. Molds are ubiquitous in nature and not all molds are harmful. Some molds such as Stachybotrus can be toxic and have been implicated in several sick buildings and in the deaths of children. If the surface relative humidity exceeds 65% to 70% on a continuous basis then molds can amplify and create a problem, particularly in the absence of light and airflow. Most molds in buildings arise from water leaks or mist carryover from cooling coils and grow in porous materials. Proper moisture control techniques, biocides and regular cleaning can control molds in housing.

Cockroach allergens. In the North Carolina study only 5% of the children tested positive to cockroach allergens and that's why we ranked the cockroach problem lower than most others. Recent epidemiological studies (1) point to the increasing number of asthmatic children (about 8.5%), especially in inner city housing, who have developed asthma because of cockroaches. Proper housecleaning and use of safe pesticides are needed for cockroach control.

Endotoxins. Airborne endotoxins are common outdoors and most likely arise from gram negative bacteria on leaves. Working with compost piles can cause asthma attacks in individuals. Indoors, endotoxins have been found in house dust and in the air in residences. Cool mist and ultrasonic humidifiers can propagate endotoxins (9). Endotoxins have been linked to severe lung problems. The sources and the prevalence of endotoxins in residential and commercial buildings is not known with a high degree of confidence. Likely sources appear to be standing pools of water (e.g. humidifier reservoirs, refrigerant drain pans which are not properly drained), large amounts of dead leaves and decaying indoor plants, cat and dog excrement etc.)

Volatile Organic Compounds and Odors(VOC's). Many VOC's and bioeffluents exist in houses, especially during the first several months. While irritating or unpleasant, VOC's are probably not unhealthy in concentrations found generally in houses, except to the hypersensitive. Proper choice of materials for construction, adhesives, finishes and furnishings can dramatically reduce VOC exposures in houses. Adequate ventilation ( with dehumidification in humid climates) should take care of the remaining VOC, odors and bioeffluents.

Fine Dust. Can be generated indoors during remodelling projects or brought in from outdoors. In large quantities, fine dust can trigger bouts of sneezing but is not generally toxic, except to the hypersensitive. Positive pressure ventilation and good air filtration can minimize the dust problem.

Radon. Recent large scale epidemiological studies using 10,000 households in Norway(10) seem to suggest that at levels generally found in houses, Radon is not a significant health risk. If it were, the strategies of positive pressure discussed in this paper should be helpful in mitigating the Radon problem.

 

The DDAMPFIRM Systems Solution

From the above discussions it appears that a systems approach to improving residential indoor air quality involves DDAMPFIRM (Drainage and waterproofing, Dehumidification, Air tight construction, Material selection, Positive pressure ventilation, Insulation to avoid cold floors, Return air ducts or transfers, Maintenance):

Please note that energy efficient construction are integral parts of the systems approach. Also, this is a work in progress, not all the answers are known yet and considerable challenges lie ahead.

Drainage and Waterproofing. It is quite amazing that given the importance of this topic, how often it is overlooked. A partial checklist of things to look for in slab-on-grade houses follows:

- The bottom of the slab or floor should be at least 8" above the top of the backfilled dirt of the yard which should be graded to drain away from the house.

- Install a tough polyethylene vapor barrier (minimum thickness of 6 mm) under the slab and take special care to seal the vapor barrier to all floor penetrations.

- Garage floor and driveway should be sloped to drain out.

- The roofs should have at least a 3 in 12 pitch and all roof penetrations properly flashed.

- All windows should be under at least a 2 foot overhang.

- Roof gutters should be used and drain out on splash blocks so water drains away from the house

- The wall system must be designed so that even if there is water penetration, it is allowed to drain out. Consult the manuals from Building Science Corporation (11) for excellent detailed guidance on this subject.

- The drain pan of air-conditioners should leave no standing water and if the drain clogs an A/C shut off switch should be installed.

Dehumidification. Whole house dehumidification in addition to central heating and cooling is recommended to control mold, mildew, endotoxins and dust mites. Room dehumidifiers are unlikely to control humidity throughout the house, although it might benefit a single room. Whole house dehumidifiers, as diagrammed in Figure 1, run independently of the central heating and cooling system and control the RH in the entire house. This is especially important in the months when the weather is humid and the temperature is mild. During these months the cooling or heating system does not operate frequently.

Air tight construction. Air tight construction is needed to avoid uncontrolled entry of dust, pollen and humidity. Good air distribution systems assure that the benefits of mechanical ventilation and central dehumidification are distributed evenly throughout the house. Several items need careful attention in this area:

- Air distribution ducts and registers must be constructed to be air tight. Figure 2 shows mastic being applied to a fiberglass outlet box whose joints have been taped with a fiberglass mesh cloth. Figure 3 shows a supply duct sealed to the outlet box with mastic. The inner and outer liners of the duct are attached to the collar with panduit straps and then sealed with mastic. Figure 4 shows a return duct inside a plenum space. Many houses use a drywall cavity alone to transport return air to the furnace in the basement. That should be avoided.

