I’m a home builder (but new to the field) and am building my first house. I’m posting the first of what will undoubtedly be MANY questions:
Due to the steep grade of my lot, my garage slab will be well above grade, and the back foundation of the garage VERY high (the foundation will be engineered, with a huge footing and buttress walls). The crushed rock fill required will vary in depth from 6′ to 16′!
Is this depth of fill even feasible?
If so, how do I manage to avoid excessive settling of the fill that would threaten to crack my garage floor?
If such depth of fill is NOT feasible, what are my alternatives?
I know that I could use precast or cast-in-place floor slabs that would enable me to recover the area beneath the garage as basement, but I’ve already got a huge basement and plenty of square footage in the house; I just don’t need the extra space or expense.
Your experienced advise, please!
Steve (aka BrokenHammer)
Replies
I saw a similiar situation on a garage being built for/by an architect.
He filled the whole thing with crushed stone. He did not do it in lifts. He did tamp the final grade though.
Most experts would advise you to fill it in 'lifts' of no more than 6-8" at a time and compact each lift as well. The crushed stone in my book is a fine idea, at least it wont shrink like some soils do.
Eric
It's Never Too Late To Become
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Edited 8/16/2005 3:52 pm ET by EricPaulson
They do deep fills on roadways all the time, so it's possible. I would think that, like roads, you would use a well-graded gravel compacted as Eric said. With a variety of aggregate sizes from fine to coarse and no organics the gravel will compact very tightly. Besides, it's cheaper than crushed stone, and that's a lot of fill!
Mike
I once had to fill an entire site sixteen feet over 5 acres for a hospital addition in a flood zone. Place granular fill, we used #57's with "fines" to fill in the interstices (holes between the rocks when laying together) in layers of 6 inches and compact with a vibratory compactor using a "fine and very light mist" of water between lifts.
Saved some dollars by (this site was a muddy clay) covering clay soil first with a mirafi fabric to keep soil separate from fill.
Results were terrific. Ten years later, there are no cracks in foundations or slabs.
Paving in parking areas held up also ( 3 inches of asphalt over the fill). Heavy ambulance and truck traffic use this regularly.
Have your excavation contractor price this for you before you make you decision as fill is never cheap, neither are "retaining" walls. Perhaps a "mother-in-law apartment or "bonus room" over a garage on grade may be more cost effective and help you sell this one.
Use clean stone, and compact it in 6-8" lifts with a vibratory compactor. We recently did a huge subterranean parking garage where some of the areas have 10' of stone under the slab, and the area between the exterior walls and the sheetpiling got backfilled with almost 40' of stone. No settlement problems to date. Some people will tell you that stone is "self-compacting", but running the plate over it can't hurt.
As an added precaution, I'd run some dowels from the foundation walls out into the slab and beef up the reinforcing in the slab just to ensure that any minor settlement doesn't create a problem.
Bob
Your replies all seem to reinforce what I "thought" I knew - that aggregate, with careful compaction, does not settle - I just wanted informed, experienced support. And you all shared that generously, and I THANK YOU!!!
Steve
A final question... Eric says "crushed stone" work great for in the job he witnessed, but then Mike recommends "well-graded gravel" as cheaper than crushed stone. And Warren refers to "granular fill...#57's with fines".
"Gravel", in this area, is usually dredged from area rivers. Is that as effective as "crushed stone"?
I was under the impression (propbably mistaken!) that "gavel" and "crushed stone" were about the same cost, but that crushed stone, because of its angles and edges, "locked" together tighter than river gravel. Any aggregate experts out there???
Steve
that crushed stone, because of its angles and edges, "locked" together tighter than river gravel. Any aggregate experts out there???
I'm not, but for driveways, you are certainly correct. A world of difference. Around here it's common to pour over several feet of non-compacted crushed stone. Pretty sure they get some voids.
