I am curious as to what type of foundations (new homes or additions) are used across the country.
Here in Texas / Houston area we must address really funky soil in some areas. To those with more technical knowledge, we have soil with highly expansive clay, and a high PI (plasticity index) factor. Meaning, the soil swells and contracts to extremes with varying moisture content.
To address the problem we use:
Good / cheapest: Structural slab / steel reinforced monolithic slabs, with insturctions to the HO to maintain consistant moisture levels around the home. See added details below.
Better: Post tension monolithic slabs: cables running both ways thru the slab are tensioned after the concrete is poured, much like picking up a stack of 8 – 2 x 4 blocks and turing them sideways without losing them….. by applying pressure to the end blocks. See added details below.
Best / most expensive: Structural slab with piers: a typical steel reinforced monolithic slab with beams resting on drilled and reamed piers. The piers are drilled at load points to a depth that is below the aforementioned “funky” soil. The piers are reinforced typically with 4 – 5/8″ rebar and stirrups @ 24″ O.C. They are drilled and poured prior to backfill of forms and ground plumbing rough-in to a height equal to the bottom of beams. Piers are usually 12 / 36, meaning 12″ shaft and 36″ bell bottoms. Good bearing soil can usually be found at 8-10′ depth, which is where the 36″ bell bottom is located. See added details below.
monolythic simply means one piece / a four inch slab rest on and is poured intergally with grade beams / reinforcement is usually 3/8″ rebar 16″ O.C. both ways in the 4″ slab / beam reinforcement is typically 4 – 6 5/8″ rebar with stirrups @ 18″ O.C. continious in all beams. Typical concrete beams are 24″ – 30″ deep and 12″ wide. Beam excavations are beveled at the top to provide better intergal transition from beam to slab.
A post tension slab usually omits most of the beam reinforcement. Sleeved steel cables are run @ 3-4′ O.C. across the slab and sometimes doubled in the beam area by drapping the bottom cable down into the beam. The cables proturde one end of the forms 12″ -16″. At the other end, the cable is equipped with a pull block that gets imbeded in the slab at pour. After the walls are framed, the post tension company comes back and pulls the cables with a machine producing an engineer specified tension, they then cut and grout the pull end.
We are installing a structural with piers for a new home now. If you do not hear form me for a couple of days it is because I am always very attentive with slab make-up and the concrete pour.
Replies
How do they get that bell at the bottom of the hole?
I was just in Ft. Lauderdale, watching piers being drilled for a new beachfront highrise...
they use a big crane operated hollow auger, it drilles the holes, then filles it with concrete from the auger tip as it withdraws, & the rebar cage gets driven in when the concrete's still wet...leaves a pretty sloppy mess at grade, I didn't stay long enough to see how they clean it up...was there for Katrina, skipped town just ahead of Rita
Wouldn't those floating slabs, even the post-tensioned ones, heave?
How do they get that bell at the bottom of the hole?
Good question: 12" shaft drilled first / reaming tool is colapsable to 12" in diameter / the reamng tool is lowered down the hole without being spun by the drillng vehicle /when the reaming tool reaches bottom the operator stats the tool to spinning/ the ream tool releases when spun and begins to cut the sides of the 12: shaft
they use a big crane
Our driller uses a skid loader with hydrolic drill head / bit / reaming tool
filles it with concrete from the auger tip as it withdraws, & the rebar cage gets driven in when the concrete's still wet...leaves a pretty sloppy mess at grade,
reinforcement is installed prior to pour / cement crew provides an elevation in the hole prior to pour and pours to elevation / elevation marker is usually a simple nail with survey tape attached for easier sighting / cement is poured slow / very clean and neat operation / little of no clean up
when you auger 40 feet deep in sand, you need a crane rig....& you have to pour as you pull the auger 'cause the sand hole collapses otherwise....
Did some 35' holes once, for a pool on the edge of Buffalo Bayou. Engineer said we needed to drill to depths below the bayou bottom (28"). We did the slury method as previously discussed. As I remember it was very messy.
We also built a long deck type walk to a tower in a swamp for City of Sugar Land Parks Department.
They sank poles for the deck and 5 -16" x 70' creosote poles 30" into the swamp floor with a crane operated pole driver. No concrete.
