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I have a concrete garage with an opening measuring 99" wide by 85" high. There is 10" of concrete from the door opening to the left and right walls and about 1' above. All walls are 8" thick and there is nothing above the garage except a wooden flat roof.

I want to enlarge the door opening by shaving off 4" of concrete on each side which requires two 8" deep cuts that are 7' long.

  1. Will it significantly affect the structural integrity of the garage? In other words is there a chance it will collapse and do I need additional reinforcement?

  2. What is the effort and materials involved in it? Can I do it myself if I rent a 14"-16" concrete saw? I will need to cut from both sides as it will not be deep enough to cut 8".

  3. Is there anything else I need to be aware of for this kind of project?

  4. Is it worth paying $800 to a contractor rather than doing it myself?

Here are some pictures to give an idea (click for full size):

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enter image description here

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If somebody is willing to do it for $800.00, I'd probably let them do it (as long as they're insured). There's likely rebar, or other reinforcement means embedded in the concrete. Not to mention what a dusty, messy, pain in the arse job cutting concrete is. –  Tester101 Mar 13 '12 at 19:42
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You will kill yourself with that saw. A guy who thinks he can do it for $800 will also probably kill himself with that saw. –  dbracey Mar 13 '12 at 19:50
    
I've used a concrete saw once in my life. Inside, with no dust mitigation. Never again. –  Doresoom Mar 13 '12 at 20:25
    
The inside photo shows a large crack at the top of the wall that may be supporting the header.For $800 dollars let them take the risk and deal with the ton of concrete you will have to dispose of. –  mikes Mar 13 '12 at 21:26
    
What do you need the extra 4" for? Anything that spans the entire doorway is already within a few inches of the walls. –  BMitch Mar 14 '12 at 1:41
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1 Answer

up vote 2 down vote accepted

Assuming the lintel I see in the second picture travels over the block wall, it should be safe to cut the opening. I'm a contractor and if I could get a subcontractor to do it for $800 and guarantee it in writing, he'd be hired. It better be a good straight cut I can frame to. Be sure to calculate the proper rough opening you really need and add an inch. It is easy to add shims, but cutting again is expensive.

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maybe dicker the contractor to $500. lololol –  shirlock homes Mar 14 '12 at 0:00
    
Thanks. Lintel is, presumably, a 2x6 joist bolted directly to overhead concrete part. I only installed it recently and garage didn't have any wood frame or roof for at least a year. –  Uncle Meat Mar 14 '12 at 0:42
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