Supporting Overhanging Granite
Building a structurally sound kitchen island. November 22, 2004
I'm building a kitchen island with a 9' seating area along one side. I normally work in face frame, so I have a stile to land a bracket on. This time I'm frameless, so how do I support the 9' x 12" span? The cabinets behind the knee hole are 12" deep backed up to 24" deep bases facing the other side. Any brilliant ideas out there?
From contributor A:
This will sound a bit trite, but you'll need to get a new designer, and then find a metal fabricator to make a piece of plate steel the shape of the counter less a bit for the edge buildup. Take this to the counter fabricator and have him laminate this to the underside of the top. The edge buildup will hide the plate steel.
From contributor V:
If it's not too late, you can build the cabs a few inches less in width and add a pillar/column between a couple cabs to land a bracket on. These can become an interesting design element as well.
From contributor M:
I agree with contributor A. I've used 5/8" plate steel runners bolted to the cabinet and cantilevered over the back side to support the granite overhang. I've filled in the remaining space with 5/8" ply. The granite fabricators appreciate it when installing the tops.
From contributor B:
Overhang in granite does not need corbels or steel support up to 12 inches. 3/4" thick granite with a 5/8 or 3/4 plywood subtop will cantilever 12" without problems. Been doing this for many years without a call-back.
From contributor P:
We regularly have a 12" overhang on all our peninsula or island cabs with no brackets or corbels. But the granite tops used are 1 1/8" thick.
From contributor D:
I too have had no problems overhanging granite. I freqently use wood corbels. The granite is very strong.
From contributor R:
If you want to overhang more than 12" but don't want to mess with plate steel, you could use 3/4 x 3/4 angle and cut kerfs in tops of cab sides and run it along back of front stretcher and front of rear stretcher and screw into edges of stretchers. If the angle faces away from the stretchers, then you only need to rout 3/4" deep on tops of sides. Takes longer to explain than do. Then I have made wooden covers for the angles at the overhang. That does take a little while, but if corbels aren't part of the look, these are almost invisible and aren't knee bangers if it is a seating area.
From contributor K:
With frameless cabinets, you can make extended supports for countertops with regular 4/4 hardwood stock. The supports between the cabinets are T shaped. The vertical leg of the T (about 2 1/12" to 3" wide) is sandwiched between the cabinets and projected forward to the same plane as the door faces and act as separators. Use a couple of dowels to attach the horizontal crossbar of the T (same 2 1/2 to 3" width as the vertical leg is fine) to the leg and install them as single pieces. The overall is the same height as your cabinet boxes.
About half of the crossbar is between the cabinets - say 11 " or so - and the other half is the actual support - as long as it needs to be. About an inch shy of the plywood rough top works. Taper the support half of the crossbar to about 1 1/4" at the end to make a nice low-profile shape.
By extending the top rail of the finish end panels to match the profile of the inner supports, there is support out to the corners of the countertop. It makes for a non-standard frame construction but solves the problem of where to put the outboard supports.
Insert filler top rails between the supports that are wide enough to lower the door top edges so they can swing past 90 degrees. If they are about 3 3/4" wide, they will accept 110 V outlet boxes and you can route the wire up between the cabinets in the 3/4" space the supports have created.
Screw the plywood rough top to the cabinets and supports and it will be very stiff and strong. A 9' back will probably have 5 cabinets, so the span between supports is only about 20". You can add matching build-down edges to the plywood edges if you want more edge stiffness or to straighten out wavy plywood.
From the original questioner:
Wow! You guys are awesome! Thanks for the replies.
From contributor D:
My granite guy likes me to cut rough top flush with cabinet. He laminates a second piece to the bottom of the top so you only see stone from underneath. I believe he uses rebar between layers, so no support is needed up to 15" or so.
From contributor T:
For an overhang up to 12", no support should be necessary. If it's specified, or if the OH is greater, we will dado 1/4" x 1-1/2" steel into the bottom of the rough top every 12-18". Glue it with construction adhesive. Screw down your rough top and you have a virtual steel rough top - fast, easy, cheap.