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Floating concrete slab

Dinosaur | Posted in Construction Techniques on June 21, 2006 10:02am

Yesterday I got dragooned into building the forms for a monolithic pour of a floating floor slab. It’s for a garage, 25×30, IIRC. The structure will be SIPS combined with timberframe elements.

The GC is the HO; he’s a master electrician and licensed carp, so he’s no dummy besides being a very nice guy on top of it all. The project is architect-designed and engineer-stamped, and aside from a plethora of gables sticking up all over the place, it’s pretty straightforward.

The plans call for a trapezoidal-section footing around the perimeter of the floor slab. Here’s what it looks like on the drawings:

View Image

The foam panels are 2″; the slab thickness is 4″; the footing depth is 16″ on the outside; top width of footing is 16″, and it’s 8″ wide at the bottom.

Here’s what happened:

We had just fininshed building and staking the forms when the concrete supplier showed up to schedule the pour. We were in the process of digging the footing trench when he got there. First thing he did start hollering it was too deep, then he grabbed a rake and started raking sand back into it and flattening out the 45-degree slope to about 10 degrees. When he got done the trench had no defined bottom section; it just sort of sloped down shallowly towards the perimeter over about 24″. He had about a 12″ depth at the outside edge of the footing.

I didn’t like this much, but it’s not my project so all I could do was mention diplomatically to the HO/GC (who had four other problems to deal with at the same time) that maybe he’d like to show the concrete guy the plans and take a decision himself as to how we should do it.

He did that, and we started re-cutting the slope and defining the trench bottom as per plan but the concrete guy just kept hollering that the plans were worthless and raking the sand to flatten out the profile. Along about this time a provincial inspector looking to check licenses on the site showed up and the HO had his hands full with that, so Mr. Concrete-head had his way. None of us were in a position to tell him to f*ck off and the pour was scheduled for the next day. So….

I bailed at the end of the day; the HO’s a nice guy but I don’t need that kind of grief.

Here’s the question: 

I know approximately buttkiss about floating slabs; I’ve never done one before and am a bit skeptical (over conservative, maybe?) about their ability to survive this kind of climate over the long haul. But it seems to me the shape of that footing wasn’t pulled out of a hat just for fun; it looks to me like it has some structural or thermal significance.

Brownbagg? Any of you other concrete experts? What’s the story on this sort of thing?

Dinosaur

How now, Mighty Sauron, that thou art not brought
low by this? For thine evil pales before that which
foolish men call Justice….

View Image

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Replies

  1. GHR | Jun 21, 2006 10:10pm | #1

    There are 3 critical dimensions:

    1) min slab thickness (4" on your job)

    2) min edge depth (16" on your job)

    3) min width at the bottom of the edge (8" on your job)

    The angle has little effect.

    We always try to follow the plans.

    1. brownbagg | Jun 22, 2006 12:06am | #5

      the width of the bottom is the bearing surface for the weight of the structure. It has to be at least a foot wide, normal is 18 inches. the height of the slab at edge combine with the width at the bottom is the footer. the 45 degree to 10 degree is not really important but the 45 will control cracking and ten will not.But very important. If you have prints with this section in detail, that is the law you have to build this way, no matter what. No matter how you hate it. If that building fails for any reason, the designer off the hook. and only thing the finisher has is a beat up truck, so which do you want to have the liability on it.I look at life like this. a truck driver is a laborer with a driver license. a concrete finisher is a truck driver with a dui. they all arrive in the same van.Its costing the concrete guy no extra money to do it by plans.get rid of the concrete guy today.added: no rebar in footing, code is 2 #5. I always use 3#5Edited 6/21/2006 5:07 pm by brownbaggEdited 6/21/2006 5:08 pm by brownbagg

      Edited 6/21/2006 5:09 pm by brownbagg

      1. DonNH | Jun 22, 2006 04:23am | #6

        My read of what he said was that the change from 45 to 10° was to flatten it out, which would essentially widen the footing and make the transition from the slab to the footing less sharp resulting in less of a stress concentration.

        Uses more concrete, though.