For your project, I'd take a look at steel bar joists with a slab over, even if you didn't bother with anything but a crawlspace under. You might find the price attractive.PAHS Designer/Builder- Bury it!
Why are you using, cruched rock. This is a very bad idea plus not being cheap. backfill with a clean sand or clay sand. Then a foot of rock. Rock does not make good backfill because it rolls around and no fines to lock it together. It might be great for misture but there are other materials that cheaper and just as good. If you have some type of retaining wall. I would backfill with clean sand. Maybe lower the elevation of the slab by excuvation. 16 feet of rock is a landslide waiting to happen.
Good clean sharp sand, compact in lifts. This question always comes up and everybody always says crushed stone. Way more money and not neccesary. Good for the excavator=$
good thing about sharp clean sand you can put in athree foot lift, flood it with a fire hose. I mean really flood it. and it will be super tight in the morning. as the waster settle through the sand it pulls the grains tighter and tighter.
I'm thinking you have different types of sand available where you live. We have mortar sand which is an orangish brown sand, concrete sand which is a light brown with larger granules and then white sand ("play sand") which as far as I know has no use in building except for maybe spreading over newly installed pavers for a cushion for the vibratory plate compactor.
Like I said before, every different part of the country has different types of aggregate available - both fine and coarse.
we have all three of those. 99 % of this area is sand.
White sand (play sand ) is not play sand It is more than likely silica sand ,loaded with silica dust ,and lung desease later in the life of the kids . Never let your kids play in silica sand.
Yep. And a whole lot cheaper.
Here, sand is roughly the same per yard as washed stone. We use gravel for bearing fill below concrete. What I was trying to insinuate in my earlier post was - if sand were used for fill, what kind of sand would it be? Nice sharp sand means nothing to me. A while back I suggested using the extra masons sand under a porch slab but the concrete guy said that we would not warranty his work if I put it under there... Also, we have no access to a "fire hose".
I still think this guy needs to at least cost out panning the slab. 16' of fill is ridiculous. This must be a fairly steep lot.
20 yards of white coarse sand , delievered here is $65. The sand with the small pebbles , is the best, but hard to get here.
Do me a favor. Send some of that sand up here to Long Island. We too live on sand. This is where one of the glaciers melted a long time ago. It left lots of the stuff. Does that make it any cheaper, no way! Just finished a brick and sand patio yesterday. Two yards of fine sand a/k/a plaster sand, with tax and local delivery $125.00. Unfortunately, my truck is not a dumper and I can't carry even a yard at a time, so I got stuck paying them to deliver. (What really stunk was that I underestimated the first time by a yard and had to get them back for a second delivery.)
Don
VaTom - do you mean Steel I Beams spanning under the slab and then v-pan with concrete? I am in a similar situation, (32x32 garage, 8 feet of fill) but cannot imagine this saving $ - although I'd do it if possible.
do you mean Steel I Beams spanning under the slab
No. Steel bar joists, like hold up the roof in most commercial buildings. Topped with a galvanized pan and thin concrete slab.
The savings won't be in material, but in the total cost. Whether or not there will be any savings at will be determined by your fill and compaction cost. Take a look at my ceiling, good for 240 tons, or 300 psf total load with a 30' span. Your car's considerably lighter.
Rarely used residentially, inexpensive, which is why they're common for commercial. 32' span, no problem at all. Last house, similar to mine was a 40' span, same loading.PAHS Designer/Builder- Bury it!
Wow - where do I get a hold of some?
Any steel co will order them for you. Here, all are manufactured in one Shenandoah Valley plant. Called 3 steel cos. (local, Lynchburg, Richmond) and got 3 prices. Mine weighed 400lbs ea.
We moved them with a small tractor and a steel cable stretched between 2 trees. Moved them sideways manually. The client house's were 600lbs, and no decent trees. Crane time. The crane guy was pumping me, never seen anyone use so much steel residentially before. When I told him what they cost, he about fell over, mentioning that I couldn't have done it as cheaply with wood, which is what he sets every day.
