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Q&A Spotlight

Does This Footing Need a Capillary Break?

The barrier is designed to keep moisture out of the foundation walls, but the building inspector isn't convinced

A waterproof coating from ProtectoWrap is applied to the top of the concrete footing at the FHB House. Photo courtesy of Fine Homebuilding.

As he works out the details for a new house, Jason Huffine has become concerned about the potential for trouble in applying a capillary break between the concrete footing and the foundation walls.

A capillary break would prevent the foundation—in this case steel-reinforced, concrete-filled block —from wicking up moisture. Huffine’s general contractor isn’t familiar with this technique, and the two of them wonder whether the capillary break would weaken the connection between foundation and footing.

“Though I’m as green around the gills as one could be and learning as I go, that sounds like a good question to me,” Huffine writes in a Q&A post.

Huffine might not be considering this approach at all except that the footings will be about 5 feet lower than a road bed at the front of the house. While stormwater drainage appears to be adequate, adding a capillary break might provide some additional insurance and help protect the foundation and footing and prevent “any potential rising damp issue.”

Are Huffine’s concerns well grounded? That’s the topic for this Q&A Spotlight.

A cold joint has only minimal adhesion

Unless the footings and foundation walls are poured at the same time, creating a monolithic concrete structure, there will be a cold joint between the two, and in that case there is only minimal adhesion, says Malcolm  Taylor.

To connect poured footings and foundation walls, a shallow groove or keyway can be formed in the top of the footing, Taylor says. When the foundation walls’ concrete is poured, it fills the groove to provide resistance to any lateral pressure. Adding rebar is also a common way to reinforce the joint and could be done with a block wall.

But the use of a capillary break in this location still hasn’t reached the construction mainstream.

“Right now capillary breaks are confined to a small group of high performance builders,” Taylor says. “That isn’t to disparage them in any way, but it means they are a niche technique most of us aren’t familiar with.”

 More questions than answers

To Jon R, there are plenty of questions about capillary breaks but not a lot of reliable answers.

He suggests an experiment in which a wet piece of paper towel is separated from a dry sheet by a piece of plastic with a tiny hole in it. Press the layers together for a few minutes, Jon R says, and the dry paper towel becomes quite wet.

“Not sure what to make of it,” he says. “Thick sheets of EPDM (vs. thinner, more delicate alternatives) are better for capillary breaks? Or concrete admixtures? That full gravel surround (under slab, under footings, against walls) is best for dry concrete?”

“I see almost no data pertaining to good, modern concrete and the various techniques,” says Jon R.

Although wet concrete isn’t a structural issue, Huffine says, it can introduce moisture into the house. “If the latter occurs, the fix is expensive and involves someone drilling into your foundation and injecting a sealant that will be absorbed by the concrete and set up to retard the movement,” he writes. “I figure if I’m already aware that moisture will need addressing, might as well get those low-hanging improvements. A few hundred on a barrier now might save a headache’s worth of problems later.”

Membrane or liquid-applied product?

GBA Editor Brian Pontolilo directs Huffine to an article by Mike Guertin on capillary breaks. He notes that a capillary break can come in the form of a membrane or a liquid-applied product, such as the ProtectoWrap LWM200 that Mike Guertin used on the FHB ProHome.

As Guertin explains, membranes can be difficult to install if there is rebar sticking out of the footing, making the liquid-applied product a little easier to use.

Another option would be to use asphalt damp-proofing, adds Taylor. “If asphalt damp-proofing is going to be used to protect the concrete from water intrusion from the outside,” he says, “and can be applied to uncured concrete and backfilled quickly, it might be a good choice to use as a capillary break, too.”

Placing the footing drain properly

Where the footing drain is located is another important detail, says Jason Cole. Most builders place it so the drain is below the top of the footing, giving water an easier escape route than through the footing.

“However,” he adds, “some contractors take shortcuts and put the drain above the top of the footing to save time and money, which just means that the lowest level that the water can sink to is just barely above the cold joint between the CMU and the footing.” To get the drain below the top of the footing would require extra work—so they just skip it.

