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water proof or dampproof crawlspace foun

dockelly | Posted in General Discussion on July 21, 2007 02:10am

which one, damp proofing seems enough since it isn’t living space. the lot flooded this week and the high water mark was 12″ up new foundation wall, inside foundation was dry though. figured some protection prior to backfill couldn’t hurt. if labor for waterproofing is the same I’ll do that. remeber once I backfill the water will no longer accumulate there, it will run away from house.

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  1. dockelly | Jul 21, 2007 05:20am | #1

    bump

  2. fingersandtoes | Jul 21, 2007 06:14am | #2

    I'm not sure what the choices are here. I've only ever heard of damp proofing. What would you do to waterproof it?

  3. VaTom | Jul 21, 2007 03:44pm | #3

    6 mil poly is adequate for our underground houses.  Scrap carpet to protect it from concrete and backfill rocks, but our backfill pressure is considerably higher than yours.  Obviously you need to get it covered before UV degradation.  Redundancy is good (multiple layers).  Water-shedding is the goal.

    Last house, the client insisted on a standard foundation drain.  Never saw any water from it.

     

    PAHS Designer/Builder- Bury it!

    1. davidmeiland | Jul 21, 2007 06:13pm | #4

      ... yeah, but if you HADN'T put it in...

      1. davidmeiland | Jul 21, 2007 06:16pm | #5

        I don't think waterproofing the foundation is going to do much if there is standing water above the bottom of the footing. Water will just seep under the footing and rise inside until its level matches the level outside. There is no real problem with your footing sitting in damp soil, although some soil types lose strength when saturated and then you have to worry about settling. From what I recall you are on sand and it shouldn't be a problem.

        On my current job I am waterproofing a section of concrete wall because it's above the interior floor level and below grade. First on the concrete will be bituthene, then a drainage mat over that to allow any water to go down to the footing drain without hydrostatic pressure against the wall.

      2. VaTom | Jul 21, 2007 09:11pm | #9

        You're probably right... 

        But after exactly the same experience at my place I didn't figure it was worth the effort.  My next place won't.  PAHS Designer/Builder- Bury it!

        1. davidmeiland | Jul 21, 2007 09:51pm | #10

          One interesting thing came up in a discussion re drainage with an engineer who is consulting on my project... subsurface drain piping helps to provide "make-up air" so that water leaving thru the soil or gravel can move more quickly. So even if no water is coming out of the pipe it may be helping water move anyway. You'd have to ask someone with initials after their name, or who charges 3 figures per hour.

          1. VaTom | Jul 22, 2007 04:02pm | #13

            That is interesting.

            After several years of no water activity, I buried my outlet (inlet?).  No apparent effect a decade later.  I think the client did the same.  Certain I'd hear if he got any water.  Wonder if that was speculation of fact-finding on their part...

            I try to stay away from engineers.  Spent a lot of money and generally got frustrated.  Has mostly to do with the local talent.  No initials (that I brag on), but some of my activities return 3 figures per hr.  I also do better with creativity than the local PEs.

            Have I missed a thread on your project?

             PAHS Designer/Builder- Bury it!

  4. User avater
    SamT | Jul 21, 2007 06:40pm | #6

    Kelly,

    Are you talking about protecting the concrete itself?

    If so, don't bother, it won't hurt it, in fact, the 'crete will just use the moisture to continue curing.

    SamT

    1. dockelly | Jul 21, 2007 07:20pm | #7

      Thats why I'm asking Sam.  Given my lot, the conditions of the soil etc. I feel like I'm doing unecessary work.  No matter what I do, what I now have is 100x better than what was there and should solve the problems I set out to solve.

      1. User avater
        BillHartmann | Jul 21, 2007 07:32pm | #8

        I don't even see any advantage to damp proofing it.The concrete and inside fill are just still going to wick lots of moisture.What is needed is inside vapor control covering both the floor and foundation walls..
        .
        A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

        1. dockelly | Jul 23, 2007 07:08pm | #22

          hey Bill,see my post, number 22, to Sam.

  5. User avater
    rjw | Jul 22, 2007 01:29am | #11

    Waterproofing a crawlspace?

    There's kind of a big hole on the bottom, ya know.

    Have good grading, extend the downspouts well past the overdig area, insulate and line the floor with plastic, and put conditioned air down there.


    With my mouth I will give great thanks to the Lord; I will praise Him in the midst of the throng. For He stands at the right hand of the needy, to save them from those who would condemn them to death.

    - Psalms 109:30-31

  6. User avater
    Matt | Jul 22, 2007 03:20pm | #12

    Damp proof.  Install a good foundation drain system around the exterior with, if possible, multiple sched 40 drain tails that exit to daylight.  It is best to put the drain tile pipe beside the footers.  Use filter fabric around the gravel that covers the drain tile. 

