When to Install a Foundation Drain
Are there any circumstances when foundation drain is not a good idea? Our soil is well-draining sandy loam to at least 80” below ground, we can’t route to daylight or sewer. We can only route to either drywell or interior sump pump. We don’t want want to bring any water inside to the sump pump, so would only consider drywell. Contractor doesn’t think routing it to drywell is a good idea as it can allegedly bring water back to the house foundation if drywell get overwhelmed with lots of water. The contractor also doesn’t believe we need foundation drain as we have a well draining soil. Under these circumstances, do we need a foundation drain or not? We are doing Tremco waterproofing with drainage board/insulation, but where will the drainage board drain if there is no foundation drain? Thank you!
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svetok,
My comfort level with leaving out foundation drainage would decrease the closer my crawlspace or basement slab was to the footings, and the deeper they were below grade.
It can be done, and is quite commonly and successfully in some areas, which is why most codes makes the requirement contingent on it being necessary.
Set against that is that problems usually don't show up until everything is finished - at which point remediation is often very difficult and disruptive.
The worry about water overwhelming the dry-well can be mitigated by installing a backflow preventer.
Thank you for your response. This would be a full basement with 9’ ceilings. That means our foundation drain would be below 9’. I don’t understand why our contractor is so hesitant to install the foundation drain. We are in Long Island, NY, so I wonder if this is due to geographic location and what everyone else is doing around here. Is it common to route it to drywell?
I’m attaching the screen shots of what NYS Code says regarding the drains. I’m just torn and not sure what to do. Do I hire someone else to install the foundation drain against my contractor’s advice?
And this is our soil report, if it makes a difference?
I wouldn't consider having an interior sump basin to be "inviting water in", it's going to be there, or not, regardless. What you need to consider, as Malcom stated, is what happens if you find that you have water under the slab, 5 years from now? If there's no water, the sump doesn't matter. If there is water, you'll wish you had it. Millions of homes have them without problem.
Alternatively, there's a seldomly used option which might work here, an external sump basin.
It works just like an internal sump basin, except it's outside the foundation walls. Usually some type of road tile stood on end, containing the sump pump and pipe to daylight. It has to be kept covered for obvious reasons, but it'll keep the pit outside if that's whats bothering you about it.
Harder to construct, and more expensive, but you might google it a bit and see if it's right for you or not.
If I connect the exterior foundation drain to the interior sump pump, do I also need to install interior French drain? How do I connect exterior drain to interior sump, is it piped through the footing or under the footing? And where do I route it from sump pump, back to drywell? If yes, then the same concern that overwhelmed drywell may flow back into foundation drain exists.
Also, all the horror stories of sump pump not working during power outages or radon gases escaping. How do I prevent having more issues once the sump pump on the interior?
As I said also, we are doing full Tremco waterproofing with board/insulation, and mineral wool insulation under the slab along with 15 mil poly under the slab. Not sure if that makes a difference. Daylight or sewers are not an option here.
Thank you.
"If I connect the exterior foundation drain to the interior sump pump, do I also need to install interior French drain? How do I connect exterior drain to interior sump, is it piped through the footing or under the footing? And where do I route it from sump pump, back to drywell? If yes, then the same concern that overwhelmed drywell may flow back into foundation drain exists. "
I think it's a good idea to do so, even a line across the middle of the basement isn't a bad idea. The most common practice is a section of pipe at the bottom of the footing, below the rebar. We're not talking about moving thousands of gallons of water here, all we want to create is a path of least resistance to the sump basin. One approach to provide redundancy is to have two sump pits / pumps all connected to the same drain lines, that way if one fails, the other will be able still be able to pump to daylight. The odds of two failures, with battery backup is nearly zero.
"Also, all the horror stories of sump pump not working during power outages or radon gases escaping. How do I prevent having more issues once the sump pump on the interior?"
Not having a single sump is equivalent to constantly living in sump pump failure mode. If that water gets there, you'll never be worse off for having a pump. It would have otherwise ended up in your basement. Most all sump basins come with a gasketed lid, so that no gas can escape. They also accept two pipes - one for drainage and one for ventilation. This is actually the best radon mitigation plan as well. It can utilize the same drain lines, and the same sump basin lids should you ever detect threshold radon levels. All that's needed is the inline exhaust fan to the roof line.
"As I said also, we are doing full Tremco waterproofing with board/insulation, and mineral wool insulation under the slab along with 15 mil poly under the slab. Not sure if that makes a difference. Daylight or sewers are not an option here."
That is a great plan, it will practically ensure that you never have moisture problems with vapor migrating through the slab, or in from the soil.
Also, this is article on which I relied when I mentioned I would prefer not to bring the water into the interior — https://www.jlconline.com/how-to/foundations/q-a-sump-for-foundation-drain_o
https://www.jlconline.com/how-to/foundations/pre-piping-for-radon_o
This is essentially the idea. Go ahead and get this stuff in there while its easy and cheap!
A general contractor is not the expert to make a determination whether drains are necessary.
