I am in the market for a new concrete sub my old one is moving out of state. On all my foundations we go with 9′ pours and everything we build is a walkout. On the walk out walls he would use a inverted footing for frost wall protection. Well I have looked at 2 crews and my problem is the don’t like to the inverted footings, the want to go with 11′ walls.
Now to me this is very wasteful to do, I have never had a problem with the old way. Dose anyone use this type of wall pour? and why? Makes me think more about starting my foundation crew even more.
Replies
Can you explain what an inverted footing is? Never heard of it,
Rik
what we call a inverted footing is a 24" x 8" footing with a 8" x 24" trench under the footing poured at the same time the 8"x24" wall provides frost protection. Basically It looks like a short wall pour turned over. By the way the 8" wall is held to the outside edge of the footing.Edited 12/11/2005 1:00 pm ET by byoung0454
Edited 12/11/2005 1:03 pm ET by byoung0454
Can you describe an inverted footing?
The 'crete subs here pour footings at about 18" wide by 8" thick, then build the wall on top.
We woodframe most all walkout walls, sitting them on the frostwall.
Rather than starting a new thread I'd recommend just giving your a first one a bump by replying to your initial post with just about anything.
Re your concrete sub issue, I'm not familiar with the term inverted footings, but it sounds like you want to build walk out basements that do not have full height concrete walls on the walkout side, which is very sensible. My advice is to keep looking for a wall crew who does it like you want. Around here, walkouts with full height concrete walls on the walkout side would be the exception.
the problem is your subs are trying to run the job and design it their way. tell them to do it your way or get off the job. It doesnt mattter what method is best, it must be done the way the print says.
I agere with you and that is how I have put it. My thing is their way is so wastful to do. The size of houses we build it could leed to 10yards of unneed concrete in my opion.
I've never seen an inverted footing, sounds interesting.
What I don't understand is why your new subs are proposing 11' walls based on just pouring you a frost wall instead of doing the inverted footing. I don't see how the two are related.
If you want 9' basement walls, that's what you get. The walk out footing should be lower than the other footings enough so that you can pour a frost wall high enough to catch your framing at the appropriate height.
They say the don't like to step the foundation wall, afraid it will be a wall crack later. So they want to dig down the the same footing height as the frost wall, that's were they get the 11' pour. To be honest I like the idea of the footings being at the same plane as the other to avoid the step in the foundation.
Edited 12/11/2005 4:57 pm ET by byoung0454
Byoung,
Your subs are either A) ignorant, B) don't care about value, C) lazy, or D) all the above.
The foundation, AKA stemwall, should extend from the footing to no less than 6" above finished grade. The top of the footing should be at or below the frostline at all points. That means step footings. It also means walls from 0" to ??, not 11' or 9' or any other arbitrary dimension.
A proper step footing and foundation will not crack beyond allowable tolerances. In the field, that means the thickness of a dollar bill, not penetrating full thickness of the wall and not extending to any perimeter of the wall, after 28 days curing.
Ya wanna no how I figger wall heights?
(Top of Footing EL + Finished Basement Floor El + Finished Ceiling El + Bottom of Main Floor Framing El + 1/4" Wall Finish Clearance) Rounded Up to nearest 1/4" = Wall Height
With my Owner Builder clients, I reverse it. First we determine their main floor finished elevation and establish a benchmark. Then we work down through their framing to the finished basement floor elevation, then determine finished landscape grade. Finally we consider the frostline. I do all their pour elevations from the benchmark we set at the first stage of this planning.
{Quality ∫ Cost}=Value
If Quality or Value is highest in your estimation, give me a call. I emailed you my number.
SamT
No, no, no Sam. You set your forms and pour to the top of the panels so you don't have to mess with trying to pour and trowel to grade nails.Your post reminded me of seeing numerous "walkout" basements in St. Louis, built by the local big-name production builders, that had 8' high EXPOSED concrete walls at the back of the house. There would be patio doors in the walkouts, trimmed to the concrete. I guess the builders didn't want to have to frame any walls for the floor system and they didn't bother setting any nailers in the concrete for siding attachment.Quite easily one of the ugliest things I see.
Moose,
Ya cain't be Blue, 'cuz we already gots one o' those.
"trying to pour and trowel to grade nails."
