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Community and Q&A

Waterproofing contractor has other ideas

Steve Knapp CZ 3A Georgia | Posted in Green Building Techniques on

My plans called for placing the foundation drain pipe next to the footer. This is a non-standard practice in my area and required digging and pouring a thicker 12 inch footer instead of the typical 8 inch footer used in these parts.

Now, the waterproofing contractor is refusing to place the drain line next to the footer. Several years ago he switched to placing the drain (a rectangular pipe) on top of the footer and thinks this is the better method.

I’m annoyed and confused since I was advised by another credible expert that placing the pipe on top of the footer would greatly increase my chances of springing a leak (thus, the 12 inch footer). My builder is inclined to go with the “on-footer” method since he’s had good experience with that approach, but he will do whatever I want.

So what is industry best practice. Putting the pipe next to the footer makes intuitive sense to me, but I know that what’s intuitive isn’t always correct. I just don’t want a basement that leaks.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Steven,
    Here is a detail for a footing drain. Note that the pipe needs to be below the level of the slab.

    .

  2. Steve Knapp CZ 3A Georgia | | #2

    Thanks, Martin.

    That is the detail I used in my plans (and which the foundation people would have ignored if I hadn't intervened). But I'm wondering why the waterproofing contractor thinks pipe on top of the footer is better, and he won't even consider doing it any other way.

  3. James Morgan | | #3

    Martin, I know that's the standard drawn detail and I've seen it a thousand times but I think it's a bad one and there are several important performative reasons that no one ever builds it that way, at least not in my area. I don't have time to go into that right now but hope to have time to post again later.

    Steven, listen to your waterproofing guy. When a contractor says it's not the way he knows how to do it but he'll build it any way you like, the second part of that sentence - whether spoken or implied - is usually 'but it's on you if it fails'.

  4. GBA Editor
    Martin Holladay | | #4

    Steven,
    Like you, I am interested in James's logic. One thing is for sure: if the center of the 4-inch drain pipe is above the top of your slab, you are setting yourself up for potential moisture problems.

  5. Steve Knapp CZ 3A Georgia | | #5

    Hi James:

    I would be interested to read your reasons for putting the drain on top of the footer. Just as an FYI, I am in an area with heavy red Georgia clay.

    I take your point on following the advice of the local person. My problem is that I have two knowledgable people who are giving me different advice. The waterproofing contractor says it has to go on top of the footer. The Earthcraft rater, who is also an engineer, says it must go beside the footer (and notes that another home in my community is having water issues because the drain is too high).

    It's hard for homeowners to know who to believe. My builder and most of his subs warrant their work for one year after the house is occupied. My experience with most man-made products is you usually have a failure right away or years downs the road. With a drain, I could imagine a scenario where it takes years for it to fail.

  6. James Morgan | | #6

    Simple really. The seam between the footing and the foundation wall is a vulnerable location but it takes actual hydrostatic pressure to push moisture through it. Perforated pipe laid along the top of the footer and running to daylight ensures that the maximum head of water is just the thickness of the corrugation, or about 3/8" of an inch. This is simply not sufficient to cause any penetration of the seam if a normal standard of care has been taken with the waterproofing application. This is the simplest, most foolproof and most reliable location. That's why all the experienced builders that I know and regularly work with all prefer to do it that way.

    The engineers and detail drafters who love to show it otherwise should probably be forgiven because they don't know any better. In addition to the increased trouble and expense, the major disadvantage of the alternate configuration is that the overdig required for the lower placement of the pipe entails a larger volume of backfill and thus an enhanced path for water to reach the footing. Martin's diagram ignores backfill considerations and shows no difference between this material and the undisturbed subsoil beneath the slab and behind the trench. Backfill can never be consolidated to the degree of imperviousness of undisturbed soil. Most codes now sensibly require that finish grade be sloped to a swale at least six feet away from the foundation wall. With a standard dig this places the swale well outside the backfill area and into the zone of undisturbed dirt: overdig brings the porous backfill closer to the swale and the large volume of stormwater it regularly contains.

