Category Archives for Mold Sources


Mold behind bed headboard

Mold on wall, floor, and back of headboard.

Most of San Francisco’s neighborhoods were built in  the decades after the great earthquake and fire of 1906. The designs of these homes were surprisingly similar. Ground floors generally had a large unfinished basement space behind a garage, and all of the living space in the homes was generally located on the second story. San Francisco was essentially built out several decades ago, so homeowners started to look at these unfinished spaces as potential additional square footage for family rooms, additional bedrooms, and in-law units.

Many of these spaces were finished without permits, and the building methods employed were questionable at best. But even the spaces built out with permits still had to contend with a problem that is ubiquitous in San Francisco…ground water. The concrete slabs poured in these garage / basement areas were poured using the methods that were employed for decades, which was essentially to smooth out the soil and then pour the concrete. This resulted in a condition that allowed for a constant transfer of ground water from the soil into the slab itself. And this was exacerbated by the same transfer taking place from the soil into the perimeter foundation. This transfer of water results in (minimally) excessive humidity and condensation, and in worst case scenarios, a direct transfer or moisture into the flooring and walls of the finished space.

Bay Area Mold Pros was called out to inspect a small in-law unit in the basement of a 1940’s era home in the Excelsior District. The client had been living in this in-law unit and had developed some chronic health issues that he feared were related to mold growth. The photo at left depicts what I found when I pulled the bed away from an exterior bedroom wall. I found mold on the floating Pergo-like floors, mold on the wall drywall, mold on the drywall-wrap around the window, and mold on the drywall shelf used to conceal the perimeter foundation. In addition, the back of the bed’s headboard had what appeared to be mold growth as well.

The lab analysis of the air sample that I collected in this bedroom revealed high levels of not only Penicillium / Aspergillus mold spores, but high levels of the dreaded Stachybotrys genus of mold, commonly referred to in internet articles as “toxic black mold.” This entire apartment will require a professional mold remediation, as the problems present in this bedroom were also present in the adjoining closet and in the nearby bathroom.

Once the mold growth in this apartment is remediated, the building owners will surely want to ensure that it is rented out to either the original tenant, or a new tenant. In order to do this, it’s possible that by using dehumidifiers and air purifiers the excessive humidity and condensation can be controlled. The more expensive solutions, which involve actually trying to control the ground water through the use of French drains and sump pumps, would be the most effective, but they can also be cost-prohibitive. I always point out to clients that the use of French drains and sump pumps are an attempt to deal with the actual problem, which is ground water. On the other hand, the use of dehumidifiers and air purifiers are an attempt to deal with the symptoms of the problem, which are humidity and condensation.

We generally inspect several of these San Francisco basement units each week, and the earlier that we can identify potential mold issues, the better. If you suspect that you might have a mold growth issue in one of these apartments, give us a call at Bay Area Mold Pros. We only have two inspectors at Bay Area Mold Pros, Rick and and his son Tyson. Both Rick and Tyson are not just Certified Mold Inspectors, they are also Licensed General Contractors. Rick has been building and remodeling homes in the San Francisco area for 45 years, and Tyson has almost 20 years in the construction industry. This extensive experience allows us to quickly and accurately diagnose issues within your home which are conducive to mold growth. So if you suspect mold growth in your home, give us a call at Bay Area Mold Pros, we can generally be at your home within a day of receiving a call.



At Bay Area Mold Pros, we complete hundreds of mold inspections around the San Francisco Bay Area every year, and at most of our inspections we determine that ground water is contributing to mold growth within the home being inspected. Ground water issues can be addressed with a combination of solutions such as French drains and sump pumps. These systems seek to divert water away from the perimeter of the home, or to remove it (via electric pump) once it has made its way past the perimeter of the home.

One of the most common issues we identify at Bay Area Mold Pros, when inspecting the home’s exterior, is that one or more rain leaders that are draining the roof water are depositing it directly adjacent to the home’s foundation, often on the “high” side of the lot. This condition is exactly the opposite of what we want to see in terms of how rain water is dealt with. Very large amounts of water can be discharged from these rain leaders, since the rain water that they are collecting might be coming from several hundred square feet of roof surface.

The solution to this condition is actually pretty simple. By connecting the bottom of the rain leaders to flexible or rigid plastic pipes, the water from these rain leaders can be re-directed around the home to another part of the property, ideally, at a lower elevation than the elevation occupied by the home. Although this won’t have any affect on the naturally-occurring ground water that surrounds the home, it will prevent the rain water that is coming from the roof from exacerbating the ground water problem present around the home.