Grade nails??? Oh you mean that cheap and sloppy way of replacing grade chamfer strips.
Gotcha covered, man.
SamT
Edited 12/11/2005 7:19 pm by SamT
I disagree that it is cheap and sloppy. On a retaining wall or something exposed I can see why you would want a nice edge on your wall, but otherwise...Why put a chamfer strip on?
In places where deep frost is a concern check out the information on shallow frost protected foundations. The following is an interesting read if you aren't familiar with the system.
http://www.cs.arizona.edu/people/jcropper/desguide.pdf
Depending on your frost line depth, this can save a bundle. It's rather new in the US, but has been catching on quickly. We've built a number of houses this way in Wyoming and it sure seems the way to go.
Cheers,
Don
Why put a chamfer strip on?
Materialwise, it's cheap. Labor wise it's very little more than just nails.
As with elevation strips, you can easily spot problems visually, but you don't have to pull chamfers out and fill the little void strip with mud.
Only chamfers allow this, even just using nails you have to either pull the nails during finishing, which takes as much a$ 1 minute per nail, or wait till the forms are stripped. Waiting will get quite a few nails out of the 'crete, but then you have to pull 'em out of the form$ and the ones left in the crete are un$afe and can be impo$$ible to pull and must be abandoned or really tear up the 'crete with all the time to repair that involve$.
Structurally they remove a stress point and provide a sealant groove, granted most builders don't seal the sills down, but it's there. If you're going to use a termite guard, they let you ea$ily get its face up tight to the wall without any interference from rough edge$.
Finishwise, they make it very ea$y to get a smooth, flat, and level surface.
Esthetically, they eliminate the raggedne$$ of an unchamfered edge.
Personally, I think that it is that last little detail that says "A professional was here."
SamT
Thanks Sam, that was a good explanation. The whole "professional" idea is one of the best ways to set yourself apart from other contractors.
Sam,
This thread has been a good read. Nice to see someone meticulously detailing the foundation. It is often the sloppiest job on a house.
TGNY,
"It is often the sloppiest job on a house."
You're right there.
Oh. And "Garunteed to crack."
I was talking to a construction office manager a while back and she got all indignant when I said that I garunteed my 'crete to not crack beyond microcracks. "You can't do that," she said, "all concrete cracks."
I think my garuntee lost me that job because of her strong belief in a myth.
SamT
Sam
I found a guy who dose the walk outs the way I have had them done, he told me that was the only way he did them unless the grade would not permit them. From what I hear of this guy he dose good work, I'm going to check out some of his work this week before I decide. I still have your number and would like to still try to meet with ya to get a bid sometime.My other thing, I did have a question on was what do you see being the problem with the inverted footing? I have been doing this on my own jobs for the past 10 years and my dad had done it 20 years before that with no problem to report of. Just curious of what you thought.
Just a bimp so I remember to reply to this tomorrow.
Byoung,
Where to start? Where to start?
The mechanics of frost heave
When watar freezes, it expand 9% in volume. For our purposes we can say it expands 9% in height. A 36" frost depth means a 3 1/4" difference in elevation.Frost heave is due to two reasons; As the soil elevates it lifts everything on top, and it tries to lift everything bonded to it. Ice will bond to almost anything, especially a nice porous material like concrete.
with a simple foundation of an unheated structure;
View Image
In this example the foundation will be lifted by "Secondary Frost Heave," this just means lifting ice bonded materials. The upward forces are transfered across the bond to the foundation. As you can intuit, there is a slight mitigation of heaving simply because it depends on the bonding of soil to 'crete, which may not be perfect. Unfortunately, the soil at the bottom of the foundation has not frozen and will collapse and fall underneath it, preventing it from ever returning to its original elevation.
An example of a simple slab;
View Image
The soil under the slab freezes, expands, and lifts the slab along with the surface of the soil. This may not be a problem for a small storage shed. Small, because a larger structure will cause, at least, uneven freezing across its section, therefore uneven lifting. The upward forces are transfered directly up to the slab, there is not even a slight mitigation. However the slab will probably return to its original elevation.
An inverted Tee foundation combines the worst of these two. There is zero chance of any mitigation from a poor soil to foundation bond and the bottom of the foundation trench will fill in preventing it from returning to the original elevation.