    But I won't pretend this is a make-or-break consideration. Experience has shown that either layout will perform perfectly well over time if the other parts of the installation are correctly done so that volume water flow and its accompanying clogging sediment are not allowed to reach the vicinity of the pipe. In twenty years of practice I have never seen a foundation water problem that's not linked to conspicuously awful surface grade conditions with roof water gutter spills being allowed to pond at the grade abutment to the foundation wall. The good news for you Steven is that your heavy red clay properly finished at the surface can provide an excellent 'roof' for the backfill to prevent stormwater ever coming close to the footing. The perforated pipe should never function as a running drain at all: think of it rather as a vent to provide pressure equalization and to allow any minor residual moisture to evaporate.

  7. James Morgan | | #7

    Postscript: I've frequently heard homeowners ask why do we need to install separate roofwater drain pipes, can't we just connect to the roof stormwater system to the foundation 'drains' we already have. I'm sure that in the absence of proper oversight there are some ignorant/lazy builders who have actually done just that. Calling it a drain leads us to expect that water will inevitably run there and the all-important surface grading can therefore be neglected. It just doesn't have to be that way.

  8. GBA Editor
    Martin Holladay | | #8

    James,
    You're forgetting an important point. There are two ways that water can reach the footing drain. It can trickle downwards from the surface, due to ponding under the eaves (as you propose). But during the spring, groundwater levels can rise from below, until the level of the groundwater is higher than the level of your slab. In that case, a footing drain pipe that is installed above the slab will work -- but the slab will still get wet.

  9. Steve Knapp CZ 3A Georgia | | #9

    I think Martin is right that we have to address surface and subterranean water sources. Since I've already prepped for a drain next to the footer and the waterproofing contractor wants one on top of the footer, I think I will do both and stop worry about which approach is "best."

  10. James Morgan | | #10

    Martin: fair enough, if your local soil, topography and climate are subject to periodic conditions of elevated ground water. Some are, some aren't, and that's where local experience comes in handy. I should have qualified my comments by emphasizing that they are based on a couple decades of experience and observation almost entirely in the central piedmont of North Carolina. I suspect similar conditions might apply in Steven's neck of the woods but that's certainly not my call.

    I'd also point out that in your drawn detail the center of a perforated pipe laid on top of the footing would still be `~2" below top of slab. And I think there's some value in having the the pipe right beside the vulnerable seam rather than a foot away where drainage paths could potentially become obstructed. Either way Steven's belt-and-suspenders approach should be fine.

  11. David Meiland | | #11

    Anyone who has formed and poured concrete footings knows that the space next to the footing necessary for setting and stripping forms is approximately equal to the space needed for a drain pipe, if not larger. I can understand the resistance to putting the drain pipe at bottom of footing IF the local practice is to pour the footing right into a dirt trench, but here we use 2x6 or 2x8 for footings and I always have the excavator over-dig enough so that we can easily set forms and then remove them. We place the drain pipe and backfill immediately after stripping forms. We also install tight line for downspouts at this stage.

    I want the footing drain well below the slab, and I want it equal to or below bottom of footing so that the bearing soil under the foundation is less likely to be saturated. I am lucky in that we rarely deal with expansive clay, but that would make it all the more important to drain the footing.

  12. Steve Knapp CZ 3A Georgia | | #12

    David.

    Here in Georgia the contractors do seem to use the trench and pour method with a 2x4 to form an edge. When I told my builder and sub I wanted a 12 inch footer, they looked at me like I was crazy ( and I am moving in that direction). I guess I'm lucky that so far the subs have been (mostly) willing to do whatever I want since the project is cost-plus.

  13. Ron Keagle | | #13

    How much pitch, if any, would be advisable for the drain tile? I would include some. Once you commit to pitch, the tile elevation has to change as the tile runs along the foundation. I would regard the bottom of the footing as being the maximum acceptable depth for the bottom of the drain rock bed.

    I would place the bottom of the drain tile on the bottom of the drain rock bed all around the foundation. So, at the lowest point of tile elevation, both the bottom of the drain rock bed and the bottom of the tile are even with the bottom of the footing.

