Speaking of Waterbeds, Refrigerators and Weight Stacks…


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Waterbeds and fully loaded refrigerators can weigh as much as 2000lbs and the only times I’ve ever seen ’em fall through a floor was on Saturday morning cartoons when I was a kid.

But how much fitness equipment can your floor handle?

Assuming your home has been built sometime after the dark ages, it’s likely you have a ¾” subfloor plus another ¾” of “finish floor” – usually plywood panels.  The top surface of this 1.5″ thick stack of lumber is what your carpet, linoleum, tile, hardwood, etc attaches to.

Current building code requires floor joists to be spaced no more than 16″ apart though there are instances in which they may be built as close as 12″.  This spacing is where you get your real support. The type of lumber (or engineered material such as Glu-Lam) are additional considerations, but the main factor which determines load carrying capacity is the size of the joists.  Other factors being equal, a 2×12 will be stronger than a 2×10 which is stronger than a 2×8, and so on.

There is an amount of deflection – or vertical “flex” – allowed by building code.  The greater the span (read: the unsupported length of the floor joists), the more deflection you’ll expect in the middle of the room.

Common vertical deflection limits are L/360, L/480, L/600 and even L/720.  Using this notation, L is the length of a joist as it spans from one supportive wall to the other.  Simply divide the length by the respective limit.  Builders then use span tables to determine appropriate materials and dimensions.

To interpret using the minimum code of L/360, let’s assume you have a room that is 12′ long between load bearing walls.  Divide 12′ (that’s 144″) by 360 and you come up with a limit of .4″ deflection in the center of the room.  That’s normal and expected in a room built to minimum specs.  Higher limits result in even less deflection, so if you’re building a new home and know you want to include space for a gym, be sure to discuss your plans with your builders.

If you don’t want to consult with a structural engineer to determine the exact limits of an existing home, but you really enjoy driving yourself crazy with calculations and the finer details of building construction, here are a few resources you might find interesting:

www.southernpine.com/spantables.shtml

http://en.wikipedia.org/wiki/Dead_load

www.awc.org/calculators/span/calc/timbercalcstyle.asp

And if that still isn’t engineer-y enough for ya’, you might want to pick up a copy of the Architectural Graphics Standards.  I hear it makes for a nice bathroom read – if you’re into that kind of thing.

While it’s tempting to say something along the lines of “a 10’x12′ room has a weight capacity of XXXX lbs”, you’d really need a qualified builder or engineer to assess the structure and provide guidelines tailored to your specific requirements.

To wrap this up with the simplest guideline I can give (it’s about time, huh?), place your heaviest objects near load-bearing walls, distribute weights as evenly as possible/practical and don’t drop weights unnecessarily.

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