What can a tenant do when s/he discoveres that s/he is living in an intolerably moldy apartment?
What follows is an email, slightly edited, from a tenant in a moldy apartment in Kentucky. The risk in her situation is increased because she suffers from a compromised immune system. My advice to her follows her letter.
Tenant describes a moldy apartment
I appreciate the user friendly format and the wealth of information on your website. I'm suffering severely from mold related illness and I need immediate help.
Two months ago I moved into a new apt. Ever since I have had terrible congestion that appears w/in a minute of entering the apt. And only clears up after hours of leaving the apt. I have gone and had allergy testing and find I am highly allergic to *most* molds.
I have found a black shadowing mold like substance on the walls coming from beneath the kitchen cabinets. The *dust* settles on the edge of the counter at the wall beneath the cabinets. The dust is large particles that look a lot like black pepper. It also sticks to wall on the way down.
Possible causes of apartment mold, possible extent of mold
I have been made aware of a leaking roof in the 2nd floor apartments so severe that requires buckets to contain. The water, I have been told runs down the walls into the ground floor apartments where I am a tenant in one. The apartments are known to be old and from the road I can see large blackish streaks across the light brown roofing.
What steps the tenant has already taken
I've just bought two HEPA filters for the bedroom and living room which has seemed to make a significant difference in the severity of the congestion. Also, I have been told that the air conditioning and heat is run on a water coil system (the air is circulated through all of the apartments) which happens to be in my bedroom closet. when I removed the vent to put a filter in I found mold covering the bacck of the metal slats in vent cover. I cleaned it with bleach.
Wants to move
I need to move because I cannot live with this building-related sickness. It is important to know what I'm dealing with before I go to management, because it seems to be such a severe structural issue, they may try to do something underhanded and cover it up.
Compromised autoimmune system increases risk to tenant
Also I have some sort of autoimmune condition(Lupus, MS they haven't pinned it down) I am no longer able to do what I went to school for. My fine motor skills are compromised(and I have slight tremor).
I have a year lease and need to handle the situation in a way that will allow me get out from under this situation w/out my being taken advantage of and I am no expert in these matters.
Please let me know when you have a moment how I can handle this terrible situation(err, the mold) thank you so much for taking the time to read this lengthy missive.
Action Advice for Tenants in Moldy Apartments
I'll help as I can but keeping in mind I'm distant and can't see all of the conditions. Therefore my advice can only be general, and we must keep in mind that there could be important observations that might change the assessment of your situation as well as the advice on steps to take.
What you describe sounds severe and building-related.
Possible hidden mold
The mold that you *see* may not by any means be the whole problem, or even much of the problem; various species could be in building cavities and in the HVAC system. Also, "bleaching mold" is never a successful remedy for a moldy building. The places where mold is growing must be found, moldy material removed, exposed surfaces cleaned, and the causes of mold growth corrected. If the area of mold growth is large (more than 30 sqft) the work needs to proceed with special procedures to avoid spreading moldy dusty debris around.
Compromised immune system increases vulnerability to mold-related illness
The fact that your immune system is compromised places you at extra risk and means that you and the contents of your apartment need to be protected carefully.
Some possible mold reservoirs in the building
You describe two apparent sources, and of course there could be other sources from other leaks or problems you haven't discovered:
Roof - can have leaked into ceilings and walls; depending on what buildng marterials used, they could be moldy with problem molds.
HVAC - If there is a common A/C duct system which has become mold contaminated, no amount of cleaning in your immediate apartment would be sufficient since it is possible that the whole system needs to be cleaned, or possibly some duct sections replaced, and the cause corrected. Also it is common for A/C condensate or water from a chiller system to leak; water could have leaked into your closet ceiling and walls, also creating a problem mold reservoir.
Very often when I visit a site I find other leaks and mold sources that need to be addressed, so I wouldn't assume these are the full extent of what needs attention.
Building management reluctance to address mold problems properly
Sometimes a buildng management is reluctant to face the expense and trouble of handling this situation correctly - which would involve a thorough building survey, evaluation, diagnosis of problem areas and their causes and specification of the steps to remedy them, followed by performing of the work followed by clearance inspection and testing by someone not at all connected with the contractors performing the remediation.