    Install a drain system inside the crawl spsce that is not connected to the exterior drain system.  This interior drain may not be as extensive as the exterior one, but must, if possible exit to daylight too. 

    Do a good job of grading.  Pipe gutter downspout water well away from the house.  Do NOT connect gutters to the foundation drain system.

    What is this crawl space foundation made of?

  7. renosteinke | Jul 22, 2007 05:03pm | #14

    I'd like to start off my post with two maxims that have served me well:
    A) Don't fix what isn't broken; and,
    B) Time spent on reconnaissance is seldom wasted.

    First of all, is there a moisture problem that needs fixing? Will a "repair" make it worse?
    If you manage to waterproof a crawl space - or a basement, for that matter - what you have made is a bucket. A bucket, as you might guess, keeps moisture in, as well as out.
    If condensation is a concern, then your solution is ventilation. Even placing a plastic sheet down is said to help ... but this practice is strongly opposed in some areas. I'd check around, and see if a plastic sheet is common near you. The plastic sheet, btw, is often placed under a thin layer of gravel.
    I will say this for the plastic sheet approach: if the ground is soft, the plastic and gravel spread your weight, making it much easier to crawl about. I've been in crawl spaces that required me to place boards in order to move about!

    Now, let me tell you about one of the darnedest things I ever saw. Imagine a house set at the base of a grassy hill. One rainy day, I went to enter the crawl space and .... not only was the crawlspace filled with several inches of water, this water was moving! Like a sheet, there was a continual flow across the width of the crawl space, where the water re-entered the earth as easily as it had exited. While the yard on the hillside was thoroughly soaked, there was no 'pooling' visible. The ground was that porous.
    To help drain that soggy yard, a 4" French drain was installed. I was impressed; at the slightest rain, water came out of that drain as if from a fire hose.

    Now, imaging if that crawl space had somehow been waterproofed. The first, and obvious, problem is that the yard would have become a lake- with water possible becoming deep enough to enter under the doors.
    Less obvious, but more serious, is that all the force of that water would have been pushing on that foundation. This almost certainly would have destroyed that foundation.

    So, moisture in the crawl space is best addressed withou8t trying to waterproof the space. Step #1 is to prevent the water from going there in the first place (French Drains). Step #2 is to give it a way out (ventilation).

    1. User avater
      BillHartmann | Jul 22, 2007 05:28pm | #15

      It might not have been clear without reading this whole thread and the other(s) that have to do with different parts of this project.But is new construction.And water proofing for new construction consists of applying a waterprofing barrier on the outside of the foundation wall so that the water will more likely flow into a drain pipe rather than wetting the foundation.But in this case the footing is setting below the water table anyway." If condensation is a concern, then your solution is ventilation."IIRC you are in Reno. He is in NJ. During this time of the year the dewpoint can be 70, maybe higher. Bring that air into a crawlspace and you can get instant rain..
      .
      A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

      1. renosteinke | Jul 22, 2007 07:38pm | #16

        Excellent memory; I am currently in Reno. I suspect that the debate over lining the floor with plastic is based upon regional climate differences, such as the differences in humidity, as you mention. Yet .... the 'river' I saw flow through one crawl space was in another area (Central California). Being set at the foot of that hill made all the difference in the world. I would not be surprised if that amount of flow was capable of actually relocating a house! The damaged / collapsed basement experience was in several areas of the midwest ...areas also known for humidity. Going below the waterline carries with it some specific engineering challenges. I've just seen too many times where a wall was sealed, with bad results. The force of tons of water pushing on the wall is regularly underestimated. Also, often overlooked, is that it is quite possible for a house to 'float' - basement and all. The effect of this can be very destructive. Here in Reno, one house I saw was severely flooded - even though the site would have appeared to have adequate drainage - by excessive snowmelt (it doesn't help when the Sierra Nevada runoff comes your way!)
        In that case, it was solved by building a (buried) barrier wall uphill of the house, with French drains on either side of the wall. This served to divert most of the water around the house ... and drain whatever got past that wall. Again, the flow from such French Drains must be seen to be believed!

