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Community and Q&A

Detailing a Subfloor Transition

user-7479264 | Posted in General Questions on


I’m in the planning stages of finishing my 1400 sqft basement, 1250 sqft of which will be partially finished (open ceiling), and 150 unfinished utility area.  I have a couple questions about transitioning between these two areas.

My plan is as follows:
– dimpled mat across finished area (careful monitoring of slab temps through last summer and this winter tell me I don’t need additional thermal break on the floor to prevent condensation/mold/mildew)
– 1.5″ faced EPS glued to the walls, resting on top of the dimpled mat, taped/foamed all seams including to the dimple mat — entire basement including unfinished area and all rim joists will have insulation
– wood framing on top of dimpled mat, up against the EPS.
– additional insulation batts
– drywall
– vinyl flooring
– ceiling will remain open for access and cost reasons, which will also allow airflow between the unfinished and finished area.

Currently I have an Ultraire dehumidifier running down there 3 seasons to keep humidity below 50%.  When I bought the house, before I had the dehumidifier, RH in the basement would reach high 80% in the summer, so vapor permeation is a real concern.  I’d like to reduce the use of the dehumidifier and rely on the vapor barrier to alleviate some of my issues.  Plastic taped to the floor hasn’t revealed any moisture issues through the slab, but I’m not so sure my tape held well enough to give me an accurate reading.  I plan to use the dimple mat regardless.

My question:
Should I seal the dimple mat to the concrete slab where it transitions to the unfinished area, so that the floor and wall vapor barriers are 100% continuous and 100% sealed to the rest of the basement air?  My concern is that any vapor that makes it’s way through the walls or slab will be able to flood into the unfinished area, which is open to the finished area, and my vapor barrier would be compromised, if I don’t seal the dimple mat to the slab.  Conversely, any new cracks that form in the foundation (currently fixing 4 minor cracks that show water staining.  never seen liquid water myself however) that allow liquid water to enter, would have no where to dry to if the entire assembly was sealed.  Does this matter?  Will small amounts simply dry back to the exterior eventually?


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  1. user_1249124 | | #1

    I am planning to do something similar; how did you wind up doing this?

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