Reluctance of building managers to address mold also comes from the wish to avoid alarming other tenants. In my experience this is always a mistaken notion, as tenants talk to one another anyway, and building-related illness frightens people - fear spreading faster than mold growth. Accurate information and the assurance that tenant concerns are being handled competently is more effective than other less direct responses by building management.
Half-baked or amateur workmanship risks increasing the ultimate cost to the building management by making building occupants sick and contaminating their belongings.
What a tenant can do about a moldy apartment
1. You should notify building management in writing of unhealthy unsafe conditions that need attention and that you are unable to live in the apartment.
2. You might be successful in identifying some of the mold suspect material you see as problematic, and you might collect a settled dust sample to see you can pick up indications of other problem molds or allergens. However identifing mold in an apartment, while it may convince building management to act, does not and cannot establish the level of exposure that an individual has had to the mold found, nor does it assure that the mold identified is the only or even the main hazard. The prime use of tenant sampling in this case is to show management that there is at leastsome evidence of problem mold in the building
Our mold sampling instruction contains sampling instructions you can follow. I'm on assignment out of the U.S. and won't be processing any lab samples until after 9/10 so if you are in a rush you should use another lab but you can still follow my sampling procedures.
3. If building management elects to make some effort to deal with the problem:
3.a. be sure that the work does not create demolition debris and mess which contaminates or further contaminates your belongings, especially soft goods like curtains, carpets, bedcovers, which may then require cleaning, and worse, upholstered furniture which might not be able to be cleaned adequately.
3.b. if your posessions are already likely to be contaminated with moldy dust they should be cleaned before taking them to a new home; soft goods can be laundered or drycleaned; hard surfaces can simply be washed or wiped. Moldy upholstered furniture is in question depending on how bad it is; surface dust can be vacuumed off of it; if upholstered furniture has been wet or has had mold growing on or in it it is probably not salvageable without complete reupholstering from the frame up.
The more you know about proper procedures to find and clean up moldy buildings the better you can assure that your situation is handled properly. The articles at these links might be helpful:
The Mold Action Guide
When to Hire a Mold Professional
FAQs about Mold
Keep me posted on how you proceed.
Best wishes.
Daniel
This Blog is about "What to do about mold in buildings"
When is mold a problem in buildings? What should be done about it? Find expert field and lab testing, inspection, remediation advice, but ... avoid "fear of mold" and bogus advice which can both cost you and yet may not really address the problem effectively. My interest is in providing expert service to my clients, protecting not only their health but their wallets. I provide field investigations to find problems and to recommend solutions to mold in buildings, and I operate a forensic laboratory in New York which accepts mold and other indoor air and particle samples for examination. In depth information is at www.inspect-ny.com and the links at that page. Website content suggestions are most welcome.
Case Histories: Here I post summaries of field and lab toxic or allergenic mold and other indoor air quality investigations. I omit private information. I describe observations, procedures, and findings helpful to readers who are trying to remedy their own mold, allergenic, carbon monoxide, odor, or other indoor air and related health concerns in their indoor environment.
Sunday, September 03, 2006
Sunday, April 30, 2006
Will "Black Mold" Return if Moisture is Kept Low?
Black Mold Question from a Reader:
I have been finding your site very informative, and have a question (actually a statement) but can you confirm if the following is mainly correct?
Black Mold is found everywhere, in nature, outdoors, indoors etc. It isnt until a constant moisture source and humidity conditions are present that the black mold might actually become a problem, forming in colonys, creating problems, toxins etc. And once those conditions are take care of, with due care to avoid cross contamination, and moisture problems are taken care of and humidity levels are under control, the mold can be properly remediated and therefor resolved as long as moisture problems are constantly checked on for further invasion and damage, and things that are installed (ie: C/A etc) to help humidity issues are cleaned properly.
Thank you,
N.R.
"Black mold" is not the issue
Reply from D.F.
Black mold is not necessarily the issue in a building. Public fear that is focused only on "toxic black mold" is a bit of confusion caused by media attention to the Stachybotrys chartarum scare.
1. Some black molds are perfectly harmless such as black mold found on much new framing lumber and which is in the Ceratocystis/Ophistoma group - a cosmetic only mold which is not harmful to humans and which
does not rot the wood.
