Installing Flooring On, Above and Below Grade
Your home's indoor humidity level can be affected by many different factors. One of the most important of these is the level at which you install your floors. There are 3 different floor levels: above grade, on grade, and below grade. Learning their differences and how they affect humidity can help you better determine how you should install flooring in your home.
No matter which floor you select or how you decide to install it, here are some general tips to keep in mind:
- For most floor types (not including bamboo, hardwood or cork) a recommended indoor humidity level is anywhere between 35-50%
- Always seal your floors as recommended by the manufacturer
- Always consult your manufacturer (or manufacturer's guidelines) prior to installation to see which rooms are covered under warranty
Below grade refers to flooring that is installed below the earth's surface (this could be anywhere from 4 inches to 30 feet below ground, or deeper). While floors made with organic materials can be installed below grade, they are not generally recommended for high humidity areas. Some of these types include hardwood and bamboo.
Note: A room is considered below grade even if only a small fraction of the floor is lower than ground level.
The soil beneath and surrounding your home constantly absorbs water from sources such as water runoff, underground plumbing and the earth itself. Even if your floor is only a few centimeters below the surface, it will still be exposed to higher amounts of moisture than a floor that sits on or above the surface. Porous floors - those which absorb moisture easily - such as unsealed cement and hardwood, can naturally wick (pull up) water from the ground. Over time this could lead to fungi growth, an eroded foundation and overall damaged flooring.
There are ways to reduce the risk of moisture damage as a result of high humidity. If you're installing flooring underground (for example, in the basement), the following tips may help increase the life of your floor:
- Properly seal your floor and the walls around the floor
- Install products that prevent flooding and push water away from your home (stand-pipes, back-up pipes, floor drains, overhead sewers)
- Make sure that gutters drain away from the house and not into the ground
If your heart is set on hardwood, engineered wood floors can be suitable for below grade installation. Engineered wood floors can withstand the moisture found in most basements, although flooding can still cause damage. Not to be confused with laminate, engineered wood flooring consists of multiple layers of real wood and a plastic laminate veneer. The wood layers are laid on top of each other at 90 degree angles for increased stability.
On-grade flooring sits right at ground level. Although on-grade flooring is less susceptible to moisture damage than flooring installed below grade, it can still warp and crack in extreme conditions. Floors that are made using woody materials (such as bamboo, hardwood and cork) tend to expand and contract in extreme conditions. More durable forms of these floor types are available, such as strand woven bamboo and engineered hardwood flooring. These floors will cost you more but they also generally last longer, which may save you money in the long run.
Instead of trying to find a floor that can tolerate your home environment, consider choosing a floating floor. A floating floor hovers above an underlayment (the layer between the sub-floor and new flooring) by way of a click and lock system. The floor is held to the perimeter of the wall by the base molding. Because a floating floor doesn't touch the sub-floor, water and air can flow underneath the sub-floor with little to no effect on the flooring. Many types of floors can be floated, including hardwood, laminate and tile.
Above-grade flooring refers to any floor that is installed above ground level, leaving at least 18 inches of room between the floor and the sub-floor (such as upstairs flooring). Above grade floors are not susceptible to ground moisture, which can make them easier to prepare during installation than below-grade and on-grade flooring. Nevertheless, an indoor humidity level between 35-50% is still recommended for good floor care.
A crawl space is the space between the foundation and the bottom floor of the house. It is typically 18-24 inches deep; which is generally enough room for a person to access the under-floor area. High moisture levels can build up in crawl spaces if ground and surface water travel through the walls of the foundation and earth floor. Sometimes this moisture can seep up through floors and damage the subfloor. You can reduce the chances of this by making sure your crawl space is properly ventilated.