Hey there.Why and do I have to lay 6 mil plactic as the manufactuter requires? BR-111 5/16 solid brazilian hickory to be stapled.

What have you done or would do?

Subfloor: 1/2 ply glued and screwed on top of 1x8s ,also screwed,dry basement under.

Thanks for replying!

Well you need it as a moisture barrier, I have put down that 3/8th bruce prefinished stuff, with the bruce plastic underlayment underneath. You need a vapor barrier to keep the moisture from reaching the wood.

If the manufactuer says you need it, It is best to put it down. Otherwise the manufactuer will not allow any defect claims etc. if your floor fails.

Using plastic isnt any fun, It seems to bunch up etc. Not user friendly like paper. I use "fuji" film paper for all of my 3/4 jobs in place of asphalt/rosin/felt paper I forget off hand what the thickness is in comparison to 6 mil plastic, you may be able to substitue it for the plastic.
If not I suggest that you duct tape the plastic to the subfloor. Or use a glue. I would strech the plastic tight, so it doesnt bunch up on you. When you are using a product as thin as 5/16 when the plastic folds over itself you will be able to feel it through the flooring (because the plastic will be 3 times thicker)

Thanks for the reply EF!

I understand the need for a moister barrier,but plastic sounds like a recipe for condensation on the top on of it.

If your letting the humidity rise that much to create a dew point, the plastic is going to be the least of your worries.

If you put 6-mil poly on top of a plywood sub-floor for a moisture vapor retarder in our area it will usually trap moisture under the poly and cause rot.
Dragonfly may not have that problem with a dry basement under his sub-floor. I would follow BR-111 instructions on this install but I would not do the job in our area if we had to put the MVR on top of the wood sub-floor.

Would you "quote" that paragraph that tells you to use a 6mil poly? You may not be reading it right. Very bad idea imo.

I could not cut and pasted it so here's the link: http://www.br111.com/pdf/516716_Install.pdf Page 69,step 5

Im located in the Ohio Valley area.I run a dehumidifier in the basement just to keep things in check.
One local installer in the area said he stapled it directly to the subfloor in his house(1st floor, 2nd,I don't know) but of course he knew he voided warranty.

Thanks To All!

I'm really surprised they have this in their specs. It is a formula for subfloor rot.


In the staple-down
application, a suitable moisture barrier (minimum 6 mil poly
fi lm) must be established over plywood (or equivalent) with
joints overlapped 18” and taped. Asphalt felt (15 lbs.) may be
used in addition to the moisture barrier, but asphalt felt is not
considered a moisture barrier.

bruce's 3/8 directions are the same way

Boy o' boy... I'm not getting that part either. Last I heard wood needs to breath some. But, a manufactures written instructions override all other stipulations.