2. Black mold, even if a toxic one may not be what is making occupants ill: Some black molds that people fear, such as Stachybotrys chartarum, are not normally airborne and become so only in response to violent disturbance such as during demolition. So even though this mold can be toxic and seems to be associated with a wide range of complaints, the fact that it is seen on a building wall does not assure that this is the mold to which building occupants are being exposed.
3. Visible mold as a moisture indicator: Black mold" in a building thus should be considered an "indicator" mold of wet conditions, and a careful inspection is in order. While S. chartarum is a "black mold" which can be harmful, almost always, when this mold is found in a building, or when other "black molds" are observed (some are not relally black but look so on a surface and outside the microscope), I find other more problematic but harder to see but more airborne molds such as Aspergillus sp. when I inspect thoroughly.
What is important, particularly if people are sick, is to have a building expert, someone who knows where and how to look for problem molds in buildngs, inspect the property to find the leak history, mold reservoirs, and to do enough mold identification to assure that the real problems, if any, have been found and that the scope of cleanup work can be specified.
I emphasize point #3 because in most of the buildings I inspect, where an occupant has become worried about "black mold" someone has seen, the dominant problem molds in the buildings are NOT the "black molds" that were observed but rather harder to see light colored but more-airborne smaller spore and often toxic or pathogenic molds such as those in the Aspergillus sp. group.
I agree that once a building has been established as adequately clean of mold, monitoring leaks and humidity are key.
I agree that if we keep indoor humidity at proper levels and do not permit leaks and moisture problems to go unattended, we would not expect problematic indoor mold growth.
More in-depth discussion of these points can be read at the following articles:
Mold Action Guide - my main "Mold Action Guide" step by step instructions on what to do about mold in buildings
How to Look for Mold
How to prevent mold list of articles
How to Prevent Mold in Buildings main article on this topic
How to Get to Mold-Resistant Level of Indoor Humidity
Responding to Building Leaks and Floods to prevent rapid problem mold growth in buildings.
If you or other blog readers have other content suggestions I'd appreciate hearing from you.
Daniel Friedman
dfriedman@inspect-ny.com
www.inspect-ny.com
This Blog is about "What to do about mold in buildings"
When is mold a problem in buildings? What should be done about it? Find expert field and lab testing, inspection, remediation advice, but ... avoid "fear of mold" and bogus advice which can both cost you and yet may not really address the problem effectively. My interest is in providing expert service to my clients, protecting not only their health but their wallets. I provide field investigations to find problems and to recommend solutions to mold in buildings, and I operate a forensic laboratory in New York which accepts mold and other indoor air and particle samples for examination. In depth information is at www.inspect-ny.com and the links at that page. Website content suggestions are most welcome.
Case Histories: Here I post summaries of field and lab toxic or allergenic mold and other indoor air quality investigations. I omit private information. I describe observations, procedures, and findings helpful to readers who are trying to remedy their own mold, allergenic, carbon monoxide, odor, or other indoor air and related health concerns in their indoor environment.
Monday, March 06, 2006
Mystery blobs - is it mold? is it Mildew? What Mold Tests do I Order?
This Blog is about "What to do about mold in buildings"
When is mold a problem in buildings? What should be done about it? Find expert field and lab testing, inspection, remediation advice, but ... avoid "fear of mold" and bogus advice which can both cost you and yet may not really address the problem effectively. My interest is in providing expert service to my clients, protecting not only their health but their wallets. I provide field investigations to find problems and to recommend solutions to mold in buildings, and I operate a forensic laboratory in New York which accepts mold and other indoor air and particle samples for examination. In depth information is at www.inspect-ny.com and the links at that page. Website content suggestions are most welcome.
Case Histories: Here I post summaries of field and lab toxic or allergenic mold and other indoor air quality investigations. I omit private information. I describe observations, procedures, and findings helpful to readers who are trying to remedy their own mold, allergenic, carbon monoxide, odor, or other indoor air and related health concerns in their indoor environment.
Email questions:
First off thanks for your very detailed website. I have a question about what to sample for a mold analysis. We are renting a home a home where there is what appears to be visible mold on some of the interior surfaces of exterior walls. I have shown this to the management here; however, they repeatedly minimize/ignore the problem and will not do any testing.