At Bay Area Mold Pros we are experts in the construction-related issues which often underlie mold growth problems. Rick is a licensed general contractor and owns his own construction company, Bruce Construction. Tyson holds his own license as a general contractor, and owns his own construction company, Tyson Bruce Construction. Both Rick and Tyson are also Certified Mold Inspectors. But what separates Bay Area Mold Pros from every other mold inspection company in the San Francisco Bay Area is the fact that Rick and Tyson have been building and remodeling homes throughout the San Francisco Bay Area for a combined seventy-plus years. So if you suspect a mold-growth problem in your home in the San Francisco Bay Area, give us a call at Bay Area Mold Pros!

Bearded Man In Shock From The Black Mold On The Wall

GroundWater Still Causing Problems in Bay Area Homes

Even though winter now appears to be over in the San Francisco Bay Area, we received so much rain over the past six months that many homeowners experienced water-intrusion problems for the first time. Most of the homes in the greater Bay Area are built on perimeter concrete foundations and have “crawl spaces” under the first-floor framing. Until recently, no measures were taken by builders to prevent naturally occurring groundwater from making its way under any nearby homes (and into the crawl spaces of these homes).

Once groundwater has entered the crawl space, it is very difficult to dry it out. When water is present in building material (or soil), it will start to move from the wet area to the dry area. So the moisture under the home will attempt to move into the living space above, and the more water that is present, the more likely that this transfer of moisture will be successful. In homes with hardwood flooring, it is common to see the “cupping” of the hardwood slats, this is a clear indication of moisture that has made its way from the crawl space, past the hardwood flooring, and into the living space above. And once this happens, this moisture will almost certainly result in the growth of mold spores, and a call to Bay Area Mold Pros!

There are several things that homeowners can do when they have groundwater in the crawl space of their home:

  • Consult a drainage expert. There are many contractors in the San Francisco area who specialize in drainage issues and the installation of French drains. These systems divert water around and away from a home, and they are very effective at addressing this problem. Sump pumps installed in crawl spaces can also be very effective at controlling this excess moisture.

  • Vapor barriers. Once the “standing water” issues have been addressed in the crawl space (through either a French drain or sump pump), a vapor barrier can be placed over the soil or concrete in the crawl space, and this will essentially prevent the moisture within the soil from making its way into the home above. There are numerous companies in both San Francisco and San Mateo Counties who specialize in this work.

  • Run a dehumidifier. Homes that are experiencing the transmission of moisture from a wet crawl space into the living space above will have elevated humidity. One of the best ways to control this humidity is by running dehumidifier machines in the most problematic rooms of the home.

So the bottom line is this…if you have groundwater that has made its way into your crawl space, you need to address it, and if you don’t, you’ll be calling Bay Area Mold Pros to inspect your home for mold…because you will have mold!

Side View Of A Shocked Young Woman Looking At Mold On Wall


I received an emergency phone call today from a client living in Los Altos. The client’s home is almost brand new, so I was a bit surprised when I arrived to find some workers ripping out drywall and insulation from the entryway ceiling.

The homeowners had discovered that a third story aluminum window had been improperly installed by the general contractor who built the home, so the contractor agreed to open up the exterior wall last week and to then re-install the window “flashing,” which is the material placed around the window flange to ensure a waterproof seal.

Unfortunately, once the exterior wall had been opened up, we received an unusual drenching of May rain that soaked the exterior of the home and made its way into the now open exterior wall. The homeowner phoned the contractor, who opted to not come out, because it was raining!

Within the next few hours, what started as a rather small problem, in one location, spread to the entire first floor of the house thanks to gravity.

Anyone who has ever suffered through a water leak within their home can tell you that where the water actually becomes visible is often quite far from where the leak originated. You can blame it on gravity. As soon as a water leak occurs, the water will start traveling downhill, and will always choose the easiest path on its downward journey. That’s why homeowners often say that water is leaking out of their recessed ceiling lights, these openings in the ceiling drywall are simply the easiest way for the water to escape.

The water is this Los Altos home travelled from the open exterior wall into the wall framing itself, and then travelled down the wall to the second story, and then travelled down the wall to the first story where it came into contact with a concrete slab. From there it travelled under the floating hardwood floors and then along the concrete slab, until it had travelled into every room on the ground floor of the home.