        Don

        1. brownbagg | Jun 22, 2006 05:27am | #7

          here how I did my garage

      2. User avater
        Dinosaur | Jun 22, 2006 07:14am | #9

        Take a look at the sketch I posted in my reply to Piffin. That profile doesn't look anything like the way you dug your forms for the garage. In your pic, I see a sloped transition and a flat-bottomed trench. Here, it's all transition slope, no bottom.

        I understand about the legal point you raised, but in that I was just there as a nail-banger that's beyond my purview. The HO/GC is a qualified carp himself as well as a master electrician; he owns a large electrical contracting company and has built or been involved with building numerous buildings. He probably knows the law on stuff like this better than I do. I did what I could do.

        What I'm interested in is learning how these so-called floating slabs work mechanically. We're in a climate where the frost line is between 4 and 5 feet down. Given that, I figure there has got to be some frost heave on a slab sitting on the surface. So how critical all these design parameters are is of real importance to me if I ever wind up building one myself.Dinosaur

        How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....

      3. ericicf | Jun 23, 2006 04:05am | #12

        Surely you jest... some of us concrete finishers are illiterate dope smoking  morons, which is usually a step or two higher than GC's who really are frustrated framers drooling for their next six pack, pretending and posturing pomposly their higher value to all those who pretend to listen.

         

         

        1. brownbagg | Jun 23, 2006 04:28am | #13

          no jest

  2. Piffin | Jun 21, 2006 10:23pm | #2

    IMO, The edge thickness is the important part but even more so, the placement of the rebar, which you haven't mentioned. I do same slabs here with 12" thickened edge but there's a dual run of #4 rebar there and 18" of compacted inch-minus...

    The crete guy sounds like a prima dona, but the angle is nothing to lose slepp over either way.

     

     

    Welcome to the
    Taunton University of
    Knowledge FHB Campus at Breaktime.
     where ...
    Excellence is its own reward!

    1. User avater
      Dinosaur | Jun 22, 2006 06:59am | #8

      To reply to your comments and the next few at the same time:

      Yes, this concrete guy is a prima donna; a classic loud-mouth, the kind you love to hate. If it were my project, he'd have been gone very quickly. But it's not; I hired on to this one as a simple carp to help the HO out of a time jam. Best I could do was diplomatically suggest he order his concrete sub to follow the plans...which he did, but that didn't work either. The concrete guy just ignored him, stated loudly in rapid-fire French that the plans 'weren't worth sh!t', and went back to doing it his way, raking sand back into the trench we'd just dug to spec for the second time.

      In any event, I walked at the end of the day for that plus other reasons. I like the HO, but I won't let his subs become my problem.

      What I'm interested in are the technical aspects of building this kind of slab. The way the concrete guy kept filling in the trench we'd dug, the edge thickness was reduced to about 12" from the 16" spec'd on the plans. He also changed the flat-bottomed trapezoid into a triangular footing with the point down, like this:

      View Image

      The angle itself may not be that important, but there's no horizontal bearing surface under that footing. That's what bothered me most but I don't really know if it's significant.

      Seems to me with all the weight of the building sitting on top of that triangle, it'll be trying to shove that pointy part down into the sand and will want to snap the whole footing right off the slab. Removing the horizontal bottom of the footing changes the angle of resistance and creates a pivot point right at the weakest part of the structure...or so I see it. Am I imagining things?

      As for re-bar, there is none spec'd but the plans call for 4x4 wire.

      The site was vibration-compacted after excavation, but the footing trench was dug and raked back in and re-dug and re-raked in again. There's a good two to four inches of loose, uncompacted sand in the bottom of that trench. No gravel added. This is all in natural sand 5 or 6 feet deep.

       Dinosaur

      How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....

      1. JeffHeath | Jul 02, 2006 10:16pm | #35

        Dinosaur

        I don't hang out much here, and just read this thread.  I'm usually over at the Knots.  However,  I've been a mudjacking contractor for 20 years, and can lend a little to this discussion, as I've been repairing these blunders for a long time. (Mudjacking is raising settled concrete, in case you didn't know!)

        First of all, the way that the grade beam (outside perimeter) of the floor was designed with a flat bottom was correct.  (That is, for a slab supporting structure.)  The way that your prima dona concrete guy changed it is way wrong.  The slab will crack where the thickness change occurs, since the pointed edge will want to settle into the uncompacted soil, especially with the load of a structure on it. 