We have explained that my partner has been having health/respiratory problems that we believe might be connected to mold, so we would like to have this identified in order to take care of our health. In turn they simply doused the area with bleach. That was a week ago and it has already started to grow back.
In the meantime, they have claimed that this was simply "surface mildew" and their lawyers have written us a letter to warn us, well, I'm not really sure what it is to warn us, but mostly it seems like an attempt at intimidating us even though they admit it is a common problem in this community. It does however seem like it could be primarily a surface problem as all the walls are bizarely impenetrable--old military housing.
Since it is a rental unit (therefore we can't do bulk sampling) and the mold is visible, we are wanting to do simple tape-lift sampling for identification purposes. Until we get some handle on what we are dealing with we can't really decide how to proceed.
The question that I have for you pertains to an unknown substance. Once we performed the first cleaning of this substance in our closet, which was heavily effected, the substance began appearing in other rooms where it had not been before (the same after they doused it with bleach). After it had spread, I found what appeared to be a simple bump in the paint on one wall. I rubbed a washcloth across it, and the bump was actually a white surfaced, kind of creamy yellow goo (not a scientific term, I apologize)--the best description that I have for it is that it seemed kind of like brie with the white outside and the inside was similar, kind of yellow, soft, etc. Underneath that was the paint. After they did their bleaching, more bumps appeared in the paint in other areas of the house, as though there were something liquid under them. (They are soft and squishy.) As I said I am no expert in mold, therefore I am not sure if this sounds like it could be connected to you. Does it sound like something that we should tested, and if so what is the best way to get that done/get it to you?
Thank you very much for your time and any insight that you can provide -- Dianna, 3/1/2006
1. There is no mildew in buildings. Mildew is an obligate parasite that grows ONLY on living plants - so unless your home is made of grapes or lilac leaves there is no mildew on it. What grows in buildings that looks like mold is mold. Some mold is harmless-cosmetic; some is allergenic; some can be pathogenic or toxic. People who are at extra risk such as with immune disorders or respiratory concerns are at extra risk.
Tips on how to look for mold are at
http://www.inspect-ny.com/sickhouse/lookmold.htm
Tips on how to use your flashlight to spot hard-to-see mold are at
http://www.inspect-ny.com/sickhouse/mold.htm#lightuse
Pictures of what mold looks like in a building are at
http://www.inspect-ny.com/sickhouse/mold.htm
Stuff that is not mold but is sometimes mistaken for it is shown at
http://www.inspect-ny.com/sickhouse/NotMold.htm
2. The mold you see might be "surface" mold or it might be the tip of an iceberg of a larger mold reservoir - the distinction depends on why it's growing where it is and where leaks have been throughout the history of the building. If all you see is a small area (less than 30 sq.ft.) it is unlikely to be the principal problem in a building but it might indicate that there is a larger but un-detected problem. My web articles discuss how to look carefully for mold.
3. Sampling - you can't do invasive inspecting like checking wall cavities but you can
- notice evidence of a history of leaks into building cavities - which raises the level of risk of hidden problems
- notice where there is visible mold and collect a few surface samples using tape www.inspect-ny.com/sickhouse/bulksamp.htm has the procedure - sample things that look different by color, texture, or by what they're growing-on (drywall vs. wood for example).
- collect a sample of settled dust from one representative area, perhaps a bedroom, to see if we can pick up unusual levels of problem mold spores in that material - which would indicate that there has been a high airborne mold level at some time.
Instructions for easy and inexpensive tape lift sampling are at
http://www.inspect-ny.com/sickhouse/bulksamp.htm
4. Bleach - if building maintainers used bleach as a "mold treatment" that suggests that work is being done by people who lack good information about how to clean up or "remove" problematic mold in a building. The object is to remove problem mold, not to "kill it" since "killed spores" even if you could kill them all (which you can't) may still be allergenic or toxic to the occupants. Further, surface treatments ignore possibly significant hidden mold reservoirs.
Finally, any demoltion or "cleaning" that blows dust all over the apartment or your belongings is at risk of increasing rather than reducing the health risk in the building.