Even with the drain below the footing, Taylor says, the area is still vulnerable to moisture because the bottom of the basement slab rests directly on the footing. A better way is to separate the two with several inches of fill.

“This both provides a path for moisture to move underneath the slab, and makes the slab less likely to crack at the edges due to differential settlement of fill,” he says.

Getting the building inspector on board

One hangup is Huffine’s building inspector, who has yet to accept nor reject the idea of adding a capillary break.

“He has expressed concern that putting another layer between the foundation and the footing would affect the frictional forces,” Huffine says. “I’ve sent information (like the Fine Homebuilding article) on it. But so far, no one feels convinced it’s the route to go.”

And it’s not just the building inspector. Huffine says he has spoken with representatives for ProtectoWrap and was told that their product is not normally used in this application (the ProtectoWrap LWM200 that Guertin described using is more often applied as a waterproof coating in window and door openings).

“It took quite a bit of conversation for them to even understand the application,” Huffine says. “Although in the end, they said it should work, they definitely acted as though this is not the norm and not in their cross-hairs. Maybe this just hasn’t caught on?”

Maybe having a capillary break isn’t even necessary, Taylor suggests. The “rising damp” issue that Huffine originally mentioned is a phenomenon of British homes, which are continuous concrete or masonry structures extending from footing to roof.

“The situation in North American stick-frame construction seems to me to be a lot different,” Taylor says. “Can someone link to the original research that showed this is a significant problem here? I think it came from [Building Science Corporation] research, but all I can find is their concern that the salts in soil may cause masonry to deteriorate prematurely.”

Our expert’s opinion

Here’s how GBA Technical Director Peter Yost views the issue:

Some great questions have been raised in this Q&A:

First, does adding a capillary break weaken the footing/foundation wall connection? When I was at Building Science Corporation, this issue came up with a building inspector on a Building America project. Joe Lstiburek was adamant: the only circumstances where we really need to worry about resistance to perpendicular shear across this connection is in really high seismic and wind areas, and with expansive soils.

The Residential Structural Design Guide: A State-of-the-Art Engineering Resource for Light-Frame Homes, Apartments, and Townhouses—2nd Edition bears this out [7.4.2 Concrete or Masonry Foundation Wall to Footing, pg. 7-24]:

“Footing connections, if any, are intended to transfer shear loads from the wall to the footing below. The shear loads generally are produced by lateral soil pressure acting on the foundation (see chapter 3) or loads in shear walls from wind or seismic events.

“Footing-to-wall connections for residential construction often are constructed in one of the following three ways (refer to figure 7.5 for illustrations of the connections):

  • No vertical reinforcement or key
  • Key only
  • Dowel only

“Generally, no special connection is needed in non-hurricane-prone or low- to moderate-hazard seismic areas. Friction is sufficient for low, unbalanced backfill heights, whereas the basement slab can resist slippage for higher backfill heights on basement walls. The basement slab abuts the basement wall near its base and thus provides lateral support. If gravel footings are used, the unbalanced backfill height must be sufficiently low (that is, less than 3 feet), or means must be provided to prevent the foundation wall from slipping sideways from lateral soil loads. Again, a basement slab can provide the needed support. Alternatively, a footing key or doweled connection can be used. In spite of the many probable locations across the country where no physical connection might be required between the foundation wall and the footing, the best practice remains to attach these two elements. Without the physical connection, this critical part of the load path arguably is not continuous. Often, problems arise that could have been reduced or eliminated if a physical connection had existed between the foundation wall and footing. This is particularly true when any extreme loading occurs, such as high winds or even a moderate earthquake.”

A second question is whether we really need to worry about wicking between the footing and the foundation wall. Yes, capillarity or wicking occurs in all porous materials, until the pores are just too small or disconnected, such as 7,000 psi concrete. Wood, masonry, concrete, and gypsum wallboard all can wick water.

