Waterproofing and Insulating a Basement
I bought a house in upstate NY (Zone 5b/6a) with some substantial “water in the basement” issues. The house – built in the early ’50s – is on a hill; the unfinished basement starts below-grade and ends up at ground-level on the other side. The concrete block basement walls are completely uninsulated on the interior and exterior I’m fairly certain there’s nothing but dirt under the concrete slab. The walls on the below-grade half were wet and crumbling in some places, especially down near the floor, with visible water trickling through after heavy rain. The work to fix these issues is already underway but could really use some feedback on final steps in the waterproofing/insulation process.
Once we’re all done, the excavator/drainage guy says he’ll backfill with “2 inch minus” gravel, which I’m all for. In the meantime, I have a giant moat around my house and need to make some decisions about any additional layers of waterproofing/insulation to put in before backfill.
The mason recommended Guy #1 who does spray-on waterproofing with “Tuff-N-Dri H8”. Someone else recommended Guy #2 who uses “Blue Max”. Seems like similar products and unless I hear a compelling case against it, I’ll have one of them come asap to spray/brush one of those directly on to the concrete block foundation exterior.
Guy #1 says he doesn’t recommend doing any additional exterior insulation or waterproofing besides the Tuff-N-Dri. He says that if it were him, he’d rather spend that money on insulating the basement interior. Ok, I hadn;t really thought too much about the interior as i don’t intend to spend much time there but this would buy me time and expense, as I could buy interior insulation and do the job myself. Guy #2 recommends 2″ XPS over the waterproofing and before backfill, and my friend – let’s call him Guy #3 – recommends I do a layer of at least 2″ EPS . After diving down the internet rabbit hole, it seems like adding an exterior layer of rigid foam is not unreasonable advice. But I’m having a pretty strong aversion to the thought of attaching underground foam panels next to my house. I know they’re stronger than a gas-station styrofoam cooler but I just can’t believe they are sturdy and stalwart enough to hold up for decades of shifting earth, freezing and thawing cycles, water coming from every which way, etc. Not to mention that it’s not exactly an earth-friendly material to make or to break down. I guess I just hate foam. Sorry, foam.
I’m leaning more towards rigid mineral wool panels between the waterproof layer and the gravel backfill. My thinking is that this will give the waterproof layer some physical protection from the backfill, as well as creating a final drainage channel before the waterproofed block. I like that mineral wool is fire and insect resistant (we’ve had issues with carpenter ants) and won’t deteriorate from water saturation. The downside is that it has a slightly lower R-value than the equivalent thickness of EPS and it’s more expensive and most guys up here are not as familiar with it as they are with rigid foam. So if I were to go that route, I’d have to find someone who knows how to install it, or someone who I am confident will take the time to follow the specs and instructions and do it right. The product I was looking at is “Roxul Comfortboard 80” because that’s what pops up on my searches. But if there are other brands or versions of below-grade mineral wool that I should be looking at, I’m all ears.
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