Straight Talk on RH Control & Wood Flooring

We've heard the story over and over again regarding the importance of RH control to maintain the beauty of our wood floors, yet no one seems to listen or remember. Whether we like it or not, all factory-made wood products (flooring, furniture, cabinets, musical instruments) have a specific RH range they perform best in, and this range is usually published on the manufacturer’s website. For example, every pianist knows the importance of RH control, because when the RH goes down, so will the pitch, when RH goes up, so does the pitch. In order for the song to be heard correctly, the pitch has to be perfect and RH has to be within that preferred range.

In this photo, we see classic guitars inside a RH-controlled cabinet (humidor) in order to preserve the quality of the instrument as well as hold its value. I took this photo as I walked through an arid-climate airport, and it goes to show that even though the environment isn't favorable, they managed to overcome the conditions and display the instruments.

Wood flooring is no different. We hear stories saying, “The floor shouldn't be sold here because it's too dry.” Just like the guitar or piano, some people overcome these conditions by making the appropriate adjustments—and it works. The same thing holds true sax players who need RH control for their reeds and use a reed humidor case. Factory-finished wood flooring is produced to be in a specific RH range (e.g., 35–55%) and typically wrapped in plastic to preserve the integrity of the product, sort of like a mini humidor. Therefore, when the flooring package is opened up to be installed, the interior RH should be within the manufacturer-specified ranged so the material doesn't have any adverse affects such as splitting/cupping. Just like the musical instrument, these conditions should be observed for the life of the floor.

The Difference between Short- and Long-Term Effects

This chart from Aprilaire shows the adjustments that should be made for RH based on outdoor temperature.When we speak of RH control, that doesn't mean we have to watch the environment like a hawk every single hour. What it means is we must be able to provide the RH control that the particular manufacturer is requesting. When looking at the RH control, we have two things to look at: daily and seasonal change. So let’s say for the most part we have our RH controlled from 30–50%, but today the windows are cracked open and it’s raining, and the RH inside the house goes up to 90%. Does this mean we just blew our flooring warranty? No, wood is a hygroscopic material, but it takes time for it to absorb the moisture. Now let's say you have a lake home in northern Wisconsin and your windows are open most of the summer. Then the flooring will absorb moisture and cause a reaction in the material. This holds true for dry winter conditions as well when outside temps drop to -10 degrees for seven days and the interior RH drops to 15–20%. Will that short-term low RH affect the wood floor? No, it's not going to split or dry-cup in that short period of time as long as you have the ability to maintain the proper RH when the outside temperature increases. For example, in Minneapolis, the coldest month is January, with an average outside temperature of 18 degrees and 32% RH. Of course it’s warmer during the day and cold at night, and we should have the ability to maintain RH during those periods of the highs and lows. Modern HVAC controllers/thermostats have the ability to read the outside temperature and automatically adjust the interior RH appropriately. This makes it easy to properly maintain RH control in any geographical location or any type of building with this type of equipment.

Extra Costs of Equipment

Could there be extra costs to the overall flooring price due to the HVAC control? Yes if the customer doesn’t currently have any type of system in their home. Just like the musical instrument, the purchase price is just the beginning, and it will require RH control to maintain the quality of floor the customer paid for. When your customers are looking to have a wood floor installed, you must look at what RH control they currently have. If they don’t have any RH-control equipment, they can get an average built-in humidifier for around $600, which is a small price to pay for a $12,000 wood floor investment.