More and more often as I speak with new clients about their remodeling projects, I am asked to comment on different aspects of those projects regarding mold and problems related to poor air quality in the home. I am providing the following information on my website to help answer some of the most common concerns and questions.

1. Vented attics
Venting the attic space is an often misconceived solution that may cause more harm than good. An attic that is not vented but well insulated from the space below will contain hot dry air. This heat will not cause any harm and will not penetrate into the living space if insulated properly. A hot dry attic is a poor environment for growing mold.

Venting an attic space in hot humid climates only introduces warm humid air into an otherwise hot dry air space. This alone may not be the cause of many problems, but when this warm humid air comes in contact with the cool dry air from a leaking air duct, moisture occurs in the form of condensation which now drips onto the ceiling where it is absorbed.

Even if an attic is improperly or overly ventilated and some of the ducts leak and even if some mold is occasionally present, this does not necessarily constitute a health hazard, but mold spores can penetrate very small spaces and can be spread in many ways. Under the correct conditions it can enter into the air conditioner coil. From here it can be distributed throughout the house.

2. Negative air pressure:
Negative air pressure in a house is generally caused by a leaking air duct system. When air leaks out of the ducts into the attic, more air is being sucked into the return air grill than is being put back into the house This negative air pressure acts to suck in the warm moist air from the outside into the inside.
Introducing this warm moist air into an air conditioned house composed primarily of cool dry air will cause condensation to form. If there is enough condensation, it will eventually drip onto adjoining surfaces making them moist. Since not all areas of the house remain cool and dry all of the time, those areas that have the right conditions can grow mold.

Mold spores are always present in our environment, but they need they right conditions to grow to enough density to cause problems. Maintaining the proper humidity and temperature is important which is usually not a problem when we are home, but leaving our house sealed up tight with no A/C running at all for a week or two can be the catalyst for problems. There are many ways we can fall victim to household air pollution and many of the causes are not so obvious.

Bruce Small wrote a great article titled "Creating Airtight and Healthy Homes" which illustrates the many ways unhealthy air can enter our homes and why it stays there. In one case he describes where a woman began to feel ill after her neighbor installed a high efficiency furnace. It turned out that the cold exhaust from the neighbors furnace was entering the walkway between the two houses and filtering through the woman's leaky walls, making her feel sick. When the exhaust pipe was extended upward away from her wall, the problem was solved.

3. Air conditioner ducts:
The recommendation here is not to install lined ducts unless there are good reasons or no other recourse. Ducts that are lined with insulation on the inside offer a very attractive environment for the collection of dust, mildew and mold spores. If the humidity and temperature are not right for their growth the spores will just sit and wait, but once the right conditions become present, they grow, proliferate and spread throughout the house. Lined ducts cannot be properly cleaned and they will stay wet once they get wet, a great place to grow things.

It is recommended to use unlined metal ducts and make sure they are well insulated on the outside. Test the system to make sure they do not leak so you have positive pressure in the house. Make sure that your system is designed by a professional HVAC engineer if you have concerns about your situation. In remodel or addition situations, it is possible that a well designed duct plan can be adapted to your existing system capacity. Many original systems are oversized to make up for the poor ductwork installed so you can add the extra space and keep the existing unit.

4. Vinyl wallpaper:
Vinyl wall paper acts as a vapor barrier and should be minimized on the inside of the house especially where humidity is prevalent. It should never be used on all four walls of a bathroom that is poorly ventilated. In warm humid climates, vapor barriers, if used, should be on the outside of the exterior walls, certainly not on the inside of the wall of the room that accumulates the most moisture. The bathroom is often full of warm humid air (steam) and can stay moist for several hours. The walls cannot breath through the vinyl wall paper leaving no escape from that room. Imagine what can happen if the entire family takes a series of showers just before they lock the house up tight as they leave for a 10 day vacation.