We need to worry about that more with new construction because we have shifted the hygrothermal balance in basement walls. Again, from Joe Lstiburek, Building Science Digest 103, pg 4:

“Groundwater exists in more than the free-flowing liquid state. Water from wet soil can also wick (capillary flow) and move by diffusion through the soil and the materials used to make basements. Therefore, the basement wall should be damp-proofed and vapor-proofed on the exterior and a capillary break installed over the top of the footing to control “rising damp.” Damp-proofing and vapor-proofing in these locations is often provided by a fluid applied coating of bitumen. In the past, capillary breaks over footings were not common. They were not needed when basement perimeter walls were uninsulated and unfinished on the interior because these conditions permitted inward drying of the migrating moisture. For finished basements they are an important control mechanism. Without them, moisture constantly migrates through the foundation, and then into the interior insulation layer and interior gypsum board lining.”

Third, how much water comes out of freshly-cast concrete (moisture of construction)? A lot, thousands of pounds, as it turns out. See this resource from the National Ready Mix Concrete Association. Is this one-time load something to worry about? It certainly can be. I was involved in a recent project where, from breaking ground to moving in (right around Thanksgiving in Climate Zone 4A), was only 11 weeks. I calculated the moisture of construction for the first six months of this building (curing concrete, drying wood, plaster, and paint) in excess of 16,000 pounds of water. Definitely a moisture load that needs to be actively managed.

Finally, I decided to check in with building scientist Pat Huelman of the University of Minnesota, who has done a ton of work for our industry related to foundations and basements. On the particular issue of the need for a capillary break between footing and foundation wall, he had this to say:

“In general, I have always used the Building Foundations Design Handbook, 1988 (and subsequent Builder’s Foundations Handbooks) as the source for this requirement. Bear in mind at that time there was considerable push back from the masonry (CMU) folks and they didn’t include a capillary break on those details.  In later details that changed as footing pins replaced the keyway. And a spray on material was allowed.

“…When there is an unfinished foundation wall of sufficient height, the water will evaporate to the indoors (or outdoors, if the wall sticks out of the ground) before reaching the sill. However, for most walls today the exterior exposure is limited and may even be covered with a coating, insulation, or both. And when the interior is covered with a low-permeability material the water will continue upwards. Depending on the foundation material and lack of drying potential, the capillary water could go tens of feet. Of course, block is a tricky one as vapor can move upward readily by diffusion and convection.”

-Scott Gibson is a contributing writer at Green Building Advisor and Fine Homebuilding magazine.

35 Comments

  1. User avater
    Jon R | | #1

    My conclusion - stick with the recommended fluid applied asphalt/bitumen footing capillary break unless you have hard data showing that something else is as effective in this application.

    It's not clear to me that the slab will prevent the walls from sliding inward if you have a strip of foam between the slab and the wall. Rebar seems to be a safe bet.

    1. Mark Pollard | | #16

      The need for rebar or a key way is unnecessary, as stated in the "Our Expert's Opinion" by 2 more experts. [paraphrased] If seismic zones, high wind zones, or non-expansive soils are non-factors, then the joint at the footing to foundation wall needs neither rebar or a key way. If numerous engineers are willing to certify designs and credible members of the building science community are willing to endorse these three tenants of footing to foundation wall connection, then it is settled physics.

      Bulk water management and vapor control are site specific. Investing in a belt and suspenders approach to the thing that holds a structure up is never a bad idea.

  2. Peter L | | #2

    Maybe an engineer can chime in but in seismic design category areas A through C, per code the cold-joint at the footing must have vertical rebar extending into the masonry assembly wall. In the photo show here (Seismic Category C), the vertical J-rebar extends from the center of the footing, through the ICF wall and then gets tied in with the next row of ICF wall rebar. So the vertical rebar extends in a continuous load/tension path from the footing, all the way up to the roof.

    I was told that cold joints are always weak points in a masonry wall assembly. Rebar is key and keeping the cold joint area clean but rough to promote better adhesion of the next layer of concrete. Sometimes epoxy and adhesion primers are used.

    Concrete plants sometimes offer special mixes for the footings that make the concrete semi-waterproof once the concrete is cured. They sometimes call these "winter mixes". Once the concrete cures, if you pour water on it, the water will not absorb into the concrete. It beads and doesn't get absorbed. Would this not create a capillary break?

    1. Malcolm Taylor | | #3

      Peter L,

      I think you are right that admixtures designed to make concrete more waterproof, like Xypex, would work as capillary-breaks. However when Martin contacted them they wouldn't say their product was approved for that purpose - although probably for legal rather than practical reasons.