        I have seen these crack off and actually push out (horizontally) as much as several inches over 30 years.  They're alot of fun to repair, and very expensive.

        If the HO is your friend, you should advice him to get rid of the concrete guy, and get a different one who will pour as spec'd.

        This slab will settle and crack, and the building will lose it's stability fairly quickly.  As a company we repair about 1500 + of these structures per year, so I've seen just about every possible mistake that can be made in construction.

        Good luck.

        Jeff

        1. User avater
          Dinosaur | Jul 02, 2006 11:04pm | #36

          Thanks for the input; as I said in that little update, I was glad to see the HO and his remaining crew re-did the excavation to spec after the concrete supplier left. Like I said up front, the HO is no dummy by anyone's standards; the main problems he has are (a) a spiteful neighbour who keeps filing complaints with every AHJ she can think of; and (b) too much work to handle with not enough time or qualified manpower available to him due to (a), among other things.

          Once the concrete guy was off site and the latest inspector had gone back to his office to 'think things over', the HO was able to take a deep breath and focus on the problem clearly.Dinosaur

          How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....

          1. JeffHeath | Jul 03, 2006 01:06am | #37

            I hadn't read the entire thread.  Sorry.

            Jeff

          2. Piffin | Jul 04, 2006 04:37am | #38

            Never apologize for contributing solid information here 

             

            Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

          3. brownbagg | Jul 04, 2006 04:48am | #39

            apologizing is a sign of weakness

          4. Piffin | Jul 04, 2006 04:59am | #40

            or of good manners, depending on the setting 

             

            Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

          5. JeffHeath | Jul 04, 2006 08:21am | #43

            The apology was tongue in cheek.  As far as I had read through this thread, nobody had given the original poster all the answers he was seeking.  I've been repairing those issue's professionally for 20 years, so I thought I'd chime in.  Being an occassional visitor to breaktime, I didn't want to "stomp" on anybody's toes.

            Anybody who thinks an apology is a sign of weakness should, well, lol, try arm wrestling with me.

            Have a great day.

            Jeff

          6. Piffin | Jul 04, 2006 08:44am | #44

            Glad you're on board 

             

            Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

          7. JeffHeath | Jul 04, 2006 09:21pm | #49

            Thanks, Piffin.  BTW, I don't know if you remember, but you helped me out about 6 months ago with info regarding replacing a floor, joists and all, in my house.  Thanks.  Your advice was excellent, and the addition turned out great.

            Jeff

          8. Piffin | Jul 04, 2006 09:27pm | #50

            So don't be shy, add top the knowledge base and the excitement 

             

            Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

          9. brownbagg | Jul 04, 2006 05:40pm | #45

            Anybody who thinks an apology is a sign of weakness should, well, lol, try arm wrestling with me.you dont watch much TV, do you.

          10. JeffHeath | Jul 04, 2006 09:19pm | #48

            No, I don't.  I work too much.

            Jeff

          11. brownbagg | Jul 04, 2006 11:09pm | #52

            that remark : "Never apologize shows sign of weakness" is from the tv program "NCIS"“Our country! In her intercourse with foreign nations, may she always be in the right; but our country, right or wrong.”

        2. jrnbj | Jul 04, 2006 06:58am | #41

          Can I pick your brains about repairing cracks in poured foundation walls?

          1. JeffHeath | Jul 04, 2006 08:16am | #42

            Ask away.  Epoxy injection is the chosen method for cracks in foundations.