Bar joist charts, which the steel co will have (as do I), tell you which one you want once you specify your total and live load. You place steel anchors when you pour your walls. We weld the bar joists to them. Decking can be welded, but much faster to shoot it to the bar joists with powder actuated. Once the bar joists are placed, one day for one man to finish the installation. Then it's set the form boards and pour the slab.
More construction photos at: http://paccs.fugadeideas.org/tom/index.shtml
PAHS Designer/Builder- Bury it!
There are several huge railroad fills near the part of Jersey where I grew up, on the Lackawanna cutoff. I mean these things go for a mile, and are at least 50 ft. high. Apparantly they were done by running RR cars out on cables, and opening the bottoms. The impact of the fall compacted the underlying layers of stone. Those fills have been there for 100 years now.Andy Engel
Senior editor, Fine Woodworking magazine
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None of this matters in geological time.
Yup- it can be done, without a doubt.
How the new job? Missing dealing with the homeowners yet? lol
Bob
Around here we can get a material the local excavators order as "item 4." I think it is a reference to a NY state DOT spec for compactable fill. It is not crushed stone, and is less expensive than crushed stone.
It was used to do just what you have described, in a 2-car garage built on a very steep hillside, right down the road from where I live. Max depth was almost 18 feet, and it was compacted in about 15" lifts with a power vibrator head on a large John Deere excavator rig.
as previously mentioned, use a crushed stone blend of 3/4" and smaller, we commonly call it modified and compact every 6" to 8".
another consideration is a pour ledge on the exterior walls combined with a reinforced 6" to 8" slab.
carpenter in transition
I just finished having a floor poured in a similar situation: 24x36' garage, front & part of right side I only had to do a 4' frost wall, but sloped back such that I had to work down to about 12' in the back left corner.
The middle of the floor ranged from about 1' below grade down to the deep section where I had to dig down the full 12', so I had a fair amount to backfill. I did all the dirt work using my dad's backhoe & bulldozer, hired out the concrete form & pouring.
Started out by having my dad haul 48 yards of "backfill sand" from a nearby pit. Big mistake. This was fine sand with a little clay. Compacted well on the surface, but would definitely require compacting in small lifts to get decent compaction. Ended up digging a lot of it back out, then using the edge of the backhoe bucket to punch down & compact the deeper stuff until I had an area I could get to with the rented compactor. (This is all complicated by trying to do stuff evenings and weekends, when the gravel pits aren't open).
Finally got to a point where I could have my dad take his backhoe/loader back home to his pit (twice as far as the other sand pit) and haul another 40+ yards of really bony gravel (I pulled out the stuff that was bigger than my head) that I pushed in with the dozer in small lifts & compacted with the rented vibratory compactor. He had a little bit of finer gravel (approx. 1/8" & smaller) that we used to top it off. This all seemed to compact very well.
I spent a lot of time levelling out the surface, then put 6 mil poly down, 2" of EPS foam, wire mesh, 3 rings of rebar around the perimeter, some more rebar where the vehicles will pull in, 750' of PEX tubing (3 loops), and 5-6" of concrete. I had a pro do the pouring & finishing, I did the rest. He sprayed a cure&seal coat on the surface right after finishing, which seems to have helped with the hot weather we had right after the pour.
It's been 2 weeks and so far looks fine. Time will tell.
Moral of this story is that I think almost any type of sand or gravel will work ok if it's compacted well as it's built up. Coarser stuff will compact more easily/completely in thicker layers. Compacting is pretty quick & easy with a large vibratory plate compactor, except where I was deep down into the trench. A smaller plate compactor or jumping-jack would have been better there.
All this has taken me since early May to get done. Hopefully the structural stuff will happen faster!
Don
I built a 36X30 garage about five years ago with a similar set of circumstances only with backfill of eight ft on the rear.
