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View Full Version : How heavy a safe will a raised fundation bear?


socalsteve
07-10-2012, 12:51 PM
Anyone know how much weight a typical raised foundation will bear?

I recently bought a home with a raised wood foundation built in 1949 and I will need to buy a gun safe (RSC) but I'm concerned about the weight.

I'd like to get something around 36" to 40" wide by approx 24" deep and 60 to 72" tall.

The bigger the better IF the floor will hold up.

njineermike
07-10-2012, 1:00 PM
Depends on the floor. What condition is the wood in? What width joists did they use? How did they support it? Me personally, I'd build in support columns below the floor to give vertical structural support to the joists, just to be on the safe side. There is absolutley no harm in overkill on that front.

Cranium
07-10-2012, 2:27 PM
I've got a "mud porch" / laundry room that was added on in the late 40s. Not remarkably well built, but better than I could do!
I've got a 455 lb (when empty) safe in there, and I threw down a sheet of plywood about a foot wider on all sides than the safe, as the floor, while done well, was kind of scary. Held up OK for the last few years. We'll see, I suppose.

GMG
07-10-2012, 2:43 PM
Depends on the floor. What condition is the wood in? What width joists did they use? How did they support it? Me personally, I'd build in support columns below the floor to give vertical structural support to the joists, just to be on the safe side. There is absolutley no harm in overkill on that front.

This would be the way to go!

Meety Peety
07-10-2012, 5:05 PM
Definitely agree with what njineermike said. There's really no "set amount" that you can expect for the structural support to be able to bear. Of course, there's a specification that was required to be met at the time the house was built, you could look it up and use that as an idea.. but you can't really be sure the spec was met in the first place, nor can you account for how well it has held up to time and other factors. The best thing to do would be to go back and reinforce the area where you plan to put the safe. Before you do that, go out and buy the biggest best safe you can get your hands on as encouragement to get the job done correctly :P

furyous68
07-10-2012, 6:34 PM
Depends on the floor. What condition is the wood in? What width joists did they use? How did they support it? Me personally, I'd build in support columns below the floor to give vertical structural support to the joists, just to be on the safe side. There is absolutley no harm in overkill on that front.

I design houses for a living. I'm not a structural engineer, but I know enough to where my engineers don't have to change much from my initial structural design.

Raised floors are only designed to handle so much. Your typical residential loads are: 10-20lbs/ ft dead load (this is for the floor covering) & 30-40lbs/ ft Live loads (this covers you, furniture, appliances, etc.) I would not trust a 63 yr old floor to handle a loaded (or empty) gun safe. Do as suggested above. Get under the floor & bring supports down to grade. You don't have to pour any concrete, but I would at least use those pre-cast concrete piers with the straps. A 4x4 at each corner of the safe attached to the floor framing would be a smart idea.

w55
07-10-2012, 7:08 PM
I design houses for a living. I'm not a structural engineer, but I know enough to where my engineers don't have to change much from my initial structural design.

Raised floors are only designed to handle so much. Your typical residential loads are: 10-20lbs/ ft dead load (this is for the floor covering) & 30-40lbs/ ft Live loads (this covers you, furniture, appliances, etc.) I would not trust a 63 yr old floor to handle a loaded (or empty) gun safe. Do as suggested above. Get under the floor & bring supports down to grade. You don't have to pour any concrete, but I would at least use those pre-cast concrete piers with the straps. A 4x4 at each corner of the safe attached to the floor framing would be a smart idea.

I would build up the floor supports also. Should be fairly simple most older homes that age have a decent crawl space. Like said overkill be better than under.

TJMarc
07-10-2012, 10:22 PM
Well the following is from an engineer's prospective...so ymmv.

Unfortunately, due to the number of variables and potential liability involved, it will be very difficult to get engineering advice without having someone come out and look at the existing conditions. The static strength case for these installations is relatively straight forward but, depending of the weight of your safe and how the weight is distributed, the item that potentially becomes an issue is the overturning force generated during a potential seismic event.