Figure 2. Applying mastic taped register outlet boxes. 1997 Orlando Health House.

- Air tight recessed can lights must be used. Code requirements in several states have caused production by several manufacturers. These lights should also be rated to allow direct placement of insulation on the lights. An alternative is to build a drywall box over a recessed can light and then foam seal the box.

- A good way to airtighten frame walls, band joists, garage ceilings and other hard to reach places is to use a combination foam insulation and air sealer (Figure 5). A recent innovation is to construct the roof and wall as a bubble i.e. foam insulate the bottom of the roof deck and the soffitt areas so that the whole shell is air tight. Figure 6 shows this construction. Note that there is no vented attic space any more. This results in the ductwork being in semi-conditioned space. Moreover the attic space becomes more usable as a storage space as it won't be as hot or cold as a vented attic. Until further research is done, this construction method (suggested to us by Building Science Corporation (11)) is not recommended in cold climates.

Figure 6. Insulated walls and roofline foam insulation results in a bubble protecting the occupants. 1997 Orlando Health House.

Material Selection. Materials should be selected to minimize dust production or collection, minimize VOC emissions and with an understanding of their moisture control properties. Easy maintenance and cleanibility are additional important factors.

- Figure 7 shows the duct system used in the New Orleans Health House. The fiberglass duct has a inner coating with a mildewcide and is fairly rigid. This should prevent loose fibers in the airstream and the hard surface should be easy to clean. The flex duct has a heavy liner to permit future cleaning. The cut lines of the ducts and the joint with the flex duct are sealed with a UL listed adhesive and sealant.

- To minimize VOC emissions, carpets should be made out of 100% Nylon fibers. Carpet cushions should be made of synthetic fibers and not from rebond or urethane.

- Vinyl covered wall papers should be avoided, especially on exterior walls.

- Choose low or no VOC paints, caulks and adhesives which are easy to use and maintain.

- Kitchen cabinets and countertops should be sealed so that there is no exposed particleboard.

- Minimize the use of oriented strand board and similar products inside the conditioned space to create built up areas.

In addition there should be no unvented combustion appliances inside the house. Correctly installed sealed combustion appliances, including the fireplace, are necessary. In garages and basements combustion appliances should be placed in permanently ventilated spaces which cannot go to a severe negative pressure.

Positive pressure ventilation. In all climates positive pressure ventilation is recommended. This is only possible if the house is air tight. Positive pressure ventilation requires only one intake and thus permits filtering and dehumidification of the incoming air. Maintaining a positive pressure minimizes infiltration of humidity and dust and improves combustion safety (as opposed to negative pressures which may cause backdrafting). In humid climates mechanical ventilation must be combined with dehumidification. Otherwise the house may experience serious moisture problems in mild and wet months when neither cooling nor heating is required. With careful product selection it is possible to construct houses with positive pressure ventilation even in cold climates. A thorough understanding of moisture control and building science is necessary before attempting this.

The kitchen and bathroom exhaust fans should vent outside of the house, not into the attic, and should be installed for point source exhausts in addition to the central whole house ventilation system. The bathroom fans should be on timers to prevent excessive operation.

To avoid excessive negative pressures from clothes dryers, either locate them outside the conditioned envelope or have a operable window in the utility room.

Filtration. Excellent filtration is a key to achieving excellent indoor air quality. For many years studies have shown that allergy sufferers feel more energetic and sometimes require less medication when using room air cleaners or good air filters. 4" and 7" pleated filters as well as HEPA filters are all good choices. Disposable filter elements are probably better than washable types. Most whole house electronic air filters produce some ozone and they should be avoided. If used, the electronic air filters should be well maintained and regularly cleaned per manufacturer instructions.

A frequent problem noted in many homes is the air bypass around furnace filters. This should be avoided by tightly sealing around the edges of the air filter.

Insulation to minimize thermal gradient between floor and air in the house. In slab on grade houses the slab is often poorly insulated or not insulated at all because of concern with termites. This creates a RH (as well as temperature) gradient between air in the middle of the room and that at the carpet, where dust mites live and breed. In order to limit the RH to 50% at the floor, it may be necessary to set the dehumidifier at 45% RH. Slab on grade houses are difficult to insulate around the slab. A promising new foundation insulation material is now on the market which is claimed to be termite resistant.

Return Air Ducts. Return air ducts or transfer ducts should be used to assure good air distribution to bedrooms even when interior doors are used. Air distribution can be augmented by the patented FanRecycler (12). This system helps equalize the ventilation, temperature, and humidity throughout the house.

Maintenance. Technology alone is not able to create excellent indoor air quality in a house unless it is regularly cleaned and maintained. The use of a outside vented central vacuum cleaner is highly recommended as it exhausts the dust laden inside air outside the home.

