I recently went through a customers basement that has a fair amount of mold growth on the sheetrock and baseboards. This basement was closed in and remodeled a year ago after a hot water heater incident on the floor above.
The house is located in Maryland, outside Baltimore (classified a mixed-humid climate), with a basement that is mostly below grade. The basement is carpeted throughout and completely sheet-rocked. As soon as you step into the basement you can feel the humidity and overall lack of ventilation. The home has a forced air system with the three supplies in the basement ceiling and no return. Upon first inspection we found a leak at the entry door which could be addressed through proper grading and gutter issues. However, mold has appeared all the way across the room where no obvious leaks are and on the ceiling. The carpet as well feels damp in a few areas. We demoed out the sheetrock two feet from the slab/carpet floor at the area of the leak, where the mold was most populated. Behind the sheetrock I found this wall assembly: 2x4walls with PT sill plate, kraft faced fiberglass insulation, poly sheeting and cinder block wall with brick veneer where it is not below grade. I have my doubts about this assembly. Isn’t it bad to have a vapor barrier on both sides of the wall? Shouldn’t moisutre be able to dry to one side or the other? There are also several pieces of equipment in the utility room (filter tanks from the well water system, etc) experiencing a fair amount of condensation which pools on the utility room floor. After taking into account all the evidence I am trouble coming up with a final conclusion so I figured I would run it past everyone here. In my opinion the prime suspects for the mold are:
1. water: from leaks, condensation, humidity
2. ventilation: lack of air movement overall in the basement providing a good environment for mold (plenty of food too)
3. wall assembly: not how I would prefer to build it but not sure whether it is a suspect or not. There seems to be various opinions and contradictions in the building science world that I am still trying to get a handle on.
If there are other suspects please let me know. Also how would you address these. At this point we are demoing all sheetrock, carpet/padding, baseboards, and casing. I have resolved the leak issue and will not close things in until I have a final gameplan.
Thanks for the feedback.
Replies
You need to figure out where the moisture's coming from. Unfortunately, probably most of it is wicking through the masonry walls and floor, and it's hard to do a whole lot about that (other than to put plastic up against the block walls).
If you can't keep the moisture out you need to remove it. This means more than a dehumidifier running in the corner -- there needs to be an established, continuous airflow through the whole area.
Thanks. To establish air flow I probably
need to bring in my HVAC guy.
They already have plastic up against the block wall. Which I figured may be an issue due to the fact that there are probably many voids in the fiberglass install that are allowing warm air in the winter to penetrate and condense on the cold poly covered block wall. Would they be better with out it (the poly) so that things could at least dry out ? I would love to start new with EPS or XPS against the block and slab but that may not be an option due to budget restrictions.
Depends on where the bulk of the moisture is coming from, and also whether the problem really is condensation on the poly (and which side) vs simply too-high humidity in the wallboard.
Understand that 99% of moisture comes from these sources:
Humid air leaking in from the outside
Human activities -- cooking, showering, breathing
In new structures: drywall and framing lumber drying out
Moisture wicking through the structure (& especially the masonry walls & floor)
Out-and-out water leaks, either from the outside or plumbing leaks inside
If you could somehow eliminate those causes, you'd have no humidity problem (and in fact the air inside would be too dry).
Also understand that basements get hit with a double whammy: Increased moisture due to wicking through masonry (and the occasional leak) and poor circulation and uneven heating, meaning that places in corners and near the floor get cooler and have very little air movement. When air gets cooler, the relative humidity increases, and when it nears 100% then mold happens (if a mold-friendly substrate is present). Additionally, the lack of decent circulation means that moisture entering the area through the masonry simply stays where it is, so that the absolute dewpoint and relative humidity are both higher in corners and near the bottom of the wall.