cac4 said:
Webmaster said:
Floors are made for what....like 40 lbs per sq foot? That would be a 4 foot square pallet - 16SF.......16x40= 640 lbs, or 1/3 of a ton! So this load is well over 100 Lb. Sq Foot.
I certainly hope not. If I'm standing at attention, thats over 200 lbs per sq. foot. (how much more, I ain't sayin'). If I jump up and down, its a great deal more. and if I can't do that, the house isn't save to occupy, for sure.
Live Load by code or residential construction is typically 40psf as Craig noted (it's 30psf for bedrooms). On top of that the floors have a Dead Load design of 15psf (subfloor, floor covering, etc.). Exterior construction like decks usually only have a 10psf Dead Load design. These are assumed to be "uniform loads" or ones that occur over the joist's entire length. Point or Wedge loads are the localized ones that do not extend over the length of the joist.
However, these are minimum numbers and most designs are implemented with a safety factor. This is usually 1.5 or 2 for residential construction - e.g. failure won't occur until 1.5 or 2 times the design weight is applied. It still might be more or less because it depends on the actual construction of the floor. If the design is 2x8s spanning 15' then it's likely that they used 2x8s everywhere and if they only span say 10' for the room in question, the safety factor is much more due to the shorter span. It also depends on how the load is distributed - e.g. over how many joists. Centered over 3 joists is less safe than spanning 4 that you could get by lining up the short edge of the pallet is on one and then they're on 16" centers...move the pallet over a few inches or line it up on the short side (for a standard 4x3.5 pellet pallet) and you've got more load over a smaller area.
If the electricians or plumbers cut into those joists in the wrong places they can compromise the design safety as well. If you put the pallets over bearing walls, you get more capacity. Bridging or blocking between the joists help spread a load onto other joists. Oak joists would be great, pine less great - and if it's cheesey pine maybe really less but you can't tell how good the wood is because it's visually graded not subjected to an engineering analysis.
You need a structural engineering analysis to be certain. The example of a fat man standing on the floor isn't relevant - it's okay he's more than 40psf because the floor spreads that load over the length of one or more joists. The weight he has is punching shear weight and is distributed - it's the 250lbs that the floor has to support not the 1,000 psf of him standing on one foot. The typical floor failure will be a bending stress fracture of the joist in the middle so if the weight is concentrated there it might be a problem. If it's concentrated near an exterior wall, it's a shear load and that's a lot less likely to be an issue. Duration of the load also matters - you standing there or jumping up and down generates less stress on the joist than you sliding a slab of equally weighted rock over the joist and leaving it there for a week or a month.
Also, the age of the house matters. In the old days a 2x10 was really 2x10 and it was made of older, denser (stronger) wood. Now that 2x10 is more like 1.5x9.25 and made of fast growing less dense softwoods. Older may often be better from a strength standpoint. This is especially true if your house was built by a subdivision builder who was building for looks not for longevity or strength (ever ask how strong the floors are when you look at a house or do you ask what the countertops in the kitchen are made of?).
You can sister the joists or add jacks but you need to do that before you add the load - once the load is there, the deflection is done and you won't spread the load over the sister joist or jack. If you add jacks after the load is in place, you need to jack them up to lift the deflection out.
Bottomline is we don't have enough info to tell if his house (or even mudroom) is about to cave in.
Feel better?