We framed to the poles / pretty close to dimension at the water level / some were 3-4' (yes feet) out of plumb at the top / a skiff, come alongs and chains helped us to produce a fine looking project / two stories with a roof
Edited 11/3/2005 9:01 am ET by txlandlord
In New York the most common foundation these days is standard poured concrete, full basement, on standard concrete footings. Much less commonly seen are concrete block (on low end jobs or additions), and some precast concrete is seen on occasion. Slab on grade is rare, and wood foundations are only used by people who don't know anything about construction but read something and think they do. ICF's are seen occasionally, but usually only when the client specifically asks for them. Builders don't promote them yet.
Just kinda curious,how you come up with your opinion on wood foundations?
Well, my opinion is just an impression based on limited experience with them. The ones I've seen are flexible and give me an impression of flimsiness. And I'm skeptical that the preservative treatment will remain effective for several hundred years, but I have no data to support my suspicion.
I don't like using chemical treatments which have a pretty fair level of toxicity to make an inherently bad material for ground contact passable. In my long experience as an engineer I find that relying on special treatments to make something unsuitable work is asking for trouble. I always try to design using materials inherently suitable for an application because that gives high reliability.
The only reason I was asking is because my wife and I are in the process of building a new home and we've used a wood foundation for our basement. A couple of people that we have talked to that have them say they are warm and dry. When I was getting bids to have ours built, I talked to two companies that specialize in wood foundations here in the midwest (Iowa)...one of them gives a warranty in writing for 25 years against water leakage and 75 years against wood rot. There is no way that any concrete foundation contractor around here would even think about a warranty against water leakage like that. One thing that has impressed me so far about ours is when we finished our waterproofing, got our floor joists installed and plywood decking on we had just gotten backfilled. That night we had about a 3" rain, got off work that day and came out to the house and found the over dig had dropped about two feet overnight and standing water up against the foundation...1-2 feet of water on about half the foundation. I took a broom handle to poke down through the muck...as soon as I felt it hit the rock it drained the water right away. Went downstairs and checked it all over...not a drop of water had made it through to the basement. I put a level on the walls, everything plumb. Even my excavator was impressed. Looking forward to having finished square footage downstairs that will be more comfortable than a concrete basement would offer.
If you've got good contractor, you'll be very happy with your PWF. Most people can't get by their first gut reaction, reject them outright and don't do any serious research on PWF's. If most men went with their gut reaction at all times, none would still be married. See, we can think things out and forward!
I've worked around about 20-25 (built by contractor friends/acquaintenances) over the years including building three.(new home building was not our main business). They are cheaper in the end. Ours in Canada don't even need foundation perimeter drain tile (now you really don't believe me-out to lunch, eh???) except to take water away to the desired drainage ditch/storm sewer.
To Wayne:
The CCA treatment has been around since 1920 or so. The first stakes installed for monitoring by the Forest Products Labs division of US Agriculture have been in the ground since 1933-35 and have about 1% leaching or so. The first PWF house in the US was built in 1938 and is still up as far as I know. They have been built in Canada since the 1960's. Some of the first were at an army base.
Side Storey:
In 1988, I was approached by a retiring Lt.Col who was moving back to his home town about 90 miles from me. He got my name somehow and asked me to build his house for him. These types are usually quite conservative so to sooth my curiosity, I asked him why he wanted wood. He'd been at the base when the first houses were built 1960 or so. He toured around and then in 1982-3 ended back at the same base in Ottawa to finish out his career at headquarters. One day he noticed that the Engineers were digging up a couple of the houses; the next day they were being filled back in. He went to check out what was going and was told: we just wanted to check on them since they're now over20 years old. We're not going to dig up any more since they're as good as the day they wewre installed!!
In the end I didn't do the house and foundation due to the travelling times each day. I found him a contractor within 18 miles that had built one for himself. We did do the heat pump and HRV systems. Had to refuse the blown attic insulation due to a stupid electrician who installed 19 uncertified potlights in ceilings that were to be insulated. They ended up building large insulated boxes over each light- doh?? wouldn't touch it!!!!
Another storey:
I had a Certified Architectural Technician on another forum contact me with a similar storey. He had the opportunity to view his father-in-law's 25 year old PWF when they had dug a section up to install an outside enclosed entry and steps to the basement. He said "It looked as good as new."