Why haven't you seen a problem so far?!?!?!?
Temperature gradients;
View Image
Ok, I blew it on this sketch, the top gradient lines should have started much higher, right up, at or above, the surface of the soil, and the slab should have been at the top. The soil next to an uninsulated heated space will not freeze untill air temperatures drop way below freezing for some time. This keeps the bonded area very small. The soil under an insulated space, like your walkout basement slabs is kept at subterainian temperatures, about 65* in our part of the world, therefore the temperature on the inside of your inverted Tee is almost always above freezing. However, the colder it gets and the longer it stays cold, the lower the tops of the gradient lines fall.
Ways to prevent frost heave, all combined in one sketch;
View Image
From the top;
Snow. Snow is an insulator and lifts the temperature gradients. Problem: Can't count on snow to be there when ya wants it.
Place waterproof insulation around the foundation. This moves the temperature gradient to the outer edge of the insulation. Much more reliable than snow. It keeps some of the water out of the soil around the foundation. More on this below. The width of the insulation must be equal to, or, greater than the frost depth. It can be placed at any angle from level to verticle. This method uses the heat of the earth to move the gradients. It is the basis of Frost Protected Shallow Foundations.
Backfill the foundation with high permeable granular fill. Because the fill doesn't have enough water to tightly bond the grains, all uplift forces will be sheared within the fill. This will be sufficient when the fill will never be water saturated above the frost line.
Perimeter footing drainage. No water = no frost heave. Combine this with 3/4" clean fill for frost heave protection and dry basements (|:>)
Tee footings. While Tee footing are usually required for support, (an inverted Tee does this too,) they also prevent frost heave. Remember that ice cells push up to lift foundations? Well, they push down with the same force. I think Isaac Newton said something about this. With an unfilled block or treated wood foundation, this would merely split the foundation along horizontal lines and other methods of frost heave protection are called for. With good concrete techniques, read "rebar," the tensile strength of the foundation will overcome the seperating forces.
Not bad for an old desert rat, hunh?
Hope this helped ya,
Byoung, you probably have a combination of good, well draining soil, a low watertable, and a favorable microclimate. Who knows.
As a Specialty Contractor to owner builders, I give a ten year warranty against settling, structural cracks, waterproofing, and dimensions. I gotta use belts and suspenders and do it right the first time. I own everything in contact with my 'crete including utility trenches, waterproofing, backfill, anchor bolts, and landscaping.
As a subcontractor under a different biz name to GCs I give them what they ask for.
SamT
Sam
thanks for the info, and thanks for the time you put into it. I will say one thing that I do do on my wals outs is I fill the over dig with 1" clean rock up to 12" from finish grade to get the water away from my frost wall.
Sam
Another thing I ment to ask ya, the new guy I am looking at asked me if I would like to use form-a-drain around my footings. I have seen this in a supply store before but never used. So what do you think of it if you know what I am talking about.
Byoung,
Form-A-Drain. . . Good stuff, I like it. Gotta be a little more careful when compacting the first foot of gravel, but that's a no cost nobrainer.
SamT
I think I going to star using this I have done some cost comparison,it is little more material wise but in labor I will get it back and it seems to be a good system. I think I will use it first in the new house I am building for my family. I guess we will see how it goes. Thanks for the input.
Edited 12/14/2005 10:32 pm ET by byoung0454
Sam,My business partner is in the permit process to build a new home for himself.We were just talking about the merits of Form-a-Drain vs. corrugated pipe. Do you think it's a better performer, easier, or both?I've been waiting for an opportunity to use it on a job but we do so few additions with basements in this area that I have not had a chance.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
Jon,
I think that if downspouts and landscaping are done right a 1' burrito of 3/4 clean gravel, no pipes, will be all the "perfomance" one needs. Stick 1 length of perfed 35 in the end so you can connect the drain to open air.
Is it easier? well of course. You replace your footing form boards with Form-A-Drain and that's the last labor you do for forms and drains. No stripping, no cleaning, no pick up and haul back to the yard. No go and buy and unroll and fight the corrugated.
Cost effectivness? you will have to analyse your material and labor costs yourself. It should be close or cheaper to use Form-A-Drain.