    And at the highest point of tile pitch elevation, the bottom of the drain rock bed and the bottom of the tile might be around mid-height of the footing depending on the pitch and length of run.

    I would backfill with ideal fill sand, and compact it in 6-8” lifts.

  14. Steve Knapp CZ 3A Georgia | | #14

    Ron:

    From what I've read, you want the drain tile level with the foundation and routed to daylight. The idea seems to be to provide a easy way for the water to move away from the foundation. Water always follows the path of least resistance, correct?

  15. Ron Keagle | | #15

    Steven,

    By pitching the tile, you make sure it drains to daylight. With no pitch, water might lie in the bottom of the tile to some extent. And if it were dead level, it might have sags in it that would pond water in the tile to some extent. So I would pitch it to flow down grade at 1% or 12" drop per 100' of run. I would continue that pitch between the foundation and the daylighted discharge or drywell if one is used.

    The drain tile would be in a rock bed around the foundation, and the rock bed would be completely wrapped in geo textile fabric. The tile would sit on the bottom of the rock bed, directly on top of the geo textile fabric that lines the bottom of the rock bed. I would use 4" perforated rigid drain tile.

    Water would drain down the floor of the rock bed as well as inside of the drain tile. There is no reason to have the tile level with the foundation. It just has to intercept water near the foundation by permitting that water to flow away from the foundation and into the drain tile and rock bed.

  16. David Meiland | | #16

    I've rarely seen the footing drain sloped out. To do that, you'd have to have enough clearance from the bottom of the footing to avoid undermining it as you cut below its elevation, and you'd have to make your cut after the footing was poured... difficult but certainly not impossible if you have the room to operate a spade. With a level footing drain, there may be a bit of water standing in the bottom of the pipe, but it can't really accumulate without flowing out one way or another. Hydrostatic pressure is low with this type of setup, and it's a whole lot better than a bunch of wet native soil backfilled against a foundation.

  17. Expert Member
    Malcolm Taylor | | #17

    Part of the problem is that in the standard detail Martin posted the perimeter of the slab is sitting directly on the interior of the footings. It is a good practice to elevate it by about 4" for several reasons. First it makes the height of the perimeter drain less critical, and second it makes the slab less likely to crack as it is all supported on the same compacted substrate.

  18. David Meiland | | #18

    Martin's detail also assumes very shallow footing depth. I've never poured a slab on the footing, even with our 12" frost depth. The top of the footing is always at least 4" below grade, and the top of the slab is at least 6" above grade, so there's 6" of elevation between, if not much more.

  19. GBA Editor
    Martin Holladay | | #19

    My own preferred method is to install the footing drain around the entire perimeter of the footing, equal in elevation to the bottom of the footing or only slightly higher (to make room for a thin layer of crushed stone under the pipe), installed dead level. The installer makes a burrito with landscape fabric (geotextile fabric), so that the pipe is surrounded by crushed stone and wrapped up to prevent fines from clogging the holes. The holes are placed at 4 o'clock and 8 o'clock.

    At one corner of the foundation, you install a T, and then you connect the footing drain to a drain pipe that leads to daylight. This pipe is solid, not perforated, and it slopes. The minimum slope is 1/4 inch to the foot, but a steeper slope is fine.

    Gutter conductor pipes should never be connected to footing drains.

    I included a detail, but that detail is not the only way to do it. As I wrote in an earlier comment, the most important principle is that the center of your footing drain had better be lower than the top of your slab. If it isn't, you can have problems.

    Obviously, if you plan to raise the level of your basement slab with crushed stone, you can put your footing drain pipe on top of the footing if you want to -- as long as you follow the basic principle that the drain must be installed at a lower elevation than the top of your slab.

  20. Ron Keagle | | #20

    I agree that you can live without slope in the tile. But I would do everything possible to heighten the performance of a basement for a high performance home. I would pitch the drain tile and the extension to daylight all the way, and place it on the bottom of the rock bed directly on top of the fabric that lines that bottom.

