Six Reasons Why Mold Appears During Home Remodeling
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Renovations can sometimes make a home worse , such as when mold suddenly appears after a renovation. Even if your home was previously mold-free and you’ve just renovated, mold can suddenly appear after a renovation for a variety of reasons. So it’s important to keep an eye on your contractors (or your own work) during renovations to make sure you’re not turning your home into the perfect environment for mold to grow after a renovation.
Insufficient ventilation
Older homes are often quite drafty. They are difficult to heat and cool, in part because the air coming from the climate control system constantly leaks out, allowing allergens and dirt to enter the living space. So when planning a renovation, people often want to make the house as airtight as possible, which is not a bad idea. But you need to provide enough ventilation, otherwise the airtightness will trap moisture, and high humidity almost always leads to mold.
Remodeled bathrooms can present a special challenge . Bathrooms are naturally damp spaces , and they almost always require a properly calibrated fan to remove moisture. The fan should be sized according to the size of the room, but it should run long enough after each shower to ensure the room is dry ( some models have a built-in humidity sensor that turns on the fan when humidity increases). Also, the air should be exhausted outside, not into the attic or walls.
Water penetration
If your renovation plan leaves any part of your home exposed to the elements—like a lack of windows, a roof, or doors—water may have gotten in at some point. This is normal for a major renovation, and harmless if your contractor dried out the area before sealing the walls and floors. It doesn’t have to be a heavy rain in your home to sow the seeds of moisture problems weeks or months later—just letting the space get waterlogged and then sealing it is enough.
Wet spots
During renovations, accidents can happen, including plumbing failures, water leaks, and drainage problems. If the problem is fixed and it is an isolated incident, such incidents are not a big deal, but they can lead to damp spots on walls, ceilings, and floors that need immediate repair. Applying a coat of primer to a damp area of the wall does not prevent mold from appearing, and may even encourage it, since sealing the area prevents moisture from evaporating.
Never assume that water stains that form after a leak has been repaired are minor. Covering up water stains on a wall with cabinets or paint before they are completely dry is a recipe for disaster. Bottom line: Any wet areas need to be thoroughly dried before covering them, no matter how small or unnoticeable they may be.
Moldy wood
Sometimes you can do everything right from a construction standpoint and still introduce mold into your home by using moldy or even damp materials. Just because you buy lumber, drywall, and other repair materials brand new doesn’t mean they’re clean and mold-free, especially if they ’ve been stored outside for a while. If the framing lumber used to build the walls or the joists that support new floors arrive too damp, they become a breeding ground for mold once they’re sealed under drywall or a subfloor. Drywall is porous and can easily absorb moisture, even if it appears clean on the outside.
It is essential to check all of these materials before installation, both visually (for visible signs of mold) and with a pinless moisture meter . The wood moisture content should be around 6% .
Wet plasterboard
Damp drywall is a near-perfect environment for mold, so make sure all drywall installed during a renovation has a moisture content of 0.5% or less and is free of visible mold. This is especially important if the drywall has been delivered and left outside: Even if it’s not raining or the drywall is covered, it can absorb moisture from the air. Priming and painting over damp drywall will look good for a while, but eventually that moisture will give mold spores all the conditions they need to thrive.
Malfunction of heating, ventilation and air conditioning systems
One of the unexpected ways that remodeling can lead to mold is with your heating, ventilation, and air conditioning (HVAC) system, even if you don’t actually do anything to it. HVAC systems are often disturbed during remodeling: ducts have to be moved, grilles have to be temporarily removed, compressors have to be temporarily relocated. And that can be a problem, because mold can grow undetected in HVAC ducts, and all that shaking and moving can disturb it, releasing spores that are then spread throughout the house once everything is plugged back in. If those spores end up in a damp area, like a poorly ventilated bathroom, mold will happily take hold.
It’s always a good idea to think about post-renovation cleanup to ensure that dust and debris don’t bother you after the workers leave. A thorough cleaning of your HVAC ducts should be included in this plan, even if they weren’t directly affected by the project.