        1. User avater
          SamT | Jul 22, 2007 07:56pm | #17

          For those who haven't read all three or four long threads, this house in on a beach. The soil is basically beach sand and sometimes the tide waters can reach around the house.The house was jacked up and the new Tee foundation poured underneath.The primary concerns with water here will be making sure there is a way for it to get out of the crawl space once in a while.SamT

          1. User avater
            BillHartmann | Jul 22, 2007 08:04pm | #18

            SamIIRC correctly the whole area, inside and outside is being filled in so that it is above the water level.But that also means that lots of moisture will be wicking through the fill and concrete walls..
            .
            A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

          2. User avater
            SamT | Jul 22, 2007 09:27pm | #19

            Bill,If my link to prospero hadn't picked just that time to go bad, my next post would heve been there berore yours.SamT

          3. User avater
            SamT | Jul 22, 2007 09:48pm | #20

            Kelly,In regards to what Bill just said and in consideration that you will be seeing high water;Insure that the crawlspace rat slab is graded so as to direct water out the access hole. Place visqueen under the rat slab to help keep the moisture level there down as much as reasonable. If I had thought of it in time, I would have suggested another access hole on the prevailing wind side. Oh well.One labor intensive solution would be to also apply visqueen or vapor barrior insulation to the underside of the house floor.Because of the odds of occasionaly having saturated sand under the house, you need to think about the fact that water needs to be displaced with air in order to flow if you use a vapor barrior under the rat slab. As I see it, you could drill 1/2" holes every ten feet thru the rat slab and underlaying visqueen without greatly compromising the vapor barrior aspects. Or, under the vapor barrior you could lay a loop of 1/2" PVC using Tee connectors whereever you connect two pipes together. No need to glue anything, just slip together with the open leg of the Tee facing mostly down. Again, leave an air vent about 10' - 12' OC. One or both ends of the vacuum breaker loop should terminate up between the floor joists with some green kitchen scrubby stuffed in it/them as a bug barrior.SamT

          4. dockelly | Jul 23, 2007 07:07pm | #21

            Hey SamMy house is on an island one block from the beach. It floods, the lot not the house, with heavy rain. I believe this is more due to it not being redeveloped in 125 years whereas all the neighbors and the road have come up in height making me the low spot. So everyone drains to me. Only with a hurricane or noreaster will the water table rise so much the rainwater flows out of the storms drains due to the bay having unusually high water. We just had an extensive beach and dune replenishment by the Army corp of engineers which should help. Never had the tide breach the old dune in many years, over 50-60 I think. I'm more inclined to put plastic under the floor, maybe with some weep holes, as a vapor barrier. Might just have it sprayed with closed cell and get insulation and vapor barrier in one. I'm still on the fence about pouring a concrete slab, I'll speak with the BI as to what's best. Only about 3 1/2 yards at 2" thick, so it's not the cost, I just want to avoid creating rather than solving a problem. As to a second access door, I have 10 vents in addition to the access door allowing about 900 sq inches of venting where only 560 is required. 5 areas in the wall had to be left for the steel to come out once they set house on foundation. I could probably stack one vent on top of the other in those location which would add 300 sq inches bringing me to 1200 sq inches. the stacked vents would not be visible due to the front and side porch so it wouldn't look out of place.I spent all day there yesterday shoveling the fill into the foundation, about 20 yards. I was there the day before with a mini bobcat and dumped some inside the wall, but most had to be dumped near the wall as the steel, etc kept me from getting in close. it's about 90% filled, except where the cribbing piles are, which I'll fill after house comes down through holes in foundation or flooring which is getting replaced anyway. fill is 18 inches from top of wall, making the dirt under house almost 2 feet higher than it was! this height was determined by neighbors lot level. I doubled checked it yesterday just to make sure, it was correct. when i back fill and grade away from house, i think i'll have solved the problem. if some future storm floods the crawl space after all this work i can always access it easily and pump it out. if i do end up pouring a ratslab i'll grade it as you say to the access door.thanks
            kevin

          5. User avater
            SamT | Jul 23, 2007 07:29pm | #23

            Why don't you put the backfill you think it'll take in piles next to the cribbing now? Then you'll just have to move it into the holes the cribbing leaves.Just a thought.SamT

          6. dockelly | Jul 23, 2007 10:59pm | #24

            The one hole left by the cribbing is by the access door the other is where two breaks in the foundation are to allow steel and the final one is almost under the hole in the floor where the fireplace was.  the fourth is outside the building.  house mover stipulates the fill be level and I box out the cribbing by at least 3" all around, which I've done.

             

            and the other reason is i'm sick and @#$ing tired of digging, at least for now:)

            Edited 7/23/2007 4:01 pm ET by dockelly

          7. User avater
            SamT | Jul 23, 2007 11:51pm | #25

            SamT

          8. Snort | Jul 24, 2007 02:33am | #26

            Have you checked with inspections? We have to have a damproofing/perimeter drain inspection before we can backfill. Drylok is what most foundations get...and most inspectors will tell you that they know it doesn't hold up over time...but ya still gotta have it!...now waterproofing, that's a whole nother story<G> Someone's got it in for me, they're planting stories in the press

            Whoever it is I wish they'd cut it out but when they will I can only guess.

            They say I shot a man named Gray and took his wife to Italy,

            She inherited a million bucks and when she died it came to me.

            I can't help it if I'm lucky.

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