I used a eight inch poured foundation which required backfilling 4 ft deep on the front and eight ft deep on the rear.
I posted a question on this site and got all kind of advice you may be able to pull this up and read some of it.
All the reinforcing and backfill (I used red Georgia dirt that was tamped only by the action of the bobcat putting it in) cost far more than I expected and some of the replies suggested the job was doomed to failure and I should tear it down and start over again.
As it turned out the back wall did not blow out and the slab has not caved in.
I have always regretted not investigating and using the bar joist and pan construction mentioned in the replies here which I suspect would have been as cheap to do and would have given me all that space underneath for whatever.
If you think you wont need the extra space you should see inside my garage now.
After compacting the garage dirt, wait as long as possible before pouring. Park your car and/or truck on the dirt, it will pack even harder by the tire tracks. Also pouring the slab in the shade of the roofed garage will reduce cracking. In very clayey dirt, the slabs are not tied to the footing, but just floating.
When reading the above replies you have to realize that in different areas of the country there are a vastly different stone products available. For example you said something about river gravel - we don't commonly use that around here except maybe for decorative purposes. Further, each area has different alpha-numeric identifiers for stone products - sometimes even quarries that are 20 miles apart call a similar product something entirely different. Another example is that when I moved from Virginia 1 state south to NC, I had to learn a whole new gravel designation system - not that it was that big a deal, but the first time I tried to order 31a here in NC I think they probably thought I was a real DA. Often the grading systems are set up by the state DOT - since road building is always going to be a quarries major source of income.
One thing to realize about crushed stone (as opposed to river rock) is that due to it's angular shape and somewhat sharp edges it tends to be self compacting, so although some compacting may be in order stone will not settle that much - although your situation is pretty extreme. Secondly, one important concept for concrete work is to get a uniform base. What I mean by this is that sometimes it is not feasible to get a fully compacted base, however if it is uniform - ie no hard spots mixed with soft spots you will be OK.
As far as specific comments on your project, I'd be very concerned about the feasibility of building a 16' high wall that could hold back the weight of that much stone without blowing out. For example, you did not say how big the garage is but lets say that it's 24' x 24' with an average fill of 11' (between 6' and 16'). Ok, so let's say the inside of the foundation is 22.5 x 22.5 = 506 sq ft x 11' tall = ~5560 cubic ft or 206 cubic yards. The type of washed stone we use here in NC is ~ 1.3 tons per yard so that would be about 268 tons!!!! So you would be trying to hold back 268 tons behind those walls - that's a bunch! Not to mention the weight of the slab. Further, let's say that stone is $15 a ton - delivered - OK, so that would be about $4k for the stone alone....
As suggested above you need to at least investigate "panning" the slab. Keep in mind though that this will require a different foundation design as you will be creating a lip around the perimeter to hold up the slab & steel. Generally, you would use some kind of steel beams with "B' metal on top of it - or at least that is what it is called around here - you know - that corrugated metal - but it is the thicker stuff.
Edited 8/17/2005 2:45 am ET by Matt
i priced a garage addition earlier this year which involved putting the addition over the removed basement of a demolished home. i priced it two ways, one to fill in the basement with modified stone mix compacting in 8" lifts with a 6" concrete slab poured on top of the fill. the other way involved a full basement under the garage with precast deck slabs.
the slab on fill was at least 25% less expensive.
on top of that we had some concerns about the homeowner's interest in a car washing bay in one of the garage bays and water infiltration in the basement.
as was the case with yours, the basement space wasn't needed.
carpenter in transition
the slab on fill was at least 25% less expensive.
What were the numbers?
