I have a mildew smell in my home at certain times of year (spring and fall) and I have been trying figure out the source for quite some time. The smell seems to come up through the return air vents when the furnace is not running and through the entire HVAC system when it is running. The previous owners of the home finished the basement and we have had some issues with water leaking during heavy rains. We believe we have fixed the leak now. We had the carpet cleaned in the entire basement and the insulation and drywall replaced where the leak was. We have also had people out to look at the HVAC system and they could not find any problems. I have made sure that all of the drain traps have water, so I do not think the smell is coming from the plumbing. I also have a dehumidifier running in the basement and the humidity is at about 40%.

The leak happened to be underneath a glass block window and when we replaced the drywall we discovered that there is a space between the brick on the outside of our house and the poured concrete wall of the basement (I am trying to put a picture in the post, but I'm not quite sure how this works). There is a draft that comes through this space and the odor seems to be strongest here. Do you have any suggestions for me? Do you think that the odor in my house could be coming from here? What can I do to fix this?

Thanks.

You may be getting maisture between the brick veneer and the interior wall. This is not uncommon since brick was is more waterproof the vinyl for example, but is not intended to be waterproof.

A properly built brick veneer should have weeps low in the veneer to allow water to drain out and very often has vents near the top to allow drying and ventilation of the cavity. These are about 2' to 4' apart and may just look like an open vertical joint between two adjacent brick. They may also look like a pirece of rope sticking out or a 3/8" round or rectangular opeing with a screen. - Do you have any vents?

Often the weeps get filled with soil or get caulked, so draining and venting cannot take place. Excess moisture in the cavity can lead odors and even mold or rot.

Very often, a brick veneer will work very well without weeps and this is the reason some builders do not always use them.

Your home appears older (or not mew).

Has there been any changes in the grading or filling around it that could plug the weeps?

Have you had any window work or replacement done? People working on windows are notoriously bad when it comes to proper installation (65% installed improperly). Replacement windows commonly have poor installation when it comes to water pentration. Some good new home builders will not even allow their carpenters to install windows, but sub it out to a certified window installer to avoid the moisture call-backs.

Have you had any roof leaks or ice dams that could possibly cause water to get into the home? The water may be getting in. but it often is never seen, but can cause problems in the veneer cavity or any other siding material.

You could always get rid of the odor by plugging the holes (mortar and foam) around the glass block window, but that would just be a band-aid approach and not solve the problem if one exists.

The brick veneer does not have weeps and the house was built in 1984. We haven't had any roof leaks or water in other locations from ice dams, etc.

Someone suggested that I fill in the entire space between the brick and the contrete with an expanding foam insulation all the way around the house. This would slow or stop any water intrusion, improve the insulation of the home and likely kill any mold/mildew by starving it of oxygen. Would there be drawbacks to doing this?

Mold/mildew do not require oxygen. Filling the space behind a brick veneer isn't recommended. The space is there for a reason. Also, doing so may create at least a partial, if not a complete, vapor retarder, which would be the second vapor retarder in the wall, a fundamental error.

Why not remove a couple of bricks in an inconspicuous location and see exactly what is happening in your wall? Foam would cost a great deal of money and besides probably not solving anything, may create even worse problems, if in fact you could ever actually completely fill the space.

I was addressing sealing the void at the juction of the glass block and the old construction. As I mentioned, this is a band aid approach and will hopefully liminatate the odor problem.

Obviously, you could remove more bricks for further investigation as to the type of construction that may be representative of the rest of the wall.

Another thing that is mportant is to address if there were any changes to the already poor construction. - Such as grading, lack of weeps and any new opeinging modifications. The roof problems may not be as obvious.

Sometimes I get a little blunt and do not write for DIYers since I normally write for professionals.

Filling the voids around the house is another band aid approach and could cause more problems than good.

The first thing to do is find the source of the odors, which may be moisture or mold.

Not enough information to diagnose without seeing the big picture.

Thanks for the input. I am fairly certain that the odor is coming from the space that I showed in the picture.

I'm not much of a DIY'er and I have done everything that I am capable of already. Now I am trying to figure out what direction to go next. The issue I have is WHO do I call to address this?

Plumber? Mason? Roofer? Mold Expert? General Contractor? Exorcist?

Thanks again for the help.

I have a few thought on this. My response is fairly long but its not that simple
I do not belive the window is the source of the issue. It may contribute to it, but not the primary reason.

If you have an AC system installed and the smells are coming during the times when you change over from Heat to AC and Ac to heat. You need to get the indoor AC coil cleaned. The coil needs to be completely exposed and then properly washed. What happens here is that the condensate that collects on the surface of the AC coil picks up dust while it runs. When you turn on the heat this causes the mildew smell.
When you go back to AC the moisture feeds the dust and mold develops on the coil and is transferred to the air. This is a very common condition. Also a sign you’re not filtering the air very good or cleaning the filters.

