FAQ
A: Re Q#1; never had this one before (although a significant number of the questions I have gotten are unique.) For Q #2: I think it's unusual for one person to smell something that others can't, but in the world of reactions to mold, some people can walk into a horrific infestation without being bothered, while others are unable to enter the home. It's possible that there is a dead critter in the ductwork. However, the possible association with the furnace raises the possibility (probably remote) that combustion gases are entering the building or ductwork. The two possible mechanisms are 1) Corrosion in the heat exchanger, allowing direct communication between the furnace firebox and the ductwork (this is a potential/inevitable happening at the end of a furnace's lifespan, about 20 or so years). It is hard to overemphasize the importance of CO alarms, especially in houses with aging furnaces (although a well-tuned furnace may not produce a lot of CO). A visual inspection of the firebox/heat exchanger might reveal any corrosion or opened seams in the latter. 2) There is the possibility of backdrafting: When multiple exhaust or vented combustion devices (water heater, clothes dryer) operate simultaneously, if sufficient replacement air is not provided, the resulting vacuum can set up a reverse flow in the weakest appliance, pulling combustion products back in. This can sometimes be detected by holding a piece of tissue paper near the opening of the flue pipe as it exits the appliance. (A small 'puffback' at startup is normal before a robust draft gets established in the chimney.) A partial obstruction in the chimney can also cause backflow of some combustion. For oil-burning equipment, backflows will have a prominent odor of burning oil.
A: First, some basic facts: Radon is a radioactive gas that is colorless and odorless. It seeps out of the ground and can collect in buildings. Its only known health effect is to increase the risk of lung cancer. Radon is present in every state in the country, with some areas having high concentrations of this gas. Radon causes more deaths than any other indoor pollutant. While radon may be distributed throughout the house from the basement by HVAC ductwork (notoriously leaky) especially if the basement is heated, other factors come into play as well. Homes without ducts can have radon problems as well. During the heating season, one important mechanism is thermosiphoning. As warm air rises in the building, it leaks out through the many small openings, cracks, etc characteristic of nearly all buildings. This creates a negative pressure in the lower portions of the building, drawing in outside air and air from the basement since there is typically good communication between the basement and first floor. Thus, radon is distributed to the living space. These negative pressures are also an important driving force to draw any subsurface gases, such as radon, into the building. Other important factors in generating negative pressures in buildings include vented combustion equipment- clothes dryers, hot water heaters, range vent fans and the furnace or boiler, except for 'sealed combustion' units. It is helpful to understand that these driving pressures can be very small-a few pascals are sufficient; likewise very small volumes of radon (on the order of a few cc's per 24 hours) can cause problems. Because of these (and numerous other) variables, radon levels can vary from day to day and hour to hour. Warm climates homes also have radon problems. Check EPA's radon map (State maps are also available.) The most important determinant of radon levels in a building is the geology beneath that building: hot rock beneath-likely high levels above. So there can also be dramatic differences between neighboring houses; thus, each house must be tested. How to communicate radon's importance? This is difficult, for a number of reasons: it's 'natural' and therefore less fearful to some, even though it's radioactive, which usually amplifies the fear factor; and it lacks immediacy-lung cancers take 25-30 years to develop. On the other hand, it is arguably the most lethal of indoor pollutants-18,000 to 22,000 excess US deaths per year (smokers' risks are multiplied by radon exposure); it's easy and inexpensive to test for, and fixing the problem can be readily done for about $1500 to $2000. I tell people that it's like having a smoke detector-while you may not have a problem, you can easily find out if you have a serious problem for only a few dollars. Another concept is that, if there are 'high' levels in your state-30 pCi/l or more-such homes would exceed the OSHA limit for workplace exposures. They would be shut down if they were uranium mines! Wouldn't you want to know this if you were living in such a home? It's easy to find out with a simple and inexpensive test. Your State radon office can provide additional information on radon, both general and local.