    That way, the whole rock bed drains along with the tile. Otherwise, if you don’t have pitch on the bed and tile; and if you have the tile bottom say two inches above the bottom of the rock bed; you can create a wet moat all around the foundation with the rock bed acting as a holding reservoir that cannot drain. This reservoir would not only fill the two inches to the bottom of the tile, but also continue filling up to the 4 o’clock level of the tile holes.

    While it is true that this reservoir level would still be below the slab, I would not want standing water all around the concrete foundation where it can aggressively wick into the concrete over a prolonged time. It might be that the reservoir comprised of the rock bed would always be full of water with the drain tile only acting as the reservoir overflow.

    To avoid this reservoir effect, I would place the tile on the bottom of the rock bed and pitch the tile and bed out. I would even extend the rock bed and the perforated tile into the tail leading to daylight to the extent that dropping elevation of rock bed can drain the water between its bottom and the 4 o’clock holes in the tile surrounding the foundation.

    I would not cut the rock bed floor lower than the bottom of the footing because I don’t want to create any issue of footing support compromise. I would run the drain tile from its highest elevation and pitch it downward in both directions from that high point. Those two opposite runs of the tile would go around the foundation and come back together where they depart from the foundation and head for the discharge.

    Having done all of this, I would not expect a drop of water to ever enter this system. I would install a standpipe just to be able to monitor whether water ever did enter the system. I would consider this entire drain system to be a backup because I would do so much detailing in the region above the tile that water would never drain down to the tile. Instead, it would flow away from the foundation on or near the surface. Part of this detailing would include using the proper backfill material and machine compacting it. You only have one chance to get things right. Probably half the basements in the world have water or moisture problems because builders did not avail themselves of the opportunity to get it completely right.

  21. Jin Kazama | | #21

    I always enjoy to read how some people try to save a few 100$ and justify it on a house construction project that costs several 100 000$ ... ????

    I have always seen people here up north in Quebec placing drains aside of the footings,
    and i don't see why one would even want anything higher than this.

    Then, please please...we are in 2013 ..
    There is just NO reason why someone would build a concrete footing + foundation and not use
    at minimum a quality tar coating or a water proof membrane or a full complement of drainage board and membrane, to protect the concrete from sucking up water through it.

    Now if wou've done as you should, the junction area between the footing and the foundation walls
    should be covered by your waterproofing method, and this method should also extend down to the top and sides of the footing.

    So water must go in the drain if it reaches the foundation wall as it slides down on the water proofing.

    Then, as Martin pointed out, why would anyone arrange to have spring/automn water leves higher than the footing ??? Unless u are protecting mature trees from base water line displacement
    and it was planned in advance .. water drain line should be as low as possible .

    Just FYI, i personally use washed stones with a perforated 4" flex pipe around footings, with a few inches under the pipes, and a minimum of 12" on top of it, all the way to the foundation wall,
    all wrapped around with the highest quality geotextile i can find ( usually use the one that looks like a rug ) and then some more stones and clean drain sand all the way up.
    All drain pipes lead toward a comon exit point that sloped down to the road ditches or muni water.

    Interior pipes are good also to provide an "eye" on water level under the slab and with the use of a pump can help out if in a heavy rain/melt water situation. ( frequent here on high $$ project or smart designers )

    we also usually all install an interior port that connects with exterior drains, to be able to move water further with a pump if required ( usually only during spring )
    normally just a tube that goes under the footing and connect to the drains.
    is this the norm elsewhere??
    although, if your grade height is planned correctly, never need to pump anything out..only serves as an "eye " .

    my .2 kw

  22. Aj Builder, Upstate NY Zone 6a | | #22

    Ron Keagle. Machine compacting?

    Never in thirty years of building have I seen backfilling of a foundation machine compacted. How many homes have you GC'd and did you do this compacting every single time? Never had a wall of your foundation fail from the compacting?

    All of you posting, are you machine compacting backfill?

  23. Ron Keagle | | #23

    AJ,

    I never said that everybody compacted the backfill. I am just talking about what I would do. But that is not all. I would take several measures to bring the basement space up to the same quality as the aboveground space, and the aboveground space would be higher quality than usual. Not only would I compact the backfill, but I would also use the ideal backfill material composition and import it if necessary.

