Re granite counter tops. Was told that 3/4 inch thickness for 32 square feet weighs 2000 pounds. Is there a weight tolerance that the floor joists can take for a counter top? Is it related to the spacing of the joists? Also quoted for 1.5 inch thick at 4000 pounds. Please advise re weight tolerance.
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Replies
Floors generally have a design load of 40 PSF live, and around 50 total. Your countertops may be enough that they could cause problems with a marginal floor. (If they weigh as much as you said)
Is this a new floor or an existing one? If it's a planned house that hasn't been built yet, your floor could be designed for whatever loading you want.
If the floor is existing, someone probably needs to look at it once you know for sure what your coutertops will weigh.
If it weighs 4000 pounds, that's 125 pounds per square foot. I think code in most codes books, dead load is more like 10 or maybe 20. If it weighs only 2000 pounds, the load is still 63 per square foot. That seems high to me. There is a limit to what floor joists are designed to take and it does depend on spacing--also depends on depth of the joints and the span. Lots of stuff to consider. (I think your weights may be high though--I've seen granite counter tops carried into houses by two guys (though they were more like 12 square feet, but I still think a ton for 32 sq. ft. is high).) If 12 square feet weighed 240 pounds (and that even seems high to me) that would be 20 pounds per sq. ft. dead load. I'm guessing its more like 10 per ft and that would make it okay for most floors. (But read on, please!)
I have never seen anyone worry about the weight of granite counter tops though--have helped remodel several where granite tops were added and no one ever beefed up the floor joists. I suppose one saving grace may be where the counters are on the exterior walls and have the foundation helping with some of the load.
See what others here have to say, but I'd be inclined to get a builder or engineer calculate what the loads are and what your particular floor system will hold. Again, though, I question whether granite weighs as much as you were told. 125 pounds for a piece 1 foot square and 3/4" thick seems excessive.
I have never heard of floors being specially engineered for granite counter tops. Further, I have seen some granite counter tops installed by 2 or 3 guys. Granted they have a special dolly to get the counter top into the house, but they do lift them in place... Which to me says that a section might weigh a few or several hundred pounds but not anything close to a thousand. So, I Googled the weight of granite and below is what I came up with:
From this web page:
Q. How much does granite weigh?
A. Granite tiles and slabs come in different thicknesses. The weight per square foot for each thickness is as follows:
And, from this web page:
Take your estimated square feet and multiply by 18# for 2cm and 23# for 3cm. This will give you your weight.
And from this web page:
Q. How much does granite weigh?
A. Granite tiles and slabs come in different thicknesses. The weight per square foot for each thickness is as follows:
· 3/8"(10mm) thick tile: 5.5 lbs sq. ft.
· 1/2"(12mm) thick tile: 6.5 lbs. sq. ft.
· 3/4"(20mm) thick slab: 12.8 lbs. sq. ft.
· 1 1/4"(30mm) thick slab: 18 lbs sq. ft.
I'm sure you can find more if you do some searching. So, my conclusion is that the weight you were given for granite is incorrect.
Along the same lines as what Matt said right before me.
I've never heard of anyone doing anything different because they were installing granite, and I've been in on maybe 100 kitchens that have granite installed.
The last kitchen that I worked on that had it(granite) the island was a about 4'X8', grainite was doubled up on the perimiter and it took 4 guys to carry it in but I doubt that it possed any problem for the floor joists.
Doug
I think someone slipped a decimal.
By my really crude math, your slab should weigh around 200 (2 hundred) pounds, not 2000 (2 thousand).
It's only a 4'x8'x3/4" sheet.
SamT
Guys that don't do things correctly the first time.....then argue that they did nothing wrong.....if made to agree to fix the problem, rarely put the time and effort into truely doing it properly. they'll just look for the quickest fix to appease you and get their money. JDRHI 84310.51
Sam, you're a little too conservative.
32x12.8=409.6 lbs.A great place for Information, Comraderie, and a sucker punch.
Remodeling Contractor just outside the Glass City.
http://www.quittintime.com/
Sam, you're a little too conservative.
You mean ma math was too crude dontcha?
at 27xx kilos/cubic meter, I did it all in muh haid.
Anywaaaay, I knew without cheking that a 4x8x3/4 slab dint way no ton.SamT
Guys that don't do things correctly the first time.....then argue that they did nothing wrong.....if made to agree to fix the problem, rarely put the time and effort into truely doing it properly. they'll just look for the quickest fix to appease you and get their money. JDRHI <!----><!----> 84310.51
Don't worry about the math.
Most of us that know you realized right away you are way too conservative.A great place for Information, Comraderie, and a sucker punch.
Remodeling Contractor just outside the Glass City.
http://www.quittintime.com/
its 32 sf, average granite is 20 lbs per sf = 640 lbs per sf, that's like 2 refrigerators:
if its a high grade granite it could weigh more like 30 lbs per s.f. and that = 960 lbs per sf.