I measured the moisture content of all of the hardwood flooring, and it was all saturated with water. All of these floors will now need to be removed and discarded. Once hardwood floors have been saturated with water, they become cupped and unusable.

So the lesson here…if you have a leak…deal with it right now! Don’t wait until the rain stops (or any other excuse), because gravity is relentless. And the water that you think is contained to a small area will continue traveling until it reaches the end of its path. And the end of the path might just be your entire home.



I’m still surprised when conducting my home inspections at how often I find examples of incorrectly installed flashing. “Flashing” is normally installed around window and door openings, and is made of a variety of material, but flashing is also required on many roof applications. Whenever a pitched section of roofing abuts a wall (or other vertical surface), flashing must be provided.

When installing roof shingles, the flashing is normally referred to as “step flashing,”and each course of roofing material has a piece of step flashing installed over the current course of roofing material and then against the adjacent wall. Step flashing is normally comprised of pieces of “L” sheet metal, but the key to a proper installation is to have the upper portion of the “L” flashing placed against the framing or sheathing of the abutting wall, and this is the important part…under the siding or stucco cover.

To save time and effort, some installers fail to remove the wall cover, and instead, place the L flashing against the wall cover. This defeats the purpose of the flashing, which is to prevent any rain water from getting behind the flashing and into the framing. The attached photos, taken at a 1930’s era home in the East Bay, depict how the flashing is actually placed on top of the stucco. This has resulted in gaps between the flashing and the stucco, and this is a direct pathway for rain water to enter the framing.

Directly below this roof section is a badly cracked and damaged section of stucco that is clearly water-damaged. And this damage is a direct result of the improper flashing. This home has mold growth problems related to a variety of issues, but one of the most obvious (and serious) issues concerns this roof flashing. And until this flashing is removed and re-installed correctly, this section of roof will continue to leak every time it rains!



I was called out to a 1930’s era home in San Francisco this week to perform a mold inspection of a large flat. I could see obvious signs of water damage around almost all of the windows, and when I started using my meters to determine if the plaster next to the windows was wet, the tenant told me, “Don’t worry, those are all new windows.”

As I moved from room to room in the flat, I could see that none of the original solid wood double-hung windows were still present, they had all been replaced by a combination of vinyl retrofit windows and solid wood retrofit windows. These retrofit windows were all installed in the original sold wood window frames, and although all of the new windows appeared to have been properly installed, the plaster adjacent to each of the windows was wet.

What many homeowners (and some contractors) don’t understand is this…when a new window is installed in an original wood window frame, the condition of the window frame itself will largely determine if rain water will eventually make its way into the home. And not just the window frame, but the surrounding wood trim as well. If the wood trim (typically a piece of 1 by 6 redwood on old San Francisco homes), fails, then rain water has a clear path to enter the wall framing. And if water makes its way into wall framing, you’ve got serious problems!

I took several air samples within this flat, and as expected, the mold spore counts were found to be elevated by my lab. There were additional issues within this unit, including water detected behind the tile above the bathtub, and elevated humidity in the basement below the unit. The real challenge for the client in this process is the fact that she is a tenant, and not a homeowner, so she must now rely on the property owner to “do the right thing” by starting to address the myriad construction issues discovered during the inspection.



This past winter was the second wettest in two decades, and all of this rain resulted in myriad mold problems for Bay Area homeowners. Even though the calls for rain-related problems started “drying up” a couple of months ago, the problems created by all of this rain have persisted.

The owners of this home in San Mateo County noticed that their crawl space was flooded with water following a particularly heavy period of rain, and they contacted their contractor who then installed a sump pump system to deal with the standing water. Once this standing water was addressed, the homeowners thought that they were good to go, but the soil in the crawl space stayed damp for weeks, even though the sump pump was removing the standing water. This dampness can spike the humidity, and this elevated humidity can lead directly to mold spore growth.

The mold depicted in this photo is growing on the back side of a standard sheet of 1/2″ drywall. The stud bay had been filled with R13 batt insulation, but this didn’t prevent the growth of mold on the drywall itself. Once mold has grown into the paper on drywall (on either side), the drywall needs to be removed and discarded.

So this case is another reminder that moisture issues need to be addressed immediately following any water intrusion event, and this includes drying out the area with commercial dehumidifiers and fans. Mold spores will start to germinate within 24 to 48 hours of being exposed to water, so homeowners need to call in the professionals immediately upon discovery of any water issues. Any delays can (very likely will) lead to mold growth, so don’t wait, make that call!