SamT
While 9% of 36 might be the 3"+ you indicate, it seems that the ground would have to be saturated over that full depth for the difference to materialize. Would moderate drainage eliminate most of this movement?
Also, are you saying the friction between the ice and the sidewalls of the foundation is what is causing it to lift or are you just talking about pushing the walls in laterally? It seems that the friction bond would be much less than perfect and alot of the power to lift a foundation wall would be lost if the bond is not there.
Edited 12/15/2005 10:53 am ET by houseboy
Houseboy,
Yeah, 3"/36" is worst case.
Drainage can eliminate frost heave. Obviously, the better drained the more elimination. However. . . an ice cell can attract water from as far away as. . . 20', IIRC.
Friction? Well, it's not friction per se, it's bonding. As the water in the soil freezes it also freezes to the wall, so the wall is part of the ice cell and rises along with the rest of it. If the bond area is relatively small the bond may be fractured and no lifting will happen.
Latteral forces obviously don't require any bonding and movement might occur even if all uplift has been avoided. That's another subject.
A really good source of information is here. This is their index of publications. Oh yeah, those are from the site of The Institute for Research in Construction of Canada.
SamT
SamT
BTW, where do you live in MO?
Lincoln County Mo
Small world. I lived in Troy last summer after moving back to St. Louis (where I grew up) from Colorado.IMHO, I wouldn't worry too much about stepping your footings. When I was doing foundations in CO, in the mountains, you can imagine how many steps we had to put in foundations due to elevation changes.If you're truly concerned about the walls cracking, you can pour continuous footings down a step and pour the wall tight to those footings. It's a little more work, but it sure is solid.When we lived in Troy last summer (it was only for about 5 mos), friends and family kept saying to us, "You know, Lincoln County is the fastest growing county in MO." It was said so often that it sort of became a running joke between us.
Byoung,
Brownbagg already said it about your subs running the job.
That said, I garuntee my footings and foundations and I will not do it for an inverted footing in-re frost heave protection. The heave protection comes from the TEE having to also lift all the frozen soil above itself and not from just existing 3'deep.
SamT,
COMO
"That said, I garuntee my footings and foundations and I will not do it for an inverted footing in-re frost heave protection. The heave protection comes from the TEE having"I wondered about that.But he said that the inverted stem wall was on the outside. And there should not be any frost on the inside of trhe "footing".But it I still wonder about doing that way.If for no other reason that they it appears that you are puting a big chunk of COLD IN THE WINTER concrete on the inside.That in thermal break to the slab would be well past the walls.
Bill,
A walk out basement has no stems above finished floor on the walk out part, there fore requiring a deeper footing, where Be uses an inverted footing, than in the backfilled areas.
SamT
I am not sure what you are saying.But I can see that keeping that inverted footing on undisturbed soil would be possible, but a real pain when you have to put in insulation and gravel under the slab.All in all I think that it could be made to work, but with lots of difficulty and less than the best performance (insulation and water proofing).BTW, my house is similar construction, but not a walkout BASEMENT. The first floor is at grade level along the fron and 1/2 of each side. The other 1/2 of each side has 4ft above ground stem walls. The back side is 12ft stemwalls where it mets up with the basement under the garge.(First floor, 1/2 flight to "basement", 1/2 flight to 2nd story, 1/2 flight to garage).I had a drainage problem and we dug up one corner between the house and garage. It had stepped footings. But the garage footings ended a short distance from the 12 ft wall. Don't remember the details, but I am thing that there was a 9-15" gap.I don't know if the foundation for the rest of the house was steped or not.
Bill,
Here is a crude drawing of what we're talking about.
View Image
Soil Line is supposed to show a sloping grade down to, at or, just below the elevation of the basement Floor Slab and the Walk Out Foundation. In other words, you open the basement door and walk out to a yard that is at the same elevation as the basement floor.
As you can see the step down footing must extend back under the regular walls the distance of the frost line to keep the footing that distance away from air temps at all times.
I form the stepdowns thusly;
View Image
It provides a ledge for the floor slab, costs a little more concrete, and saves some forming and rebar since the footing has no unequal lateral forces. . . well, a little from heaving, but not enough to overcome the inherant strength of concrete if you have adequate drainage and good backfill techniques.
SamT