Fill Alternatives?

[vtjon]

Hi folks, I am planning to build a 32x40 detached, stick-built garage. The location where I am planning to place it is somewhat slopped front to back (5' in the back right corner, 7'-ish in the back left corner).

I am planning to have poured concrete footers and stem walls with fill then a concrete slab on top. "57" gravel fill is the recommended fill around since it compacts well. It's hard to estimate exactly how much fill I will need, but I'm estimating somewhere between 200-225 yards which will cost around $5900 around here plus labor to spread and compact it. This will be a workshop mainly though it needs to work as a regular 2+ car garage. I won't be installing a lift.

Does anyone have any alternative suggestions? This will be a permitted project but the county seems relatively easy to work. The foundation contractor mentioned grade beams and then you could fill with compacted dirt. I don't fully understand how this works though and seems like it would just require more concrete. Can anyone explain how this would work?

I contacted LiteDeck and I'm waiting for a price estimate but I don't expect it to be competitive with fill. Metwood Building Systems (local company) also produces a suspended floor system but would still be more expensive than fill.

I don't particularly want to excavate for a basement under this garage as it doesn't have good driveway access and we might hit rock anyway.

 

[couch67]

In my limited experience fill is normally cheaper than the alternatives (unless you can find another location!)

 

[mvusse]

Bank run (all sizes mixed together) is usually cheaper because they can skip the sorting and compacts much better. I used 60 ton of it under my concrete floor and with the pit only being ~5 miles from my house I still paid more for the delivery than I did the material.

 

[ConCretin]

If I understand correctly, your foundation walls will extend from frost depth to slab elevation and the structure will be 'filled in' with crushed stone? My first thought would be to make sure the walls are adequate to support the lateral loads imposed by the fill behind them. It should be pretty manageable but it is a consideration.

I think your foundation contractor's grade beam suggestion involves incorporating integral beams (reinforced areas of thickened slab) to transfer slab loads to the foundation walls instead of relying on the base materials. Basically using the base as a temporary form for a structural slab. This would theoretically save money on the quality and compaction of fill materials but I doubt it would be significant over the added cost of a properly engineered structural slab.

Another option would be to do a structural fill and bring the entire area up to grade and then build your garage on a monolithic slab (assuming of course your building codes allow it). You'd obviously use more fill material but you would save a bunch on concrete. I have a 28 x 32 garage that is built this way up here in Maine and it worked just fine. I only had to bring my grade up 3 or 4 feet but the concept is the same. Obviously it's important to prep the area correctly, use a good material and compact it very well.

 

[larry4406]

vtjon - welcome to the forum.

Go here and read this, the links, and study the pictures. It will provide you with the information you are seeking.
https://www.garagejournal.com/forum/showpost.php?p=8117419&postcount=14

Have your concrete guy put the slab ledges on the inside of the foundation walls and the pockets for the grade beams. Backfill with any fill you wish (no organics) and no need for compaction. Then prep and pour a structural slab.

 

[firebirdparts]

I would guess in southwest virginia shale would be the best option. I don't know what it costs. in Poor Valley it was everywhere under your feet.

 

[vtjon]

vtjon - welcome to the forum.

Go here and read this, the links, and study the pictures. It will provide you with the information you are seeking.

Have your concrete guy put the slab ledges on the inside of the foundation walls and the pockets for the grade beams. Backfill with any fill you wish (no organics) and no need for compaction. Then prep and pour a structural slab.

Larry,

This was extraordinarily helpful and I really appreciate your insight. If I needed 4 beams for my size, I'd need around 5-6 yds more concrete which would be around $1000 plus steel. I also assume a structural slab like this would be less prone to cracking since the settling doesn't matter. The excavation contractor (and fill/stone guy) suggested with 57 that we only needed to compact it at the end since it's basically self-compacting instead of doing it in lifts.

I noticed that you mentioned in your post that these were based on stamped designs. Are there prescriptive designs for this? For the walls around here, it seems folks just reference the rebar chart so I wasn't sure if this could be similar.

 

[kbs2244]

Whenever I see a slope like this I think "basement"
Be sure to get a alternative quote by a contractor that has done "walk out basements" and is not afraid of concrete plank floors.

 

[larry4406]

Larry,

This was extraordinarily helpful and I really appreciate your insight. If I needed 4 beams for my size, I'd need around 5-6 yds more concrete which would be around $1000 plus steel. I also assume a structural slab like this would be less prone to cracking since the settling doesn't matter. The excavation contractor (and fill/stone guy) suggested with 57 that we only needed to compact it at the end since it's basically self-compacting instead of doing it in lifts.

I noticed that you mentioned in your post that these were based on stamped designs. Are there prescriptive designs for this? For the walls around here, it seems folks just reference the rebar chart so I wasn't sure if this could be similar.

All of our construction is to approved stamped plans. Not sure what you mean by prescriptive designs? Common knowledge type designs? If so, not sure. Talk with your concrete foundation guy - he should have experience and be able to help you.

Weigh the costs of filling in the foundation with #57 stone to permit a slab on grade design vs the structural slab with more concrete and steel.