If your afraid of the arsenic, go to this gov't website and stop eating these foods: http://ehp.niehs.nih.gov/members/2003/6407/6407.html
To Quote:
"The general population is exposed to arsenic through drinking water, dust, fumes, and dietary sources, with the highest concentrations of arsenic reported in seafood, rice, mushrooms, and poultry (Tao and Bolger 1999).
The NRP conducts monitoring and surveillance of meat, poultry, and egg products to determine the presence of chemical residues, including animal drug residues, pesticides, and environmental contaminants (USDA Food Safety and Inspection Service 2001). We used monitoring data from the NRP to estimate mean arsenic concentrations in meat and poultry during the years 1989-2000 and to calculate possible dose exposures acquired through consumption of chicken. Arsenic is an approved animal dietary supplement and is found in specifically approved drugs added to poultry and other animal feeds. Roxarsone (4-hydroxy-3-nitrophenyl arsonic acid) is the most frequently used additive among a group of organic arsenic compounds added to feed of broiler chickens to control coccidial intestinal parasites. Roxarsone contains organic arsenic in the +5 oxidation state. Most of the excreted arsenic (found in litter) remains as the parent compound or as the amino-metabolite. The forms found in chicken muscle have not been reported in the literature."
PWF's are my favourite and the CCA in them does not scare me (follow the instructions). And I do environmental consulting/investigation of homes and am recommended by the only enivironmental clinic in our province. See http://www.ahi-ns.ca
Now that CCA is gone, wouldn't we have to build PWF's using ACQ? (At least we'll never have a shortage of three letter acronyms....;-) ) There's also copper napthenate, which works very well as an end-user applied treatment. I don't know if it's kosher by code. Does that put the whole PWF longevity issue back to square one?
-- J.S.
In Canada, I believe PWF's are still using CCA but ACQ is in deck/playground materials. In a PWF, there is very little chance of child hand/mouth contact that has people worried with the decks and playgrounds.
CCA is not banned but is being voluntarily removed without even moderate public pressure. Do we have a law suit that has been won against CCA yet?? Do people read the instructions of how to handle and use it in construction?
It's very interesting that a few years back a local TV station here went out and did swab testing of playground equipment at a school, having it analyzed by private lab. The levels were quite a bit lower than local soils!! Don't let your kids play in the grass!! Everyone is jumping on band wagons!!
Same here WayneL5.
blue
"wood foundations are only used by people who don't know anything about construction but read something and think they do."
Why would you say that? Wood foundations have a very good track record. They do have their failures when people don't follow the instructions. I have worked on about 20 or so in my building career. The last one was in 2000 when we lifted an 1882 house (with 18 corners), removed the partial stone foundation and installed a permanent wood foundation (PWF).
It is my preferred foundation. The GC gets to make money on the foundation and gets to control the quality- no worries about psi and leakage after shrinkage occurs. You're ready to to finish the basement interior- no interior walls to construct. It also makes the house cheaper to build. In my area, the first one was built in 1977- the owner still says he'd do it again. Want to put a new larger window in the basement or install a set of exterior steps to the basement...just get out the skilsaw!
"In New York the most common foundation these days is standard poured concrete, full basement, on standard concrete footings."Big brouhaha in Amherst, NY....lots of houses built on substandard soil, now cracking & sinking
Council. Army Corp. of Engineers, lot's of tax dollars on consultants....proposed new local spec. to add a bit of rebar to the slabs...Council approved the spec., then the Builders Assoc. & their lobbyists in Albany killed it..."too expensive"Basically, scr*w you, Mr.Homeowner....
Here in LA, slab on grade is the cheap approach. Old houses more often were perimeter footing and stemwall, with pier and post for the interior. Today it's footings inside instead of pier and post for raised foundations. True basements are virtually unheard of. For apartments, often they dig down about 5 ft for parking, leaving some room to vent exhaust above grade, and build the units over that. Those can have problems when it rains, though.
-- J.S.
Well, in my explanation of foundation types here in Texas I overlooked foundations similar to one you describe.
You will find perimeter and interior grade beams, with blocks above to desired elevation. Funny, these seem to be in lower priced homes, or homes in which the builder is trying to duplicate an old time look. We have done one in the past, but used stem walls of treated 2 x 4 instead of block. We added lattice as a skirt.
I own a design / build company. We did not design the foundation, except some details. The home looked great at completion.
We have no basements in this area of Texas. Recently, I saw a plan with a "Texas Basement". The "Texas Basement" was a room finished in the Attic.