5. Wall blisters? From your description of blisters appearing only after someone bleached and washed the wall surfaces (superficial and perhaps inadequate mold cleanup) I don't know what you've observed or even whether or not it's mold - yellow goo? It sound ass if your observations may be leak or moisture related which in turn are key factors in assessing mold risk. If the walls were treated with strong bleach and water it's possible that that substance has damaged, penetrated, and is causing blisters in the paint. I'd try pricking a blister and collecting the liquid for analysis.
I'd inform the "lawyers" that the cost of making you sick or sicker, or the cost of having to do extra cleaning if the apartment people don't follow proper procedures, or the cost of having to inspect and clean the building repeatedly because they're starting off with shortcuts are all likely to ultimately cost the building owners a lot more than the cost of doing it right the first time.
-- Daniel Friedman 3/1/2006
When is mold a problem in buildings? What should be done about it? Find expert field and lab testing, inspection, remediation advice, but ... avoid "fear of mold" and bogus advice which can both cost you and yet may not really address the problem effectively. My interest is in providing expert service to my clients, protecting not only their health but their wallets. I provide field investigations to find problems and to recommend solutions to mold in buildings, and I operate a forensic laboratory in New York which accepts mold and other indoor air and particle samples for examination. In depth information is at www.inspect-ny.com and the links at that page. Website content suggestions are most welcome.
Case Histories: Here I post summaries of field and lab toxic or allergenic mold and other indoor air quality investigations. I omit private information. I describe observations, procedures, and findings helpful to readers who are trying to remedy their own mold, allergenic, carbon monoxide, odor, or other indoor air and related health concerns in their indoor environment.
Client asks about indoor mildew, strange wall blisters, and what mold to test for
Email questions:
First off thanks for your very detailed website. I have a question about what to sample for a mold analysis. We are renting a home a home where there is what appears to be visible mold on some of the interior surfaces of exterior walls. I have shown this to the management here; however, they repeatedly minimize/ignore the problem and will not do any testing.
We have explained that my partner has been having health/respiratory problems that we believe might be connected to mold, so we would like to have this identified in order to take care of our health. In turn they simply doused the area with bleach. That was a week ago and it has already started to grow back.
In the meantime, they have claimed that this was simply "surface mildew" and their lawyers have written us a letter to warn us, well, I'm not really sure what it is to warn us, but mostly it seems like an attempt at intimidating us even though they admit it is a common problem in this community. It does however seem like it could be primarily a surface problem as all the walls are bizarely impenetrable--old military housing.
Since it is a rental unit (therefore we can't do bulk sampling) and the mold is visible, we are wanting to do simple tape-lift sampling for identification purposes. Until we get some handle on what we are dealing with we can't really decide how to proceed.
The question that I have for you pertains to an unknown substance. Once we performed the first cleaning of this substance in our closet, which was heavily effected, the substance began appearing in other rooms where it had not been before (the same after they doused it with bleach). After it had spread, I found what appeared to be a simple bump in the paint on one wall. I rubbed a washcloth across it, and the bump was actually a white surfaced, kind of creamy yellow goo (not a scientific term, I apologize)--the best description that I have for it is that it seemed kind of like brie with the white outside and the inside was similar, kind of yellow, soft, etc. Underneath that was the paint. After they did their bleaching, more bumps appeared in the paint in other areas of the house, as though there were something liquid under them. (They are soft and squishy.) As I said I am no expert in mold, therefore I am not sure if this sounds like it could be connected to you. Does it sound like something that we should tested, and if so what is the best way to get that done/get it to you?
Thank you very much for your time and any insight that you can provide -- Dianna, 3/1/2006
Our Response - Sounds like water and bleach behind paint - excessive and improper "surface cleaning" does not correct a problem mold reservoir
1. There is no mildew in buildings. Mildew is an obligate parasite that grows ONLY on living plants - so unless your home is made of grapes or lilac leaves there is no mildew on it. What grows in buildings that looks like mold is mold. Some mold is harmless-cosmetic; some is allergenic; some can be pathogenic or toxic. People who are at extra risk such as with immune disorders or respiratory concerns are at extra risk.
