Granite Overhang support - does my plan work?
I have read a tonne of similar posts, but none seem to apply specifically to my case...so here goes...
I have a granite island 54"x38" on a 30x24" base cabinet with 12" overhangs on 3 sides. The granite is a 1.25" thick slab and I am right on the fence of supported vs non-supported overhang from what I have read. I am considering adding some supports although I am alredy following the 2/3rds rule for cantilever 1.25" granite: 24" supported with a 12" overhang front to back and 30" supported with a 12" overhang side to side.
The granite will sit on the 3/8" inch furniture board edges which were reinforced with some 3/8" plywood on 3 sides. Due to the unbalanced overhang front to back, I planned to put a couple of L brackets on "3rd" side. These will be hidden and without gussets. Additionally,I thought of perhaps running 2 steel "strips" across to pick up the two side overhangs (as pictured).
1. Are the steel flatbars required? Or is it overkill to have one or both as pictured?
2. Is 1/4" steel appropriate for the brackets and flatbars? or would there be enough rigidity and support in 1/8" thickness?
3. Does a 3" wide vs 2" wide flatbar provide any greater strength, or is it just surface area contacting the granite at that point
4. The flatbars would sit on the cabinet edges which would be notched out to allow the steel to fit flush (i.e. I hadn't planned on adding a plywood top to the cabinets since it wouldnt have any middle support... is this ok?
5. My plan was to have the 1/4 steel stop 2" short of the edge (so theyd remain hidden), i.e. supporting 10" of the 12" overhang? Would I be ok with supporting only 8" of the 12" overhang?
6. Will the 3/8" cab edge + 3/8" plywood (on part of three sides) as a perimeter edge provide enough of a gluing edge for the granite?
Comments (11)
User
11 years agokles
11 years agoRelated Discussions
Does granite overhang need support?
Comments (1)It is necessary. There's been a few recent threads on this topic (you can find Search at the bottom of the front page, right before the 'Post a Message' section). Anything over 10" needs it according to the experts. Also depends on how thick the stone is though, 2cm or 3cm? 3cm is good out to the 10", not so with 2cm. - D...See MoreSupport for 18 inch Granite Peninsula Overhang
Comments (10)cawfee, I've seen large tables made of 2cm granite, without any plywood. (!) They've never cracked. I've seen many renovators who overkill things, just to be sure. Most do. In fact, they all do. Otherwise things would crack or move later. How many simultaneous dancing 200-pounders do you want to support on your countertop, this is the question. I've seen kitchens that were more solid than the walls and the house. How many future earthquakes and foundation cracks will your house live through before your countertop also cracks, this is the question. At some point you have to let go of the wish to overkill, and call it good enough. This is up to you. Sooner is usually the best time. Otherwise you go crazy trying to do ever better. So, "... Obviously, this needs supports ..." is true, to an extent, but what to do next is up to you , and up to your sense of overkill -- Part 2. "... seen mention of 2x1 rectangular steel pipe as supports (12-16 inches apart)..." Search on the term box girder to reassure yourself about "... rectangular steel pipe..." It's the strongest. For its size. But, this following statement isn't knowledge: "... I know I need to support at least 12 inches of the overhang (13-14 to be safe)..." It's a judgement call or a hunch, like most other rules of thumb. You choose "... plywood sit on top of these metal pipes or are the pipes routed into the plywood..." You choose because it doesn't matter. "... screwed down to the cabinets or is the weight of the slab sufficient to hold them in place..." golly, is the weight of the slab a lot of weight? do you want to drill a hole and screw it down just for greater overkill? -- Here it appears you want to save 0.75": " ... lower profile of the 2x1 over the 1 3/4 ..." I'm not sure what you are referring to. I read a lot. I remember a lot. If I don't know what you are referring to, I'll bet that the other readers also don't. I'll bet that most pro installers don't. I think you need to be more diligent about your descriptions. For your slab, nobody knows " ... how much deflection can granite handle ..." Therefore, nobody knows "... What wall thickness ..." But, in my estimation, there is nothing wrong with getting heavyweight wall thickness tube ("square pipe") since overkill is the objective. But, not much is lost if you get lightweight wall thickness tube. All you lose is a bit of the excess overkill. In Engineering, it's called a margin of safety. But it's the same thing. If you are willing to crack a few slabs under very tightly controlled conditions you will know factually how much weight cracks them (and how much microdeflection they will take). It's just a stone from a quarry. It's not a processed material from a factory made and "scientifically studied" material with "known" properties. Don't ask for answers that won't be good numbers. Anyone can invent a numerical answer for you if keep insisting on having numerical answers. How much overkill is enough? Hard to tell, not seeing anything from my keyboard here. Do you know anything about the flex in your floor? This is a big thing. This is the one thing that I recommend you to go look into before proceeding....See MoreSupport for granite overhang