32 s.f. x weight per s.f. , be careful when using heavy materials in older homes, granite makes the perfect outdoor countertop, there are a million options for indoor use.
sorry, 640 lbs, and 960 lbs. of course spread across whatever is holding up the floor in whichever direction.
Sounds like someone confused cubic foot weight and sq foot weight.
Dont think you need to worry unless the floor is inadequate in the 1st place.
maybe not inadequate, but perhaps designed prior to the use of stone countertops.
a floor joist is a floor joist
What is the existing floor framing--joist size, spacing, and span?
Until we know that, nothing can be said. I have seen large island cabs with granite tops placed in the middle of a floor and cause it to sag to the point that it needed fixing. If your framing is close to the limit then the same may happen.
Agree that your slab does not weigh 4000 lbs.
Reading what others said, I do think the info you had either had the decimal in wrong place or was talking weight per cubic foot. At any rate, the cabinets would probably be crushed before the floor gave way if it weighed 2-4000 pounds for 32 sq. ft.!
I found a website that listed granite at 166.5 lb per cubic foot. That's 10.4 lb per square foot for a 3/4" thick slab, 17.3 lb per SF for 1-1/4" thickness. Any properly designed floor system can handle that.
the weights these guys are giving you aare right on the money.i took a pc 2 sg foot and weighed it for our tops.i wanted to know how many guys it would take to lift it. mine came in at 15.5 lbs 1 1/4 thick. about 35 sq. ft. i had 6 guys to grab it and it worked out well with the lift. larry
hand me the chainsaw, i need to trim the casing just a hair.
Floor specs should always be considered, unless we're talking about building minimum code apartments or rentals.
The results may not be seen this year, or next, but having remodeled a few old houses that had marginal floor joists in the kitchen I can say without hesitation that building for the actual loads being placed on the floors is a necessity. Do you really want your work to have noticable sags in 50 years? Sure, you'll be gone, or at least chasing widows at the old folks home, but that level of building isn't something that I'm interested in.
Park a fridge in the middle of a 40lb/10lb span and come back in 20 years to measure the sag. That's almost hack work.
Good building.
Beer was created so carpenters wouldn't rule the world.
I knew I was going to have heavy furniture, stone counters and lots of tile in my house, as well as frequent live loads (large family). I designed my floor joists for 100 psf live, 25 dead. Not taking any chances. Overkill? Yes, but it's MY house.
That's exactly the right thing to do, especially with tile. Deflection is the enemy of tile and grout so over building really isn't over building, it's simply common sense good construction.
Cheers
Beer was created so carpenters wouldn't rule the world.
yep
Dude, go back and retake fourth grade science. Water is 62.4 lb per cubic foot, varying by a few ounces with extremes in temperature and altitude. ASTM gives a minimum weight of granite at 160 lb/cf, which is at the upper end of the weight scale for natural stone (marble being higher by 2 lb/cf). I've always used 150 lb/cf as a rough estimate of the weight of cured concrete, and you can't tell me that granite weighs more than twice what concrete does. Your 2.5 to 2.7 number is on the money, however, if the proper weight of water is used.
You are right, I pressed "X" twice!
I'm the biggest kid in my class, and I am the starting center on our basketball team.
Water weighs about 135 lbs/ ft*3
Water = 62.42796# ft3
Puts granite at 170# ft3
SamT
Guys that don't do things correctly the first time.....then argue that they did nothing wrong.....if made to agree to fix the problem, rarely put the time and effort into truely doing it properly. they'll just look for the quickest fix to appease you and get their money. JDRHI 84310.51
I work with a lot of outdoor kitchens and new construction. But my home is a 1960's home with a full basement. I would not even consider using a countertop made of heavy granite. or a stone that is anywhere near or above 30lbs per sf. just because this is an older home, and its not really a material I would want in my indoor kitchen, I would prefer soapstone, or a nice laminate. Which would be so much easier to change when the next update comes around. If I was building a home for myself and knew for certain I would love a certain granite forever I would design with it in mind. But with stone all different types are different weights, with granite there is a large variety with the 2" think average at 30 lbs per sf, but thats an average, darker granite slabs are heavier than light colored. It all depends on the amount of granite etc in the slab. Just remember that in a home that is older, it is better safe than sorry. Yes a refrigerator may weigh about 200 lbs as well, and should be placed in a position to stand that weight. The older a home gets the more you will see dead load effects. Never underestimate the long term effect. That is just unethical and rude to the unknowing homeowner, unless its yourself, then hey go put an elephant in your kitchen who cares.
....also, I must interject into the primary issue: that a 2 in thick and 32 sf slab of granite could easily weigh around 960 lbs, going with a midline 30 lbs per s.f., could be more could be less.
However, the real issues is the configuration of the slab of granite and how the slab and countertop lays across floor joists or along the joist length, also if it is on a slab, and then how thick that slab is. You can do what you want, but granite is the most common element on earth and in my opinion I am not paying average 90 dollars a s.f. to have it installed. Then someday hate it... even if money is no object why pay so much for something so common, soapstone is a much better choice. In fact there are many many options. Granite is just the poodle of the century.