When I priced precasts, I found them to be very expensive also. Steel bar joists came in about 1/4 the cost. Even when I got the engineering for casting my roof on site, bar joists were incredibly cheap. The engineer who did the design pointed out that's why bar joists are so popular.PAHS Designer/Builder- Bury it!
i really don't remember what the numbers were, 8 months ago seems like 8 years.
if i was going to do a garage with living area beneath, i doubt that i would consider using bar joists and metal deck especially in Pennsylvania. corrosion would be a factor due to salt on the winter roads. i have already seen this occur in a couple of similar locations where the metal deck was eaten through by rust.
carpenter in transition
I understand. Don't buy it, but understand.PAHS Designer/Builder- Bury it!
don't buy what ?
the corrosion ?
carpenter in transition
Corrosion related question.I need to rebuild my PA bridge over small creek. I was thinking of using VaTom's method. Won't be any salt but so what if the pan rusts...just supports the fresh pour, isn't structural, right? Or am I missing something?Todd
The pan isn't structural.. use plastic pans if rust will be a problem..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!!!
Thanks. I'll probably be back with questions about fine bridgebuilding. The neighbor had his bridge over same little creek and paid 22K. I gotta dimyself, don't have that kind of dough.Neighbor also spend a year in the permit process, various departments involved. Kinda funny - the state worries about the environmental impact of his new bridge when a mile upstream the are a few hundred dairy cows standing in the same stream crapping all day. Occasional lagoon overflow, too.Todd
so when do we get started....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!!!
Ah, a volunteer!Like to get it in before freezing temps, so I'll be back in prior to that to get a working plan together. Later, and thanks,
Todd
I put the predacessor to that one in, in consistant -30 + temps... get the holes dug now and plugged to keep out mother nature...
paint or finish yur precut pieces indoors and put it up like a kit... that one is 2.25" out of square in 8' to blend with the crapola construction of the house...
all pieces are dadoed and were done off site...
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!!!
you are correct that the deck can be designed as a non-structural element.
do you want the metal pans rusting and falling into the creek ? probably not, after all the work that will go into it. plastic deck is an option as is forming with plywood and stripping. pre-cast deck is also a possibility.
are you planning on using bar joists or I beams for the structure ?
the permitting process is incredible. we have one at 10 months right now, still waiting.
how large is your bridge's span ?
where are you in PA ?
carpenter in transition
Tim,
No, I am probably more environmental than most, no crap in the stream bed is great. Again, I am a dyi, done some flatwork both nothing like this. Didn't know that plastic was an option, sounds ideal.The span isn't much...maybe 16-20 feet. I'll post some photos of the existing bride and sketches of my plan in a few weeks...if you could chime in then it would be greatly appreciated.I am in central PA...the county with only one red lite. County just started the construction/permit process a few months ago. Just a little different than Boston or San Fran, etc. When I read what you guy's go thru I am amazed but understand the reasons.Sorry to hijack this thread a little, hope you'll check back in with input when I post again in a few weeks. Off to a fishing vacation in Canada tomorrow!Thanks, Todd
Tim, you said "if i was going to do a garage with living area beneath, i doubt that i would consider using bar joists and metal deck especially in Pennsylvania. corrosion would be a factor due to salt on the winter roads. i have already seen this occur in a couple of similar locations where the metal deck was eaten through by rust."
Wouldn't make much sense to suggest you didn't see any "corrosion", would it?
But to infer that steel bar joists and decking are inappropriate because they CAN rust is silly. That'd be like saying that wood is bug food and will rot if left wet, therefore it's inappropriate for building a house. Even if I didn't use wood to build my shell.
If road salt was causing the rust, which you apparently don't know, that means either the design was flawed, or the slab was. Or both. Not particularly complicated. I've seen lots of rusty bar joists and pans, pick them up whenever I can at auction. Quite certain none of it was due to road salt here. Just bad design.
I was concerned about using bar joists above an indoor pool, a considerably worse environment than the one you fear. When I checked into it, I learned that you just need to be careful about what finish you use, not leave them primered like I did here.
What it looks like is fear of the unknown on your part. Clearly, to have success you need to design appropriately. Doesn't matter which material. Steel bar joists can work fine, or not, if used inappropriately. The only reason I promote them is they are extremely cost effective. And DIY friendly.
