Basement Floor Assembly Details
I’m in the planning phase of finishing my basement and have a few questions about the floor assembly.
Details:
-House built in 1987
-Poured concrete foundation
-Climate zone 5a
-Painted foundation wall and slab (this was done by previous owner, no clue what paint was used)
-Observed water entry in foundation during house inspection 2 1/2 years ago through two pin prick holes (approximately 6″ above slab). Very slow flow rate, only about a teaspoon of water pooling on the slab. Have not seen water entry since.
-8ft from slab to sub-floor
-2 x 10 joists
-Humidity levels hover around 65-70% currently.
-Observed efflorescence under some of the rugs on painted slab.
-Plastic test on foundation and slab did not show any condensation.
-Floor feels dry, but descriptors like damp are open to interpretation, and hard for me to definitively say yes or no to “damp”.
-Spray foamed and air sealed rim joist.
With the details above, the floor assembly I’m considering is delta fl, 1″ eps, and osb – with carpet.
Questions:
-How do you address the increase in floor height with the last step of the stairs? With this being a fairly common assembly, I have not seen any details on how to deal with the stair offset at the landing.
-Is 1/2″ of foam ok for this assembly? Mostly concerned with how it might affect the carpet (unfortunately my wife is set on carpet).
-Does it matter if the eps foam is faced or unfaced? The big box stores near me only carry foil faced eps.
-Is the delta fl necessary based on the details above? I would love to omit this for labor, floor height, and cost savings. However, I’m concerned the high humidity, observed efflorescence, and observed water entry (albeit very small and have not seen water entry since) may necessitate this.
-There are 3 floor drains (two 5″ and one 4″) within the area I plan to finish. Can I just build directly over these? Or will I have to notch out holes through the floor assembly?
Thank you.
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Replies
If you check out the other questions listed on the right, you'll see that this is a common topic here. I recommend reading through some other Q+As and come back if you still have questions.
Thanks for the reply Michael.
I ended up paying for a subscription to read up on locked content and have managed to answer 3 of my original questions and 1 I'll just ask a plumber about. However, one additional question popped up.
The questions I still have are:
-Does it matter if the eps foam is faced or un-faced? The big box stores near me only carry foil faced eps. (I unfortunately can't find a solid answer on this. )
-Is eps foam rated @ 10 psi adequate for the floor assembly, with 2 layers of 1/2" osb floating over the foam? (The only info I can find anywhere is here: https://www.greenbuildingadvisor.com/question/eps-rated-at-10-psi-compressive-strength-ok-for-basement-floor-insulation?cid=274335&discussion=response#comment-173785 - Being new to this site, I've quickly come to recognize Dana as quite the authority figure here. I certainly value his answer. However, I'm unable to find any other info on the site where others have successfully used 10 psi eps foam under 2 layers of 1/2" osb floated.)
Dana is great but he's not very active here anymore. I have probably researched it as much as anyone and would say that 10 psi might be enough if there are no heavy loads and the finished flooring can handle some movement (vinyl planks yes, ceramic tile no), but I would rather see 15 psi or 25 psi foam. Foil-faced should be fine.
It's been a journey consolidating all this info. You have been a big help in this process. Thanks again!