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Is it a good idea to install vinyl plank flooring (7mm thick, 7 inch wide) over new cement board / backer board? The cement board will be screwed to a 3/4" T&G plywood subfloor which is supported by 2x10 I-joist 12"o.c.

The reason of this bizarre application is that I have settled floor that needs to be raised up by 1/2". I know traditionally it's done by adding a layer of underlayment grade plywood or OSB. However cement boards just seem to be far superior in terms of price (at least right now) and easiness to handle since they are small and can be scored to cut. The work area is pretty small (bedroom of about 150 sqft).

I can't seem to find information of this type of application online. I also called APA and James Hardie and they can't answer me because this is not in their guideline.

Any thoughts or comments are appreciated!

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  • And the depression is consistently 1/2" and doesn't slope? I ask because planing or sanding the flooring for level is pretty common and you don't want to do that on cement board. Jul 15 at 21:40
  • @UnhandledExcepSean I did simplified the question a bit in fear of TLDR. The floor is sloping from 0" at the ridge to -3/4" at the exterior wall but it is very gradual. My plan is to add 1/2" substrate where the depression is over 1/2" (basically the entire bedroom and stops at the bedroom door), and then use self leveler in areas where depression is less than 1/2" and slopes up to 0" ( which is a very small area in the hallway). This way I am not adding a whole bunch of weight to the floor. Jul 15 at 22:57
  • There is rarely a TL;DR issue in questions. More detail will get you a better answer.
    – FreeMan
    Aug 15 at 15:29

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Backer boards are the strongest, sturdiest substrate for flooring just after concrete floor.

Will not bend or flex or rot.

Use the screws specially made for backer boars.

Use a leveler to mount them evenly.

It is an overkill for vinyl floor, but it will work well.

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  • But for a vinyl plank floor, you really don't need to worry about bending or flexing. If OP was putting down 12" tiles, then yes. But for vinyl plank, no. The vinyl plank is flexible anyway. I would go with the 1/2 wood (OSB panels?).
    – SteveSh
    Jul 15 at 22:24
  • @knowitall Not sure if "chosen wisely" is sarcastic but thanks for the reply! Jul 15 at 22:59
  • @SteveSh my main concern with OSB is that it may swell if water ever gets in and potential squeaking if it looses hold to the screw. Although I have 30 year old OSB underlayment in kitchen and bathroom and none of the above had happened yet lol Jul 15 at 23:02
  • @Midnightlawnmower - I had a delam problem with a plywood subfloor in a bathroom. Bathroom was original, 1956 or there'bouts. When I went to tile the floor, the area under the vanity looked like it was made of shingles. The glue in the plywood had completely disintegrated, probable due to water splashing & leaks over the years.
    – SteveSh
    Jul 15 at 23:08
  • Generally, @MIDNIGHTLAWNMOWER, there isn't that much worry about water on the floor of a bedroom, which is where you're putting this down.
    – FreeMan
    Aug 15 at 15:30

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