Piers
Pilings
Monoslabs in frost protected settings
Wall on footing ( whether concrete or block or ICF wall)
Rubblestone walls
Trench rubble foundations
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I was following and understanding until: Rubblestone walls / Trench rubble foundations
If you have time...explain briefly.
here in New England, there is a lot of stone ( rubble) loose in the fields. Dig a hoole for a foundation and you will have even more of it. A hundred years ago and more, bricks had to be shipped a ways to get here, but all that stone was just laying around. So the foundation walls are usually about six feet tall, with 18" standing proud of the ground. 24" wide at the base and 18" through at the top. all laid in mortar, no footings. Some have the rubble up to the ground level and then rough dressed granite from there up to the sills.Sometimes a person didn't want to go the the cost of a full excavation, so they simply dug a t4rench about 18" deep and 24" wide and rolled stones and boulders in, slathered some mortar around, and then laid brick or gqrantie atop that. It was not below frost level, but many have lasted fairly well. They do move and settle, but generally, these were for smaller houses and the sill beam would be an 8x12 continuous, so the main piurpose waas to keep it up out of the mud. That would be a trench foundation
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Have you built or know of builders in Maine using frost-protected shallow foundations?I've been looking for land to build on around Waldoboro, ME, for the last year but find most of it comes with an old cape. After looking at the swimming pools that pass for basements/cellars in Maine this very wet year, I'm convinced that staying away from the water table is a good thing.I'm also interested in building a house as energy efficeint as possible and this style of foundation is supposed to reduce the heat loss.For details about frost-protected shallow foundations follow this link;
http://oikos.com/esb/43/foundations.htmlIt would be nice to hear from someone who has built these types of foundations in the northeast.
I'm on Islesboro and yes I have.I know what you mean about wet celars, but I found when I moved here that most of the old-timers build starting with the attitude that there is no way you can build and keep all the water out - then go aheada and use that as an excuse to barely halfway try to build dry. Depending on the land and soil of the lot you find, a dry cellar can be built.Your theory that building above the water table is good on the face of it, but there is more to it than that.A frost protected foundation involves more than just insulating against frost. It means maing sure to use drainage to keep the water out from under, replacing soil with structural draining mineral gravel such as inch-minus compacted in lifts aas it is placed over the drains, and then insulating. The two keys to frost protection are to keep it warm enough not to freeze, and to keep it dry enough that there is no water there to expand and heave if it does freeze. I wouldn't trust either one all alone by itself.So a FPSF can cost as much for thje dirt guy as a fuill foundation. It will save some concrete cost, but then you don't have the space created either. usually the FPSF is the option when the site has ledge that prevents deep work and a full foundation anyways. Proper site selectionand house/foundation location and design can deal with the groundwater problem.
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> You will find perimeter and interior grade beams, with blocks above to desired elevation. Funny, these seem to be in lower priced homes, or homes in which the builder is trying to duplicate an old time look.
Slab on grade here is mostly post WWII. Before the war, it was almost only used for garages. Perimeter footings and pier holes were dug by hand, or sometimes they'd use mules and plows to break the hard surface. I've seen pictures of mules in use building Hollywood Bowl in 1927.
The other really bad thing about foundations in those days is that they didn't level the top of the concrete stem wall and step it. They pretty much let it follow the slope of the land, and then cut the cripple studs to get a level first floor deck. When a quake breaks the friction between the sill plate and concrete, that angle gives you a component force helping to push the building off its foundation. Retrofit bolt down and shearwalling is a specialty business that's doing quite well out here.
After the war, tracked earth moving machines became cost effective for residential work, and development moved from the basin to the flatter lands of the San Fernando Valley. (That's how Victory Blvd. got the name.) So, slab on grade became the cost effective choice.
-- J.S.
Interesting.....No need for quake proof items arond here. I've heard and read about quake resistant design.
I just started a home in "Inland 2", the one mentioned in my original post. Inland 2 is one of three designations used on the coast for hurricane / windstorm resistance.
They alls have Inland 1 and Seaward with Seaward requiring the most work, and Inland 2 the least.
Now, if Piffin will just get back to me on those "rubblewall" foundations.
I am enjoying the reading very much. I ma building a new home about 300' out my back door....easy to supervise and get into Breaktime ....when I have a breaktime.
Thanks to the BT Crew for the info.