 

Research Results

In this paper results are presented for two allergy resistant homes in Orlando, FL and New Orleans, LA (labeled AR1 and AR2 respectively) and two conventional houses in the same cities (labeled C1 for the Orlando house and C2 for New Orleans). All except C2 are owned and occupied by a single family. C2 is a two story bed and breakfast place, about 100 yrs. old whose owners live upstairs and rent out the first floor rooms. AR1 is a conventionally built home where a whole house dehumidifier and ventilation (DV) system was added during construction. AR2 is the New Orleans Health House sponsored by the American Lung Association of New Orleans and Minneapolis. It features a energy recovery ventilation (ERV) system and a central vacuum cleaner which is used regularly. All houses except C2 have wall to wall carpeting. C1 is a conventional home constructed in 1991 which is more airtight than average.

Figure 8 shows the measured temperature (T) and relative humidity (RH) data at the carpet level in the Orlando area homes during 1996-7. Note that in AR1 the RH is well controlled even during the winter months whereas the RH in C1 exceeds 65% frequently in the winter months.

Figure 9 shows the measured T and RH data at the carpet level in the New Orleans area homes during 1996-7. In AR2 the RH levels are higher than AR1 for the winter months. In C2 RH levels are even higher.

Figure 10 shows the measured dust mite allergen (Der f I) levels. In each month several locations in each house were sampled and analyzed. The maximum allergen level among the samples from each house is plotted. The critical dust mite allergen level is 2 units. As expected, the allergen levels of the conventional houses are high. The allergen levels in the allergy resistant houses are negligible even though the RH levels are higher than 50%. This is believed to be due to the thorough cleaning (weekly to twice weekly vacuuming) practices of the AR1 and AR2 homeowners.

The energy consumption of the DV system in AR1 varies between 5.5 and 11 Kwh/day while the ERV system in AR2 uses about 3.5 Kwh/day.

 

Conclusions

It is encouraging that these allergy resistant houses have negligible dust mite allergen levels. An earlier paper documents the data from two other houses in the Orlando area. One of them had high dust mite allergen levels despite having a DV system (13). However, that house did not have a central vacuum cleaner. The authors are continuing this research with these and other houses.

 

References

1. D.Q. Haney, "Cockroaches are a Factor in Severe Urban Asthma, Researchers Warn", Associated Press, July 14, 1996 as reported in many major newspapers including the LA Times, 1996.

2. A. M. Pope, R. Patterson and H. Burge (editors), Indoor Allergens. National Academy Press, Washington, D. C. p. 67, 1993.

3. Thad Godish, Indoor Air Pollution Control. Lewis Publishers. p. 29, 1989.

4. S. Chandra, R.F. Lockey, L.W. Alidina, D. Beal, R. Codina, and K. Gehring, "Adverse Health Effects and Elimination of Dust Mites in Humid Climate Housing," Proc. 7th International Conference on Indoor Air Quality, Nagoya, Japan, July 21-26, 1996. Vol. 3., pp. 433-438, 1996.

5. E. Fernandez-Caldas, R. W. Fox, G. A. Bucholtz, W. L. Trudeau, D. K. Ledford and R. F. Lockey. House dust mite allergy in Florida - Mite survey in households of mite-sensitive individuals in Tampa, Florida. Allergy Proceedings, Vol. 11/No. 6, pp 263-267, 1990.

6. A. M. Pope, R. Patterson and H. Burge (editors), Indoor Allergens. National Academy Press, Washington, D. C. p. 52, 1993.

7. L. G. Arlian, Water balance and humidity requirements of house dust mites. Experimental and Applied Acarology, Vol. 16, pp 15-25, 1992.

8. M.K. O'Rourke and M.D. Lebowitz. "Environmental Allergens and the Development of Chronic and Allergic Obstructive Lung Diseases," Chapter 13 of Environmental Respiratory Diseases. Eds- Cordasco, Demeter and Zenz. Van Nostrand Reinhold. p.303, 1995.

9. D. K. Milton "Bacterial Endotoxins: A Review of Health Effects and Potential Impact in the Indoor Environment" Ch. 11 of Indoor Air and Human Health, second edition, CRC Press, 1996.

10. K. Magnus, A. Engeland et al "Residential Radon Exposure and Lung Cancer -- an Epidemiological study of Norwegian Municipalities," Int J Cancer vol. 58, pp. 1-7, Jul. 1, 1994.

11. Building Science Corporation, Westford, Massachusetts. Phone - (508)-589 5100.

12. FanRecycler, U.S. patent #5,547,017 by Armin Rudd, Florida Solar Energy Center.

13. Chandra, S., Beal, D., Lockey, R.F., Codina, R., Orr, G.W., Astry, D.W. and L.W. Alidina PERFORMANCE OF HEALTH HOUSES IN WARM HUMID CLIMATES. Proc. Healthy Buildings/IAQ '97 Conference , Washington DC, Sept. 27 - Oct. 2, 1997.