I'm not that expert either, but I'll offer a thought. When you site a septic system, you check two properties of the soil. The first is percolation, how well it drains. You test that by digging a hole, pouring water into it, and seeing how long it takes to drain out. The second is whether the soil has ever been inundated. When soil has been flooded and dries the structure of the soil changes. If you dig a careful hole with a face exposed you can see a line that marks the highest the groundwater has ever gotten. It's a bad idea to put a septic system above that line.
I would think the same two tests would apply to the foundation of a house.
Is percolation rate the same as leaching rate? I see the leaching rate on our Plans when the architect specified the septic tank and leaching pool.
Did an engineering firm do your soils report? If so wouldn't they be the ones to recommend a drain or not? In sandy gravely soils with no history of water I'd feel pretty safe without a drain but I'm just some random internet stranger, not an expert or local builder.
I got the soil report from https://websoilsurvey.sc.egov.usda.gov/App/WebSoilSurvey.aspx
Do you think we need to hire an engineer? Is it geotechnical engineer? Thank you.
I just looked at my house on that site. It says I have sandy soils. Some of my neighbors do but I do not. I have poorly drained clay.
I would say if you want to omit a drain you should get an geotechnical engineer to approve the idea. Not a good idea to trust general info online, this stuff is too site specific.
To answer the question in the title the answer for me always and just after the concrete forms come off.
“We can’t route to daylight or sewer.”
This quote describes the most undesirable of building lots to my ear. If it is not to late consider a different lot. If the 40 acre around you all drains to your lot it might be a miserable place to live.
If you want a drainage system that will work have an engineer design one for your lot and put his stamp on the plan. Will the system be small an inexpensive I doubt it but it will never cost less than now to put in the right system. My guess is it will be cheaper than cleaning the annual spring basement flood.
My house is near the top of the hill with a drain to daylight and I decided having several inches of gravel under the basement slab and an empty pit was cheap insurance.
Walta
Climate change is changing rain patterns everywhere, so if you don’t need them today you might in ten years when it would be hugely expensive. The idea that the water will always drain through your soil the way it does today is, frankly nuts. Do the best you can; if you never need the pump, be grateful. Simply the worst place in the house to save money or cut corners.
Not trying to save money or cut corners here. In fact, we insisted on the foundation drain, but the contractor is saying it’s not a good idea to route it to drywell.
You can also raise the house and fill around it, or forget the basement and enlarge the garage.
Bob,
Almost every house here on southern Vancouver Island has either a crawlspace or slab on grade. We have recently had an influx of newcomers moving from Alberta where basements are an expected part of every house. I've had a lot of luck doing as you say and including a half submerged (daylight) basement when I design for them. While you do forgo the more immediate relationship between the main floor and the surrounding lot, the basement becomes a much nicer space, with windows, easy access to grade - and importantly, much less chance of water intrusion problems.
So based on the comments above, our options are:
(1) hire a geotechnical engineer and forego the foundation drain if he says we don’t need one
(2) install foundation drain and route to interior sump pump (to route water where?)
(3) install foundation drain and route to drywell with backflow preventer
Did I get them right?
To answer the "route water where" question, where are your downspouts going to go? Send the sump pump water to the same place. You should know the answer to that before you break ground on the foundation.
There's nothing magical about water that's been through a sump pump.
Downspouts are going to drywell. But if I’m routing foundation drain to sump pump to drywell, how is it different than routing foundation drain directly to drywell? The end result is exactly the same.
I'll turn the question around. If the drywell can't handle the downspouts then that water is going into your basement, one way or another. Sump pumps aren't really made for groundwater, they're for rainwater that doesn't get directed away from the house and makes its way to the bottom of the foundation. The meta-question here is whether you can get all of the rainwater that falls on the house directed far enough away that it doesn't cause problems in the basement. A sump pump is one way to get that water far away. Another is grading. Another is downspouts. Another is just letting it soak into the ground.
Unless your house site is at the bottom of a bowl it's usually safe to get water ten feet away from the foundation and downhill. I don't like relying on sump pumps because they can fail, but one advantage is they can more water a pretty good distance. I've installed a sump pump where the discharge line was 120 feet long, that was how far we had to go to get a spot downhill from the house.
We do have 2 concrete drywells on the property about 30 feet from the foundation 8’x10’ and 10’x10’ - this where all of our gutters going to drain. So all of the surface water is planned for and taken care of (it’s required by local Code), the architect performed the calculation and sized the drywalls to collect all surface water from our lot based on 3” of rain.
As long as they're air-gapped so they can't backflow I don't see any problem dumping the sumps into those drywells then. The amount of water from perimeter drains is going to be miniscule compared to what's coming off the roof into downspouts.
Civil engineer checking in.
Web soils survey is unreliable. It's like your mileage may vary. It's a birds eye view of the soils in your area, but is not completely accurate. It's a very very coarse snap shot of the soils in your area. Nobody designs off web soil survey. It's always a geotech report (commercial anyway).
As far as your options...
You can bring a geotech in... very limited scope... i.e. do we need foundation drains or not? They will most likely do testing at the foundation elev. and give you a recomendation. Whatever comes out fo that... if you deviate from their recommendation, that's on you.
Alterantively, put foundation drains in, stub them out, cap them, and then if you need to do something in the future you can. It's much cheaper to put them in while everything is excavated than after the fact.