"Now, if Piffin will just get back to me on those "rubblewall" foundations."Nag
Nag
Nag;)Some of us have to sleep and work too, ya know, LOL
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" I've seen pictures of mules in use building Hollywood Bowl in 1927."
You comments made me think of something Dad once told me.
He said that back in the 1940s he had helped dig a couple of basements with horse-drawn slip scrapers. They would dig a ramp to get in and out of the basement.
To finish the corners, they would dig with shovels and throw the loose dirt into the scrapers.
Here's a pic of one, for those who aren't familiar with them:
View Image
A chip on the shoulder means wood further up.
That looks like what some of the Hollywood Bowl mules were pulling. Others were hitched to old fashioned wagons.
-- J.S.
Funny, these seem to be in lower priced homes,
Which seems a tad dumb, for lack of a better word. The true low-enders just have corner & space blocks (usually-hopefully--on footers) to hold the floor up.
or homes in which the builder is trying to duplicate an old time look.
Old-time look worth the effort in my book. Uses a lot less expensive concrete and gives a good elevation for the house (the better to wrap it in a nice sun-shading porch).
We have no basements in this area of Texas. Recently, I saw a plan with a "Texas Basement". The "Texas Basement" was a room finished in the Attic.
Usually tucked in over the detached or semi-detached garage, appears to be the "rule" for a TB.Occupational hazard of my occupation not being around (sorry Bubba)
I've video'd the Japanese building an 8 story apt bldg about a stone's throw from my 3rd floor balcony here in Tokyo (bummer, I lost "my" great view). Anyway, the augur/concrete pumper cranes drill down about 4 stories and then lifts and places a 2 story section of @2.5 ft wide precast/steel cylindrical tubes into the hole (5 - 6 inch weep holes evident throughout the column). Then the ground crew slips some restraining wire hawser attached to plate steel over this monstrosity and releases the crane from it and the crane swings over and picks another one. The second one is lifted above the one suspended in the hole and a connecting ring is attached (believe it or not, with some sort of bolting arrangement - I always thought bolts were too susceptible to stress, but...). Anyway, once attached, the crane lifts the entire thing up a couple of feet, the ground guys undo the wire stopper and the crane lowers the rest of the assembly into the hole. A concrete pumper hose is attached to the crane and the crane rotates the entire cylinder as it pumps concrete into the 'sleeve'. After a few minutes, the crane is disconnected from the sleeve and it moves to position it's auger attachment over the next location. The entire process takes about 45 minutes per hole.
On the top of these cylinders are 8 steel attachment points to which 10-12 foot by 2" (or maybe 3") rebar are welded with an amazing machine that I dubbed the "Bolt of Lightening" machine: It takes one huge KaBlam spark and the attachment is done. The guy that does it has the coolest job on site - well, maybe the guy that gets to melt successive ends of 2 or so inch rebar together is a close second place (that is one cool honkin' machine, too).... Anyway, all the columns (and floors) are attached to these going on up - very interesting and likely hugely expensive Earthquake 'proof' construction here in the land of 'wa'.....
Looks good from my house....
In central Illinois, probably 98% of new construction is poured concrete. The footings are about 24" by 8", and the walls are mostly 8" thick. Probably 80% of new houses are on basements. All basements used to be 8', but now something like 2/3 are 9'.There have been a few ICFs go in. I've seen a few concrete block foundations for crawlspaces, but have never seen a block basement.Superior walls has done a few around here, but I haven't seen one yet. I've never seen a wood foundation, but I'm curious about them.
Don't confuse busywork with productivity.
Here in the foothills of VA poured concrete rules but just yesterday I saw a block foundation going up. I myself have become an ICF addict. Two years ago was the first time I'd used them and the local inspector had never seen them used but after that time I'd never go back. They are so easy and painless. The last project was a 3,200 sq ft footprint and a 9' above floor wall and with floor and footings cost 20k. Can't beat it with crowbar for what you end up with.
I lived in VA from 1964 - 1971 / 4th grade to 11th grade / Vienna and Alexandria.
Beautiful state. A friend from high school in VA told me there has been so much growth that I would not recognize the place.
If you haven't been back since then you sure wouldn't. My frist trip to that area was in 84 and even since then it has changed a great deal. I live about 100 miles SW of the metro area and growth is coming out here also. Land selling at $800/acre in 88 in now $20,000/acre if you buy 50 or more.