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# Positive pressure basement waterproofing

A small price to pay for a dry basement
 (+2, -1) [vote for, against]

Keep water from seeping through foundation and basement walls by maintaining an overpressure compared to the outside world. Ideally this could be done by recalibrating WKTE whole house positive pressure systems that mitigate radon infiltration. You might never be able to open your windows, and you’ll need an airlock at all entries - but it’s a small price to pay for a dry basement.
 — a1, Sep 27 2022

Positive pressure systems https://www.propert...essure-systems-faqs
[a1, Sep 28 2022]

Stairs in new waterproofing system https://moa.byu.edu...tivity-1024x981.jpg
[a1, Sep 29 2022]

A dry basement wouldn’t suit everybody https://ibb.co/XDrSsNr
[a1, Oct 08 2022]

So at 3 meters that's 4 psi ish right? And if there is a leak you'll need to pump in air to maintain pressure. It definitely won't blow a large steel panel across the street beheading anyone's dog.
 — Voice, Sep 27 2022

 Not blowing a steel panel across the street - are you considering that a plus or a minus?

Your calculation of a standing water column looks about right - so yeah, if there's a big enough leak that's what it might take. But usually I think you'd just need enough to offset infiltration through concrete. Despite their porosity, the basement walls should still be doing MOST of the work.
 — a1, Sep 27 2022

I was snarking. A 1 square meter panel contains 1500 square feet. 5 psi*1500=7500 pounds. And that pressure is over the whole interior. It's enough to lift your house up from the bottom. Better use a lot of rivets.
 — Voice, Sep 27 2022

 // 1 square meter panel contains 1500 square feet //

 You mean square inches? 1 square meter covers 10.7639104 square feet, real close to 1550 square inches.

Regardless, I don't think you need that much pressure to hold back water infiltration. If someone punches a hole in the wall or even a good sized crack, that's going to require a conventional repair - but under ordinary circumstance I think just a slight overpressure should hold back seepage through concrete.
 — a1, Sep 27 2022

Yeah, inches, feet, some kind of freedom unit
 — Voice, Sep 28 2022

I have a radon system. It sucks rather than blows. Negative pressure underneath the concrete is the theory. Not a clue if it actually works.
 — RayfordSteele, Sep 28 2022

 // Negative pressure //

Yep, there's more than one way to do it. Some suck and some blow. See link on positive pressure. For radon mitigation they don't really pressurize the basement - they just draw a lot of air from above ground into living spaces to keep radon from seeping into house from below.
 — a1, Sep 28 2022

 It's interesting to model how this would work. Essentially water is flowing from (partially) saturated soil/aggregate etc. through a partially permeable barrier eg. concrete. This is happening because the basement is an artificial air space made underground, gravity is pushing the water/rock etc. down evenly, but the basement represents a density anomaly. The heavy water wants to flow in displacing the lighter air upward. Now, air pressure can clearly supply enough force to offset gravity AND once pressurized will require no additional energy to do so but would it work in this context? I don't think so.

 So if we simplified this to a large concrete tank in just water, what would happen if we pressurized it and then punched a 6" hole in the bottom. Nothing much, if you got the pressure exactly right, you'd just see a circle of water through the hole - like a diving bell. Now lets try to do that on another surface, the side wall, what happens? Well water flows in through the bottom of the hole and air flows out through the top and your model basement will fill with water until the water rises high enough to seal the hole stopping the egress of air.

Now concrete isn't usually full of 6" holes, it's full of tiny voids which are, demonstrably, somewhat water permeable. So we know the water can flow IN, so we only need air pressure to be able to escape through the same route to show that we can't keep the water out. So is concrete gas permeable? Yes. Not VERY gas permeable in the same way that it's not VERY water permeable. So your basement would fill with water more slowly, but it would.
 — bs0u0155, Sep 29 2022

Why not build the basement above ground level?
 — pocmloc, Sep 29 2022

 // Why not build the basement above ground level? //

Tried it, but then the attic was underground. I also thought of building the house sideways so any leaks in windows on one side would just flow out the other - but the stairs became ... treacherous. (linK)
 — a1, Sep 29 2022

 // your basement would fill with water more slowly, but it would //

That's about all any basement "waterproofing" ever manages to do - reduce / slow seepage of water. For a truly waterproof basement, you'd need a completely seamless, impermeable shell around it. Or as [pocmloc] suggests, build it above ground.
 — a1, Sep 29 2022

a1, you do realize that I would give you lots of buns except I rarely have remotely any idea of what you meant?
 — blissmiss, Sep 29 2022

 [blissmiss], that's okay. The voices in my head understand perfectly.

 Oh, no we don't!

Oh, yes we do!
 — a1, Sep 29 2022

Thought about it. Giving it a (+) for ingenuity.
 — 2 fries shy of a happy meal, Sep 30 2022

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