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Help with basement design

Leonidsg | Posted in Green Building Techniques on

Hello All,

I am working on refinishing a play room in the basement that was recently damaged from water coming through the slab because my gutter was not hooked into the corrugated pipe that takes water away. So I now I want to refinish a playroom for my 1 year old son in the basement, making sure the health and safety is the priority.

I have included a picture of my plan and wanted some advice on some small questions i have. My plan is to use 2″ XPS on the wall, seal the top and bottom per BSC, then place a steel stud wall with the bottom plate on a piece of XPS 1″. I was not planning on putting additional insulation in between the studs as my basement is comfortable now without any insulation so the R10 should be enough. I dont want to putt fiberglass insulation in because I am worried about mold on the fiberglass. I then plan to finish the wall with Densearmour. For the floor I plan on using Platon, then 5/8OSB and then vinyl plank.

My questions are

1. In general does this plan seem sound?
2. What is better sealant and adhesive for the XPS: caulk/adhesive approved for foam board or great stuff made for foam board?
3. I need help with where all I need to place beads of sealant, recommendations?
4. How should I tie the floor into the wall? Should I place platon first then place the xps on the platon making sure to seal behind the xps board where it comes to contact with the platon or should I abut the platon against the XPS foam under the bottom plate and seal the gap between the XPS and platon? Or is there a completely better idea the I havent thought of.
5. Should I leave a gap around the parameter for the OSB?

Please let me know what you think. I greatly appreciate the help.

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  1. GBA Editor
    Martin Holladay | | #1

    If you have had water entry in your basement in the past, it's risky to finish your basement -- even if you have corrected the problem with your roof gutters.

    Most experts would recommend that you install a layer of rigid foam under the OSB that you plan to use as a subfloor.

    The rest of the details are OK -- as long as you don't get future water entry. You might want to read:

    How to Insulate a Basement Wall

    Fixing a Wet Basement

  2. wjrobinson | | #2

    Roll of the dice project. You want it... so roll away. Your details are expensive. Owens Corning sells a wall panel system that is removable if you get water again. And some floors click together along with new ones that are water resistant. Cheap click floor is NOT water resistant. If you loose lay carpet and it gets wet, you can throw it out and replace it. There are ways to do your cellar for 1/3 the cost and very fixable if ruined.

  3. user-757117 | | #3

    Before you commit to finishing your basement, I would definitely investigate further into why your basement had leaked.
    It is not a good situation if your basement is finished and the only thing that is preventing leaking is proper downspout placement - what if a downspout is accidentally moved or detached again and goes unnoticed?

  4. Leonidsg | | #4

    I am definitely working on making sure the water problem is taken care of. I am going to remove everything from the wall and floor and leave the basement alone so I can observe what happens during some heavy thunderstorms. I am no particular rush to finish the room probably something I will tackle next spring. I do believe the water problem came from the gutter not being properly connected. I am not particularly worried that it will happen again as I have screwed it into place. There is some concern that the corrugated pipe becomes clogged from leaves coming down the gutter. I will say besides this incident we have never had water problems in that part before. From my research on BSC and here it seems like I am on the correct path. I greatly appreciate everyone's help. I will take a look at the articles Martin recommended. Let me know if there are any other suggestions.

    Thank you

  5. Expert Member
    Dana Dorsett | | #5

    It's probably cheaper to use 2.5-3" EPS and 1x furring through-screwed to the foundation, and by using multiple layers you can better seal the seams by overlapping them. It's greener too, since XPS is blown with a high global warming potential blowing agent (HFC134a, which is ~1400x CO2) compared to EPS, which is blown with pentane ( ~7x CO2). As the blowing agent leaks out over the next several decades the performance falls to that of EPS anyway- any advantages are temporary.

    If you can't find TapCons long enough at the local box store you can either order them online or drop back to 2" on the EPS. (For 3" of foam you'll want 4.5" fasteners for the furring, which would give you 3/4" of penetration into the concrete or CMU)

    The foam layer adjacent to the foundation can be sealed with housewrap tape, but on the layer facing the interior fiber-insulated duct mastic is better. The foam expands/contracts with time, and it's common to see substantial gaps opening over a few decades, but duct mastic won't come undone the way tapes will. The tape trapped between the foam layers will still do it's job even if the glue gives up as the foam expands & contracts. Sealing the top edge of the foam to the foundation and foundation sill with can-foam is worth it.

    It's also worth putting an inch of EPS between the OSB & Platon to keep the temperature at the bottom side of the OSB above the dew point of the room air in summer. If you do that, run both the foam and the OSB all the way to your wall-foam.

    If you actually had standing water an inch or more deep in the basement, stop the both the furring & wallboard at about the high-tide mark from your previous water intrusion, which would keep it from wicking up moisture should it recur, and use vinyl boards for the kickboard at the floor.

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