How to support span of granite countertop?

[Aaron Hastings]

I recently installed cabinets in our basement kitchen area. We have a 62" under-counter bar fridge than will be placed under granite. I planned to support the granite over this span with (2) 1x1" angle iron, 1/8" thick.

Any opinions on whether this should be sufficient?

Thanks in advance....

AH

[Jamie Buxton]

That strikes me as insufficent. Get yourself a piece of that angle iron 62" long, and lean on it. You'll see it flexes pretty easily. A 2x4 is stiffer.

I'd bridge the gap with construction lumber -- 2 x 6 or 2 x 8 . Not one or two lengths, but an entire 24" of depth.

[Stephen Saar]

I'm not an expert on this but if the expanse you have to support is 62" total, and you have supports on each side then you only have to account for 31" worth of leverage. Another question is how thick is your counter top. If it's 6" of solid granite I would worry about it, but if it's 1/2" of particle board I would definitely put some thicker supports. From the metal work I have done, I would think something like a 1.5"x1.5" inch angel iron at .25 inches thick would definitely suffice, but it all depends upon how everything else is setup, and how much force you anticipate this counter to be under.

-Stephen

[Aaron Hastings]

I got the angle iron, and you are right, it flexes and that won't do for granite.

I think I'll stack two higher quality 3/4" plys. That makes the counter 3/4" higher than I wanted. I would think it might be enough. Would that be similar to laying 2x6s in there? I would guess stacking ply would provide less bend than 2x6s......

I've seen granite span over 60 inches, but I don't know how they supported it.....

[Jamie Buxton]

I got the angle iron, and you are right, it flexes and that won't do for granite.

I think I'll stack two higher quality 3/4" plys. That makes the counter 3/4" higher than I wanted. I would think it might be enough. Would that be similar to laying 2x6s in there? I would guess stacking ply would provide less bend than 2x6s......

I've seen granite span over 60 inches, but I don't know how they supported it.....

Solid lumber is stiffer than the same thickness of plywood made from the same species.
Google Sagulator for numbers.

[Aaron Hastings]

Solid lumber is stiffer than the same thickness of plywood made from the same species.
Google Sagulator for numbers.


Thanks for the info.

There's 0.001" more sag per foot with fir ply vs. solid pine at the same thickness.

[Sam Layton]

Aaron,

You may also want to ask your installer what he recommends. If you are the installer, ask where you purchase the granite. Granite does not flex very well.

Is it possible to place a support to the floor somewhere within that 62" span?

Sam

[Jamie Buxton]

Thanks for the info.

There's 0.001" more sag per foot with fir ply vs. solid pine at the same thickness.

You can look at the numbers any way you like, but the way I see it, fir plywood sags about 75% more than fir lumber of the same thickness.

[David Cefai]

Angle iron flexes but box section is much more rigid. I have no experience with granite but when I want rigid I use 20mm square box section.

You could consider using box section butyou'll have to decide whether it is rigid enough.

[Chris Parks]

Two or three torsion boxes all narrow but deep in ratio, or one big one for that matter. Not knowing the clearance under the granite I am guessing but it would work given the depth of the torsion box(es) is enough. You could also make a small I beam out four bits of suitable sized angle and a welder, that would work also. Weld two lots of two pieces back to back then join the flanges together with a series of butt welds along its length, voila! one small I beam made to order.

[John Downey]

I'd go with a few hardwood ribs on edge, maybe two inches tall. Maybe three or four if its a two foot deep counter. Depends on your slab thickness too, thicker slabs need less span support. If you're getting thick granite - say 1 1/4" you might get away with less support.

Stay away from steel. On the scales we're looking at wood is stiffer and stiffness is what you're looking for. Torsion boxes are good too, but flat plywood is too flexible, even with two layers glued together. You'd be better off with a 1 1/2" tall oak rib instead of two plywood laths.

[Mike Hollingsworth]

Granite comes in 2cm (3/4") and 3cm (1 1/8") thickness. I'll bet 3cm would span that 5 feet no problem.

[Chris Parks]

Stay away from steel. On the scales we're looking at wood is stiffer and stiffness is what you're looking for.

Not right, I could fabricate a steel beam to be as stiff as any torsion box or piece of timber. Torsion boxes need as much work as fabricating a steel beam, much the same thing just two different materials. For the woodworker the obvious thing is to think in timber as he can fabricate a torsion box easier as a general rule. If a welder is available steel would be done and dusted by the time a torsion box was built.

[Aaron Hastings]

Well, after much discussion with the granite folks, we decided on two 2X8s reinforced their entire length on 2 sides with 1.5 X 1.5 X 1/8" angle iron, secured with 5/16" X 1.25" screws every 12". On the wall we took another angle iron and secured it into the studs with 2.75" X 5/16" screws.

So in total:

5 angle irons
2 2x8s
Cabinet support on each end.


