Supporting a large overhang with a steel frame
Hi,
I have an 8 foot by 4 foot island in my kitchen. Attached to the back of the island (in the center of the 8 foot lenght) is a 24″ by 30″ base cabinet that is the base for the granite table top I will be putting counter height bar stools around. The table top is planned in size for 4 feet by 5 1/2 feet.
I do not want to use any corbels or legs on this attached table top, just the attached cabinet base. The granite overhang on the two sides of the table top will be 18″. The granite overhang (or should I call it an extention?) on the last side of the table top, opposite the 8 foot island, will be 24″.
The granite table top (4 feet by 5 1/2 feet) that will be sitting on the 24″ by 30″ base cabinet will obviously need more than a plywood sub top for support.
My questions are:
- How much steel should we use?
- Are steel straps enough?
- Should we use a solid Steel sub top with the plywood?
- Should we use marine plywood with the steel or just regular plywood?
- In choosing the steel, is there a certain kind or thickness?
- Can I go with a longer overhang/extention than the 24″?
I want to put six 20″ wide counter stools arount the granite table top (that only has 3 sides) and it appears that the 4 feet by 5 1/2 feet dimension my be too small to fit all six of the stools. I think I may need to add 6″ to 12″ more to the 24″ end of the granite overhang/extention making the overhang/extention 30″ to 36″. Is it possible to go with that long of an extention with just the steel support and not adding legs or corbels?
Thank you for any advice you can give me.
Susie
Hi Sue,
The information about Santa Cecelia helps because some granites colors are denser and stronger. This one is just about average. I still do not know what thickness you are going to use so that also doesn’t allow me to understand the strength of the stone. For example, 1 1/4″ thick is common on the East Coast, while 3/4″ with a built-up edge is more common on the West coast. The 1 1/4″ thickness is much stronger.
Anyway, you can do what you want with steel but because of the huge overhang, you will need to build a complete steel frame under the countertop and affix it to the cabinet. Since it is interior you really don’t need stainless but you should prime the steel, nonetheless. I recommend using galvanized steel and then prime it with a Rust-Oleum metal priming paint.
You can not cantilever granite with flat steel bar because the steel will bend and since the granite will not flex, the granite will break. You have to create “T” shapes in the frame and I recommend 1/4″ thick steel for this huge overhang. You will have to have it welded. The legs of the “T” should be about 1″ tall and the top of the “T” about 3″ wide.
This might seem daunting but all you really have to do is draw it up. Then go to a small steel shop (there are little pockets of these shops near every town) and have them cut and weld it up for you.
Make the frame as big as the underside of the granite countertop so that it slip in behind the nosing. Also, remember to have the steel shop weld 14 gauge clips to the frame where the cabinet edges are so that you can screw the frame on to the cabinet. Have them punch holes in the bottom of the clip so that you don’t have to drill through it. Note that you need to test the frame after it is place to be sure that screwing down to the cabinet has been down adequately.
Again, start with a piece a paper and just draw out the frame. Then do the measurements. Show cross “T” bracing at least 18″ apart in both directions. Make sure that there are at least two cross braces at every overhang area, extending to the nosing (perpendicular). Once you have your accurate drawing, the rest is easy.
Best wishes!
