Crawlspace drain
I am here in Idaho to help my parents build their house (climate zone 6). Their crawl space will be conditioned. ICF block stem walls, peel-and-stick waterproofing on exterior of stem walls, footings poured into Fast Form foot material, 1.25” crushed drain rock on floor (about 14”+ deep to top of footings, r10 EPS insulation on top of drain rock, vapor barrier over the foam. French drain around exterior of parameter footings. The interior will be broken up by pony wall footings (compacted 3/4” gravel with fines under interior and parameter footings).
I am wondering if we need to provide for any internal crawl space drainage. If so, what is recommended? Sump and pump? Drain tiles passing under the footings to daylight? Nothing?
With the configuration described above, what happens if there is a plumbing leak? Or if somehow water seeps under the footings and up into the crawl space?
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Hi Brent.
Sounds like you are doing all of the right things on the foundation walls for this crawlspace. In my experience, interior perimeter footing drains are more the exception than the norm and are either a judgement call based on site conditions (particularly wet sites should have them) or a belt and suspenders approach by cautious builders.
The perforated pipe you will need to add the interior drain is not going to have much impact on the budget of a new house build, so if you are unsure of whether it is needed or not, I say go for it. If you can run it through the footing and to daylight, that's a nice option that doesn't require a sump and pump.
+1 on Brian's post. In addition, you should still consider interior perimeter perforated drain pipe in the crushed stone for use as a radon collection system. Adding the pipe during construction is cheap. If you can run it through the footings to daylight, it will act as a passive radon vent, potentially eliminating the need for an active system. Be aware that if you need to add an active fan in the future, you might have to disconnect the crossovers, so make some allowance for that in the designs. if there's no radon in the local soils, don't worry too much about this.
Also, you mention concern about plumbing leaks and water rising up through the slab. Plumbing leaks will always be an issue, whether you have a drain or not. Put a water alarm on the floor and hope for the best. As far as water rising up, that shouldn't be an issue if the perimeter drains are working. Again, draining to daylight is best, if you have the slope for it.
Brent,
De0pending on where you are a floor drain in the crawlspace may be required. Canadian building codes say the lowest level of the h0use has to have a floor drain. Depending on local regulations this drain is either connected to the storm or sanitary system. If it is too low it would require a sump pit and pump.
Running some drain tile around inside the crawl space sounds nice for radon purposes as well as a fall-back safety for water issues. But the crawlspace subfloor is going to be pretty chopped up with various pony-wall footers. See the attached image for an approximation of the foundation. The 3/4 gravel is already compacted. But I supposed I could dig some trenches into it to run drain tile under the interior footings to create a loop around the interior of the foundation. Then I could run it out to daylight under a parameter footing. But if I do that, would I be okay to place the drain tile in a little trench, cover it would a bit of gravel, and just wet it and tamp it down a bit with the end of a shovel handle or something? I don't want to have to rent a compactor for this alteration. And would I be okay just placing drain tile in that way without a sleeve or compression wrapping or anything like that? Should the sections going under the footings be non-perforated tile?
Brent,
What's your plan for the finished crawlspace? Are you pouring a scratch-coat (rat slab)?
When we pour interior footings for pony-walls we always have a short concrete stem-wall on top, as the level of the finished grade should be at least 6" inches above the level of the top of the footings for moisture control. With a stem-wall, you can run drainage pipes right through them and out the exterior walls to connect with the perimeter drains outside.
Digging under the footings means the interior drains are the lowest place in the system, and likely at some point to bring water into the crawlspace.
See the attached diagram for some of my plan for finishing the crawl space. Does this look acceptable?
Brent,
Yes that makes sense. I'm sorry I don't know enough about radon systems to be much help. It doesn't seem like a good idea to have any drains below the level of the footings and exterior perimeter drains. I'd try for a solution that avoids that.
Okay. Fair enough! And you think my plan looks okay without short stem walls for the pony walls?
My concern is the pony walls being at the same level as the top of the footing. It's mitigated somewhat by using a treated bottom plate - probably fine.