            Jeff

          2. jrnbj | Jul 04, 2006 08:06pm | #46

            Here's a post from a few days ago, describing the situation....."The previous HOs had done a sloppy patch job on the wall, so one day I thought I'd chip off the patch, investigate the damage, & maybe get one of those nice epoxy crack injector kits & try & seal it off right.
            I started chipping, but got tired of wet sludge on my shirt, so I had the bright idea of drilling a 1/2 " relief hole down by the floor, to let the seepage drain in a controlled way. Ten minutes with the trusty AEG & bit, & here comes the flood (see the pics). I'm sure I've hit a water line (the water coming out is clear as daylight), but there is NFW, given the layout of the house. Well, no worries mate, it'll just run down the channel to the floor drain...not!! (see my New York plumbing post).
            Basement starts to fill up...I do the Dutch boy act, grab a scrap of wood, whittle a plug, pound her in, and catch my breath; then spent the next 2 hours with 2 jugs, must have drained 100 gallons into the sump pit before the reservoir ran down to the level of the hole. Rain or shine, ever since then, I pull the plug & out comes the flood.
            I spent lots of time on the web, checking out structural crack repair kits (Hilti no longer carries the kit, just bulk lots of epoxy, ports, etc. plus expensive guns).
            Been putting it off, hoping it'll dry out a bit more this summer....not!
            Last week, a neighbors' having some flatwork done down the street, & so I end up chatting with the concrete guy, ask him if he knows anyone up here that carries professional grade crack repair stuff...no, but he has the RIGHT way to fix it.
            Chip out the crack, with a nice dovetail, from above outside grade & down to the slab, & chip out about a square foot of the slab. Get a piece of 3/4 plastic hose, bed it in the crack & down into the gravel below the slab. Mud up the slab & a foot or so up the wall, pull up the hose, & repeat the process till above outside grade. Water drains down the hose hole, & off to the sump pit.
            I'm thinking, sounds brilliant...but will it work.
            What do you all think, & what kind of mortar would you use. I spent ten minutes at the HD, looking at Sikka's quick patch, and Quickcretes' different offerings-non shrink grout, waterstop, patching cement- and walked away wishing manufacturers had to list ingredients...sometimes I think Quickcrete has 1 mix, & just puts it in different bags (cynical, I know....)
            I'm gonna try the hose thing, but can't decide on the mortar...I'm leaning toward the NS grout, but I could be convinced otherwise..... "For what it's worth, I've been in construction for 30 years, so I'm not flying blind here....
            Once I saw cut & chip out the crack, & lay the tube in there as described above, I'll have a 2 inch wide by 2 inch slot, which is pretty big for epoxy, and anyway, I probably wouldn't be able to slide the tube out. I'm pretty much committed to trying the tube thing, but I still haven't figured out the best mortar to use.....I can go with a nice latex modified repair mortar, or Tapcon a board to the wall as a dam & use more of a flow-able grout mix (the slab part will be regular fast set concrete, of course)
            All-in-all, the whole thing's a big PITA....the proper fix (of course), as some other people posted, is to attack the water problem from the outside, but I'd have to demo my garage slab, which I can't do at the moment.
            The crack isn't structural, it's a seeping cold joint....I need to fix the inside now, & then eventually I'll redo the garage slab, & fix the drainage then. Just can't settle on the mortar for the temporary fix.....

          3. JeffHeath | Jul 04, 2006 09:18pm | #47

            OK

            Proper repair technique would be epoxy injection.  The water is not a problem.  Actually, it will help a great deal.  We use hydrophobic epoxy, which comes in a 2 part gel pack.  It will require a special injection caulking gun, about $45, which is a drop in the bucket compared to what you're dealing with.

            You will drill 3/8" holes into the crack about every 12" to 18" from floor to ceiling, about 2" into wall.  Then, insert some semi rigid 1/4" tubing (the port for injection) into the holes, and leave it about 1" proud. 

            Now, forget that crap at Home Depot.  You need some topical epoxy, 2 part mix, made for masonry.  We use a product called Rezi-Weld.  Mix it up, and smear with a 4" trowel about 3/16" thick down the entire crack, making sure to seal around the "ports" real tight.  Let it harden till it feels like glass.

            Hydrophobic epoxy reacts with water and swells (just like that spray foam insulation crap) with immense pressure into all the cracks in the wall.  We can sometimes see it coming out the outside of the wall if squeeze in too much, which is not a bad thing. On dry cracks, we actually have to squirt water into the ports to get the epoxy to react.

            Now, and here's the important part, have enough 1/4" X 2" hex head machine screws on hand to screw into the "ports" to cap them so all the epoxy doesn't ooze out.    Inject from the bottom port up, and keep squeezing the epoxy in until it comes out the port above, and cap, and move up, etc. etc. etc....

            You should be able to find these products at your local concrete supply house.  I have 2 with 10 minutes of my house, so I'm sure there's one near you.  They'll have all you need.

            Forget the dovetail, and forget the quickrete water tite cement crap from HD,  none of that stuff lasts long.