Tips on how to look for mold are at
http://www.inspect-ny.com/sickhouse/lookmold.htm
Tips on how to use your flashlight to spot hard-to-see mold are at
http://www.inspect-ny.com/sickhouse/mold.htm#lightuse
Pictures of what mold looks like in a building are at
http://www.inspect-ny.com/sickhouse/mold.htm
Stuff that is not mold but is sometimes mistaken for it is shown at
http://www.inspect-ny.com/sickhouse/NotMold.htm
2. The mold you see might be "surface" mold or it might be the tip of an iceberg of a larger mold reservoir - the distinction depends on why it's growing where it is and where leaks have been throughout the history of the building. If all you see is a small area (less than 30 sq.ft.) it is unlikely to be the principal problem in a building but it might indicate that there is a larger but un-detected problem. My web articles discuss how to look carefully for mold.
3. Sampling - you can't do invasive inspecting like checking wall cavities but you can
- notice evidence of a history of leaks into building cavities - which raises the level of risk of hidden problems
- notice where there is visible mold and collect a few surface samples using tape www.inspect-ny.com/sickhouse/bulksamp.htm has the procedure - sample things that look different by color, texture, or by what they're growing-on (drywall vs. wood for example).
- collect a sample of settled dust from one representative area, perhaps a bedroom, to see if we can pick up unusual levels of problem mold spores in that material - which would indicate that there has been a high airborne mold level at some time.
Instructions for easy and inexpensive tape lift sampling are at
http://www.inspect-ny.com/sickhouse/bulksamp.htm
4. Bleach - if building maintainers used bleach as a "mold treatment" that suggests that work is being done by people who lack good information about how to clean up or "remove" problematic mold in a building. The object is to remove problem mold, not to "kill it" since "killed spores" even if you could kill them all (which you can't) may still be allergenic or toxic to the occupants. Further, surface treatments ignore possibly significant hidden mold reservoirs.
Finally, any demoltion or "cleaning" that blows dust all over the apartment or your belongings is at risk of increasing rather than reducing the health risk in the building.
5. Wall blisters? From your description of blisters appearing only after someone bleached and washed the wall surfaces (superficial and perhaps inadequate mold cleanup) I don't know what you've observed or even whether or not it's mold - yellow goo? It sound ass if your observations may be leak or moisture related which in turn are key factors in assessing mold risk. If the walls were treated with strong bleach and water it's possible that that substance has damaged, penetrated, and is causing blisters in the paint. I'd try pricking a blister and collecting the liquid for analysis.
I'd inform the "lawyers" that the cost of making you sick or sicker, or the cost of having to do extra cleaning if the apartment people don't follow proper procedures, or the cost of having to inspect and clean the building repeatedly because they're starting off with shortcuts are all likely to ultimately cost the building owners a lot more than the cost of doing it right the first time.
-- Daniel Friedman 3/1/2006
Saturday, January 14, 2006
How Low Should You Keep Indoor Humidity to Avoid a Mold Problem
This Blog is about "What to do about mold in buildings"
When is mold a problem in buildings? What should be done about it? In depth information is at www.inspect-ny.com/welcome.htm#environ and the links at that page. Website content suggestions are most welcome.
Case histories: Here I post summaries of field and lab toxic or allergenic mold and other indoor air quality investigations. I omit private information. I describe observations, procedures, and findings helpful to readers who are trying to remedy their own mold, allergenic, carbon monoxide, odor, or other indoor air and related health concerns in their indoor environment.
We're going to discuss maintaining an anti-mold low humidity level in a building which does not currently have a mold problem. No dehumidification system will be up to the task of preventing mold if a building has serious leaks, flooding, or water entry. (© Daniel Friedman 2006 All Rights Reserved.)
And no dehumidifier, no "air cleaner," no "ozone generator," nor other magic machine, spray, or air treatment will correct a mold problem in a building if there is a significant problem reservoir. For that case, what's needed is to find the mold problem, remove it, and correct its cause. And as a last warning, there are about 1.5 million mold species - some of them may be able to grow in very dry or very wet or other inhospitable conditions.
We're therefore focused this article on the common indoor problem molds in this article. The genus I refer to include some common problem indoor molds such as Aspergillus sp., Penicillium sp., Stachybotrys sp. /S. chartarum /Memnoniella echinata, Trichoderma sp. /T. viride, Ulocladium sp. /U. chartarum, and at a less significant level of concer, Cladosporium sp. - the king of molds and its competitor Alternaria sp.
Suppose a building does not currently have a mold problem, or a mold cleanup project has been completed.