Other than the obvious strength issue, other considerations are (but not limited to):
With overturning, the issue may not even be the strength of the floor framing but the connections not being able to resist the uplift force from your safe trying to pry itself up. Something like this could be mitigated by changing the desired installation location or adding a few uplift straps or even well placed nails/screws, but requires the consultation of an engineer.
Another issue other than strength is going to be deflection of the floor members...this will be very dependent to where you place your safe.
Potential items like these can easily determined by a quick site observation, provided the structural framing is exposed.

If you don't have a competent concrete slab to anchor to (garage?) or your dead set on installing it on your rased floor, my recomendation is you consider having a local "structural" engineer come out and do a review for you. Unfortunately, they are not cheap but will be able to give you an general assessment of your potential installation. If you do go this route...you should have have a few options, locations and safe models (they are primarily concerned with height, weight, footprint and anchoring locations), in mind before hand. Make sure to have a realistic weight (including all the stuff you plan to put in there) to provide the engineer. Typically they bill by the hour for something like this (get a not to exceed fee from them)...so streamline it as much as possible. If your lucky, the engineer will tell you no worries that guy on the internet is way overly conservative and you are fine...give you a quick anchorage sketch and send you on your way.

(As always the above is not to be taken as engineering advice and no guarantees are given or implied. Please consult a licensed professional for your specific installation)

furyous68
07-11-2012, 7:45 AM
^^ This

I should have mentioned in my post that I was only considering the dead load itself. There are a lot of other factors that need to be taken into consideration. Definitely consult w/ an engineer. It would (should) cost less than the safe itself for something this small, and give you some peace of mind.

paul0660
07-11-2012, 8:00 AM
steve, if you can get under the floor draw us a picture of what the joists and girders look like. Depending on the distance to the grade it isn't a big deal to reinforce it. There is no way to tell what was required in 1949, or if it was done correctly. A modern design would not have a problem supporting a safe.

ducktapeguy
07-11-2012, 9:00 AM
I wondered the same thing when putting my safe into a 100 year old house. I think you'll notice problems with flexing of the floor before the strength becomes an issue. In the worst case scenario, if you locate it in the center of the room away from any support, you'll probably feel the floor bounce everytime you're near it.

What I did was locate safe next to exterior wall or load bearing wall. This puts it near the foundation supports. This worked fine and I probably could have left it like this forever with no issues. However, i decided to go one step further and added additional supports directly under the safe using a couple of concrete pier anchors. If you do it ahead of time it'd probably be easier, but I already had my safe in place so I used a scissors jack and block of wood to jack up the joist before putting the vertical supports in place. That eliminated any sagging that might have occurred. Worked great, I could jump right next to a fully loaded safe and not see or feel any movement.

I wouldn't overthink it. Even if you were to have a 1000lb fully safe, that's equivilent to 4-5 guys standing next to each other, or 1 large guy jumping up and down. Unless you have a lot of termite damage or rot, I bet most floors could handle a lot more. Earthquakes are another issue, just be sure to strap it down or to a wall.

paul0660
07-11-2012, 9:02 AM
I had the same issue when putting my safe into a 100 year old house. I think you'll notice problems with flexing of the floor before the strength becomes an issue. In the worst case scenario, if you locate it in the center of the room away from any support, you'll probably feel the floor bounce everytime you're near it and see the safe sway.

What I did was locate safe next to exterior wall or load bearing wall. This puts it near the foundation supports. This worked fine and I probably could have left it like this forever. However, i decided to go one step further and added additional supports directly under the safe using those pier anchors. If you do it ahead of time it'd probably be easier, but I already had my safe in place so I jacked up the floors slightly with a car jack before putting the vertical supports in place. That eliminated any sagging that might have occurred. Worked great for 5 years, I could jump right next to a fully loaded safe and not see any movement.

Plus one to all of the above.

socalsteve
07-12-2012, 12:58 PM
Thanks for all the replys.

I'm getting seperated and moving into a different house and I doubt I'll be able to move my current safe into the new - old home.

Right now I have an older TL30 safe thats 3800 pounds empty.

I figured a raised wood foundation won't hold over 4000 pounds but I might be able to get a 1000 lb, safe and do a little reinforcing.

I'm going to put the new safe in the corner of the bedroom against outside walls.

I guess I'll see about adding some concrete blocks with 4x4's under that corner.


Do you think the precast concrete piers - I like the idea of 4 - with an attached 4x4 needs to bolt to the floor joists? Maybe with soem kind of simpson tie?

