<BIG><BIG><B><BIG>Wood Floor Design Loads</BIG></B></BIG></BIG>
<BIG>In the United States the minimum design floor live loads are stipulated in pounds per square foot (psf) by either state or local building codes. An example of typical design live loads might be 200 or 150 psf for a storage warehouse, 100 psf for a public meeting room, 50 psf for an office and 40 psf for a single family residence or apartment building. So, your home should be able to safely support a uniform live load of </BIG><BIG>at least</BIG><BIG> 40 psf. But keep in mind that this design live load is theoretically spread uniformly over the entire floor from wall to wall throughout your entire house. It is not a maximum load on any given area of the floor, it is just a theoretical average load that is used to design the floor for loads that are initially unknown. Some people find this confusing because in reality it is not the floor pressure (in psf) that matters at all, it is the floor load in pounds that really creates the stress in the primary structural framing members. </BIG>
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<SMALL><SMALL><SMALL><BIG><BIG><BIG>Myth #1</BIG></BIG></BIG><BIG><BIG><BIG>: </BIG></BIG><BIG><B><BIG>"According to the building code my house can only support a maximum total load of 40 psf anywhere on the floor."</BIG></B></BIG><BIG><BIG> </BIG></BIG></BIG></SMALL></SMALL></SMALL>
<BIG>No, the 40 psf is a theoretical uniform design live load over your </BIG><BIG>entire</BIG><BIG> floor. You might have a whole lot more than 40 psf directly under your aquarium, but that's okay because you didn't fill your entire room with aquariums either.</BIG>
<SMALL><SMALL><SMALL><SMALL><BIG><BIG><BIG>Myth #2</BIG></BIG></BIG><BIG><BIG><BIG>: </BIG></BIG><BIG><B><BIG>"So then, if I fill my entire room with aquariums that weigh more than 40 psf, my floor will collapse."</BIG></B></BIG><BIG><BIG> </BIG></BIG></BIG></SMALL></SMALL></SMALL></SMALL>
<SMALL><SMALL><SMALL><SMALL><BIG><BIG><BIG>No it shouldn't. I said that the 40 psf was a </BIG></BIG><BIG><BIG>MINIMUM</BIG></BIG><BIG><BIG> design load and I also said that it is a </BIG></BIG><BIG><BIG>SAFE</BIG></BIG><BIG><BIG> load. That means that your floor could be (probably is) stronger than the 40 psf minimum in many places, and it also means that the full safety factor is still there to prevent a collapse</BIG><BIG>.</BIG></BIG></BIG></SMALL></SMALL></SMALL></SMALL>
<SMALL><SMALL><SMALL><SMALL><BIG><BIG><BIG>Myth #3</BIG></BIG></BIG><BIG><BIG><BIG>: </BIG></BIG><BIG><B><BIG>"A structural engineer designed the floor structure in my home for a live load of 40 psf.</BIG></B><BIG>"</BIG></BIG></BIG></SMALL></SMALL></SMALL></SMALL>
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<BIG>No, probably not. First of all, your floor was probably never actually custom designed. What builder would ever want to pay a structural engineer to design something this repetitive and simple. All an experienced contractor has to know is that 2 x 8'</BIG></BIG></BIG><SUP><BIG><BIG>
<BIG><BIG><BIG>s</BIG></BIG></BIG></BIG></BIG></SUP><BIG><BIG>
<BIG> span ?? ft then he starts using 2 x 10'</BIG></BIG></BIG><SUP><BIG><BIG>
<BIG><BIG><BIG>s</BIG></BIG></BIG></BIG></BIG></SUP><BIG><BIG>
<BIG><BIG><BIG>.</BIG></BIG></BIG></BIG>
<BIG><BIG><BIG> </BIG></BIG></BIG><BIG>
<BIG> See</BIG></BIG>
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http://www.mcvicker.com/resguide/page013b.htm (not my site!)
<SMALL><SMALL><SMALL><SMALL><BIG><BIG><BIG>Myth #4</BIG></BIG></BIG><BIG><BIG><BIG>: </BIG></BIG><BIG><B><BIG>"A building inspector inspected my house or reviews calculations to make sure that homes can safely support a minimum design live load of 40 psf."</BIG></B></BIG></BIG></SMALL></SMALL></SMALL></SMALL>
<SMALL><SMALL><SMALL><SMALL><BIG><BIG><BIG>Maybe, but in many locations the building code is only concerned with public</BIG></BIG><B><BIG><BIG><BIG><BIG> </BIG></BIG></BIG></BIG></B><BIG><BIG>buildings. How strong you build your own private residence is of little concern to them. Of course, they still want their cash for the building permit.</BIG></BIG></BIG></SMALL></SMALL></SMALL></SMALL>
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<SMALL><SMALL><SMALL><BIG><BIG><BIG>So now we know that your floor can safely support no more than a uniform 40 psf live load, right? Wrong! If you go into the basement and look up you will probably see that the exact same floor joist size (and 16 inch spacing) was used throughout your entire house. So 2 x 10'</BIG></BIG></BIG><SUP><BIG><BIG><BIG>s</BIG></BIG></BIG></SUP><BIG><BIG><BIG> spanning 8 feet in your kitchen are a whole lot stronger than the 2 x 10'</BIG></BIG></BIG><SUP><BIG><BIG><BIG>s</BIG></BIG></BIG></SUP><BIG><BIG><BIG> spanning 15 feet in your living room.</BIG></BIG></BIG></SMALL></SMALL></SMALL>
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<SMALL><SMALL><SMALL><SMALL><BIG><BIG><BIG>Myth #5:</BIG></BIG></BIG><BIG><BIG><BIG> </BIG></BIG><BIG><B><BIG>"If the floor in my kitchen can support the 500 lb refrigerator then the floor in my living room should be able to support my 500 lb aquarium."</BIG></B></BIG></BIG></SMALL></SMALL></SMALL></SMALL>
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<BIG>The reason that there is a rather large safety factor built into the floor design is to take care of as many unknowns and imperfections as possible. Did the plumber cut a notch in the bottom of your floor joists for his piping? Is there any insect damage or maybe a little dry rot? Is there a split or knot in the wood in a zone of high stress? No one wants to have to replace their floor because it is not in perfect condition. So if your aquarium loads your floor over the </BIG><BIG>safe</BIG><BIG> load limit, you might not be in danger of collapsing the floor, you might just have less safety factor than recommended. If you're stretching the load limits of your floor structure, then be absolutely sure that your floor structure has no imperfections.</BIG>
<SMALL><SMALL><SMALL><SMALL><BIG><BIG><BIG>Myth #6:</BIG></BIG></BIG><BIG><BIG><BIG><BIG><BIG> </BIG></BIG>"I put that huge aquarium on the floor and nothing bad happened therefore the floor is safe."</BIG></BIG></BIG></SMALL></SMALL></SMALL></SMALL>
<BIG>If you choose to think of "not collapsing" as safe you are certainly free to do so. But if you have a safety factor of only 1.05 in your floor structure, you probably don't know it, and there is not a structural engineer in the land that would tell you that it is "safe."</BIG>