1. be sure there are no ongoing building leaks, water entry, or venting problems.
2. keep the indoor humidity level in the mid-comfort range. A maximum indoor relative humidity of 55 should be ok, 50 better, 45 for an attic knee wall provided there are no ongoing leaks and the attic space is not one which is being vented to outside (in that case you're not in control of the humidity. If you run humidity too low or too high the building occupants will be uncomfortable.
Technical background on indoor relative humidity (RH) control:
this is getting slightly more technical about measuring the relative humidity.
If the RH in the center of a basement is 55% it is likely that at the walls or corners, where there is less air circulation, the RH may be different. The local temperature difference close to a cool masonry wall surface means that both temperature and measured relative humidity close to the wall will be different than in the center of a room.
But it's at the cooler wall surface that condensation may be expected to occur.
If you measure the RH at the worst-case location such as the most-suspect-of-dampness corner of a basement and you're 55% close to the wall you're likely to be ok.
In the case of an attic crawl space, perhaps a knee-wall area abutting an upper floor bedroom, the risk of excessive inside humidity at a wall is much less than in a basement. In the attic we don't face a cool concrete-block wall surface in the attic.
But what about an un-vented attic in a cold weather climate? Heat loss into such a space and warm moist air leaking into such a space can indeed create high levels of problme moisture - enough to wet surfaces or even form frost and later drip onto the attic floor.
On the other hand, if the attic is vented to outside (ridge vents and soffit vents as I recommend) you'll never control the attic RH. You'll be trying to control the whole outdoors.
On the third hand (if that's possible), if an attic is not vented to outside, the RH
there is most-likely a function of and approach the levels of the humidity levels in the air in the rooms abutting and below the attic area.
One client said he could keep the basement at 55 but didn't want to push it below that. Is this enough safety margin?
At 60% indoor RH we're entering the indoor problem mold-formation risk zone of high interior moisture in building wall or ceiling cavities or on wall and floor surfaces, possibly conducive to mold growth.
If you set the RH target at 55%, you're operating with **not much safety margin** of dryness. A small change in outdoor conditions (spilling water by the foundation) or indoor conditions (a nearby roof, wall, window, plumbing leak) can increase the moisture and RH into the problem zone. If for reasons of dehumidification cost you have to operate close to the edge, extra attention to leaks, moisture proofing, roof and surface drainage are even more important.
If a building has been damp for some time, moisture has been absorbed into various materials such as wood framing and masonry surfaces. It may take weeks or even longer to drop the humidity in such an area, as the moist materials also have to dry out, not just the air. Using a fan to increase air movement in the area being dehumidified can speed this process.
Warning: if you cannot get the indoor RH down to a low level in a below-grade area such as a basement or crawl space, I'd suspect that too much moisture is continuing to enter through the slab or masonry walls. Attention to outside drainage may not be enough. In such cases, coating the walls with a masonry sealer (Thoro-Seal(TM) or Dry-Lok(TM) are example products) might help.
If you want to get past this practical discussion of indoor humidity and mold, check out "Understanding Ventilation," by John Bower. The Healthy House Institute, 1995.
More than a normal person can stand to read about what to do about mold in buildings is at my website. You might start at the "Mold Information Center - What to Do About
Mold in Buildings"
Hope this helps.
Daniel Friedman dfriedman@inspect-ny.com www.inspect-ny.com/welcome.htm#more
When is mold a problem in buildings? What should be done about it? In depth information is at www.inspect-ny.com/welcome.htm#environ and the links at that page. Website content suggestions are most welcome.
Case histories: Here I post summaries of field and lab toxic or allergenic mold and other indoor air quality investigations. I omit private information. I describe observations, procedures, and findings helpful to readers who are trying to remedy their own mold, allergenic, carbon monoxide, odor, or other indoor air and related health concerns in their indoor environment.
What indoor humidity should we maintain in order to avoid a mold problem?
We're going to discuss maintaining an anti-mold low humidity level in a building which does not currently have a mold problem. No dehumidification system will be up to the task of preventing mold if a building has serious leaks, flooding, or water entry. (© Daniel Friedman 2006 All Rights Reserved.)