    In the whole scope of creating a high performance basement, compacting the backfill is no big deal. Furthermore, it is the one thing that can make the most difference in water and moisture issues. It can be done without bowing the walls if you are careful, use fill sand, and work in lifts.

  24. David Meiland | | #24

    No machine compacting. We backfill with drain rock against concrete walls, it's a crushed product and it's 95%+ compact as soon as you dump it it. If I'm feeling compulsive I might walk around with a hand tamper and flatten it a little bit, but the reality is we're going to trample all over it while framing and siding, so it doesn't matter. I do compact the hell out of the same stuff when under a slab (vibe plate) and compact fill placed in a utility trench, which often has a lot of loose soil.

  25. James Morgan | | #25

    David: I don't understand why you would use drain rock as backfill. Haven't you just created an expedited pathway to the bottom of the excavation for stormwater on the surface?

  26. Jin Kazama | | #26

    I saw some pictures of a few products i can't remember the name a few years ago ..

    plastic plane sheets that one could set a few ft deep in the backfill at an angle to direct water away from the foundations while it is in the soil ...
    can't seem to find anything in google now though!

    one of the product had some kind of ribs similar to steel decks ,
    and was made out of a soil resistant plastic ..damn memory

    i've seen some people use 1" XPS for that purpose also same time as giving somewhat of an insulative "break" to the soil around the building

  27. GBA Editor
  28. Ron Keagle | | #28

    I would not backfill entirely with drain rock because I do not want surface water going down to the drain tile. I would use the approach shown in the detail that Martin posted with the rock wrapped in fabric like a burrito, as he mentioned. That rock drain bed is only to broaden out the collection area to better intercept any water migrating toward the tile. The fabric is a silt filter. The drain rock is only slightly compactable and can be hand tamped to consolidate it to its fullest potential.

    But I don’t want a free draining path from the surface grade down to the tile. I want a surface that is impermeable and pitched to drain away from the house. Ideally, the drain tile will never get wet.

    Therefore, I would backfill above the drain tile rock bed burrito with compacted fill sand. This is a granular material with enough clay to make it ideally compactable. It will also drain, but that is not its purpose. Perhaps, more importantly is the fact that it simply will not hold water, so it is not expansive during winter frost.

    The main purpose of compaction is to prevent future settling which would disrupt a properly pitched drain surface. I realize that compacting backfill is almost unheard of for residential construction, but I believe it essential to a proper job. Simply rolling the excavated soil back into the trench until it is full is a recipe for future problems. If the soil is heavy with a lot of clay content, chunky, or is rain saturated while being in the stockpile, or has big rocks; the backfill will be full of voids, and uneven consolidation. I regard this typical loose backfill operation as being as problematic as poorly installed fiberglass batts.

    Walking on the loose backfill surface will compact only the first foot or so. It will settle further over time with the influence of the freeze-thaw cycle. Proper compaction has to be done in layers one at a time. It also requires the proper soil, and the proper moisture content. Wet clay, for instance, cannot be compacted.

    As the backfill is completed and compacted, the surface is pitched away from the house as a finely graded and finished surface. That surface meets the foundation about a foot below the target finish grade elevation. That surface is covered with a sandwich consisting of heavy duty polyethylene sheet topped with geotextile fabric. Then a foot of ¾” crushed rock is placed on top of the film-fabric sandwich and lightly tamped to consolidate it. Rain water will pass through the crushed rock and drain away from the foundation on top of the film-fabric sandwich.

  29. T Shepp | | #29

    Got to agree with Ron. Compacting back-fill is essential...if the back-fill material requires it...to one degree or another. Even sand should be tamped a little...see the picture just below the cultured stone. That crack is huge and the sidewalk is also cracked and is a tripping hazard.

  30. Zenon Tymosko | | #30

    Have you heard of "Fast-foot"? It's a waterproof sheet product that you use to make the footing forms. Then you connect the sheet to the waterproofing system both on the walls, and under the slab. So that there is NO concrete that would ever sit in ground water. And they recommend putting the drain tile BELOW the level of the footing, so there is no water at that level in the first place. Yes, that means "over excavating" and putting footings on the proper aggregate, and NOT on undisturbed soil. Which is a twist that I'm expecting my local contractors to balk about. But apparently it's become code in the Vancouver area.