Or, could I put a 2 x 12 board flat under the joist and have the 4x4 support it?

ducktapeguy
07-12-2012, 4:31 PM
3800 lbs? Damn that's a real safe. For that kinda weight I'd pour a new foundation directly under the safe. I thought you were talking about ~1000 lb safe.

For a <1000lb, 4 supports are probably overkill, but if it makes you feel better than there's no harm in doing it. I think 1 support would be more than enough, I'd locate it on the outside corner, so if there is any sagging it'll just tilt the safe tighter against the wall.

I can't remember if i used a tie to anchor the 4x4 to the joint, i think I did but I may have just sistered a 2x4 next to it and screwed the two together. Even a flat metal strap would be adequate. All you're doing is preventing the 4x4 from shifting sideways, so strength isn't an issue. I don't think I'd rely on friction to hold a flat board in place, when the wood shrinks or the dirt settles, your support would just fall over.

paul0660
07-12-2012, 4:34 PM
3800 pounds? I would live IN the safe.

joeblo
07-13-2012, 9:35 AM
I'd worry more about getting the safe to the reinforced area more than anything else

njineermike
07-13-2012, 10:04 AM
I'd worry more about getting the safe to the reinforced area more than anything else

Yep. close to 2 tons is a LOT more than I thought he was talking about. Did you steal it from Fort Knox or something?

glockman19
07-13-2012, 11:02 AM
It's a fairly easy calculation:

How to Calculate Floor Load Capacity

Instructions

1
Write down the beam strength formula: Maximum load in pounds = FBd^2 / 9L.

2
Fill in the values for B, d and L. B is the breadth of the joist, in inches. If your floor system uses standard 2-by lumber, this will be 1.5 inches. d is the depth of the joist in inches, which you will have to measure. Most floors use 2-by-8 or 2-by-10 joists; the depth of a 2-by-8 is usually 7.25 inches, and the depth of a 2-by-10 is usually 9.25 inches. L is the span, in feet. The span is the unsupported distance over which the joist must bear its load.

3
Determine the value for F, which stands for the fiber stress in bending of the wood. This may be difficult to find, because it depends on the species of tree that your joists came from. If the joists are relatively new, the F value may be stamped right on the piece of lumber. If you know the species of the wood, you can refer to a lumber manual to find the corresponding F value. If all else fails, you can safely use 1,000 for F, as almost all graded lumber will have an F value of 1,000 or higher.

4
Calculate the maximum load in pounds that one of your floor joists can support. For example, if you have 2-by-10 joists spaced 16 inches on center with a span of 14 feet, the calculation would be the following: ( (1,000) x (1.5) x (9.25^2) ) / (9 x 14) = 1,019 pounds per joist.

5
Calculate the total area supported by one joist according to this formula: joist spacing (in feet) x span (in feet). Continuing the previous example, 1.333 x 14 = 18.7 square feet.

6
Divide the maximum load of one joist by the area supported by one joist: 1,019 pounds / 18.7 square feet = 54.5 pounds per square foot. This number tells you how much load your floor can support for each square foot of floor space.

7
Multiply the maximum load per square foot by the total square footage of the floor. If the example floor is 20 feet x 30 feet, the total area is 600 square feet; 600 x 54.5 = 32,700 pounds. This number tells you the total load capacity of your floor.

socalsteve
07-13-2012, 12:09 PM
NOTE - I am NOT moving the TL30 safe its too heavy.

Also, I think you are right one 4x4 support should be enough if I put the new safe in an outside corner.

My current safe is a real safe a TL30 rated - has the metal tag even.

Not fire resistant but it probably takes awhile to heat up 1 inch thick solid steel - besides the fact that on 3 sides there is drywall - the door is even thicker - I haven't measured in years but its at least 1.5 inches thick solid steel.

My current safe is nice but I am not going to move it to the new house.

Right now its on a concrete slab and I moved it into the room before building the doorjam into the room and the closet next to it.

I could pull it our easy enough but I might have to remove the entire door jam to get it out of the current room.

I'll probably leave it for my wife to use until we either sell the house or I decide to sell the safe.

For the price of moving it I can buy an RSC.


I bought is used froms Deans Safes in the San Fernando Valley.