 

[ConCretin]

Larry,

This was extraordinarily helpful and I really appreciate your insight. If I needed 4 beams for my size, I'd need around 5-6 yds more concrete which would be around $1000 plus steel. I also assume a structural slab like this would be less prone to cracking since the settling doesn't matter. The excavation contractor (and fill/stone guy) suggested with 57 that we only needed to compact it at the end since it's basically self-compacting instead of doing it in lifts.

I noticed that you mentioned in your post that these were based on stamped designs. Are there prescriptive designs for this? For the walls around here, it seems folks just reference the rebar chart so I wasn't sure if this could be similar.

Unfortunately, I think you'll find that a grade beam design for your garage will be significantly more expensive per Sf than the one Larry posted due to the longer spans. Larry's plans were for a 20' wide garage while yours is 32'. This is an exponential difference when it comes to structural concrete. I also think you may be underestimating the cost of the steel reinforcing for the beams.

I'd also point out that I suspect Larry's example would have a relatively low load rating, which may or may not be an issue. How much weight would you think a lightly reinforced 4' slab spanning 8' would bear? It's a structural slab by the loosest of definitions.

Your current option calls for trucking, placing, lightly compacting and grading 200 cy of stone. Substituting trucking, placing, lightly compacting and grading 200 cy of an alternate material that costs $10(?) less per Cy for a savings of what, $2k at the most? There is no way in hell you'll upgrade to a 32 x 40 structural slab for anything close to that. Not to mention how tough it will be to find someone who will even do it.

I used LiteDeck in the Concrete Underground and while I don't recall the price per Sf, it wasn't cheap and requires temporary supports every 5' during placement. The other thing I think you'll run into is that LiteDeck won't span 32' without at least one intermediate support and that obviously adds even more cost and complexity.

Sorry to be so negative. Just trying to give you some information to keep you from spending too much time on options that are unlikely to save you money so you get to building your new garage!

 

[vtjon]

Thanks guys. By prescriptive design, I meant layouts/span tables like you find in the Wood Frame Construction Manual. I figured this was unlikely.

I am coming to the same conclusion that the 32' span will present a problem and just require me to add another foundation wall or other support. I might save a few thousand on fill but would have to get an engineer involved. There is also the possibility that once we grade, I won't need quite as much fill as I might expect. As LLWillysfan noted, I have spent way too much time on alternatives as I would just like to get to slab before the weather gets too bad here.

As it seems to be the case in most areas, it can be hard to get contractors. We have basically a single foundation contractor for poured walls. He is very good but very backed up. I'd really like to apply for my building permit this week but I haven't gotten his estimate yet nor the details that I can submit with the permit.

I really appreciate all of the help.

 

[larry4406]

You can also place a sonotube at the intersection of the grade beams to create an intermediate poured support to reduce the spans. I have done that before as well.

 

[vtjon]

I thought I'd post a quick update though no resolution yet. I'm finally starting to get some numbers. It looks like my foundation cost will be around $15k for walls and footers plus $9k for fill plus labor to spread/compact. I'll have over $25k in my foundation which seems absurd even before I get a slab. It could be I'm just not current on what things cost

I'm trying to figure out other options though I might end up just biting the bullet. If decreasing the span a few feet helped, I would consider that.

I could do the grade beams but have to haul fill dirt plus all the rebar and labor. I'm guessing I'd also have to get an engineer involved.

I could do the structural slab but I'd have to put a beam down the middle in most cases. I might get a basement out of it but I don't think this is too common around here. I talked to my custom home builder about putting a room under my current garage but was talked out of it.

I was also trying to find a way to do a structural slab on piers with some type of metal beam and pan but I can't seem to find any references and I'm not sure how expensive piers would be.

I have another location with less elevation change on the building pad (maybe 3-4 ft) but will have to run a driveway about 75-100ft and the elevation change is probably 20 ft over that 75 ft. The location isn't ideal but I'm also concerned about being down hill from everything else and water getting into the garage. I think I'd still have to pour footers and stem walls though block could now be an option.

I don't know what I'm answer I'm looking for but thought I'd share my thought process.

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[macdabs]

Without pictures or an elevation lot plan I think your best thing to do would get with a surveyor to look at the lot and what would be the best way for excavating the lot . Change your grade and approach into the building . If you can work with what material you have on site and get the difference down on the back corners and maybe live with a bank in the one corner you might be able to save some money.

I built on a hillside and have a drop of at least 30 ft between my garage and my home . There is 150 ft between the house and my 40 x 80 . I had piers on the right rear corner that are 6 ft deep not to have a settle issue on a red iron framed building . We used grey slate or shale in 6" lifts in that rear corner 10 years ago no issues.
A good excavator or surveyor can look at a lot and should be able to tell you the best way and least expensive to accomplish what you want to do.

Mac

 

[spudley]

Whenever I see a slope like this I think "basement"
Be sure to get a alternative quote by a contractor that has done "walk out basements" and is not afraid of concrete plank floors.

