Build Garage Over Basement

Old 02-16-15, 09:04 PM
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Build Garage Over Basement

Searching this forum, I found this thread where Charlie (mascdm) described a project [of building a garage over a basement] very similar to one I'm considering. Does anyone care to estimate what this should roughly cost today? Feel free to make assumptions. What other construction methods should I consider?

Really appreciate anyone's help.

Last edited by ray2047; 02-17-15 at 06:48 AM.
Old 02-16-15, 09:22 PM
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Post moved to its own thread to avoid confusion.
Old 02-17-15, 08:02 AM
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Any questions on estimates are almost impossible to answer remotely like this. Best bet is to get three or more local bids so you can compare.
Old 02-19-15, 05:23 PM
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Thanks for the help with the new thread, will remember that in the future.

I'll certainly get multiple bids, just thought some folks might have a ballpark idea of the description Charlie provided, at least of the poured foundation/walls and pre-stressed concrete floor planks.

I'm also wondering if there might be additional construction methods to be sure are considered with the bids or if anyone has done something similar with any advice.

This is a great forum! Thanks again!

Here's Charlie's post for reference:

I'm building a 2-1/2 story garage that will be connected to my house by a 12' wide breezeway/deck.

The first floor of the garage is a "walk-out" basement like the house it will attach to as we built into a rather steep slope. As such 2 sides of the basement level of the garage will be excavated into the ground with the garage doors on the fully exposed side (back of house). The fourth side of the garage basement is fully covered at grade in the front sloping to basement grade at the back. I have constructed a steel reinforced 3,000# poured concrete wall on three sides with the bay ends (back) open. The foundation is 24 feet wide and 42 feet long.

Over the top of the basement level I have crane set 8" hollow core pre-stressed concrete floor planks spanning 24 feet. These panels are 24 feet by 8 feet pieces with two cut pieces at each end. The bearing ledge over the concrete foundation wall is 5" along the sides (8" walls) and 7" in the front (10" wall). There is a 3" rim joist bearing on the outside perimeter of the foundation made up of 2-2x12" planks the inside of which is tap-conned into the hollow core planks using 4-3/4x1/4" TapCons yielding a 3-1/4" inbedment with spacing about 24" O.C. Each plank has 2 14" #4 re-rod dowels at each end connecting the plank to the foundation after drilling 14 degree holes through both plank and foundation. All planks are joined at key joints and grouted. After the rim joists and framing plate has been built-up and leveled, it will serve as a perimeter for a 2"+ topping over the planks. Due to the 1-1/2" camber of the planks, the edges of the pour will have close to 3-1/2" of topping which will yield a flat second floor to the garage. This structure will have live, dead, and point loads sufficient to store four 6,000# vehicles on this second floor (parking deck).

A stick-built wall will surround this second level and the entrance will be on the opposite (front side) of the house. This will give the appearance of a simple 1-story 2 car garage connected to what appears to be a 1-story house.

12" rafters will support the attic floor, allowing for a second clear-span 24' wide garage. The attic will be constructed of trusses.

Eventually a dormer out of the 42 foot side of the attic will connect to the house and form a covered breezeway over the deck.

Since a garage needs a floor anyway, which must require excavation/site work. The "extra"/basement floor of my garage basically cost the height of the 8' concrete walls and the cost of the hollow core planks.

It was surprisingly affordable when compared to what an outbuilding such as a pole barn might have cost.

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