GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Finish Floor for Slab-on-Grade Assembly

rajibroy | Posted in General Questions on

Hi GBA Readers,

I have a slab-on-grade new construction in Vermont (CZ 6A). Five months after pouring concrete, it is time laying floors.  My sub grade assembly from bottom to top is: Coarse gravel + R15 foam + Stego vapor barrier + 4 inch concrete slab. The concrete slab has a thermal break from the frost walls (R15).

One of the young family members have sensitive lungs, and get irritated by molds. Thus, control of air quality, and moisture is a priority. I have installed ERV, and MERV-13 filtration for slim duct units (to catch dust and mold spores).

For flooring choice, I am interested in Vinyl plank for durability, and ease of maintenance; but it might create a moisture trap/sandwich for the concrete slab. Does leaving under cabinet/closet floors bare slab (1/15th of total floor area) is adequate?

Shall I opt for higher priced wood flooring? Does engineered wood vs  solid wood differ in vapor permeance? Is the extra cost justified? Or am I over-thinking?

When reading thru manufacture specs, what should I scan for?

Thanks in advance for your valuable insight.

Regards, Rajib

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. rajibroy | | #1

    To clarify: I have a R15 foam on the vertical frost protect wall (or stem wall) and a R15 thermal break to isolate frost protection wall and concrete 4" slab.

  2. plumb_bob | | #2

    Hard to say how much residual moisture will be in the slab from the curing process, probably very little at this point. The slab assembly looks sound if detailed well, rising moisture should not be an issue.
    For wood, you would need to install sleepers or some other system to fasten the wood strips to, have you planned for this with door heights etc?
    I would vote for vinyl for ease of installation and durability. Maybe you can get the slab tested for moisture before putting anything down, for peace of mind.
    I have a kid with asthma too.

  3. plumb_bob | | #3

    On re-reading, I see you have a concrete ring wall with non structural slab. Bulk water control is critical for keeping the moisture down, including foundation drainage, damp proofing, and site grading, roof drainage. Hopefully this was done well.

    1. rajibroy | | #4

      Thanks for the input.
      Yes the site is elevated from surrounding that helps with drainage. The ring wall cavity is back-filled with washed crushed stone. Also planning on using rain gutter and landscape grad to divert water away from the building.

      Testing slab-moisture is a good idea. Any kit that can be purchased online? Hopefully upcoming winter weather will help to dry out some residual moisture on slab.
      Thanks again.

  4. plumb_bob | | #5

    There are hand held devices that measure moisture in concrete, you may be able to find an engineering company or home inspector that can do this for you. Or rent one from a rental company. Or just buy one.
    Good luck!

    1. rajibroy | | #6

      Thanks so much!

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |