Why do new homes have more moisture and mold problems than older houses?
Monday, June 25, 2018
Let’s get one thing out of the way up front: this is not a home inspector’s rant about how the old ways of building a house were better and “they don’t build ‘em like they used to.” It’s about how building technology advances that have made homes more energy efficient, along with the addition of features that make a house more comfortable to live in and are now considered standard, but would have been luxuries in a pre-1950 home, have provided more routes for moisture to get into a house and be trapped.
Older homes, especially in Florida, were designed for ventilation—to “breathe.” Big openable windows, corner windows for cross-ventilation, a whole-house fan that sucked outdoor air into the house, then up and out through the attic vents, and louvered transoms over bedroom doors to provide air flow even when the door was closed. You could close everything up in the winter, but air leakage through jalousie windows was unavoidable. It didn’t matter because heating was relatively cheap, and it was more important to be comfortable during the summer in the era before air conditioning.
New homes are designed to be air conditioned and heated all year, and must be well-sealed and insulated to maintain the temperature and humidity differential between the inside and outside while keeping energy costs reasonable. Many of the problems today relate to having one continuous temperature and humidity level on the inside of a wall, and widely variable temperatures and humidity on the other side of the wall, with minimal air exchange between the two sides.
This fact is often repeated as the main problem with modern homes, but it is also why they are more comfortable to live in than their predecessors; and it is not accurate to blame everything on houses being “built too tight.” Here’s our list of other factors that have changed over the years and contribute to a higher likelihood of moisture and mold problems occurring in a newer home:
- Every plumbing fixture in a home is a potential location for leakage, either of incoming water or outgoing waste. Most older homes had plumbing at only two places inside the home: the kitchen and a single bathroom. The water heater and laundry were often in a utility room behind the carport or an attached laundry shed. Today’s homes have at least two bathrooms, a dishwasher, water and ice service at the refrigerator door, an indoor laundry and water heater. That’s the basics. Then there’s the optional spa tub in the master bath, wet bar, and laundry sink.
- Manufactured roof trusses, beginning in the 1960s, made it easier for a builder to make complex and appealing rooflines that would have been prohibitively labor-intensive to construct on-site previously. But that means more flashings at the intersections of all those gables and hips that are usually the first place to fail on an older roof. Add in a few skylights and you’ve got more potential locations for water intrusion. Any roofer will tell you “it’s not if a skylight will leak, it’s when.”
- Construction materials are constantly being improved, but not all new building technology holds up over the years. Wonder materials of a few decades ago, such as polybutylene piping and composition wood siding, proved to be water-intrusion headaches still lingering around in some homes. Complaining homeowners and lawsuits eventually removed them from the market.
Synthetic stucco, also called “EIFS,” is a newer exterior siding material that got off to rocky start and, after widespread incidents of wood rot and mold behind it from water entrapment, the installation specs were changed to allow drainage behind the material.
- People today are more conscious of the potential danger of living in a house with mold. Growing up in South Florida in the 1960s, we were both used to hearing “Oh, honey, that’s just a little mildew. Nothing to worry about.” Not anymore.
- A big advance in efficient home construction was the concrete floor slab, which became the norm by the end of the 1950s. It’s faster and much less expensive than framing an elevated wood floor over a crawl space, but that air gap provided a barrier to water intrusion from the ground and an easy way to verify if there is a moisture problem under the floor.
- Landscape sprinkler systems are standard-issue for new homes in Florida, except for the low-end of the market. Without regular maintenance adjustment, they start spraying on the walls of a home. When we see wood rot at window trim, we turn on the sprinklers to see which one is soaking down the wall.
- Pressure washers are really better labeled as a “hand-held hurricane.” They are great for driveways, but terrible for houses. When a homeowner uses this popular power tool on the exterior walls of a home, they force water at high-pressure into siding and loosen window caulking. Plus, the pressure often pops the seal on double-pane insulated windows, making them lose their insulation ability and eventually turn cloudy between the panes.
Pressure washing an asphalt shingle roof loosens the tab adhesion at the leading edge of the shingles and blasts away surface granules that protect the shingle from sunlight UV-deterioration. Granddad didn’t have one.
A lot of good research has been done to improve air exchange rate and indoor air quality, while keeping homes weathertight. We think that’s great and don’t want to go back to the the old days. Just want to point out that there are more reasons for moisture and mold problems in newer homes than simply that they need to “breathe.”
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