    It strikes me that this would be the absolute best solution to moisture wicking into the foundation. And to ground-water drainage.

    Ron Keagle goes into tons of effort to handle storm water, which is definitely a concern. But around here, the ground water levels - especially in the spring - are a WAY, WAY bigger source of moisture around your footings than any bad grading in a thunderstorm.

    I like the idea of keeping the whole assembly perched up high and dry.

    And I cringe at the standard construction method in these parts. They pour a footing on "undisturbed soil", but that soil often is saturated with moisture - and stays that way. Then they pour foundation walls on top of the footings, with no capillary break. So for the life of the structure, the footing/wall combination sponges up the ground moisture and releases it into the basement - often behind an interior "finished basement" assembly with "vapour barrier" (with 9,000 staple perforations in it) and paper-backed drywall/mold food.

    And we wonder why there is a mold problem in many/most basements.

  31. Zenon Tymosko | | #31

    photo of "rising damp" solution from Fast foot.

  32. Ron Keagle | | #32

    Zenon,

    For the ideal basement, I have two objectives:

    1) Prevent surface water from draining downward around the foundation.
    2) Prevent any contact of the concrete with the soil and with the interior living space air.

    Item #2 is to prevent the concrete from absorbing soil moisture. Item #1 prevents the concrete from absorbing free water which can flow past barriers intended to prevent moisture wicking.

    However, as you mention, free water can rise from below as well as drain down from the surface. I would not build on a site that has the potential of the water table rising to the elevation near the bottom of the footings. I would also not build on a hillside because they often have water moving beneath the surface, following the downward slope of the surface.

    If I had to build on either of these two site conditions, I would dewater the soil 10-40 feet out from the foundation by a drain tile and rock bed set at a lower elevation than the bottom of the footings. That way, there would be no ground water rising beneath the footings and reaching the point of contact between the ground and the footing bottom.

    I can see the point of your diagram showing the footing resting on a rock bed, and placing the tile below that elevation. But I would worry about cyclical soil saturation there allowing the footing to settle if the saturated soil is displaced under the load, and rises to fill the spaces between the rocks in the drain bed. Aside from that soil displacement, just the cyclical saturation can cause expansion and contraction, which might affect the footing support. One way to combat these issues would be to place the drain tile considerably lower than the bottom of the footing, and thicken the rock bed to a foot or more, and broaden it to spread the load out more.

    However, if the water is intercepted and drained further out, the soil beneath the foundation should stay free of water saturation.

  33. Zenon Tymosko | | #33

    Ron
    Thanks for your note. I will bring up cyclical soil saturation as a concern to my foundation people, civil and soil engineer. That is a good point, as I already don't understand how "self compacting" fill could ever really be as stable as undisturbed native ground. But I do really want to keep the footings out of the water. So I'm going to push for some solution that allows free-draining under the footings and into a drain-tile system that is lower than the footing level. I will probably get laughed at.

    Of course it would be nice to have a site that was guaranteed to never have seasonal or occasional groundwater near the footings. Or to install some kind of de-watering moat system. But if that was a prerequisite here, we would probably have 80% fewer houses! If it's not in the code, people just don't do it. So we have moist basements.

    With the various underground springs and veins of water around here (and I suspect in much of both the USA and Canada), I don't think even a de-watering moat would guarantee that a spring or vein doesn't exist under or near a foundation. It's an interesting idea, that's for sure!

    I'm debating starting a new Q&A about this, because my question/proposal is a bit different from the OP. Plus I think I got into this thread a little late. Should I?

  34. Steve Knapp CZ 3A Georgia | | #34

    Just out of curiosity, what do folks on this thread think of precast foundation walls that sit on a layer of compacted aggregate. I was looking at the Superior Walls site, and it appears that their system goes in without a footer--although I noticed a drain tile embedded in the aggregate well below the slab layer.

