Hardwood Flooring in Winter

Today's post is about Hardwood Flooring in a Saskatchewan Winter!  We live in one of the harshest climates in North America - Warm and Beautiful in the Summer, and Cold and Dry in the Winter.  Not necessarily the most optimal climate for hardwood (or people!).

Here is a bit of information on how to keep your floor (and your health) at it's best during a Cold Saskatchewan Winter.  As I write this, it's -35 with wind this morning...

During the winter, even the most carefully installed wood floors tend to dry out and shrink. The floor behaves that way because of wood's relationship with moisture in the air. Air with a low moisture content, or low relative humidity (RH), causes wood to lose moisture. When wood loses moisture, it shrinks. What can we do about it?

To control winter-related shrinkage of flooring and the consequent gaps (what some call "cracks"), we have basically two options of controlling the moisture in the home.

Gapping and associated noises usually occur when the flooring dries significantly from its summertime high moisture levels. So, to reduce winter gapping, reduce the annual range of moisture levels. Or, more specifically, to reduce winter gapping, don't let the indoor RH drop too much. (Or don't let summer RH levels get too high—but that is another post.) A good annual range for the best flooring performance is a swing of 20 percent RH from wettest to driest. This means that in BC, they may work in a range of 40 to 60 percent RH, while here, we use 25 to 45 percent. All will work, as long as the RH range isn't too wide - but sometimes in the winter, the RH tends to dip too low.

These numbers can be monitored by using an inexpensive hygrometer (available at BestBuy - or we even have some here at the office).

There are two approaches to keeping winter indoor RH elevated.

Moisture Option 1: Reduce Ventilation

Because of the relationship between temperature, moisture and RH; ventilation of a house in the winter tends to dry it out. When you bring cold outside winter air into a house and warm it up, the RH of that air drops significantly. For example, air at -1 degrees Celsius and 50 percent RH when warmed to 21 degrees will be at 10 percent RH. To get the RH of this air back up to something respectable, we would need to add moisture. The more ventilation that is occurring, the more this dry air is drying out your home, and the more moisture you will need to add. Therefore part of the solution is to reduce ventilation.

Ventilation of a house is measured in air changes per hour (ACH). As an example, a house that is 1,800 square feet with 8-foot ceilings has a volume of 14,400 cubic feet (1,800 x 8 = 14,400). Changing all the air in this house with fresh air once an hour would be one ACH.

Current building codes and standards recommend home ventilation rates near 1/3 ACH. Average homes have ventilation rates near 1 to 2 ACH, while some old, leaky homes are near 7 to 10 ACH. Weatherization and home energy audits typically measure ventilation rates. These programs can also pinpoint leakage sites and direct sealing efforts to reduce excessive ventilation rates. Old windows are often major leakage sites, as are recessed lights and other holes in ceilings and floors  These are normally set at the 1/3 ACH – so as you can see by the chart, turning it down during the winter will save a lot of humidity.  That all said – while it is good to turn down your Air to Air, you cannot turn it all the way off!  In our cold winters, to turn off the unit would most likely cause a buildup of ice in your locks and cause water problems with your windows.

 

House Size

Outdoor Temp

Ventilation

Moisture Needed (pints / hour)

Square Footage

Degrees C

ACH Rate

30% RH

35% RH

40% RH

1800

-1

1

1.4

2.3

3.4

1800

-12

1

3.8

4.8

5.8

1800

-23

1

4.8

5.7

6.8

1800

-1

2

2.8

4.6

6.8

1800

-12

2

7.6

9.6

11.6

1800

-23

2

9.6

11.4

13.6

 

Moisture Option 2: Add Moisture

As I mentioned above, bringing in -1 degree air at 50 percent RH, then warming it to 21 degrees causes its RH to drop to 10 percent. To raise the RH, we need to add moisture. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) publishes charts showing moisture and air relationships. Using these charts with our example house from above, we need to add about 1.4 pints of water per hour to raise the inside RH to 30 percent. If the ventilation rate is higher, we need to add more water. If it's colder or warmer outside, the amount of water needed changes. If we want the RH to be even higher, we need to add more moisture. Table 1 shows some examples.

As you can see from Table 1, colder outside air requires more moisture. Higher ventilation rates require more moisture, and higher target indoor RH levels require more moisture. Since the ventilation rate and moisture needed are related, an economical approach is to reduce ventilation rates, then add moisture.

Moisture is added to indoor environments from normal household activities and use. When this moisture is not sufficient to meet the needs, a humidifier can be added. Table 2 shows some typical indoor moisture sources and amounts.

According to Table 2, a family of four contributes about ¾ pint of moisture per hour. This number is likely smaller than that shown, because people aren't home all day and don't clean every day. So I would suggest ignoring household sources when determining moisture needs.

Adding moisture then boils down to using humidifiers. Humidifiers can either be stand-alone or attached to a central forced air furnace. Typical residential systems can provide up to about 6 pints per hour. This is an important number: 6 pints per hour, maximum. Table 1 shows that more than 6 pints per hour are necessary to get to 40 percent RH when it is real cold outside in a relatively tight, 1,800-square-foot house.

Source

Estimated amount

 

(pints)

Bathing

0.12 per std-size bath

Showering

0.52 per 5 minute shower

Cooking

2 per day

People (4)

0.44 per hour

Plants (5 - 7)

0.9 per day

Cleaning

2 per day

Dishwashing

0.9 per load

Average Household

0.75 per hour

The goal is to keep the relative humidity at approximately 40% with a temperature of 21 C.  Of course, in our climate that is just not possible, so we aim to keep the humidity level above 30% year round.  

Bottom line: Winter weather dries out wood flooring, causing gaps, possibly increasing squeaks and opening surface cracks. Wood will be wood. Don't expect your humidifiers or other sources of moisture to prevent normal winter movement. Humidifiers can help some, as can choosing the right wood flooring for the right situation, but only to a certain extent.  With our climate, it is generally accepted that hardwood flooring (along with all other woodwork in your home) will shrink during the winter – and then once humidity is released back into the home in spring, the floor will move back. 


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