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Grade Levels & Wood Flooring

by Jeff Hosking – Hosking Hardwood Flooring
© 2004 - 2012, Copyright protected. All Rights Reserved

What is a Floor Grade Level?

Determine the grade level Before you even begin to search for that perfect hardwood floor for your home, you need to be aware of where you plan on installing the new wood flooring. The different levels of the home are often referred to as "Grade Levels." For example, in most cases, when you walk into a home through the front door, that ground level floor is known as "on grade." Every floor located above this ground level on grade is considered to be "above grade." Leaving the basement level to be commonly referred to as "below grade."

The Grade level where you intend on installing the new hardwood flooring will dictate what construction(s) of hardwood flooring you will be limited to.

The Best Floor Construction for Your Grade Level

Some wood flooring constructions (like 3/4 IN. thick solid wood flooring) are limited as to where they can be installed due to these solid boards being more susceptible to moisture. These 3/4 IN. thick planks are generally not recommended for basements or for installation over concrete slabs. Solid wood floors generally perform better at on or above grade floor levels of the home, where the relative humidity levels may not build up as high. This is because windows and doors are being opened more frequently and air conditioning and/or dehumidifiers are being run.


Basements are known for being closed in, causing damp or wet conditions which can cause solid wood flooring to absorb excess moisture. This moisture, in turn, migrates through below grade cement walls and slabs. Wood flooring that has absorbed excess moisture can swell in size causing the edges of the boards to cup and/or buckle the wood.

Quality engineered flooring, on the other hand, is manufactured to have better resistance to higher* or lower than normal moisture. Below the top decorative hardwood wear layer on the surface, there is a plywood type center core with 3-7 thin layers of plywood cross-layered in opposite directions to each other. Each layer is glued and bonded together, helping reduce expansion and contraction during seasonal changes in humidity levels.

*That doesn't mean engineered flooring will withstand an excessive amount of moisture or being flooded with water. All wood flooring should be maintained at a normal relative humidity level. Remember, water and wood never mix.

solid wood floorsSolid wood floors should be maintained at between 30-50 % relative humidity throughout the year, which equates to normal living conditions.


engineered wood floors Engineered wood flooring should be maintained at between 30-50 % relative humidity throughout the year, which is still in the normal comfort range.


Remember: Even the best wood flooring will react to the presence of moisture. In the dry winter heating months, moisture leaves the wood causing the floor to contract, which can leave unsightly gaps between each plank. In the summer months when the humidity is higher the wood will absorb excess moisture and expand and the gaps will disappear. If there is too much moisture it may cause the wood planks to cup, or buckle. This is why it is important when installing a wood floor to acclimate the wood to the home from 4 to 7 days or more prior to installation and to leave the proper expansion gap around the perimeter and at all fixed objects. It is also important to keep the home's relative humidity level at between 30 - 50% or what the manufacturer recommends. Doing this will help minimize any movement within the wood flooring later.


digital hygrometer A small digital shelf top type hygrometer can be purchased for about $25.00 at most any hardware store and is used to monitor both room temperature and relative humidity levels within the room areas.

To help you determine which type or style of wood flooring can go where, we have placed a house diagram on each of our wood construction article pages for engineered, solid and floating wood floors. The installation method(s) recommended for a specific product will also determine where are floor can go, so be sure to read our articles Install Methods as well as All About Subfloors to make sure you're browsing through hardwood products that would work in your specific situation.


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Page Reviews

Web Page: Grade Levels of the Home
Overall Rating: 3.8 stars - 4 reviews

Date: August 18, 2022
Page Rating: (5.0/5)
R. Holden, the "grade level" doesnt refer to the wood at all. It is actually referring to the "level of the home". Thanks for being patient.
Date: March 13, 2015
Page Rating: (5.0/5)
Very informative and useful. thanks
Date: April 24, 2013
Page Rating: (1.0/5)
Please define "Grade Level". Is it the type, quality, or size of the wood?
Date: November 10, 2012
Page Rating: (4.0/5)
I have been reading several of your excellent articles. I cannot locate the page that describes the grade level descriptions. Please advise.

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