Update: The following is a comment from a reader and Dr. Ponessa's response. Since there was mention of a smoke detector and the very commonly installed type has concerning radioactive components, I thought of sharing the information: ATP://ecphoria/radioactive_fire_detectors Thanks for your comment! I really welcome comments and questions relating to my FAQ's and to other housing/environmental issues. Regarding ionization smoke detectors (the most common type), this raises a good point- these contain a small amount of Americium, a radioactive element. However, in the several decades that I have worked on radon issues (and smoke detectors) I have never seen any concern expressed that the use of such detectors poses a health threat in homes. The important take-away message, to the best of my knowledge, is that these devices should be disposed of in a responsible manner. At the end of their 10 year life span (manufacture date is on the back of the detector) I take the detector to my county's hazardous waste center (you might also send them back the the manufacturer-ask first.) Do not discard in a landfill, and do not send to an incinerator. It is difficult to capture (and explain) all of the significant facts about radon in a couple of paragraphs. The concern about smoke detectors brings to mind another fact that provides a valuable perspective: According to the National Council on Radiation Protection report (1987) on exposure of the US population to ionizing radiation, 84% of our exposure comes from natural sources, with about 2/3 of this attributed to radon. Thus, if you are concerned about exposure to radioactivity, you should know that about 54% of our exposure comes from radon. This is a pretty powerful argument to test for radon, and to fix high levels. Another comment, sent privately, stated that my posting suggested that radon problems mainly affect homes with basements. It was pointed out that homes without basements can have radon problems too. This is quite correct, and I apologize for not making this clear; the original questions that I responded to directed attention to basements, and my later posting should have made it clear that homes on slabs can also have serious radon problems. Likewise, homes in warm or tropical climates are also vulnerable to radon intrusion, (I believe this applies primarily to air conditioned, enclosed structures.) Ultimately, the intensity of radon release immediately beneath the building is nearly always the most important determinant of indoor radon levels. Again, thanks for your comments!
A: There are multiple aspects to this problem, but it definitely needs to be addressed. In no particular order, here are some thoughts:
1. I presume the humidity reading is correct. Assuming it is an electronic hygrometer, these are pretty reliable, although initial calibration may be off. It would be useful to test it, such as taking it outdoors in a moderate-temperature rainy day & checking for a reading of 100% RH. Alternatively, you could place it in a plastic bag, along with a cup full of water, wait a while, and look for a 100% reading. (I don't know if the device would function properly outdoors in Montana in January, but you would expect to see readings near zero outside on a cold day).
2. The windows should be at least double-glazed (or have a storm window). Triple glazing is probably more suited to MT. At 46% RH and an indoor temp of 70 deg F, condensation will occur on surfaces at about 43 deg F, the dew point for these conditions. So if the window surface temp is 43 degrees or below, condensation will occur.
3 If the hygrometer is wrong and moisture is higher than 46% RH, you need to look for a source of excess moisture. Many sources are obvious, some are not. One big source is unvented combustion. The furnace should be checked for backdrafting. Sometimes in cold climates, the large amounts of moisture in the chimney will freeze as gases cool in the upper parts of the chimney, blocking exhaust. Another cause of high humidity is a humidifier whose control malfunctions, causing it to operate continuously.
4. The ventilation devices-Heat Recovery Ventilators-are generally a good idea, but sound considerably overpriced. They provide ventilation while capturing most heat in the exhaust stream and remove heat from incoming summer air. An alternative would be to install a short duct with a timer control to bring in outdoor air to the return duct of your furnace, assuming that this is an accepted practice in your climate, and assuming that your house is too tight. This will have an energy cost, however.
5. Some possible solutions include: a) adding a plastic storm window (or insulating window treatments) to minimize room air reaching the cold glass surface. Briefly, the expense of doing this relates to appearance; functionally, anything that creates a small airspace from the window-poly film, vinyl or rigid acrylic-will likely solve the problem, but the cheapest will be the ugliest. b) You could also try running a dehumidifier, but this is costly to operate. You might put some effort into reviewing moisture sources in the home, against the possibility that your hygrometer is not accurate; you should be able to find lists of moisture sources in the home on the web, or in your Extension office.