I can jump on it.

[Aaron Hastings]

Granite comes in 2cm (3/4") and 3cm (1 1/8") thickness. I'll bet 3cm would span that 5 feet no problem.


It'll span it just fine. But if there's adequate pressure in the middle (stand on it or sit on it), the granite folks say there's a good chance it'll break.

If this $1000 slice of granite shatters, I'm getting a fabricated iron "mattress".

[Mark Smith, too]

How about a wooden I-beam? Use 1 by material for the top and bottom and plywood for the web. I'll bet it wouldn't have to be too tall to be pretty rigid. Dado the top and bottom pieces and glue in the web.

[Gord Clement]

BUMP**

Any follow up on this? What did you end up doing in the end?

I have the same problem with almost the same length.

[Ole Anderson]

Think about how much that granite has to flex before it cracks, almost zero. Now think about how much the wood/steel will flex with the same weight it took for the granite to flex before it cracked and you realize you need something as stiff as the granite, good luck. Yea don't jump on the granite to test your support system. Once it is installed, I would gently push a thin tapered wood shim between the granite and support beam to preload your support with about the same force as you would get by leaning heavily on the bar. That way when someone does lean heavily on the bar, it just puts the granite back to where it would be without any load and without the support, and now you have a safety factor.

Edit: Oh, wow, I didn't see the date of the original post. Oh well, here is an idea for someone else with the same problem.

[Rick Moyer]

BUMP**

Any follow up on this? What did you end up doing in the end?

I have the same problem with almost the same length.


Well, after much discussion with the granite folks, we decided on two 2X8s reinforced their entire length on 2 sides with 1.5 X 1.5 X 1/8" angle iron, secured with 5/16" X 1.25" screws every 12". On the wall we took another angle iron and secured it into the studs with 2.75" X 5/16" screws.

So in total:

5 angle irons
2 2x8s
Cabinet support on each end.


I can jump on it.
He answered your question a few posts above your post.

[Rob Sack]

Granite comes in 2cm (3/4") and 3cm (1 1/8") thickness. I'll bet 3cm would span that 5 feet no problem.Granite is a natural product that can and often does have internal cracks and fissures that might give way if just the right amount of force happens to be applied at just the right place. I've seen it happen on breakfast bars of natural stone that were not adequately supported. A 200# person pushing down on the counter to lift themselves out of their seat is all it takes. As much as I like to use torsion boxes, if it were me, I would use several pieces of square steel pipe running from side to side with as thick a wall and as large an overall outside dimension as possible and hope for the best. If there is not enough vertical clearance for this support system, I would epoxy 1/4" steel flat stock pieces, each piece 3" - 4 " wide, to the underside of the the thickest granite available.

[Gord Clement]

Rick,

Thanks for posting that. I think the thread was messed up. When first load it it doesn't show that reply post. If I click on the hybrid view I can catch that response.

So if I were to run 2x8's the length does anyone have recommendations on how to fasten them with the most support. I could screw them into the cabinet from inside the cabinet screwing vertically or I could chisel a U-Joint in the cabinet and lay the 2x8 in it and screw downward into the 3/4" cabinet end?

Thanks everyone for their help!

[Ryan Baker]

I did a section about that size in my kitchen. I fabricated a ladder frame out of 1X2" rectangular steel tubing, which is held up by angle brackets of the same material at every stud (plus other supports at the ends). Works great. I wouldn't do it with wood, because it will be way too oversize by the time it is stiff enough (with the exception of some torsion boxes -- but that takes too much time and effort). If you can't hang your weight on it without it flexing at all, it isn't stiff enough.

[Gord Clement]

I did a section about that size in my kitchen. I fabricated a ladder frame out of 1X2" rectangular steel tubing, which is held up by angle brackets of the same material at every stud (plus other supports at the ends). Works great. I wouldn't do it with wood, because it will be way too oversize by the time it is stiff enough (with the exception of some torsion boxes -- but that takes too much time and effort). If you can't hang your weight on it without it flexing at all, it isn't stiff enough.

Thanks Ryan,

How did you make the ladder frame out of the steel tubing? Did you have it welded?

[Curt Harms]

Angle iron flexes but box section is much more rigid. I have no experience with granite but when I want rigid I use 20mm square box section.

You could consider using box section butyou'll have to decide whether it is rigid enough.

1" square tubing is what Corian installation manuals recommend for long spans. I'd imagine Granite is as heavy or heavier so thick walled and/or larger square steel tube should work.

[Ryan Baker]

Thanks Ryan,

How did you make the ladder frame out of the steel tubing? Did you have it welded?

Yes. I did the welding.

Here's a picture to give the idea. The leg at the right was added because it is attached to a half-wall and it needed some support to keep from pulling the half-wall over. :) It's all hidden with cherry facing now with green/black granite on top.
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