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Old 09-08-2012, 06:20 PM   #1
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Anchoring existing garage to new concrete slab


Here is my situation and my solution after talking to a million people and reading what I could find in this forum.

My 10x18 "shed" had studs and floor joists (all 2x4s) resting directly on cinder blocks which had sunk below grade over the years (since before 1977) and were rotten to the point of being able to kick some of them apart when I pulled up the plywood floor. I raised the whole structure and cut off the bottom 6" of the shed (all rotten). I poured an 8" slab (4000 psi) as a new base. It was my first time, and I got everything right except I went to place the anchor bolts too late and the concrete had set up....this is my problem.

My solution: drill into concrete and use 1/2" x 6" expansion anchors through a 2x6" pressure treated sill plate over a sill gasket. The anchors should penetrate the concrete by about 4". The tech specs on this size bolt require it to be at least 2.5" from concrete edge, so I think this prevents me from using a 2x4 sill plate (studs are 2x4). I can't seem to find requirements on spacing so as the wall studs are 24" o.c., I thought I'd put an anchor between each stud (9 per long side, 5 on end, 2 on end with garage door). Then I'll lower the garage down, toe nail the studs to the sill, sheath the wall ensuring it is nailed also to sill and call it a day.

I'm in Toronto. No hurricanes here but will this be sufficient hold down strength? I'd like everyone to say that this plan will work fine. So, let me hear that (or the bad news)...

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Old 09-08-2012, 06:28 PM   #2
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Anchoring existing garage to new concrete slab


Could you drill closer to the edge and epoxy to secure the bolts instead of expansion anchors?

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Old 09-08-2012, 06:41 PM   #3
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Anchoring existing garage to new concrete slab


I don't know. I would assume that any fastener too close to the edge would have a decreased load capacity. Aren't epoxy fasteners more expensive as well?
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Old 09-08-2012, 07:10 PM   #4
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Anchoring existing garage to new concrete slab


You may want to call and find out if hurricane straps are required in your area.

As far as wedge anchor vs epoxy, this thread had detailed info on epoxy Anchor Bolts Red Head Vs Epoxy
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Old 09-08-2012, 07:24 PM   #5
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Anchoring existing garage to new concrete slab


Rule of thumb, center of anchor no closer to edge than five X diameter of anchor. But 2 1/2 fits on a 2X4. Your 2X6 idea will work. Your studs are hanging all snaggly tooth now, no bottom plate? Mark off sill plate for studs, drill anchor holes thru plate, set plate on slab, drill thru enuff with masonry bit to mark slab, move plate and then drill slab. Easier to mark and miss studs with hole than mark anchor positions on sill, drill and hit anchor. Slightly over size hole in plate helps get it in position.
Anchor spacing is one at each end within 12 inches of end of plate, including ends at garage opening, anchors in between, no more than 6 feet apart.
Might check with local code folks on depth, size and spacing tho, Probably all metric anyway. Physics teacher, my son teaches physics, you oughta be able to figure this out, once your garage is all fastened down for when the repeal the law of gravity, you can clean it witha perfect vacuum.
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Old 09-08-2012, 08:55 PM   #6
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Anchoring existing garage to new concrete slab


Allthumbs: The epoxy/anchor link was a very helpful read. Hadn't though of hurricane straps. Thanks.

notmrjohn: What was that "gravity" thing you mentioned? I've seen that word in my textbook, but didn't pay it much attention.

Sounds like we are on the same page. I have heard 6 foot spacing reference as well (only 4 anchors on an 18 foot wall???), it just doesn't sound like enough to me so I figured that upping to every 2 feet couldn't hurt.
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Old 09-08-2012, 09:36 PM   #7
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Anchoring existing garage to new concrete slab


I don't know the height on your shed, door location and your height, but with 6" hacked off, is your head going to clear the door header?

Although it would only give you extra 1.5", you might want to consider doubling up on that 2x6 sill plate (obviously you would have to buy a longer bolt).
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Old 09-08-2012, 10:17 PM   #8
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Anchoring existing garage to new concrete slab


"(only 4 anchors on an 18 foot wall???), it just doesn't sound like enough" remember that gravity thing you were askin about? Also sometin called friction is involved. look this was all figured out by engineers, folks who actually have to make things instead of just thinkin about it. But more won't hurt, just more work.
thumbs, I saw that movie (cue ominous music) bum bum bumbum bumbum,, "We're gonna need a longer bolt!" SAWS all about a giant man chewin Misubishi miter saw. Scaaaary

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