A: A closed crawl space is generally a good idea for moist, humid (summer) climates, since ventilation during these conditions introduces more moisture than it might remove. However, it is not unusual for unexpected factors to come in to play when applying novel solutions to such problems; therefore, it is important to do regular inspections of affected areas. This will help identify any problems that may not have been anticipated. It might be worthwhile to invest in an electronic hygrometer (available in electronics stores for about $40) to check on moisture levels; generally, these should be no higher that 50-60% RH in conditioned spaces. The problem with basement (or crawl space) dehumidifiers is that, due to the low temps in the basement, their coils may frost up. You can buy models with a defrost cycle, but it may be worthwhile to simply operate a conventional unit for a while, checking regularly for frost. I had used a regular dehumidifier in my own basement, together with a heavy-duty cycling timer that shuts it down for 10 minutes every hour. Three years ago I omitted the timer and have not noticed any problems. A colleague in South Carolina was able, in a one -story rancher, to direct hot air from the attic into his basement to accomplish dehumidification there during the summer. (I doubt that you would see much benefit from October through May.) A large fan was used to push hot attic air into the basement, and he found that operation for just a couple of hours in the afternoon was sufficient. Some precautions: make sure there are abundant openings in the attic for replacement air to enter, and the same in the basement. Any imbalances in air flow can cause pressure differences that can cause problems; e.g., suction in the attic can draw air from the house and, if the AC is on, you lose efficiency and, by drawing outside air into cool rooms, may get condensation on cool indoor surfaces. Pressure or wind in the basement/crawl space may blow out pilot lights if equipment is located there; (suction in basements/crawl spaces may cause backdrafting in flues, as well as bringing in radon.) Be vigilant! AND... first of all: do the easy things to keep moisture out of a crawl space: Cover the soil with 6 mil poly and make sure rainwater does not pond near the foundation. Other tips, mainly for basements, can be found athttp://www.rcre.rutgers.edu/pubs/publication.asp?pid=FS257
A: Some early work was done on this topic in the late 1980's by a Dr. Wolverton and was funded by NASA. He identified certain plants, such as spider plants, golden pothos and several other common houseplants as having the ability to remove formaldehyde and other volatile organic compounds (VOC's) from the air. Subsequently, vendors have been marketing things like indoor greenhouses as air purifying systems, and a trade association had, at one time, hired Dr. Wolverton in an effort to promote this idea. Meanwhile, other researchers have looked into this issue, and Wolverton's data, and concluded that, while this works qualitatively - plants can absorb some VOC's - the numbers don't work out. If a serious VOC problem exists, an impossibly large number of plants would be needed to remedy the problem. Certainly, plants can be a great indoor amenity, and they may provide a small contribution to indoor air quality. The downsides are that: 1) some allergic occupants may be bothered by the plants; and 2) the damp soil may be a breeding ground for mold. Remember too, that virtually all the water provided to a plant is ultimately put into the air by the leaves. So an 'excessive' number of plants can lead to a moisture problem.
A: From the brief description, it sounds like a growth of Poria incrassata (or related species), "The house eating fungus." It's found throughout most of the US, but is particularly common in the southern coastal states & the Pacific coastal areas. There is a pretty good description (although somewhat dated in a few details) in this book chapter: http://entomology.ucr.edu/ebeling/ebel5-2.html Basically, this fungus can grow in a damp crawlspace, often getting its start on wood construction debris left there. The key feature of these molds is that they send out long growths (rhizomes) that can enter walls, extending even to the second floor. The key mechanism is the capability of these growths to convey water (from the earth) along their length, allowing continued growth as wood is consumed. Ultimately, serious structural damage results. The simplest cure is to cut these rhizomes, provided that there are not other sources of water in the walls (such as from condensation or leakage). Some chemical treatments are also effective.