I'm a bit confused by the photos. Is the compacted stone we see going to be the pad and the footings go on top? If so, will you fill the interior with enough stone to cover 3" pipe? That would make placement of the drain pipe easy.
If not, I think I would probably skip them, unless radon is a big risk in your area. That close to the mountains, I'm guessing that your soils are pretty free-draining. If so, I would definitely lean towards skipping interior drains. It also looks like your crawl floor is going to be close to grade level. Even less risk of water rising up under your slab.
Answering your questions: the interior pipe doesn't have to be wrapped in a sock. if you expect a lot of water flow, a sock can help to keep it from silting in, but you probably won't have any flow anyhow. And yes, the pipe going through the footers/stem walls should be solid pipe. Note that it should go through, not under the footings/stem walls.
Yes, the compacted stone that you see in the actual photo is what the footings will be sitting on. The area between the footings will then be filled with the crushed drain rock up even with the top of the footings - so yes, plenty there to cover 3" pipe. But that crushed drain rock also extends down approximate 5"+ below as well. See the attached diagram for a better idea of what I am looking to do. If I put 3" pipe in level with the bottom of the footings, there will be about 6" of drain rock above the pipe, and about 5"+ below the pipe. In that case, would the pipe be very useful? If I were to dig that pipe down lower, it would end up below the grade of the footings.
I talked with a guy at the engineering place that has done structural engineering for this project, and he didn't seem very comfortable with the idea of pipe going through the footing. He seemed more comfortable with it going under the footing. Running the pipe under the footings would put it down close to the actual soil grade.
Maybe I should just skip the drain pipe. As I recall, I saw something online showing that a lot of Idaho has high risk for radon, but the county where my parent's house will be was more moderate. But I would like something in place in order to reduce any risk from radon. It is just a bit more complicated with all those pony wall footings cutting through the crawlspace floor.
Would one passive radon stack with a pipe up through the roof and teed out for several feet in one of the sections between footings be helpful? In that case, there would not be radon pipes going through footers to all the different sections, but maybe it would reduce the pressure a little under the vapor barrier to help prevent radon getting into the conditioned crawl space and thereby into the house?
Also, any suggestions for how to detail the vapor/radon barrier through the pony walls? I was thinking to run it over the footings and build the wood portion of the pony wall on top of it. But that means it would have holes in it from the pony wall J bolts.
You can run the VB under the foam instead of on top of it, and just go straight across under the pony walls, between the footing and the sill. That will also help to keep the sills dry. Whether the VB is above or below the EPS, you're going to have to use relatively hard EPS to take foot (and knee) traffic. I always like to have at least a rat slab (2") of concrete on the floor. If you float the slab smooth, you ca scoot around in the crawl on a mechanic's creeper. You have no idea how nice this is until you forget something when you're working at the far end of the crawl space.
For the interior drains, I would put them at the same level as the exterior drains or even slightly above. You want the exterior drains to do the work. How are the exterior drains draining? Do they drain to daylight, or something else? If not to daylight, then there's no point in connecting the interior and exterior drains. The interior drains can then drain to a sump pit. Get one with a sealed lid if in radon area. The lid itself can be the radon suction point if necessary. I wouldn't worry a bit about running the drains through the pony wall footings. You only need a single pipe around the whole perimeter, and the reinforcement in the footings can go over the pipes and still be in the middle of the footing. Or, you can run the pipes near the top of the footing and run the reinforcement under the pipes, still with plenty of concrete around the reinforcement to do its job. You just don't want the pipes higher than the footing and I wouldn't run them lower either because then they will collect rising water before the exterior drains do.
The exterior drains will drain to daylight. But I am thinking I like the idea of doing a separate drainpipe circuit on the interior that runs into a sealed sump pit. We could do one with no pump in it or exit pipes attached and just have it there in case it is ever needed for water or radon. Does that make sense?
Yes, that's done all the time. Putting interior pipes around the perimeter to a sealed pit with no sump pump or radon pipes is a common treatment. This work is relatively cheap during construction and very expensive after. If you need either one, installing a pump or radon pipe later is relatively easy.