Comments (10)Oh, I meant to mention that shorter people (or shorter-legged people) will be more comfortable than taller (or longer-legged) people with a less than desirable overhang. Our family ranges from 5'10" (me) to my DS (6'6" and still growing) and I'm fine w/the 15" overhang on our counter-height overhang, but my DH (6'5") and my DS think it would have been nicer with another 3"! That's why it's a minimum, I guess. I would assume if we had bar-height we would feel the same way regarding the minimum overhang (12" would be OK for me, but a tad too little for my DH & DS). If you're not planning to use it that often for seating and when you do not for any length of time, then 9" will probably be OK for you. It is your kitchen, so it's up to you what you do! Good luck! [BTW...we recommend one-level counters here to maximize the usefulness of the counter. One-level counters offer a wonderful expanse of workspace for large projects such as baking, crafts, homework, science fair, gift wrapping, etc. But, again, it's up to you. Bi-level counters not only cut into available workspace, but they usually have very little space on the top level (when the top is 42" high). Remember, if you plan to eat at the counter, you need room for a plate...usually they're around 10" in diameter...as well as "wiggle room" so the plate isn't easily knocked off the counter. Then you have drinking glass room...]...See More15" Granite Counter Overhang Supports
Comments (15)You'll need new skins, wider than 48''. Detach the full height cabinets under the proposed overhang. Attach 2 2x4 pressure treated pieces of lumber to the slab with a Hilti or ramset where I show the RED lines. Also use some construction adhesive. Yes, I like belts and suspenders. :) Build a 34.5''H pony walls with conventional framing techniques, taking the wall to the end of the cabinets. Attach the existing cabinets to the pony wall. Reattach the full height cabinets to the pony wall studs. Here is where you will need the custom steel for the 33'' long steel pieces (BLUE) needed to support the overhang. You will also need 12'' ones for the side overhang. They cannot be flat steel, as that is too flexible. 1'' tubing is too thick for your full overlay cabinets, even with the doors adjusted as far down as they will go. You could use 2''W flat 1/4" steel with a 3/8'' ridge welded to it to create rigidity, in a T shape, flat side up. Holes would need to be drilled into it to attach to the pony wall. Once the steel is sourced and created, you can rout out the pony wall (2 step process, once for the ridge, once for the flat stock) and top of the face frame to accept it. Once the steel is attached, then the skins (GREEN) can be applied to the sides and ends to cover the pony wall. You may want some Outside Corner molding and Batten molding as well to hide the seams. This is a serious design deficiency on your KD's part. He should arrange for the cabinetry materials gratis, and also pay something toward the steel. Labor for this will need to have good experience dealing with finished cabinets and routing, so let the KD pay something towrds that as well....See Moredebrak_2008
11 years agokles
11 years agoUser
11 years agodebrak_2008
11 years agodebrak_2008
11 years agoFirst I will show you the layout to show you the shape of the island.
Note the end on the right side (no cabinet) will be radiused.
This is what our installer approved for support. 3/4 inch plywood glued to 1/2 plywood out to within 3 inches of the edge. A steel support will be in the middle of the radiused end which supports 660 lbs which is way more than the granite weighs.
For extra insurance this is what we are doing/did. 1/4 inch plywood (smooth finish) at the bottom, then 3/4 inch plywood on top of it. Note we did this to provide a smooth surface underneath the island and had these materials already on hand. Ok then 2 1/2 inch wide 1/4 inch thick flat steel bars laid about 5 inches apart. 1/4 plywood in between the bars and over the rest of the island. Note no bars over the cabinet. All these glued with locktite glue, lots of clamps and heavy weights were used for several days. We used alot more than what is shown in the pics.
Here of some pics of it now.
Our case is a little different as on top of all of this we are laying a floor heating pad to heat the granite. That is why we went to 3 inches of the edge. Our installer/granite yard showroom has a similiar island on display that we looked at. In that case the plywood only went to 12" of the edge. We plan to add wood trim under the granite to have a nice edge to cover all this plywood. Our installer said we could also angle the edge back if that makes sense.
The only cabinet in at the end by the sink and is 36" wide and 24" deep. Will be building a box behind the cabinet not only for extra support but to run electrical lines in for the heating pad and for electrial outlets that will be in the box.
Hope that all makes sense! Any other questions, just post here or email me directly.
kles
11 years agoUser
11 years agokles
11 years agoMaybe I don't know the difference between framed and frameless (scary, perhaps since I am the one preparing the base cabinet)
I have attached a photo, one showing the frame and one showing how I will laminate the 3/8" plywood to the existing frame. I also have 3/4" ply laminated to the inside back and - not pictured - I will also have 3/8 plywood laminated to the back on the outside.
Here is a link to the manufacturers product spec page, I have the "select" middle category of cabinet
http://www.aristokraft.com/custom_serv/faq/compare_chart/index.cfm
debrak_2008