A: For the vapor barrier, 20 mil sounds like overkill. However, this might be appropriate if there is 'traffic' expected in the crawlspace; for example, to service HVAC equipment located there. More customary is 6 or 10 mil, placed on the ground and overlapped 6" or so. The best applications involve carrying the plastic up the foundation walls for about a foot, sealing it to the walls. This strikes me as a lot of extra labor for, probably, a small benefit. In any event, though, this stuff is cheap relative to the labor involved in installation. I don't know much about costs for doing the plastic or installing insulation; getting a couple of bids, for the same specifications, seems like a very good idea. The area involved is, obviously, an important factor. Also important is the headspace available. If it's three feet, installation is a lot easier than if it's 18 inches. The high water table is a tough issue to deal with. If liquid water is regularly seen (and gutters are performing properly, and there is proper grading away from the building) a sump pump might be in order. Local practice can offer some guidance; if neighbors have them, and if they improve things, then this might be part of the solution. But a plastic ground cover (and proper rainwater disposition) are the first steps. If mold is found, it should be removed. This needs to be done safely, by someone who knows what they're doing, so that the rest of the house is not contaminated, and neither workers or occupants are exposed. Killing the mold is not sufficient if there are large areas involved-more than 10-20 sq ft.
A: While I can't absolutely guarantee that this would work, I have recommended the treatment of house odors based on the remediation that is used after a house fire (to get rid of residual smoke odor, after the soot has been physically cleaned): Hire a firm that does fire damage restoration/cleanup to provide an ozone treatment for the house. This is done, of course, while the house is unoccupied. This method is used in hotel rooms also, when a smoker has occupied a non-smoking room. Although ozone is a strong pulmonary irritant, it is a highly reactive chemical that dissipates quickly and should pose no lingering threat. A good airing afterwards should dispose of any byproducts of ozone reactions with volatiles in the home. It would be best to do this treatment in an empty house as much of the odor may have penetrated upholstered & fabric furnishings and the ozone treatment may not be fully effective on the furnishings. I would imagine that the sellers would agree to a contingency in which the transaction would depend on the success of this treatment, to be determined several days after the treatment. While this instance with the curry seems pretty specific, it's applicable to some other odors as well, but not if a quantity of material is embedded in a surface, like, say, cat urine. IMPORTANT NOTE: It cannot be emphasized too strongly that ozone is a potent irritant, and 'consumer' ozone generators, meant to be used in an occupied space, are a bad idea according to EPA and the American Lung Association.
A: Since you associate the smell with the AC system, the most likely culprit would be the condensate tray beneath the cooling coils of that system. The coil unit is located above or near the furnace, where the return ducts meet with the supply ducts. This part of the system is known as the Plenum. When the warm, moist return air hits the cold coils, condensation occurs and the water falls into the condensate tray. The little tube that drains this tray often gets plugged up, the tray fills with water, and mold colonies form. If you can gain access to view the coils or tray, you should be able to easily confirm mold colonies. I would think a duct cleaning service would be best equipped to tackle this job, provided that they do it in a safe fashion, without stirring up a lot of mold debris that would contaminate the ducts. (Duct cleaners, though, do not usually get into the plenum area.) Those who service your furnace should also be able to do this work, although they may not be skilled in doing it in clean, safe fashion. You might even be able to do this job yourself, if you are able to get access to the tray. The job must be done in such a way that it does not contaminate workers of the surrounding area and ducts. Take a look at the EPA booklet "Mold Remediation in Schools and Commercial Buildings" for vital information on personal protection for those doing the work.Update: A colleague (Ted Funk, Cooperative Extension Specialist, University of Illinois, Urbana.) Added these valuable comments:
1. Such odors from AC systems are often described as a 'dirty sock' smell.
2. The offending mold often grows on the coils themselves.
3. An AC technician would ordinarily be best qualified to clean the coils.
A: I assume that you're taking readings of moisture content with a moisture meter; as I recall, wood at moisture content above about 16% is susceptible to mild growth, although the progress of growth is temperature dependent. If the sheetrock itself is reading 22%, this sounds quite high and I believe there is a serious possibility of mold growth. (Citation: Lstiburek, J. Moisture Control for Buildings. ASHRAE Journal. Feb. 2002. pp 36-41.)