Many of my clients arrange an inspection with Bay Area Mold Pros, and then tell me that there was a leak, “…several weeks ago.” Mold spores are a part of our environment, and they are present in almost all of our homes. But these mold spores can’t grow until they are exposed to either water or excess humidity. Once exposed to water, mold spores can begin to germinate within 24 to 48 hours.

And there’s the problem for people who may be prone to procrastination. If there is a water intrusion event in your home (plumbing leak, roof leak, ground water leak), you must deal with it immediately! That’s why remediation companies usually have phone lines that are answered 24 / 7. Their crews will not only try to respond within hours, they will generally have their machines (fans, dehumidifiers, negative air pressure machines) set up and working within hours of arriving.

The photo below depicts the condition of the wall drywall in the basement of an old San Francisco apartment building. A plumbing leak occurred in one of the commercial street-level office spaces and the water made its way into the below-grade basement that became flooded. The water was allowed to evaporate, which took several days. But by the time the water had evaporated from the concrete slab, the wall drywall had been saturated for several days.

Mold spores are looking for organic matter to grow on, and they absolutely love the paper face of drywall. The air samples taken next to the drywall in the photo were found by the lab to contain not only the standard species, but a fair amount of the dreaded Stachybotrys, which is referred to in many internet articles as “toxic black mold.”

The lesson here…if you have a water intrusion…don’t wait! You need to dry out the area immediately, and you may need professional assistance. Don’t procrastinate, unless you don’t mind sharing your home with some moldy roommates!



If you own a home that was built in the 30’s or 40’s in San Francisco, or on the peninsula in San Mateo County, you may still have one of these tiled stall showers. They were generally placed adjacent to a separate cast iron bathtub in these old bathrooms. It is pretty amazing the number of these showers that are still in service, given the eras in which they were constructed.

My grandmother purchased a “brand new” home in the Mission Terrace neighborhood of San Francisco in 1936 for $5,000! That was a considerable amount of money in the depths of the depression, but she managed to pay it off early, and the home remains in our family to this day. The bathroom was finished in “art-deco” tile, and believe it or not, the shower is still being used every day, is still in pretty good shape, and it doesn’t leak!

But our shower is the exception to the rule. The shower depicted in the photo is in a 1940’s era home in San Mateo County, and it is no longer serviceable. During an inspection of this home by my company, Bay Area Mold Pros, my meters detected moisture behind the tile on all three walls, and under the tile in the shower pan. I took air samples both within the shower and in the hallway adjacent to the shower, and both samples came back with elevated mold spore counts.

If your home still has one of these original stall showers, it would probably be wise to have a mold inspector determine what you’re breathing when you’re using the shower. There is really no way to “repair” these old showers, they’re simply too far gone. Most of the pans have failed (they used either a “hot-mop” waterproofing, or a sheet metal pan in this era of construction).

If you determine that your shower is still serviceable, remember to keep it clean, and you may wish to apply some grout sealer. The grout on these old showers is often missing in places, but you can prolong its life with frequent applications of a modern grout sealer.



In modern construction, you’ll always see a space from grade level to framing. This space varies, but it will minimally be about 8″ at the low point. This space helps to address two problems: pests such as termites, and ground water; both of which are trying to enter your home. In older construction, it is common to find the mud-sill at the same (or sometimes even lower) elevation as grade. This is a potentially serious problem, as both termites and water have direct contact with the framing.

When I first looked at the exterior wall depicted in the above photo, I thought it looked pretty sound. The stucco ended at a weep screed, and there was about 8″ spacing between the weep screed (which represent the bottom of the framing / sheathing) and grade. But then I realized that the foundation vents were within the foundation wall, which is unusual. Foundation vents are normally placed atop the mudsill (or higher), but they are almost always placed in the framed portion of the flooring or cripple wall above the foundation.

As I looked more closely, I saw that what I thought was the concrete foundation was actually several long pieces of galvanized sheet metal. So the builder who had performed the last remodel of this home had stripped the old stucco off, sheathed the framing with 1/2″ CDX plywood, and ran the plywood down to the original mudsill, which was at grade.

This resulted in plywood (and the floor framing behind the plywood) extending to grade. So the builder decided to cover the lowest section of the framing with sheet metal, hoping this would provide a “break” between grade level and the stucco and weep screed. Only time will tell if this decision will accomplish what it’s intended to accomplish. In any case, it’s probably preferable what existed previously, which was likely direct contact between the framing and the adjacent soil.