PAHS Designer/Builder- Bury it!
Tom
you're right, in the most notable case, I didn't see it. one of my fellow managers did, though. we were called to look at a garage with a basement below. it was constructed with bar joists and metal deck as described. he did the inspection. his comments included that about 50% of the deck was missing and the bar joists were heavily rusted and deflecting. piles of rust laid on the concrete floor below. we were asked to price the removal and replacement of the system.
did road salt cause the corrosion ? I don't know, maybe, maybe not. Perhaps some of the problem came from high moisture levels in the basement itself. The cause of the problem didn't come up in our brief conversation. I question whether the average DIY guy or even the professional is going to use the proper methods to prevent such a thing from occuring. my feeling was that precast panels simply solve the problem.
can you use bar joists and metal deck to construct a garage floor ?
absolutely. i'm sure with the right precautions it can be done with success.
it just wouldn't be my first choice of materials. and that's just a matter of opinion.
based on the fact that I have never seen one parking garage constructed with bar joists, I have a feeling that there might be a few others that might agree.
carpenter in transition
Edited 8/19/2005 6:01 pm ET by timkline
Maybe it was something as simple as the steel was not painted... and then especially being in contact with damp concrete...
Tim, you're right about the parking garages. But there are a lot of other factors at play. I wouldn't think bar joists appropriate there either, for one large reason. All it'd take was one idiot deforming a couple with either something too tall, or thinking they'd make a good anchor, to compromise the whole shebang. Not to mention assembly time. A home garage, particularly over a crawl space, is a different matter. The rust I've seen on my recycled material was due to improper use, not storage. I'm only suggesting that they can be safely used in this application, not that they always are. I don't know of any building material that can't be misused.
My recycled pans are never galvanized. My engineer specified painted pans too. It was the steel company who suggested I might want something more rust resistant. Clearly the painted pans can be made much more rust resistant, but probably few are.
I once salvaged an air-over-hydraulic lift from a commercial garage. Heavier than I expected. Plan was to raise it from the overhead (roof) barjoists and back my truck under. I backed off before deforming the bar joists, but I could see somebody else maybe not so concerned.
If the budget allowed, I'd also take precasts over bar joists. Would have here, but my pile of cash was way too small. Huge difference in cost.
One technique not mentioned so far is post-tensioning. Would seemingly work for these small apps very nicely, if a crew can be found nearby. That was another plan I looked into before discarding.
Here's my "parking garage". No rust over a decade later, but also no road salt (or anything else) leaking in. My design worked just fine:
PAHS Designer/Builder- Bury it!
Sorry I've been absent in my own thread! I wasn't able to login...found out I had to delete my cookies (sounds gross, doesn't?)
To answer some of your questions:
-- three-car garage will be 41' wide, 24' deep
-- back wall is being "engineered", and will essentially be a 14"-thick Retaining Wall with two buttress walls, then a 12" wall on top of that.
THANX for all the good info Eric, Mike, Warren, Bob, Brian, VaTom (I'll definitely keep the Steel Bar Joist method in my files for futer use - and THANX for your pic and website link - it was worth a 1000 words!), guyatwork - your informative reply GREATLY appreciated, Don, etc.
I'm off to the phone now... to price out crushed rock fill VS. steel bar joists
Steve (aka BrokenHammer)
my garage slab will be well above grade, and the back foundation of the garage VERY high
Ok, maybe I'm missing something. If the garage floor is "well above grade," how does the driveway reach it?
My first thought is to lower the garage, rather than engineer a huge solution.
If the garage elevation is fixed, and the driveway engineering is complete, then my reflex would be similar to VATom, just span the garage space with a metal deck pan on LW joists, and then top with concrete (just leave some sort of access to the space underneath--you may no need or use it, but somebody else might, 50, 75 years down the road).