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Finishing Out a Basement- How to Handle Moisture

cm_glb | Posted in General Questions on

Hi Everyone! Although I am on GBA everyday reading and going through these Q&As, this is my first post so go easy on me!

I’m putting together a proposal on a project to finish a basement in an early 2000’s house, climate zone 5. House is nothing spectacular, I’d say it was a semi-custom builder grade house. CMU Foundation is about 3/4 day lit out the back and completely in ground at front. From my first site visit I observed the following: slab in good condition. foundation looks to be in relatively good shape, no observable cracks or distortions with the exception of the very back corner, where there is some efflorescence and evidence of past dampness. Homeowner moved into the house about 2 years ago and did tell me that there was a downspout/gutter problem at that corner that was since fixed, as well as he re-graded the landscaping, and he has not noticed any water there since. The basement didn’t seem to have any noticeable damp or wet smells. My guess is that there is no foundation wall or under-slab insulation. There is a sump in the basement that was dry, and it appeared there is a foundation drain that either goes to that or daylights in the back.

I was leaning towards the following wall and floor assemblies, but wanted to get some input and opinions from everybody here.

For the walls- coat of dryloc on walls for extra insurance because why not. 2” or 1.5” Layer of rigid foam (probably XPS) sealed. 3/4 furring strips in areas that don’t have electrical or space is a concern, 2 by 4 framed walls where there is electrical. I am debating doing a rock wool comfortbatt in the 2 by 4 cavities mainly for fire and sound. 1/2 drywall (MMR?) and the standard finishes.

For flooring- ceiling height is an issue, and unfortunately the main ducts hang down even lower down the center of the basement (homeowner is 6’2 or 6’3 so he wants it as tall as possible). I might try to do a layer of rigid and layer of 3/4 subfloor, floor covering will probably be a LVP floating. In the event the head height is still an issue, any thoughts or experiences with doing an LVP directly down on the concrete (with or without underlayment based on manufacturers recommendation)? I know it’s not ideal and I’d really like to have insulation underfoot, but I also don’t want to cut the height too short! If I do the rigid and subfloor the partitions and wall framing will sit on the subfloor, otherwise they will sit down on the slab with treated plates.

Also, a section at the one end will now become a dedicated mechanical area. I was planning to leave this untouched with the exception of rocking the back of the new partition wall. Debating if it worth insulating and rocking this area as well depending on the budget, however i don’t know if the juice will be worth the squeeze of adjusting mechanical locations to allow for the rock and insulation.

Please let me know your experiences with similar projects, thoughts/input, and any recommendations! Do you think I am being too cautious about moisture, or do you think I need to do more to manage it? In a perfect world with unlimited resources I’d either dig up and waterproof the foundation or add an interior drain just so I know for sure we are managing the water, but as we all know the budget is never unlimited. But nevertheless I’d like to do everything I can to provide them with a durable and comfortable new space without moisture issues!

Thanks in advance for the help!

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