Crawlspace : Divert soil water and soil Radon gas in & from crawl space

I have two major problems I'm looking to solve. I have Radon gas infiltrating from my open crawlspace floor and into my house, and I have water penetrating through my crawlspace walls and/or floor from the yard. I have a natural spring that saturates the soil above (and north) of my house and flows toward my house in the Spring to mid Summer months, and in the Winter/Spring the snow pack/melt I think also saturates the soil around my crawlspace. It saturates about 20" of the soil and makes it too damp in the crawlspace for 4-5 months out of the year.

I'm trying to fix the drainage and the crawl space radon problem as passively as possible while also cleaning up the air quality in the crawl space, insulate it a bit, make it drier, and make some storage room for seasonal items. I've already plugged the 3 small vents and rebuilt the crawlspace door to make it pretty tight from the exterior openings.

I'm trying to solve the issues as passively as possible, without installing unnecessary materials and/or electrical devices (like sump pumps or radon fans).

As-is, on the wetter years like this past one I get about 1" of standing water on the part of the crawlspace clay floor that borders my west facing yard. it stays close to that westward wall, about 36" from it, and only about 3/4 to 1" deep at wettest time of the year, for about 2 - 3 months. I don't ever see water on the crawlspace walls, but I can see the salts leaching on them on the north and west sides, where the yard is really wet and higher in elevation.

I bought an electric radon meter. The radon reads between 15 and 30 in the crawlspace. Not super high but above the EPA's random 4 measurement.

I think I need at least a 20" deep PVC/gravel drain dug and installed in my yard, about 75 to 100' length, around the northwest corner of my house. It needs to divert water away from my crawl space walls/floor. This water comes from the natural hillside spring, as well as snow melt that comes from above the home's elevation. The drain can empty a few feet away from my home's southwest corner. I'll use it to water those small trees and such I have that can use the water. Maybe even fill a small 4' pond for the dogs.

After the drainage is fixed, I need my 36" to 40" tall crawlspace (that's floor to top of wall height), which is a 26' x 31' rectangle (or 806 SF) to be leveled enough to place 2 layers of 10 mil poly down and pour 3" of concrete throughout its floor. My crawl space floor is relatively clean and level at present but it will require some material to be moved around to pour the slab level, perhaps. I have saved some scrap plastics to put down below the new 10 mil plastic is laid to help protect it from punctures and provide extra insulation between the dirt floor and concrete.

So if the yard drain takes care of 90% of the yard water from reaching the crawlspace walls, but I still receive some slight water from underneath the crawl space floor, will the dual layers of plastic and 3" of poured concrete keep water from coming into the crawlspace from underneath? Or will drainage need to be installed on the inside of the crawlspace also, underneath the slab?

I want to avoid a sump pit and pump if possible. My crawlspace floor has a natural slope towards the south, so maybe a sump pump is not needed and the water can just be directed to drain through the CMU wall or under it, into the yard?

Suggestions on what is likely the best long term and most economical and simple fix for these issues? How's my plan sound? Thanks. Andy

No experience with radon. but for the water you need a perimeter drain around the house at footing level and as you have clay soil, you need to add dimple board to direct the water down to that drain.
In Canada we seal the poly under the slab to the foundation and then add a sill gasket around the edges, but the goop we use to stick it there is not available in the US so not sure what you use down there.

OK thanks. Are you saying I must install the exterior french drains at the same depth as the crawlspace footers else it won't help? I was going to put the bottom gravel about 18" deep at most. Will that not do very much?

Yeah, where I am the bottom of the footing is only around 18" below ground level and the perforated drain goes just above that, set in gravel and another pipe to take water away from downspouts and both are piped away to drainage are, storm sewer or french drain away from the house.
I would think if you were about 14 inches below ground level inside, you would be doing much to keep the space dry.

You're exacerbating the radon problem and the moisture sealing off the crawlspace. It needs to be either properly ventilated or fully encapsulated, nothing in between.

If you encapsulate it, you'll need to add a radon vent system. If the levels are low enough, a passive PVC pipe ran through the roof or to 3' or more above any roofing within 4' horizontally on the outside. By code radon pipes must be painted orange for identification purposes up to the roof-line. Some local codes now require powered radon vents so for that you'll have to inquire locally.

If you re-open to get better ventilation and the radon level is still just a bit high, a powered foundation vent or two may get it low enough. That's the approach I'd take first since it's cheap and easy. Where I'm at there's mostly granite underneath the ground, and lots of radon coming from it. When houses were not so tightly sealed it wasn't a problem, but with today's craze for energy efficiency radon can get so bad that a 1500 sq ft home can need a encapsulated crawlspace and 3 powered radon vents to render it barely inhabitable.

Phil

Passive is a good goal, but don't get hung up on that. Do what it takes to get the crawlspace up to par.

When one looks at homes built 1-2-300 years ago, the first thing you see is that they are as sealed up as a window screen. And that is exactly what allows them to endure when newer "better" home often rot away long before 100 years pass. Wood wants to 'breathe' so you let it, and then it lasts. Block that movement of air and it fails. Wood can handle extreme moisture- ships and barrels were made from wood- but there was always some ability of the wood to breathe on one side.

So now we build non-breathing wood houses and find myriad problems with them that didn't happen before. And codes often require us to build that way whether we want to or not. People scream for low utility bills but they want a freezer in the desert or an oven in the arctic just because it's possible- and they won't have anything else. I guess we're supposed to overlook the inhabitants of those same areas who lived there for thousands of years without that ability.

In the hills around here are houses built on stacked rocks every so often with nothing else holding them up or closing them in. The wood used for the framing was poor pine because that's what they had. The siding was usually cedar because they couldn't afford to paint it every few years and cedar wouldn't rot. Many of those shacks are at least 100 years old and will go that much longer if they don't get attacked by pine beetles. Termites don't like them because their tunnels are too exposed and their natural predators find and eat them. There's so much air movement everywhere that nothing can stay wet for long so nothing rots. Any radon (and there's a lot of that up there) never makes it up into the house before being blown away, and what little that does make it leaks out the many unsealed places in the house. Most have a fireplace for heat, and in the winter they're still chilly inside but nobody freezes to death. In the summer most are fairly cool inside comparatively because of the thermal mass of those 'outdated' plaster walls. It makes you pause to think about whether our newer homes are actually better. More efficient, more sealed, and more costly, yes. But better? Hmmmmm.....

The old ways still work as well as they always did, and in my humble opinion a crawlspace needs either plenty of ventilation or none at all; anything in between is big trouble. And if you choose 'none' it's not really a crawlspace anymore but rather part of the interior of your house which then needs to be treated accordingly. If it's interior then you might as well make a basement of it to take advantage of the space instead of wasting it while paying to do that. But of course it's your money and your home so do whatever you like with it.

Phil

You could go to the location of the spring and provide a path for that water to bypass your house. That could be pipe or it could be a surface channel. Have you searched the threads here on the forum? There was a thread in the last year or two that went extensively into what it takes to seal a crawlspace (sorry, I don't have a link, but you can search it out). There is also a lengthy and informative link by JMR about his nightmare crawlspace.