            I gave a lifetime warranty on all our work, and in 15 years as a waterproofing contractor, I had to redo 1(ONE) crack.

            Jeff

      2. Danno | Jul 04, 2006 10:32pm | #51

        IMHO, you are right. Sand raked back into the hole doesn't sound like something to rest a footing on. And a wedge shaped footong, seems to me, will want to plow its way deeper into the earth and put stress right where the slope changes from horizontal to ten degrees. Just sort of my "intuition". The main thing is, like others said, you had a stamped plan, the concrete guy should have followed it.

  3. User avater
    IMERC | Jun 21, 2006 10:33pm | #3

    yur lacking #4 or #5 rebar at the bottom third of the footer..... is there any...

    Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming

    WOW!!! What a Ride!

    Forget the primal scream, just ROAR!!!

  4. sungod | Jun 21, 2006 11:09pm | #4

    Did you get the feeling the concrete guy was try to get the sharped angle out to prevent a crack or was it done to reduce amount of concrete? Hopefully the dirt was fully compacted underneath it all, after loosening it.

  5. User avater
    draftguy | Jun 22, 2006 05:27pm | #10

    I agree with the other opinions, FWIW. No rebar. Lack of depth/thickness at the edges. And the only time I've seen the slab turn that shallow is when the floor is coming to an opening (i.e., the garage door), and then the slab is keyed into a poured foundation below.

    And I'm kind of surprised that the original design doesn't meet frost depth (I originally thought from the first detail that the slab was just coming to the inside edge of the foundation and the owner wanted to make extra sure the slab didn't heave anywhere).

    Maybe a dumb question: if it's a detached garage is the 2" of foam necessary? Will he be using it as a workshop also? Seems like some misplaced values to worry about the cold if so little consideration is going into what's holding the walls up.

    1. User avater
      Dinosaur | Jun 22, 2006 07:03pm | #11

      No, there's no frost wall. What I drew is what he's got. They call it a 'monolithic floating slab'; the theory I've heard is if there's any frost heaving it will move as a unit and not crack. This is where my innate conservatism kicks in...but my intellectual curiousity also wants a piece of the action. Hence this thread.

      Up until about '95, no one had ever done one of these around here and local authority wouldn't approve them (although they were common in Ontario). Then the father of one of my former carps got stubborn (he's an engineer) and pushed the issue for a chalet he was building for himself. It took him a while but he bullied them into approving the project. I haven't heard how it worked out, though.

      Yes, he'll be using it as a workshop. There is an attached garage on the main house for vehicle storage. This one will be for storing the ATV's, tools, and toys. There will be electric radiant heat in the slab; again, this is something with which I don't have any personal experience, as it's not common here except for the kind of very high-budget projects I don't usually get near. I vaguely remember reading something about the insulation being there more to keep the ground cold than to keep the building warm, but it was a long time ago. I could be mixing up two articles about different topics. Damned CRS....Dinosaur

      How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....

    2. Piffin | Jun 23, 2006 11:32am | #16

      Some of your questions would be answered by researching the term "frost protected shallow foundation" which is what we call a floating slab like this 

       

      Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

      1. User avater
        draftguy | Jun 26, 2006 05:06pm | #27

        'Some of your questions would be answered by researching the term "frost protected shallow foundation"'Will do. I've heard of the concept before but thought it was used in more southern climes. Maine and Montreal are a lot further north than where i'm at, and i'm pretty sure our permit officials would have some problems with it (even despite proof to the contrary).

  6. User avater
    trout | Jun 23, 2006 05:19am | #14

    There's a good two to four inches of loose, uncompacted sand in the bottom of that trench.

    That's good for at least a half inch of settling.  If the ground in the middle of the slab is well compacted there are some stresses that don't need to be there.

    What I don't like about many concrete guys is that they are never around when the cracks start showing up and can't be held responsible.  Many also don't check on their work after it's poured and don't learn anything from their mistakes.

    Frost protected foundations aren't anything new.  The foam insulation under the slab and projecting out from the slab helps retain the natural heat rising from underground and thus altering the frost line near the foundation.

    Here is a very good source of information:

    http://www.cs.arizona.edu/people/jcropper/desguide.html

    Unlike the foundations, I've never seen guidelines on using foam insulation to protect shallow pipes from freezing, but we've used it successfully when plumbing has to cross rocky areas.  4" of ridgid foam extending 3' on either side of a pipe is very unlikely to freeze in the coldest months of the coldest locations.

