Excavation for garage floor questions

[alia176]

Hey fellas,

I'm new here so pardon what may be dumb questions!

Anyway, attached is a jpeg file of what I'm trying show via Acad here

As you can see, there's a downhill slope where I'd like to place an approx 25'x35' size metal building. There is an existing gravel driveway that'll become the driveway in front of this future building. The garage floor will be made of concrete that'll support a 9,000# car lift on one side.

In terms of the concrete pad, I'd like to explore various options that may be available to me but I'm not aware of due to my lack of education on this matter.

The soil in my area is mostly rocky and stable. My elevation is 7,000' and the future metal building will meet the snow/wind loads. I'd make the garage deeper but I think the septic leach field is in that area. I located the septic tanks and they're a safe distance away from the future garage site. My friends are telling me that the excavation/concrete costs will be more than the actual metal building

Questions:

1) Is it possible to build a suspended floor for this project so that I can use the basement as a potential storage area? Mind you, this will be a shallow basement but storage is storage. Can this be done for the load? I ask because I saw this at a friend's house where the floor of his house was made of concrete (painted to look like large tiles) and he had a basement that he used as a wood shop. This is a huge two story log home but the actual basement was small. I assume it's only under the main living room floor where no rooms are built on top.

2) If I had to use traditional excavation means of building the floor, then I assume this entails: pour a stemwall around the perimeter first, back fill the area surrounded by the stemwall, compact the dirt, drive down pilings where the lift will be and finally pour concrete. Is this a valid assumption?

3) any other options I should be considering for the concrete floor? Perhaps a floor made of different material? I like concrete for the ease of the use of creepers, clean up and abuse resistance to metal fabrication, welding, cutting, etc.

4) what are the different style of concrete pouring techniques? I hear something called monolithic pour which sounds to me like one giant slab of concrete.

TIA,

Ash

 

[Kevin54]

With a monolithic slab it would be one pour as it states. It looks to me like all you need is a retaining wall on each side, backfilled and poured. But I would add rebar to help tie everything together. As far as materials are concerned, concrete is about the best way to go. Look at the "Bunker" thread for ideas about a basement underneath. I think that would be rather costly but feasible.

Kevin

 

[russlaferrera]

Look at the " Bunker" in the Garage Gallery. He did something similar. Looks very $$$.

 

[alia176]

I'm off to the Bunker thread. Thanks.

Ok, I'm back. Yiiiiikes, that bunker is quite awesome I must say. If I were to translate this technology to my build, here are my options:

1) I go with the bunker style construction (as stated in the thread above) and use metal beams and super wide footings as the floor of the garage then pour concrete. I get a storage basement.

2) use traditional width footings, haul in and fill with 1 1/2" stone (per another thread), compact then pour the concrete. I get no storage basement.

Not knowing the cost of metal or the excavation/fill/compact in my area, can I venture a guess that the steel beam method would cost me more? I'm assuming that I'll need to hire a structural engineer to come up with the drawings and specifications for the concrete company?

Thanks.

 

[Franz©]

You might check to see if prestressed concrete slabs are available in your area. Generally if available they deliver better performence at lower cost than poured in place concrete.

 

[Charles (in GA)]

You can afford to put up a lot of metal building for the cost of a basement and garage concept that will support cars, a lift, etc. The Bunker build did it because of a severe space and height limitations. If you are not short on space, spread out. If space is limited and you do not have height restrictions, make the building tall and add a mezzanine deck in part of it.

Charles

 

[flesburg]

Bunker has an wonderful building,

But, he said he is going to have a cool quarter million in his building. I would not invest that much in a bunker, and put a metal building on top. I would want mine brick covered on the outside and lined with walnut on the inside. And then I would want a couple of Porsche's on the inside, or even Lambos....

 

[flesburg]

Now seriously,

Most lift manufacturers will have minimum specs on the floor, and they will drill test holes to verify. They usually require 5 or 6 inch thick slab at least 12 feet square or some such, or they will not install and face the lawsuit if their lift falls over with a car 6 feet in the air, and kills someone (you?). Get info from them.

I would dig out dirt until you can pass compaction test, put in a footer, and walls, backfill with gravel (or highly compactable fill) and set floor on the wall or on a brick ledge inside the wall, and I would cross rebar the walls, and tie them into the floor with rebar. I would also cross rebar the floor on at least 2 foot centers.

