I am in the planning stages of putting up a new detached garage. Code dictates footings 48″ below grade. The garage would be approximately 28 x 28 on a sloping lot with the garage doors on the top of the slope. The drop over 28 feet is approx 5 feet. Is it crazy to consider putting a basement under the garage? If anyone has done this, please give me some feedback. What would you do different or not at all? Thanks in advance.
brian
This 654-sq.-ft. ADU combines vaulted ceilings, reclaimed materials, and efficient design, offering a flexible guest suite and home office above a new garage.
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Replies
Some houses in a friends high$ development use the cambered precast sections to make the garage floor, and they have handball courts underneath!
I kid you not!
Forrest
It's actually been done here in residential buildings 'cause the space is worth the cost of the ceiling in that basement. City -- everything is very tight spacewise.
You are talking about holding up the weight of cars to get basement space in a garage. If you're lot is big enough to fit a separate garage, I can't see how it could be worth it. Build a bigger garage.
"Let's get crack-a-lackin" --- Adam Carolla
"You are talking about holding up the weight of cars to get basement space in a garage. If you're lot is big enough to fit a separate garage, I can't see how it could be worth it. Build a bigger garage."Don't forget the amount of drop and footing depth. He already has a "basement".The question does bring in tons and tons of fill to support the garage floor or does it dig it out a little more and then support the floor by a strutural floor of some type.
I've never don it, but I do have a neighbor who did it with his garage. He uses it for storage of his various toys and lawn tools. He didn't put stairs in, the entrance to the basement is a single car garage door in the side that slopes toward a small creek. It is dry, but then it is poured and treated with waterproofing. Wish I had the space.
Yes,proably.
Oh, I thought you asked if you where crazy.
But putting a basement under a garage is not crazy.
I have one, although I am crazy.
In my area (KC) it is common to put up temp shoring and pouring an elevated slab. That is the way mine was done in 79 and within the last 5-10 years there where two additions in my neighborhood that did the same thing.
Other places cast prestressed "planks" are used.
But if I had to do it again I would use ICF's for the foundation walls and also ICF to form the floor. The ones that I have seen in the past also required bracing during the pour, but after curing could span 30ft or so.
But I think that I have heard of some that where self supporting during the pour.
Specially go for the ICF's if you want to use it for shop space and thus heat it.
I've done a few quotes for doing floor trusses for garage floors. But once they find out how much it costs, no one has ever gone through with it.
Spancrete is the only thing I've actually seen done in this situation.
I am getting ready to just this at my home in southern Wisconsin. The plan it to build a conventional 8 inch poured full basement foundation wall. Then, I can have Spancrete planks installed. Google that and read more. They will make the 4 foot wide x 28 foot planks, deliver them on a flatbed truck, and with their crane lay them in place. Although they caulk them during installation, you still need to put some sort of heavy water barrier and then pour a concrete floor above that. My garage will be 36 feet long with a clear 28 foot span. Underneath this garage (supporting my truck and car) will be my commercial woodworking shop.
The Spancrete floor will add about $8,000 to the cost, but then again, I don't have to build a floor. Oh, and they install this in one day.
Good luck.
Joe
Re: Structural Garage Floors with Full Basements.
I think the idea is a good one, especially in places where land costs are high.
I have done 5 or 6 over the years, and have often wonder why more people do not see the value in them.
ICF walls would be a bonus for sure.
Your structural slab's costs can be offset in part, by the lack of backfill materials and compaction and equipment rental costs to backfill the garage.
The structural slab can be formed in numerous ways, but must have a P .Engs involement to satisfy Code and Safety requirements.
The slab can use precast core slab, Litedeck ICF systems, steel bar joists and steel pan decking, steel bar joists and formply ie Hambro System, or can be formed in place using conventional Aluma Scaffolds. Many choices here.
Find a local Formwork and Concrete Pro who keeps a foot in both residential and commercial worlds, and he will have some ideas for you on local choices.
Consider this,put the garage on grade, put the shop above it. Entrance to the shop on the high side of the slope. With seven foot garage ceiling you will have less than three feet to step or ramp up to the doors.You will save considerable money,and you can put windows in your shop. Getting material in and product out will be easier too.
mike
Yes can be & is done quite often.
I mainly do large commercial / industrial plumbing jobs + high rise residential
Weapon of choice now days is PT slab-- post tension slab is about 7" thick span about 40'
Other jobs use bar joist & pan decking slab is about 4" thick in the deep wells.
Next year I'm starting my shop cut into my hillside 15' high poured in p[lace wall 35' long, opposite wall will be split face cmu , roof will be bar joist & pan deck, stamped concrete sloped 1/8" per foot.
Roof will be even with my basement so I'm using it as a large extended patio.
Do you look to the government for an entitlement, or to GOD for empowerment. BDW
About 10 years ago, I used the precast planks to create a second floor over a commercial property I was rebuilding. The block supporting the slabs had to be filled, and we had to leave a ledge around the perimeter both to tie the planks in, as well as to provide a level surface for the block to continue (remember, the planks are cambered). Everything went pretty well, the precast guys were off site before lunch, as I recall.
The application also included a stairwell. Everything fit.
The only real problem with these floors is that you need a topping on them. We used a self-leveling gypsum floor mix (Gypcrete)because the 2nd floor was to be office space, and that stuff literally poured through the seams in the precast. I'd take greater pains to tape/foam/stuff the joints if I did it again. You'll have to use some kind of lightweight concrete topping and make sure that the planks are engineered for the thickness and density of the top pour.
Other than those minor details, it was a good solution.
It's been discussed here before, using either Spancrete or bar joists. If you do a search it should show up. If I remember correctly, VaTom posted a good argument for the bar joist method.
I'm a fan. Very inexpensive and simple.
First time out I spanned 30'. Next house got 40' and they turned out to be very little more expensive. First time I welded the decking to the bar joists. Second time I shot it.
Here's my "basement":PAHS Designer/Builder- Bury it!
We have a basement under the garage and love it (sitting in it right now). We have set up a home theater in it - sound is great.
My neightbor just put one in as well. He put 12'' engineered floor joist on 12 inch centers, with a support beam mid-span. Ours has a support beam as well. 3/4 PT Plywood on the joist, then about 4 inches on concreat poured in.
I always thought that would be good for your neck of the woods for use as storm shelters. That would make the connection details of slab-to-walls critical and would probably lend itself to more of a poured reinforced concrete wall/slab scenario, but I think you could end up with a nice space for refuge from a storm and all the supplies and equipment necessary to ride it out (couch, fridge, TV, all fed from an external generator...) A lot more comfortable than a closet sized safe-room I would think.
As for my neck of the woods - I'm thinking this option might allow me decent space for a shop under a double(+) garage. Just plan in a good double door bilco exit to get the projects outside and voila!
We just don't have the property to build out enough square feet for a good sized workshop and I would really hate scraping ice off the cars in the winter if I gave up the garage to the tools... A little extra investment takes care of both problems.