San Francisco is a city with microclimates and sub-microclimates—local atmospheric zones where the climate differs from the surrounding area. Due to the city's varied topography, weather conditions can vary as much as 10 degrees from block to block. The region known as the Bay Area can have a wide range of extremes in temperature; the average maximum temperature in July is about 64 degrees at Half Moon Bay on the coast, 87 degrees at Walnut Creek only 25 miles inland, and 95 degrees at Tracy, just 50 miles inland. Due to the proximity of the ocean, relative humidity (RH) fluctuations are affected as well; the San Francisco Bay Area average RH is 80 percent, while Tracy is 38 percent.
Why You Should Care
What does this have to do with you or your job? A flooring contractor may service 100 square miles or more, an area that could experience huge swings in climate conditions. Flooring selection and installation techniques used in one area may or may not work in another area close by. This also applies to seasonal changes. For example, my home state of Minnesota experiences huge swings in seasonal conditions. During late July or early August, the average temperature is 84 degrees with 78 percent RH; however, in the same location during January, the average temperature is 18 degrees with 50 percent RH, with lows reaching minus 25 degrees. These sub-zero temperatures have a large impact on a building's ability to maintain proper interior RH.
Microclimates—Emphasis on "Micro"
Microclimates may refer to an area as small as a few square feet (for example, a garden bed) or as large as many square miles (like an entire valley). In Minneapolis' single-family housing, basement RH may range from 60 to 70 percent during the summer (if left uncontrolled) while the main floor can fluctuate from 40 to 50 percent. In multi-family housing (high-rise condos), the winter average interior RH may be 30 percent on the fourth floor, while the penthouse on the 27th floor may have only 9 or 10 percent. Furthermore, it may be nearly impossible to maintain the RH specified by the flooring manufacturer or the NWFA without window condensation.
How You Identify Them
Microclimates are generally easy to identify as the wood flooring contractor visits the project. Conditions may vary from room to room due to, for example, radiant heat in the new addition but a forced air furnace in the remainder of the house. Basements and crawlspaces can also create microclimates in some areas of the house. As mentioned, you can expect microclimates in any high-rise project. A job-site visit is the best way to identify all the microclimates, but, sadly, most flooring choices are made from blueprints or in dealer showrooms without visiting the project firsthand.
Working with Microclimates
Regardless of where you live, microclimates do exist in your territory. Before you can intelligently suggest any floor covering to a client, you must qualify the flooring product to fit the intended environment or application.
For example, you may have a job site that has a living room with a wood burning fireplace, while the adjacent kitchen has a laundry room beneath the wood floor. The same flooring product may not be successful in both applications—one room will be dry, while the other will gain moisture from below.
This applies to high-rise living as well, where RH fluctuations play a big role in flooring success or failure. Humidity always falls to the lowest point in a building, so the 27th floor may experience a 10 to 20 percent lower RH than the fifth floor. Consequently, the penthouse may not be a good candidate for some exotics due to face checking unless additional HVAC equipment is installed to offset the RH deficiency.
Understand Your Risks
We do not need to be afraid of microclimates; we must understand them and the risks involved. For example, the NWFA does not recommend solids be used below-grade or in basements, but, on the contrary, Minnesota residents have been using solids in basements since the '40s. Understanding this microclimate makes it possible to accomplish a successful flooring installation. First, we must identify the extreme RH seasonal swings, which in summer are somewhere around 55 to 65 percent, or 9 to 10 percent Equilibrium Moisture Content (EMC). So, the wood flooring has to be acclimated to the projected summer EMC to avoid buckling. Also, the flooring width is kept to a minimum (1 1/2- or 2 1/4-inch) to minimize cupping; the flooring cut is either rift or quartered. Combined, this usually provides a successful flooring application. The side effect of this application is winter gapping, but since the flooring is narrow, gaps are minimized.
This information should be fully disclosed to the end-user before the project begins. Also, keep in mind that even though this system has been used for over 60 years, you will stand alone regarding liability if it is not recommended by the flooring manufacturer or any trade associations. Even if you understand the product and the microclimate, it still might not be the wisest choice.
The Big Picture
Whether you are a flooring contractor covering 100 square miles or 10, and whether you work with single-family or multi-family dwellings, you must be familiar with the flooring product requirements, temperature and RH targets, and end-user expectations. A product that may work fine in a single-family dwelling may be the wrong choice for a high-rise penthouse, while a product that works in one room of a house may not work in another. Identifying the microclimate by geographical location or within the building itself will help create a successful flooring application. And remember the No. 1 phrase heard by most claims managers: "I was never told that!" Full disclosure of side effects to the end-user before the project may keep you out of the courtroom or help prevent a wood flooring inspection.