      1. Blake Schatz | | #11

        Xypex has also told me their products are not vapor barriers.

    2. Blake Schatz | | #9

      Yes, I believe for SDC B and up, dowels out of the foundation are required. SDC A has very limited requirements, but the addition of dowels is minuscule compared to the cost to repair a foundation that has slid -- which can occur from events other than seismic.

    3. User avater
      Jon R | | #21

      @Peter L:

      > in seismic design category areas A through C

      I see the tied-in rebar requirement for D0, D1, D2.

      > must have vertical rebar extending into the masonry assembly wall

      But when I look at the concrete wall section, I don't see that requirement. 2018 IRC.

  3. Brendan Meyer | | #4

    Slate course. All good historic buildings in DC from before 1875 had a course of roofing slates in a mortar joint about 5 or 6 courses above grade. The slate was a capillary break that prevented rising damp in the bricks.

  4. User avater
    Michael Maines | | #5

    @Brendan Meyer, that's interesting, I didn't know that. Good idea.

    As for the discussion on capillary breaks above footings, considering how much weight there is at the joint, and the somewhat irregular surfaces involved, I can't imagine that the choice of capillary break material makes a measurable difference to the coefficient of static friction between the footing and wall.

  5. Andrew C | | #6

    @ Michael Maines - I agree with your point,
    I'd just phrase it differently. The coefficient of friction may change a bit, but the normal forces are so high that the friction forces resisting sideways movement should remain very high. I'd definitely add a capillary break of some sort.

    I'd prefer to add a keyway or rebar, but that's just engineering judgement. Seems like a relatively low cost design feature that's not really fixable once initially built. Of course, details like this would increase the up-front costs of my dream house.

  6. User avater
    Geir Gaseidnes | | #7

    With a key drawn in and rebar jutting out of the footings, I opted for a liquid solution to the capillary break challenge. Painting the tops of the footings with two coats only took a few hours plus drying time, and practically all of the dimples and contour remain there for a solid mechanical connection.

  7. Tyler Keniston | | #8

    I don't see the concern when key-ways and/or rebar are involved.
    Bear in mind I'm not an engineer, nor concrete contractor, but I was under the impression these connections were designed by largely ignoring bond strength at that cold joint anyways... but I didn't realize some connections are designed without key or dowel.

    If there was concern, perhaps there is a capillary coating that can double as an adhesive? Though at that point, it seems likely to be cheaper to just add a key or bar.

  8. Lance Peters | | #10

    My only concern with the thinner spyay-on approach is whether it would be durable enough to withstand the abuse of having wall forms assembled without being compromised. A thicker peel-n-stick solution might be better?

    I’m planning to use a capillary break in my foundation and was leaning towards a keyway and thick membrane approach.

    On a somewhat related note, after attending a class on concrete reinforcements I’m sold on using stainless steel rebar in my foundation. Carbon steel rebar corrosion creates outward pressure on concrete, causing it to crack. Concrete bridges are now commonly built with SS rebar and the cost increase is negligible.

    1. Lance Peters | | #13

      Thinking a little further into this, I'm in CZ6A which requires R20 basement wall insulation typically consisting of 2" of foam board covered by an insulated 2x4 wall. If the foam board is viewed as an impermeable vapor barrier, "rising damp" moisture is likely not an issue from a basement humidity standpoint.

      It could still cause rebar/J-bolt corrosion and/or sill plate rot in the case where the foundation is insulated above grade.

    2. User avater
      Jon R | | #14

      There is a huge difference between a bridge (often seeing salt) and a foundation (should be salt free). But that doesn't mean that foundation/wall rebar/j-bolt rust isn't an issue.

      When it comes to mold, anything that leaves any gap has some risk. Stop the water with a capillary break and let anything remaining dry to the interior.