The general recommendation of the Institute of Inspection, Cleaning and Restoration (IICRC, a trade association that sets standards for water damage remediation) is that flooded materials need to be dried out within 48 hours before mold growth gets out of control, although this criterion may be stretched a bit in cooler temperatures. Generally, it is only possible to salvage drywall that has been slightly wetted, but saturated drywall is usually cut out (in increments of 2 feet) to a point above the line of flooding, and replaced after the framing has dried.
Follow-up Comments Regarding Use of Bleach to Kill Mold
I'd like to provide some additional info on the usage of bleach; my response to last week's question involved a very narrow issue and I think it is appropriate to discuss this in a wider context, especially since some groups oppose the use of bleach under all circumstances. This is a somewhat difficult question: to use, or not to use bleach. My opinion is that, while bleach (from the jug) is a pretty potent material that deserves a great deal of respect (i.e. Follow The Directions! Always! Really!) it can be safely used in the appropriate circumstances/rules. Bleach can cause burns to eyes, mucous membranes and other sensitive tissues, and can cause asthma attacks in susceptible persons. While I'm aware that some environmental groups discourage bleach use, I did not find such prohibitions in a quick scan of the websites of the American Lung Association, the EPA or WebMD. From above: The appropriate circumstances/rules for bleach use include:
1. People with asthma or sensitivities to bleach should not use it, and should not be around when it is used.
2. It should not be used around groups of kids, since some might be vulnerable to it.
3. Label directions must be carefully followed-adequate ventilation, dilution and usage according to directions; NEVER use straight bleach. (Dilute bleach may take a few minutes to work, but it's definitely worth waiting.) Dilute as directed-No Cheating!
4. Don't mix with other products: Ammonia, and products containing ammonia compounds, react with bleach to produce a deadly gas similar to the nerve gas used in WW I.
5. Keep bleach containers away from children when it is stored and during use.
With regard to when to use bleach (and when not to) - this is important too. Bleach has two uses- it bleaches/whitens things, removing stains; and it kills germs, mold and other things. BUT, there is a VERY big exception regarding mold-see below. My response last week involved a question about removing mold stains from household items, and I listed some alternatives for items that bleach might damage. In fact, it might have been better for me to have recommended using the weaker products (rubbing alcohol or hydrogen peroxide) first. For laundering, non-chlorine "oxy" type bleaches are available. The MOST IMPORTANT THING to understand about bleach and mold, according to the EPA and others is that for large, thick mold infestations-a few square feet or more-bleach is NOT the way to go. Killing the mold is NOT the right approach, since killed mold spores and debris does not inactivate its harmful properties. The mold should be safely removed (using soap & water) and the moisture problem fixed. Other situations where dilute bleach (sodium hypochlorite) is used for its sterilization property include swimming pools, water wells that have become contaminated, and recovery from "blackwater" flooding after the safe removal of mud, mold and other debris. Blackwater flooding refers to floodwaters that have been contaminated by sewage or floodwaters. This flooding, and all groundwaters are considered to carry silt and harmful organisms, requiring cleaned surfaces to be sterilized as well. (Please be aware that while 'germ killing' is very important in some specific situations-the above mentioned, along with food prep and in consideration of persons with medical vulnerabilities-we as humans are not designed to live in a sterile environment, and have survived since the beginning of time in the presence of microorganisms. In fact, some research indicates that exposure to microorganisms early in life is important for normal development of our immune system which fights infection.)