Yep. I used Spancrete, 40" wide cut to length planks installed by a crane.

That way he can double his available space with a basement and follow the golden maxim of keeping twice as much junk as he needs.

 

[vtjon]

Yep. I used Spancrete, 40" wide cut to length planks installed by a crane.



That way he can double his available space with a basement and follow the golden maxim of keeping twice as much junk as he needs.

Yes, the prestressed panels would be ideal here. There are no local providers for these panels that I can find. The closest I can find is 150+ miles away and I assume trucking would kill this.

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[vtjon]

Yep. I used Spancrete, 40" wide cut to length planks installed by a crane.

That way he can double his available space with a basement and follow the golden maxim of keeping twice as much junk as he needs.

I found a provider a few hours away and got a general price. It's a little more expensive than fill but not too terrible if I can get a basement out of it. I would have to add a foundation wall due to the span though.

Did you have a contractor set your panels? What do I need to account for beyond a crane?

 

[spudley]

I found a provider a few hours away and got a general price. It's a little more expensive than fill but not too terrible if I can get a basement out of it. I would have to add a foundation wall due to the span though.

Did you have a contractor set your panels? What do I need to account for beyond a crane?

This was an attached garage on the house I built 35 yrs ago. I was the GC so I dropped off a set of blueprints at Spancrete. I agreed to their estimate and called them when the foundation was almost finished. A week later they set the panels in place. I did add an outside entrance (Bilco door style) so I needed a steel beam over that opening. After they set the panels we poured a 4" slab on top, with a slight slope to the doors.

As I recall it was just about $2000 for what Spancrete did (35 yrs ago).

In my case, by zoning rules I needed to come up 2-3 feet in elevation to match my neighbors lot heights so I was able to use the material from the 24' x 34' x 9' excavation to get my grade right.

So I either needed to spend on bringing in several hundred yards of fill, or dig up my own. In the end it was almost a wash, plus I got lots of extra space.

 

[NUTTSGT]

With a good back, wheel barrow, shovel and a used tamper, you could save some cash. Have the stone/gravel delivered and take of placing/tamping yourself.

How much time do you have, how much do you want to save ? Sweat equity.

 

[vtjon]

In this situation, the labor is not that expensive. The stone delivered is $9K or more depending on how much we have to grade. Of course, it is hard to stomach spending $10K to fill a hole in the ground.

 

[teal95]

Yes, while rolling ground has its appeal (things were absolutely flat where I grew up) it does have it's downsides. When I had my 40x40 built the highest corner was level, to the right of it took about 2' of fill and the back corners were around 5' and a little over 6'. It sucked spending $8k just for ground prep.

 

[NUTTSGT]

In this situation, the labor is not that expensive. The stone delivered is $9K or more depending on how much we have to grade. Of course, it is hard to stomach spending $10K to fill a hole in the ground.

Wow, I guess how nice it is to have a local quarry nearby. We can get it for about $20/ton for limestone. The other quarry farther away sells bluestone for about half that.

 

[vtjon]

Wow, I guess how nice it is to have a local quarry nearby. We can get it for about $20/ton for limestone. The other quarry farther away sells bluestone for about half that.

I'm not far off that number but I'm estimating 400 tons to fill.

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[NUTTSGT]

I'm not far off that number but I'm estimating 400 tons to fill.

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About double what you originally thought ? Ouch.


If I were to put a building up at my parents, the location I'd like to use is low and swamppy. After tree removal, it would take a serious amount of fill too.

 

[jives]

From a cost effectiveness perspective it really seems like three options here, that is, without having to go to the pre-made concrete panels.
1. Build a basement, or just half of one. At least you get more square footage, and if it is walk out with a large door, a large number of items can be stored. Garage floor will need to be reinforced, but that is not difficult.
2. Frost protected slab (AKA floating or Alaska slab). Bring in bank run (cheap) to level the site, compact with heavy machinery, then build the frost protected slab on top. No footers, no stem walls.
3. Level the pad with bank run, compact with heavy machinery, build a pole barn structure.

 

[vtjon]

be stored. Garage floor will need to be reinforced, but that is not difficult.
2. Frost protected slab (AKA floating or Alaska slab). Bring in bank run (cheap) to level the site, compact with heavy machinery, then build the frost protected slab on top. No footers, no stem walls.
3. Level the pad with bank run, compact with heavy machinery, build a pole barn structure.

Are these really options with my grade? It seems like filling 80" - 96" and compacting it without walls would be tough. I guess they build roads like this but over larger areas.

 

[jives]

Are these really options with my grade? It seems like filling 80" - 96" and compacting it without walls would be tough. I guess they build roads like this but over larger areas.

It is true that the fill will need to be sloped, and thus require more fill. We brought in 240 tons of bank run, compacted by heavy equipment in 6" lifts, and cost $6K for a pad for a 32 x 42 pole barn. The grade needed to be filled about 60" at the low side.

With the 8' slope differential, it seems that filling that all in would be a waste, and it would be better to have a basement, or partial basement. Or, build it on piers, like this shed. Of course, this pic is a small idea of what could be done.