I have seen lifts installed on the second floor or with a basement under them, but they were poured concrete commercial buildings with 12 to 18 inch thick concrete floors, and the lifts were through bolted to the concrete.

On my last garage the lift installer drilled through the concrete to test for thickness and fastened the lift down with great big bolts that had folding anchors on the bottom, (great big versions of wall anchors used on drywall) so that the lift was held to the floor in compression.

 

[alia176]

Excellent info, thanks for shedding some light. Height restriction is not an issue in my area so I'll go tall and have a mezzanine for storage and what ever else.

I'd like to start this process by getting some ideas of excavation/concrete/cost/etc. Can I simply call a excavation company to come out or do I need to call a concrete forming company? I have a drawing from the metal building company but until I pay for the actual metal building, I don't think they'll release a real architectural schematic for this thing. Perhaps my assumptions are incorrect?

 

[boiler7904]

I'd look into using precast concrete planks with a lightweight concrete topping to form the main garage floor. They should be able to design the planks for the point loads of your lift and anything else that you know will be in there. If you go that route, you'll need to find a good concrete guy to pour the walls and set the embeds so that everything can go together easily.

My mother in law works for a homebuilder that had a site similar to yours. He excavated, poured a traditional foundation wall and backfilled before pouring a slab on grade for his garage a couple of years ago. After the fact, he looked at pricing precast planks. When he found out that he could have added about 800 square feet to his basement for the same price he paid for a slab on grade, he was not happy.

 

[alia176]

After 13 years, I finally get to move on this project. I bought a 12k Challenger 2 post hoist two days and ready to use that thing. I'm going to do my own excavation work to level out the site then find out from the county if I'm allowed to pour a 25x35 pad and then eventually construct footers & stemwall few years later. Eventually, I'll put up walls and build a real building. The county might not allow me to do this but it's worth inquiring.

 

[ConCretin]

Here's my take;

1) Is it possible to build a suspended floor for this project so that I can use the basement as a potential storage area?

It is but it won't be cheap. There are a number of options for a suspended slab system but all are several times more expensive than a slab on grade. Add to that excavation costs, taller concrete walls, waterproofing both the foundation and the suspended slab and you start to get the idea.


2) If I had to use traditional excavation means of building the floor, then I assume this entails: pour a stemwall around the perimeter first, back fill the area surrounded by the stemwall, compact the dirt, drive down pilings where the lift will be and finally pour concrete. Is this a valid assumption?

You have it basically correct but it's unlikely you'll need the piles. Bearing pressure for a slab on grade even with a lift are quite low for most soils.

3) any other options I should be considering for the concrete floor? Perhaps a floor made of different material? I like concrete for the ease of the use of creepers, clean up and abuse resistance to metal fabrication, welding, cutting, etc.

Depending on the area you have available, you could do a structural fill and simply place a monolithic slab. Same rationale as the last question. It's not that hard to achieve the necessary soil capacity for a slab or a whole structure. You'd build up an area a few feet larger than the building and taper out the fill at 45 degrees or so.

4) what are the different style of concrete pouring techniques? I hear something called monolithic pour which sounds to me like one giant slab of concrete.

Basically two options. A foundation (footings and walls) with a slab on grade floating within or a monolithic slab, which is a slab on grade with thickened edges that act as footings for the structure above. It can 'float' on the frost (if you get frost) or it can be frost protected using rigid insulation. A monolithic slab is far more cost effective than a foundation for a detached structure.

In your case, a full foundation would retain the soil under the slab minimizing the footprint of the project while the monolithic slab would affect a larger area to accommodate the structural fill and slopes.

Hope that helps.

 

[Firebrick43]

In my icf build I did a composite steel slab over my basement which is a 14 ga specially corrugated steel pan poured with 5.5” of concrete. The max span was 14’ with this product and therefore a large steel beam was placed down the middle of the pan as I was spanning 28’. The floor was designed with a load rating that would easily support a 1 ton truck.

I place not only the icf forms but the beam and pan itself. I had the pour done by a pair of guys that contract flatworm.

I did it as I wanted infloor heat and it was cheaper for me than a wood floor with either warm board or a thin slab and significantly cheaper than precast floor panels with a thin pour on top. My installed cost for the suspended slab was around 10$ a foot but that was three years ago and I did nearly everything except the pour.

If you hire it out it’s expensive because you significantly limit the pool of contractors as most wont touch something they had never done and it’s uncommon in many locals.