Q: We live in a single-family home and recently discovered mildew on the inside of our north- and northeast-facing walls. Unfortunately, these are bedroom walls. The mildew was so bad that it had grown all over a dresser that was up against a wall. We’ve tried using bleach and leaving the furniture a couple inches from those walls but nothing seems to kill it. Can you make any recommendations, other than moving? Our house is not insulated but it does have double-pane windows. Also, because we knew there was the potential for this problem we used an anti-mildew additive to our paint when we painted about four years ago. Does its effectiveness diminish over time?
A: We’re not going to suggest you move, but before you insulate you should locate the source of the mildew. You’ve done all the right things to cure the symptoms; now you need to find the cause.
Bleach, mildewcide added to paint and fresh air can retard or kill mildew, but they do not cure the conditions that cause it.
Mildew is a fungus that needs moisture to grow. The north and east sides of homes tend to get less sunlight than the south and west sides and tend to be more prone to mildew problems, both inside and out. Insulation can help prevent condensation on the interior walls but has little effect on exterior walls. Double-glazed windows have no effect on moisture in the walls.
We believe the source of the mildew is moisture penetrating the walls from outside. We’ve said many times that water can be a home’s worst enemy. You’ve got to eliminate the possibility that moisture could penetrate your home. To identify the cause of your problem, you’ll have to do a little observation and detective work.
Go outside and take a good look at the exterior walls. Start from the bottom up. Prune or remove any foliage growing on the walls or pressed up against the foundation. Regrade the dirt so that at least 6 inches of the foundation is visible and the dirt slopes away from the house.
Next, inspect the siding. Pay special attention to areas around windows and doors. Whether it’s wood, stucco or some other material, inspect for cracks where water might penetrate. If you find cracks, it’s probably time to repaint.
Seal the cracks with caulking and then apply a good coat or two of paint. We prefer a latex top coat for its elasticity and durability.
Next, take a look at the roof and gutter system. Is the roof worn and possibly leaking? We’ve seen gutters attached so that they actually allow water to penetrate the house rather than channel rainwater away. Unless you’re confident that you can spot problems in a roofing system, we’d suggest that you contact a licensed roofer for an inspection. You can expect to pay about $100 for this service.
Finally, crawl under the house and check the area below the walls with mildew. If the area is wet, you should see staining. If there is a white film on the wood members, this is evidence of fungus. If you see either condition, we recommend that you call a licensed structural and pest control company to investigate further.
This is something that should be done sooner rather then later. Moist conditions in walls and crawl spaces not only make an ideal petri dish for fungus, such as mildew, but also for toxic mold.
The bottom line is that we believe water from outside is penetrating the wall spaces where the mildew appears. You must stop the leak to solve the problem.
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