5. Carpet
Carpets that are clean, well maintained and dry are an excellent floor covering. Carpets that are dirty attract the moisture that results from the relative temperature change when the air conditioner system cycles on and off. The floor is often cooler than the air above and condensation then collects in the dirt in the carpet. Soon thereafter, little things gain a good environment to grow.
This can be especially true in schools and commercial buildings where the carpet may not be cleaned regularly and the a/c system is shut off for weekends and summers. The worst cases involve schools that shampoo the carpets once a year during the summer and lock up the water laden carpet for several more weeks. No wonder the schools have mold problems. Be aware that some carpets also have a vapor impermeable barrier. Do not install these carpets on concrete floors.

6. Brick:
Brick soaks up water like a sponge! Then it releases the stored water as water vapor. This ok on the outside of the house but bad news for the inside of the wall cavity. It is therefore important to make sure that this moisture does not penetrate into the wall stud area where it can collect and condense on these cooler surfaces. A good water barrier includes a well sealed thermal barrier on the outside of the stud wall and flashing at the bottom with weep hole to allow the moisture to escape completely and freely. Remember, in warm humid climates, we want to install the vapor barrier on the OUTSIDE of the wall cavity, not the inside.

7 Air Dilution:
Air pollution comes in many forms and can be caused by many factors. One of the most common answers to resolve the problem of indoor air pollution has been something called "Air Dilution". This simply means that we push more air through the structure by increasing air flow. In more technical terms this is referred to as increasing the air exchange rate. The theory is that if we push more air through the building and it will clean itself up. While it may be true in some cases, it does not attack the root cause of the problem.

Instead of attacking the problem of indoor pollution directly by installing or removing the products that produce the air pollution gases or even identify the sources, we often try to mask the problem and move on. Sometimes, it is not just the way the building is built but how we use and maintain it. We are rarely informed about these conditions nor do we always know how to approach the solutions. The problems created by using synthetic building products is being amplified by our misuse of them and yet we sometimes continue to point our fingers of blame in the wrong directions.

If you suspect you have an indoor pollution problem, make a concerted effort to find out the cause and beware of solutions that offer temporary solutions or do not work to remove the source. Your health may depend on it.

8. Follow Directions:
When it comes to indoor pollution, there can be many different approaches to solutions. Be especially careful of those who offer a "quick fix" solution to such important problems. Take some time to verify the facts before you jump at the first method offered. Ask yourself if it makes sense. Talk to at least one other professional in that specialty to see if they agree. If they do not, then you need to check further. By all means, if you do select a solution to a problem, be sure to follow the directions given and stay with the plan.

For instance, some recommendations are that using a 10% solution of bleach and water will kill mold and mildew on the walls on the exterior of your home. Just because 10% bleach will work does not mean that a 50% solution will work better. It has been discovered that mold has a unique ability to "lock out" the stronger solution of 50% making it useless. The 10% mix gets through this defense mechanism and enters the living cells where it destroys the organism, while the 50% solution not only does not affect the mold but can also damage many surfaces to which it is applied.

9. When Remodeling, be aware:
Ask your contractor to report any signs of the causes of potential mold growth. A good contractor will report any leaks (even very small ones). He will make sure if dried mold is encountered that it is clean up or removed and the cause of the problem is located, reported and repaired. Make an effort to stay away from flying dust and debris. A good contractor will clean the job site at the end of each day. All plumbing should be pressure checked before the wall is closed. There should be NO moisture present on the pipes while the water pressure test takes place. Verify that all flashing is properly installed according to manufactures recommendations. Make sure you’re a/c system has been checked for negative air pressure and that the ducts do not leak.

There is no substitute for a good contractor who has comprehensive experience in all phases of the building trade. If you have doubts during the construction process, ask. If you feel you are not being given a good clear answer that you understand, you can always hire a third party inspector or architect to verify that everything is being done properly.

10. Never allow a suspicious leak or intrusion of water to continue:
Get a good contractor, inspector or architect to assess the situation and have the needed repairs done as soon as possible. It will be far less expensive to fix the immediate problem at the source now than wait for later complications.