Feature

There's Something Rotten in the City

by Terry Meany

“You have dry rot.” These dreaded words could mean anything from past wood damage that was never repaired to extreme weathering that is misread by a contractor. In any case, dry rot needs to be understood and repaired before it spreads.

For starters, dry rot is a misnomer. Rot only occurs when certain decaying fungi meet up with certain levels of moisture, temperature and a food source. Older masonry structures where wood butts up against brick or stone are more susceptible to rot than predominantly wood structures. What we view as rot, nature views as normal deterioration that keeps the ecosystem healthy. It’s terrific in Muir Woods, but not in your building’s foundation.

Rot differs from weathering, mold and mildew. Weathering happens when unsealed wood soaks up water, expands, and then shrinks when it dries. If this happens to your unpainted siding or peeling windows often enough, the wood begins to splinter and deteriorate. Paint or other coatings on an exterior prevent this by sealing wood against water and allowing the wood to maintain moisture content below 20 percent. This percentage stabilizes the wood and prevents splintering, cracking and splitting.
Mildews and molds are staining fungi that are microscopic critters. They are not as damaging as rot, but nevertheless need to be booted out of your property. More on that shortly.

Decaying fungi are also microscopic. They are present everywhere and are normally harmless, but the spores grow in damp, stagnant, dark areas with temperatures above 40 degrees Fahrenheit. A poorly ventilated crawl space or wood framing that is wet from plumbing or roof leaks become 24-hour fungi buffets. Brown rot fungi attacks softwood, which potentially includes any piece of framing, siding, subsiding, sub-flooring, trim and window sash in older buildings. New buildings aren’t immune, either. Wood is wood and if the conditions are met, fungi can move in.

Check It Out

How do you know if you’ve got dry rot? Look for the obvious—soft, crumbling wood and cracks resembling small cubes (this is due to the wood shrinking), brown coloring in the wood or, if painted, heavily peeling or discolored paint. If you see sawdust, call an exterminator because you most likely have some kind of wood burrowing pest to evict. Check any areas that have experienced leaks, especially under broken gutters or missing roof flashing. Rotting framing is much harder to detect without some visible sign such as deteriorating plaster or siding.

Realistically, dry rot isn’t as much of an issue in San Francisco as are weathered wood and mildew. All exterior wood requires regular, steady maintenance to keep it sealed and protected. Even in a down economy, expensive painting is better than the costlier alternative of replacing damaged wood. A regularly sealed piece of wood will last for centuries (you never know, your great, great, great grandchildren might inherit your property some day).

Interior mildew and mold grows in poorly ventilated bathrooms, kitchens, laundry rooms, closets, and behind window coverings inside inadequately heated rooms. Tenants trying to keep their heating bills down can keep a dwelling so cool in the winter months that it never really dries out. Bathrooms and kitchens without good fans, or at least operable windows—and ones that tenants willingly open for a good airing, typically get mildew on the ceilings and upper walls as steam settles and puts out a mildew welcome mat.

Prevention and Cure

Rot, weathering, mildew, and mold all require water in one form or another. Control the water and its infiltration, and you will control these building menaces. On the exterior, be sure your gutters are clean of debris and are not overflowing onto the siding or soffits. Gutters should be intact, without holes or breaks in the seams. Check your roof flashing, especially around chimneys and skylights, and any and all flashing at window and door headers. Examine any area that has been penetrated by a pipe, wire, or add-on such as a staircase or deck (too many contractors fail to install flashing between a deck and the attached building). If your building has an accessible crawl space, be sure any exposed soil is covered with 6mm plastic and the area is ventilated.

Examine any suspicious looking wood. Insert an awl or knife blade to check for softness. Pay special attention to windowsills, lower sashes, sill plates in the basement, and any exposed rafter ends, as well as wood near the gutters. If you are satisfied the wood is intact, seal any openings with a good grade elastomeric caulking (a rubberlike, flexible and longer-lasting than latex caulking). This can be used in a pinch where any door- or window- header flashing looks compromised. Give the caulk at least a day to dry before painting it.

Other Repairs and Fixes

What do you do if you find further damaged wood? If it’s only split or cracked, you can fill the voids with a quality epoxy such as West epoxy systems, available at several marine suppliers around town. Follow the application instructions for sanding and drying and apply one coat of primer and two coats of paint over the epoxy. Automotive body fillers work, but only if you buy the better grades labeled as waterproof or buy those specifically intended for marine repair. Be sure any wood you repair is completely dry, and all loose and damaged wood is removed.

More extensive rot repairs might require the removal of damaged sections, as well as another twelve inches in those cases with heavily damaged wood, and then the installation, or splicing in of new wood
sections. In the case of structural repairs, you can often “sister” in a new piece of wood instead of going for a total removal and replacement. The remaining wood might require treatment with borate fungicides as a preventative measure.

Always use pressure-treated lumber if your repair involves contact on concrete. If you must install against dirt, use wood rated for ground contact. Structural repairs must meet the building code. San Francisco has had its share of collapsed decks in recent years, with more consequent suffering than anyone deserves.

Exterior mildew often shows up on the north side of a building and behind dense landscaping that does not allow wood to dry out. Trim anything back that is in the way. Adjust your sprinklers if they are soaking your building more than your plants. Scrub off any mildew with a mixture of hot water, household cleaner and bleach. Do not try to paint over the mildew without cleaning it first; it will just stain through the new paint.

Interior ventilation will do wonders against mildew. Do not install small fans that meet only the most basic minimal requirements and take forever to do the job. A fan that draws out 100 cfm (cubic feet/minute) will quickly clear the steam from a bathroom and do wonders in preventing mildew growth.

Preventive maintenance is a property owner’s mantra. It saves money, avoids headaches and keeps tenants safe. Get to it now while the weather is still warm and dry and you can ignore even the most rotten winter rains.

The opinions expressed in this article are those of the author and do not necessarily reflect the viewpoint of the SFAA or the San Francisco Apartment Magazine. Terry Meany is a former contractor and landlord. He is now a full-time writer and author of “Working Windows: A Guide to the Repair and Restoration of Wood Windows”; Lyons Press. He’s cost conscious, but not cheap, and knows deferred maintenance always costs more in the end. He can be reached at tfmeany@msn.com.