First things first: in case you don’t already know what underlayment is, it’s the material laid on top of the sub-floor before the bamboo floor is installed (the subfloor is pretty much the raw floor of your house, whether it’s a concrete slab or plywood resting on floor joists).
The long and short of it is that you need bamboo flooring underlayment if you are nailing down or floating a bamboo floor. However, you do not need underlayment when gluing down a bamboo floor. Using underlayment under your bamboo floor can provide soundproofing, moisture protection, and stability and reduce wood on wood squeaking. Bamboo flooring and an underlayment/vapor barrier can be installed on any existing floor, including concrete, laminate, wood flooring, vinyl tile, linoleum, tile, etc., as long as the floor is flat and solid.
What type of underlayment is best with bamboo flooring?
If you’re nailing down a floor – use 15 lb felt paper.
The most common underlayments used when nailing a floor down are 15 lb felt paper (i.e., roofing paper) and red rosin paper. Most installers prefer 15 lb felt paper. This is because rosin paper tends to leave behind red dust that can stain walls and clothing. This dust is often hard to remove.
There is a common misconception that 15 lb felt paper is a vapor barrier – it is not! While it does help to wick away moisture from the bottom of the flooring planks, it is not meant to serve as a vapor seal. Therefore, when installing over wet crawl spaces or basements, you need to seal them first. 15 lb felt paper would not protect your floor from sub-floor moisture. Another advantage of installing 15 lb felt paper is it reduces wood on wood squeaking.
People often ask if they can use 3 in 1 foam/rubber underlayment under nail down floors.
The answer? It’s not recommended.
These underlayments compress slightly when walked on, and the vertical flexion can result in loose nails and squeaky boards.
If you’re floating a floor – use a 3 in 1 underlayment.
While bamboo flooring is extremely durable, like all hardwoods, it is vulnerable to moisture. When floating a floor, a 3 in 1 underlayment is a must, especially if there is excessive moisture emitted by the sub-floor, such as a concrete slab or crawl space. Even if you live in a relatively dry climate (bamboo flooring can be installed in dry or humid climates), there’s no guarantee that your subfloor won’t have moisture issues. That’s why it’s essential to choose an underlayment with a built-in vapor barrier. The vapor barrier provides complete protection against moisture.
Stability – added benefit of 3 in 1 underlayment
If your subfloor is slightly uneven, underlayment can smooth out small imperfections. This means that when you lay your bamboo, it lays a little flatter. This benefits more than just your balance — your floor is less prone to damage and buckling when it’s installed correctly, thereby extending its life!
Sound Absorption – added benefit of 3 in 1 underlayment
A 3 in 1 underlayment prevents a louder, hollow sound and provides a fuller sound when walked on. It also dampens the sound from impact or sound transmission noises. The higher the STC and IIC rating, the more soundproof and sound absorbent it is.
IIC = Impact Isolation Class *ASTM E492/E989
STC = Sound Transmission Class ASTM E336/E413
These ratings relate to the sound traveling through the total floor/ceiling assembly between upper and lower floors/spaces.
Are you someone who sleeps in a while your significant other is an early riser?
Do you have a new baby that wakes at the slightest sound?
Do you live in a condo or apartment building?
You should look into a 3 in 1 underlayment with the highest STC rating you can find.
Installing over Radiant Heat – always use 3 in 1 underlayment or glue down with a vapor lock adhesive
Have an underfloor heating system? If you’re floating an engineered floor over it, be sure to use a high-quality 3-in-1 underlayment. The underlayment should have a minimum thickness of 2mm to insulate and protect your floor. You can use both engineered floating and solid glue down bamboo flooring over radiant heat subsystems as long as the floors are properly installed and maintained. If you’re gluing down a bamboo floor over radiant heat, ensure to use an adhesive with a vapor barrier, as the adhesive will help insulate the floor from sudden changes in heat.
Note: The color or thickness of the underlayment has no relationship to the amount of thermal resistance. This is measured purely by tog ratings.
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