  35. Zenon Tymosko | | #35

    I know that "rubble trench foundations" or "rubble trench footings" have been used for thousands of years. I don't think we really NEED to be using the standard concrete footing. But because it has become convention, it is now hard to get anyone to question it or to think outside the big-concrete-footing box.

    If you Google rubble trench, there is tons of info on it. One site says it's only good for slabs on grade (frost protected if that applies to you) and crawl-spaces. Presumably that means it's not good for full basements. But elsewhere it says you excavate below the frost level, and fill with rubble.

    I think it's one of those things that the building codes don't talk about, and hence nobody does it - except the "extremists". But it's scientifically sound.

  36. David McNeely | | #36

    Joe Lstiburek says that foundations should provide both screens and barriers (RR-1015: Bulk Water Control Methods for Foundations). He says the drain screen can be free-draining backfill (gravel or sand), or a synthetic drainage board, or combination. The goal is to direct water downwards to the perimeter drain and prevent a hydrostatic head from forming against the foundation.

    This is what my structural engineer has to say about backfilling: BASEMENT AND RETAINING WALLS SHALL BE BACKFILLED WITH ASTM D448, #57, #67, OR #78 CRUSHED STONE. STONE SHALL EXTEND VERTICALLY FROM BASE OF WALL TO WITHIN TWO FEET OF FINISHED GRADE, AND HORIZONTALLY FROM BACK OF WALL TO ½ THE WALL HEIGHT. PLACE IN LIFTS NOT EXCEEDING 24” THICK, AND DENSIFY. THE STONE FILL SHALL BE SEPARATED FROM ADJACENT SOIL FILL BY AN APPROVED FILTER FABRIC.

    It occurs to me that it is desirable to have a capillary break between foundation wall and soil, just as it is between slab and soil. I once looked at a house for sale during a rainstorm, and the basement had water coming out of the basement foundation with such force that it spurted two feet before arching to the floor. No waterproofing would have prevented that!

    On my upslope lot I have a soil deficit, meaning some fill will have to be imported. I am happy that my whole house will be built on compacted rock fill—no water will be able to get near concrete. We go to great lengths to provide a rain screen between siding and sheathing; we put clean rock between slab and soil; we put a drain screen between foundation wall and soil; we put drain tile between the side of the footing and soil: why not between the bottom of the footing and soil, and drain the whole thing as a system instead of a trench? The chief of building inspections in my town even recommended this approach to me.

    I am choosing to use Superior Walls because of their moisture impermeability; as mentioned, they are placed on a gravel footing.

    Not mentioned in this thread is the use of perforated pipe on the interior, below slabs, for both drainage and radon remediation. My plans call for 4" perforated pipe with at least 1" clean fill above it, about 12" from the perimeter walls, draining to daylight, and connected to a solid riser that goes up through the roof. Redundant drainage perhaps, but why not?

  37. Zenon Tymosko | | #37

    David - what does your structural engineer say about putting the appropriate self-compacting crush underneath the footings - or underneath the Superior Wall (same concern)? Is there a concern about the soil underneath somehow percolating up into the crush, and undermining the footing support? (is your engineer on speed-dial? haha)

    The Superior Walls seem interesting. But their claim is that the moisture impermeability comes from a special concrete mix. Have they somehow changed the nature of concrete to no longer be a sponge or a wick for water? Or do they rely on the sheet foam products to prevent the wicking from coming into the house? I looked up Superior Walls in the rest of the GBA site, and the comments weren't that great. Why would one want all the insulation on the inside, when one can have it all on the outside, where it belongs? It gives up all that thermal mass benefit. And how can panels be waterproof when they are by definition connected together with some kind of sealant? Sealant's aren't forever.

    As for the radon, you will have a second set of drain tile then? Both inside and outside the footing/exterior walls? I was thinking of doing the exact same thing. Except only for added assurance about staying dry. The radon I was going to pipe and vent separately. I'm not sure you are supposed to combine the two.