      1. Lance Peters | | #15

        Agreed. The (older) gentleman that gave the course had spent his career as a consultant for large concrete construction projects, many of which were bridges, parking garages, and other structures that are affected by the use of road salts in colder climates. When I asked him whether he thought stainless rebar was worth considering in a residential foundation application he discussed the slight cost increase (1-2% overall on bridges), then the unknowns of the ground water in different soil types (pH etc.), and the conclusion was why wouldn't you use stainless rebar? If not throughout the entire foundation, at least in the footings where you could reasonably expect high levels of moisture all the time (assuming a capillary break to keep the foundation walls dry).

        He did say that the foundation around a residential garage could be affected by road salt, though admittedly far less than a bridge.

        As far as mold goes, with mandatory 2" foam against the interior of the foundation walls there could be a mold risk, but as long as there's a good seal from the interior it might never be a problem. I say "mandatory" only because a code compliance official told me that's what they expect to see on basement interiors here.

        1. Malcolm Taylor | | #17

          Lance,

          it might be worth confirming the price increase go with stainless steel rebar - although it doesn't represents much of the cost of a foundation.

          1. Lance Peters | | #19

            Absolutely. I would assume a foundation contractor would consider this an extra charge item even beyond just the material cost, given they would have to order in material special for your job. Even if the cost increase was $500 on a $40k foundation, that's only 1.25%. Worth it in my eyes.

            An interesting thing this fellow said, was that crews who started using stainless rebar eventually grew to like it more than carbon steel rebar because it was so clean to work with, and that productivity increased enough it offset most of the added cost of the material.

        2. Mark Pollard | | #18

          Site conditions are just that, conditions specific to the site. Homes less than one hundred feet apart can have drastically different bulk water or water vapor control issues. It is up to the individuals involved in the project to make the call. The general contractor was presumably hired for general expertise and should know enough to call in experts when site conditions appear abnormal. Granted, this is completely subjective, one contractor's normal is another's red flag.

          If there are persistent bulk water issues at the footing level of a frost depth wall or full basement wall, someone screwed up.

          Lance, regarding steel vs stainless steel rebar, if there is enough bulk water or water vapor present to deteriorate steel rebar to the point of concrete failure, someone screwed up. Also, stainless rebar isn't going to stop other issues inside the structure
          from presenting themselves over time. Tailoring a building to the conditions present on the site is key.

          1. Lance Peters | | #20

            You may be right, but the property we're building on is low-lying and the footings won't likely go more than a foot or two down. The lot will be heavily back-filled once the foundation is in place.

            With a typical french drain unable to keep water levels below the bottom of the footing, even if the ground water naturally resides lower the footing will likely be wet any time the drain has water in it. That can happen every day for weeks in the shoulder seasons.

  9. Blake Schatz | | #12

    Peter Y's quote of Lstiburek mentions the difference between vapor diffusion and bulk water transport -- each are different phenomenon and should be treated differently. For example, crushed rock placed under a polyethylene sheet. The crushed rock is used to stop liquid water transport through capillarity, and the sheet is used to limit vapor diffusion through the concrete.

    Lstiburek's quote however seems specific to finished basements. What if we just have a buried perimeter footing? Does the exterior face need a vapor retarder? Section 4.2 in the Building Foundations Design Handbook (linked above) shows the vapor retarder turned up the exterior edge. With this detail, I can see potential for bulk water running down the face of wall & getting trapped between the sheet vapor retarder & concrete footing. Granted the detail shows step flashing above, but there's still plenty of chance of trapping bulk water. Personally, I would opt to eliminate the upturn edge of sheet vapor retarder and let any absorbed vapor dry out. Or use a liquid-applied retarder on the face.

  10. DavidSilva | | #22

    Hi all. In Massachusetts and footing has already been poured. I want to add a liquid applied membrane capillary break before the walls get poured. I have the weekend to apply. Anyone know of a place that stocks BASF MasterSeal HLM 5000, ePro Ecoline-R, Henry CM100, ProtectoWrap LWM200, Tremco TremProof-250gc, or similar liquid applied membrane? No luck on places I've called so far. Note that the list of products above have come mostly from other GBA articles. Thanks in advance.

    1. User avater
      Michael Maines | | #23

      David, your local masonry supplier might have one of those. The kind of place where masons buy block and other materials. If you don't have one nearby, or if they don't have it in stock, you can use UGL Drylok, available at most big-box stores.