This was the idea I was going to offer. install and cap for later if needed. Also could bury some burial tape to help find the ends later if needed
Great point about the tape, thank you!
Going to retain a geotechnical engineer to see what they say, but I do like the idea of adding a drain just in case we need one in a future. Thank you!
After speaking to few geotechnical engineers, it appears the cost to retain one ($5k) is almost as much as the foundation drain ($8k). So now thinking about foregoing the engineer and just installing the drain until we figure out whether to route to sump pump or drywell.
When speaking to engineers, in general, you really need to narrow down the scope of what you want. Often, they will try and put in some fluff to fatten the contract. I'm guessing the 5k is a lump sum type deal... site visit, maybe soil composition analysis, determination of seasonal high groundwater, and 1 or two double ring infiltration tests (typically, the standard infiltration test done for stormwate applications), and a report.
But the beauty of soft costs is that they are always less than hard i.e. construction costs. The last rental I lived in the basement would flood due to poor down spouts and poor grading at the back of the house. When we moved out, the landlord was on the hook for 4k in drywall repair/mold remediation costs (we were off the hook).
So lets say you do nothing... bad storm rolls through. Basement floods. Now you have to repair any damages AND spend the $$$ to put in a sump pump plus footer drain. 5k sounds cheap though, now, right?
In my experience, most water issues stem from poor grading around the structure and poor gutters/not getting the water away from the foundation. You do those right you're 90% of the way there.
Best course of action I would recommend, put the fnd drain in, stub it, put a clean out a few feet before the stub so you can find it again. The cleanout will act as a sort of "monitoring well". You'll be able to keep track of any head in the pipe.
I think we are going to put it in and just connect it to function properly. I’m going to speak to the contractor today. Would you route it to sump pump or drywell? If we are doing sump pump, do we also need interior French drain? Or can the sump pump be installed without interior drain? Thank you
"Would you route it to sump pump or drywell? "
The only places I would send a perimeter drain is either a place on the surface more than ten feet from the foundation and more than a foot below the level of the perimeter drains, or if such a place doesn't exists, to a sump pump.
The only places I would send the discharge of the sump pump is either to a place on the surface more than ten feet from the foundation and more than a foot below grade at the foundation, an engineered infiltration tank, or to a municipal storm sewer.
I wouldn't send the discharge of either a perimeter drain or a sump pump underground, you'd never know if it wasn't draining. It would probably be OK to put a dry well below the discharge, although I'd rather it just flowed on the ground.
"If we are doing sump pump, do we also need interior French drain? Or can the sump pump be installed without interior drain?"
A sump pump can be installed with exterior drains.
Personal preference: Dry well.
I am leery of any uneccesary penetrations in the slab/basement wall. They never end up getting sealed properly, and it becomes another failure point.
Residential contractors are often a different breed than commercial guys, where sub slab plumbing is very common. And to that effect, most commercial is slab on grade where high seasonal gw is not an issue.
A dry well can be something as simple as a stick of 24" dia HDPE pipe /w a plastic lid. HDPE has unfortnately went up in price, but at least stone is cheap.
But like I said earlier, proper downspouts and grading around the structure will get you 90% there. You should be able to point to any place on your property and say ok if a water drop lands here if flows there. If you can't answer that question, then it could be flowing against your house. Another common issue I see with water damage, is they have the entire town draining into their back yard.
Joe Lstiburek, one of the best building scientists in the country, recommends designing for the possibility that your backups won’t work. So what can you change to make sure that a basement full of water is most easily repaired? Design for the possibility that the power goes out and the batteries fail. For starters, your insulation and finish choices and should be materials that will dry out in place, so if the hopefully-never flood happens, it’s a pia rather than a disaster.
We’re building an investment property where I counted on having useful basement space, but when we realized that there was no way to drain a full basement without relying on electric pumps, we eliminated the full basement. Less space, but less chance of damage if everything goes wrong at once.
Unfortunately, we cannot eliminate the basement as all the houses in our region have one. It would basically be a house with poor resale value. So trying to do everything correctly and minimize the risk. That’s why we didn’t want the sump pump as everyone we know who had always had issues with it when the power was lost during storms. Our original plan was Tremco waterproofing with foundation drain to drywell.
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Post #34
We already have 2 concrete drywells on the property about 30 feet from the foundation 8’x10’ and 10’x10’ - this where all of our gutters going to drain. So all of the surface water is planned for and taken care of (it’s required by local Code), The contractor seems to believe if we tie our foundation drain to it, it may overwhelm the drywell (in rare event) and would bring the water back to foundation. He suggested tying foundation drain to interior pump - which doesn’t make sense to me as the interior sump would have to be tied to the same drywells that he believes could get overwhelmed. I’m going in circles here trying to find the best solution with the assumption that those rare events will become more of a norm. New York experienced unprecedented amount of rain last summer (during Ida and Henry), and lots of houses in our neighborhood got flooded - although none on our block as we are on somewhat higher ground. So trying to plan for those rare events with the best solution. I appreciate everyone’s advice on this thread and this is a lot of information to digest, especially for a lay person like me.