    In areas that litterally have no other choise but to leave the pipe shallow and insulate the heck out of it, it's quite easy to monitor the installation to make sure it's below the frost line by using an inexpensive remote thermometer.

    :-)

    1. User avater
      Dinosaur | Jun 23, 2006 06:30am | #15

      We use foam board to insulate shallow water lines in the manner you speak of, but we also usually install a heating wire inside the pipe itself out to where it gets deep enough in the lake so it can't freeze. That's about 5 to 6 feet down in water. In a bad winter where there's severe cold before the first big snows, ice can get 4 feet thick quite easily.

      The most vulnerable point on those water lines is where they pass into the lake. Dredging a deep trench right into the lake bottom is usually not an option because of environmental regulations, so the pipe is at ground level where it enters the lake. Until there's three to four feet of snow cover on the ground, a water line with still water in it can freeze right there in a very short time when the air temps hit -40C. The heating wire makes it possible to melt it clear.Dinosaur

      How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....

      1. BryanSayer | Jun 26, 2006 05:31am | #25

        I'm so glad you mentioned putting the heating wire in. I'm amazed at the number of people who seem to think that insullation some how HEATS pipes. The thought that if it stays at 30 degrees F long enough, it doesn't matter how much insullation you have never crosses their mind. I remember one person asking how much insullation they needed around the pipes of their summer cabin to keep them from freezing in the winter when the cabin was not occupied for 4 or 5 months.

        1. User avater
          Dinosaur | Jun 26, 2006 08:02am | #26

          Yeah, and I'm amazed at the number of people who think insulation only works in one direction, too. You gotta sing them the Flanders and Swann version of the laws of thermodynamics and even then they often don't get it.

          Just tell 'em: "Think of cold as a sponge that soaks up heat...."Dinosaur

          How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....

          1. BryanSayer | Jun 26, 2006 05:21pm | #28

            You would think with all the thermos bottles out there that "keep hot foods hot and cold foods cold" they would make the connection. Oh well.

          2. User avater
            Dinosaur | Jul 02, 2006 03:29am | #29

            Huh. That presupposes they know how to read....

             

            (Sorry I didn't see this last week; I never got the notification--at least I don't think I did. Spammers been jamming the inbox a lot lately....)Dinosaur

            How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....

          3. User avater
            Dinosaur | Jul 02, 2006 03:38am | #30

            An update seems in order on this slab. I had to visit the site again last week to pick up a check from the HO, and while waiting for him to get back from the lumber yard, took a look at the slab...which still hadn't been poured.

            I was pleased to note that excavation had been re-done again--this time inconformity to the profile and depth specified in the plans. They'd also added 2 rebars to the footing, properly tied off and floated, and laid in the blueboard properly. The specified wire grid was also laid in, and the underslab electrical runs done correctly in pvc conduit with emt risers and w/t unions. So everything looks kosher and the HO should be okay as long as numbnuts doesn't bring his rake with him when he shows up to do the pour....

            The only thing I couldn't figure out was one 12'-long section of in-slab heating wire along the perimeter which was zigzagged deliberately on a 6"-wide pattern (tied off to alternating sides of the grid row), while the rest of the heating wire runs were straight loops.Dinosaur

            How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....

          4. jrnbj | Jul 02, 2006 03:55am | #31

            Get's more heat at the edge, where you need it more......

          5. User avater
            Dinosaur | Jul 02, 2006 05:38am | #32

            Yeah, that would be logical, but it was only for about 12' of a 30-foot run, and only in that one spot. Can't figure it. Oh, well....Dinosaur

            How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....

          6. User avater
            BillHartmann | Jul 02, 2006 05:39am | #33

            Is that where there is going to be an apron and door?Probably more loss in that area.

          7. User avater
            Dinosaur | Jul 02, 2006 06:19am | #34

            I wouldn't think they'd put the door there; it's in the front half of the left side, facing the woods. Possibly there's a walk-in door slotted to go there. The vehicle-access side is covered by the return loops. I'll ask the HO next time I see him. We may be able to go back later in the summer if he gets his permits squared away. A lot depends on how persistant in filing complaints his gnarly neighbour is, tho.Dinosaur

            How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....