And no dehumidifier, no "air cleaner," no "ozone generator," nor other magic machine, spray, or air treatment will correct a mold problem in a building if there is a significant problem reservoir. For that case, what's needed is to find the mold problem, remove it, and correct its cause. And as a last warning, there are about 1.5 million mold species - some of them may be able to grow in very dry or very wet or other inhospitable conditions.
We're therefore focused this article on the common indoor problem molds in this article. The genus I refer to include some common problem indoor molds such as Aspergillus sp., Penicillium sp., Stachybotrys sp. /S. chartarum /Memnoniella echinata, Trichoderma sp. /T. viride, Ulocladium sp. /U. chartarum, and at a less significant level of concer, Cladosporium sp. - the king of molds and its competitor Alternaria sp.
Suppose a building does not currently have a mold problem, or a mold cleanup project has been completed.
How low should we maintain interior moisture to avoid a mold problem?
1. be sure there are no ongoing building leaks, water entry, or venting problems.
2. keep the indoor humidity level in the mid-comfort range. A maximum indoor relative humidity of 55 should be ok, 50 better, 45 for an attic knee wall provided there are no ongoing leaks and the attic space is not one which is being vented to outside (in that case you're not in control of the humidity. If you run humidity too low or too high the building occupants will be uncomfortable.
Technical background on indoor relative humidity (RH) control:
this is getting slightly more technical about measuring the relative humidity.
Controlling Humidity in Basements
If the RH in the center of a basement is 55% it is likely that at the walls or corners, where there is less air circulation, the RH may be different. The local temperature difference close to a cool masonry wall surface means that both temperature and measured relative humidity close to the wall will be different than in the center of a room.
But it's at the cooler wall surface that condensation may be expected to occur.
If you measure the RH at the worst-case location such as the most-suspect-of-dampness corner of a basement and you're 55% close to the wall you're likely to be ok.
Controlling Humidity in Attics
In the case of an attic crawl space, perhaps a knee-wall area abutting an upper floor bedroom, the risk of excessive inside humidity at a wall is much less than in a basement. In the attic we don't face a cool concrete-block wall surface in the attic.
But what about an un-vented attic in a cold weather climate? Heat loss into such a space and warm moist air leaking into such a space can indeed create high levels of problme moisture - enough to wet surfaces or even form frost and later drip onto the attic floor.
On the other hand, if the attic is vented to outside (ridge vents and soffit vents as I recommend) you'll never control the attic RH. You'll be trying to control the whole outdoors.
On the third hand (if that's possible), if an attic is not vented to outside, the RH
there is most-likely a function of and approach the levels of the humidity levels in the air in the rooms abutting and below the attic area.
Choosing the target humidity RH level
One client said he could keep the basement at 55 but didn't want to push it below that. Is this enough safety margin?
At 60% indoor RH we're entering the indoor problem mold-formation risk zone of high interior moisture in building wall or ceiling cavities or on wall and floor surfaces, possibly conducive to mold growth.
If you set the RH target at 55%, you're operating with **not much safety margin** of dryness. A small change in outdoor conditions (spilling water by the foundation) or indoor conditions (a nearby roof, wall, window, plumbing leak) can increase the moisture and RH into the problem zone. If for reasons of dehumidification cost you have to operate close to the edge, extra attention to leaks, moisture proofing, roof and surface drainage are even more important.
When have you reached your RH target?
If a building has been damp for some time, moisture has been absorbed into various materials such as wood framing and masonry surfaces. It may take weeks or even longer to drop the humidity in such an area, as the moist materials also have to dry out, not just the air. Using a fan to increase air movement in the area being dehumidified can speed this process.
Warning: if you cannot get the indoor RH down to a low level in a below-grade area such as a basement or crawl space, I'd suspect that too much moisture is continuing to enter through the slab or masonry walls. Attention to outside drainage may not be enough. In such cases, coating the walls with a masonry sealer (Thoro-Seal(TM) or Dry-Lok(TM) are example products) might help.
If you want to get past this practical discussion of indoor humidity and mold, check out "Understanding Ventilation," by John Bower. The Healthy House Institute, 1995.
More than a normal person can stand to read about what to do about mold in buildings is at my website. You might start at the "Mold Information Center - What to Do About
Mold in Buildings"
Hope this helps.
Daniel Friedman dfriedman@inspect-ny.com www.inspect-ny.com/welcome.htm#more
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