      1. Andrea S | | #24

        Hi,

        Would adding the KIM product (krystol Internal Membrane) to the wall concrete mixture stop the rising damp?

        Would spraying a footing with Foxfire crystalline sealer stop the rising damp?

        Thanks

        Andy

        1. User avater
          Jon R | | #25

          At a minimum, use products that specifically say they are recommended for use on footings. I don't see that for ProtectoWrap’s LWM200 or Drylok.

          I also have a preference for large, well established manufacturers.

        2. Malcolm Taylor | | #26

          Andrea,

          KIM is very similar to Xypex (see my post #3 above). I suspect it would work, but the manufacturers do not approve it as a capillary-break.

          1. user-7061227 | | #27

            Hi,

            I contacted the company last year and they agreed that their product would work as a cap break for footings. See attached. So we used it.

            It is VERY difficult to get local building people on board with the cap break theory (and any building science improvements for that matter).

            Thanks

            A

      2. DavidSilva | | #35

        Thanks Michael. Local Masonry Supply worked for me and I was able to get HLM5000 in stock. $200 bucks for 5 gallon pail. It was a roll on formula like I used for basement waterproofing in my last house. Took a while to roll and brush the footing. I had the concrete guys spray the wall with Tremco H8. Seems like the spray stuff covers better than roller applied.

  11. Ron Keagle | | #28

    I can understand placing the capillary break on top of the footing to prevent moisture from entering the foundation wall, but what about the wall itself? I would use heavy (.012" thick or more) polyethylene on the walls and under the slab. If a person felt that more protection was necessary, why not just extend the poly to be continuous under the slab, under the footing, and up the walls?

    1. User avater
      Jon R | | #29

      Unlike vapor transport, capillary transport will move lots of water through small pin holes. I expect poly will usually have some.

      The standard (for capillary transport) is gravel under the slab. Not clear why that isn't also superior for footings (with drains lowered to match).

      1. User avater
        Michael Maines | | #30

        Jon, I'm curious about your statement that pinholes will allow a lot of water movement. I've searched this site, the web and Bill Rose's book, Water in Buildings, for info supporting your statement but I can't find any. It doesn't make logical sense to me but I'm willing to learn something new. Do you have supporting information?

        I agree that gravel (specifically, a freely draining material) properly compacted under footings are a good idea.

        Ron, the damp-proofing required by code on foundation walls is a capillary break. It's not waterproof, but keeps damp soil from reaching the raw concrete. When I'm designing foundations that need to be waterproof, I spec an elastomeric membrane on the exterior, and/or a dimple mat leading to foundation drains.

        1. User avater
          Jon R | | #31

          I base the statement on a simple test with some plastic sheet and wet/dry paper towels. And knowing the high pressures that capillary transport can achieve. But would be interesting to see data for specific cases (eg, real footings).

        2. Tyler Keniston | | #32

          Found this experiment (not completely unlike Jon's): https://www.subsystems.us/diffusion-vs-capillary-action.html

          Maybe this will mean something to someone:
          https://buildingscience.com/sites/default/files/2009-01-24-Capillary_Moisture_Transport.pdf

          I'd still take tiny pin holes over no protection at all, but I can see how capillary action could move quite a bit of water through small bridges (due to the strength of cohesive and adhesive forces).
          Free draining material is definitely a big plus with this in mind. Am I mistaken, though, that some insist footings rest on undisturbed 'virgin' soil? Maybe that's an old-timey thing?

          1. User avater
            Michael Maines | | #34

            Tyler, the IRC building code requires foundations sitting on any type of fill to be "designed, installed and tested in accordance with accepted engineering practice." (R401) If you place the footings on undisturbed soil, you don't need to deal with engineering and testing as long as the building official trusts your classification of the soil.

            Thanks for the testing info.

            https://codes.iccsafe.org/content/IRC2015/chapter-4-foundations

    2. Tyler Keniston | | #33

      Martin's article below gives the following reason for why poly below the footing is less effective:

      "Because the bottom of a footing is usually lower than the holes in the footing drain pipe. That means that footings are often wet — in fact, in some cases, footings are basically sitting in a puddle."

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