Another issue is the carpet. I do not want to sound over bearing, but, you wasted you money on the cleaning. It may have looked ok, and even smelled ok for a few days, but even with the best intents and equipment to do the job, the underside of the carpet is filled with dust mites, and mold. This will simply not get cleaned out. AS soon as the cement floor underneath gets damp, and it does, it feeds the mold. Also the cleaning process also will feed the mold. If you have small children, keep them off the floor. Remember they are breathing air from a different level as we adults do; their face is close the floor on many occasions as they lay down and play with the toys. Ever wonder why they get so many ear aches?

If you can get your hands on a moisture meter. They sell them at many home centers and lumber yards. Does not have to be to fancy, just as long it has two pins on it that can stick into the carpet. Check the carpet all around the edges. You should see reading no higher then 10 to 12% Any readings higher then that indicates that there is a water issue and that the carpet needs to come out and the water issue solved.

AS far as the leak under the window. Yes that may cause the issue but not in as much as the carpet. You must remember a few things about mold.
It needs three things to develop.
1. Air.
2. Food source
3. Moisture.
Remove any of these three things, no mold no smell.

The only thing you can control is the moisture. To some extent you can control the food source, but as long as the mold spores can digest what ever you have on the walls, or floor or ceiling and the other two items are present. You have mold.

My suggestion is this.
Get a moisture meter and check the dampness of carpet and the walls. If the carpet does not have any reading that’s good. As sometimes you may not get one if its really dry. Any moisture reading over 18% on walls should be a concern as its getting to a point that mold not only can develop but continue to grow. Even if you remove the source of the moisture, the mold still stays until it gets wet again.
After checking for the moisture. and if you do not find any high moisture levels. Then get air tests done. One in the basement. If you have access to the back of the walls. One test should be done there, One in any unfinished space in the basement if you can. One in the finished space. One on the first floor where you seem to smell the mold the worst when it happens. and one air test on the outside of the home to use as a control. The tests should provide mold ID as well as spore counts. Having this data can help determine what types of mold is growing as well as the amount that is in the air. If you find lets say Cladosporium in the air, and you live in a wooded area. You will find this in all areas of the home. AS this is a common mold found both inside and outside of the house. But if you find that the spore counts are really high in the basement, and real low outside and in other areas of the home. This indicates that there is something still wet and allowing this to grow. Oftentimes it is a wood material that allows this to grow. By knowing the type of mold that is present. The inspector can determine what its growing on and help find the source. AS each mold tends to grow better on some surfaces then others. Sort of like your veg garden. You may grow tomatoes real good but cannot grow pumpkins worth a darn. Same goes with mold.

My guess its the carpet, Very common and as someone who does this type of testing and cleanup. I would say its one of the most common issues.

Be sure that the person that does the mold testing provides not only the testing, but does the anylisis of the mold test results themselves. Many companies rely on the lab to tell them what is going on. Its the labs job to tell you what you have, not what is going on in the home.

Testing should be done after the moisture tests and all attempts to be sure everything is dry. It can get expensive fairly fast.

One last thought . I would go to the Local book store or Amazon.com and purchase a book written by Jeffrey May. its called "My House Is Killing Me" Its paper back about three hundred pages. It will shed some light on many of your household issues as well as this.

No doubt the moisture/mold issues you've been discussing need to be addressed, but I'm wondering why the indoor odor seems to be centered around the HVAC since it should be an essentially closed system. I think I would invest in a good ductwork cleaning and inspection in addition to the other work you'll be doing.

The primary reason for the odor out of the AC system is that it tends to pull basement air into the air flow. Most AC/Heat systems do not have enough return duct size to properly allow for the air to get back to the furnace. The result is air being drawn into the air stream. Thus the smell.
A simple test is in order. Turn on the Fan only switch on the thermostat. Stand at the top of the basement step and close the basement door so its just cracked open. If you put your face near this crack you will feel the air being pulled into the basement after a short while. Some homes are so lacking in return air flow that the door will be pulled shut.
If you read the furance install instructions many recommend that the side of the furnace be cut open completly around the entire side where the retun leg fastens. But if you check on how this was done. You will see that it is not completly cut out. making the opening smaller results in less air and the issue this person is having.

I do agree to some extent that the ducts may need to be cleaned. But if you have a zink coated duct system. Galvinized steel, the zink will kill any mold spores that are present in most cases. That is why they use zink strips on the roof to prevent this from growing.