    Steven - I don't see how the thickness of the footing has anything to do with where the pipe goes. A properly sized footing is meant to distribute the weight of the structure onto the earth below. Why does a drain pipe on top of the footer necessitate a thicker footing? Is this in your code somewhere? That placement of the drainage tile drives the footing size?

  38. J. Eric | | #38

    Martin,

    I understand how having geo textile fabric over top of the gravel/stone would be beneficial, as it would help shed surface water away from the foundation, but I don't understand the logic of wrapping the geo textile fabric underneath the layer of gravel/stone. The fabric would become clogged and would inhibit potential ground water from an elevated water table or underground spring from rising up through the gravel/stone into the 4 inch perforated drain, allowing the soil underneath the geo textile fabric, and potentially underneath the footer, to become saturated and soggy. It seems to me that 3 feet or so of geo textile fabric extending from the foundation wall and placed directly over top of the gravel/stone would be enough, maybe even with the fabric covering the side the gravel/stone in the foundation drain trench - between the side of the gravel/stone and side wall of the trench - but not underneath. It just seems that by placing the fabric also underneath the gravel/stone you would be preventing the 4 inch drain from being able to do what it was designed to do, and that is - to allow water to rise up into it from below, shedding the water away to daylight instead of allowing it to remain in the trench beside the footer.

    It would almost be like having the perforated pipe wrapped in fabric drain "sock" as some call it, if you've ever tried that method. We tried it one time, because it seemed like a good idea, but the fabric became clogged with soil and prevented surface and ground water from entering the 4 inch foundation drain -We dug out the 4 inch drain and stone, took the fabric off, put clean stone back in the trench and around the 4 inch drain, covered the top of the stone with burlap, which would eventually rot away - well after the soil above it had time to settle and compact - and the drain functioned perfectly, as it was designed - and we know this because water was no longer pooling up at the foundation- we could literally see it coming out of the end of the drain where the drain terminated at daylight. When the perforated drain was wrapped in fabric, no water was exiting the end of the drain in the spring or during heavy, prolonged rains - it seems that the burrito method that you have detailed with the geo textile fabric would essentially be almost the same as having the drain itself covered in a fabric "sock" ... the only difference being the gravel/stone would also be encapsulated by fabric ... essentially the same thing. In your method the only entrance for water to flow into the drain, after the geo textile fabric becomes clogged with soil, would be the fine line between the side of the footer and the edge of the geo textile fabric at the the bottom of the drain, and the fine line between the foundation wall and the edge of the geo textile fabric on the top. Water could not enter the drain quickly enough at these two locations, it seems, to effectively shed it away from the foundation and footer to daylight.

    1. Expert Member
      Malcolm Taylor | | #39

      J. Eric,

      I do much as you suggest, and drape the fabric over the rock before backfilling.

      1. J. Eric | | #40

        We do an extra step of installing what I call a "rain hood" (I'm not sure of the exact terminology) from the foundation wall to the edge of the footer. This "rain hood" is nothing more than steeply sloped concrete that diverts surface water that permeates through the soil (and water that runs down the foundation wall towards the footer) and sheds it to the side of the footer, into the trench that holds the foundation drain. We build up the gravel/stone in the footer drain to the height of the "rain hood" and then backfill. We use burlap or loose straw to cover the gravel/stone before backfilling - this gives the soil above the foundation drain time to settle and compact so that the initially loose soil fines cannot permeate through the gravel/stone. This method is highly effective - and it makes it impossible for water to stand next to and saturate the mortar bed joint between the footer and first layer of block

        I have dug in and around footer drains designed this way years after they were installed, and the gravel/stone is not clogged with dirt as some might suspect it would be. Installing the straw or burlap is key, because they will eventually rot away and will not inhibit water from permeating through the soil and entering the drain from above - this is especially critical on a downhill grade with surface water running towards the foundation - and depending on how deep and steep the finish grade is, we may install a second, wider "rain hood" at the finish grade with a french drain (with 4 inch perforated pipe, just the same as the footer drain that would be below it) at the edge of the "rain hood", without any topsoil over it, but instead covered in finished landscaping material to hide it. Some might call this overkill, but we've solved many foundation water intrusion issues using these two methods.

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