    2. Piffin | Jun 23, 2006 11:42am | #17

      " 4" of ridgid foam extending 3' on either side of a pipe is very unlikely to freeze in the coldest months"The Univ of Maone did some research testing on this dealing with the foundations for pods under light poles in parking lots. Since the snow gets plowed opff there is none to temper the frost and several were heaving out and tilting. As I remember they used thermometers buried at several locations and determined that 2" of foam XPS extending 4' on each side when buried a foot below surface would protect from freezing. 

       

      Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

      1. User avater
        trout | Jun 25, 2006 12:51am | #18

        As I remember they used thermometers buried at several locations and determined that 2" of foam XPS extending 4' on each side when buried a foot below surface would protect from freezing.

        Thanks for passing that on.  It's a subject that is hard to find real information on, or even adecdotal non-scientific examples.

        As you know, rocky points are favorite vantage points for foot or home bound gawkers.  There are a bunch of these ridgetop mountain lots with lots of rock under a shallow layer of topsoil.  Getting lines from the well to the house and from the house to the leach fields can sometimes be interesting.  

        1. Piffin | Jun 25, 2006 12:44pm | #19

          Yeah, the house I'm just finishing currently has the line 2.5' down. My design elevations call for adding another foot of soil right there but the landscapers are trying to circumvent that, so we argue...Mother Nature will win that arguement 

           

          Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

  7. Hainesportwoodworker | Jun 25, 2006 07:06pm | #20

    If that concrete guy had shown up on my job and touched any of my work I would have shoved that rake up his .... I would assume the plans were the product of an engineer or architect that were at some point prior to construction reviewed by the local code official. At that point you have no option other that to follow the plans without deviation. I could loose my liscense by doing otherwise and probably fail my footing inspection.

    Didn't the local code official inspect the forms prior to pouring the footing?

    Also, the lack of rebar is strange - based on past projects we would have probably used 3 - #4 rebar - we use the plastic triple rebar chairs that don't require wire ties

    Additionally - we are real careful never to "fill" or rake any loose soil into our prepared forms - you really need to mechanically compact this fill if you do, and then, only in layers or 6" at most.

    1. User avater
      Dinosaur | Jun 25, 2006 09:39pm | #21

      Your assumptions are all correct, and your impulse is the same as mine. I couldn't do anything about marrying the rake to the concrete guy's nether regions because it wasn't my project; I was there as a nail-pounder, not as a PM.

      I don't know if the 'city' inspector came to watch the pour; I was gone by then. I won't work on a project where that sort of stuff goes on.Dinosaur

      How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....

      1. brownbagg | Jun 25, 2006 10:15pm | #22

        the bad part is. I meet people like that daily, you can either argue for hours and hours are you can pour it wrong and be home by lunch time. It has gotten lately, "I cant see it from my house."

        1. User avater
          Dinosaur | Jun 25, 2006 10:39pm | #23

          I figure I can fix just about anything once time has its way and stupid decisions catch up with the people who made them. But fixing a foundation once the building is built isn't worth it. Also, I don't like thinking about the builders and future occupants who won't know until it falls on their heads and they get hurt or killed.

          So if it looks like it's gonna go south and I can't stop it, I wash my hands and vote with my feet. I always hope the failure will be incremental rather than catastrophic...but I won't bet on it.Dinosaur

          How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....

  8. woodway | Jun 26, 2006 03:09am | #24

    I have two comments and one suggestion:
    Anyone who uses the word "plethora" in a sentence is probably right much of the time.
    How many times have we all heard or said the words, "down to undisturbed earth".

    Now my suggestions, get a different concrete guy cause he is a total nut case. Any fool who's in the concrete business and would rather improperly fill in a footing with loose soil to avoid selling more concrete is not someone who's fully in charge of their faculties. Sounds to me like his mother is still buying clothes for him.

    Tell the homeowner the full story and make sure he's aware that loose soil in the footings is not good practice. If he's a licensed carpenter, whatever that means, then he probably already knows this.

    If the homeowner is a nice guy, make sure he finds some other source for concrete. There's a reason that concrete suppliers and just that and not in the framing/forming business.

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