Hey Y’All,
I need to figure out (roughly) how much a houise weighs, or more to the point, how much weight is being borne on a footing.
I ran the search engine ’cause I know this was discussed here before (“How much does a house weigh?”), no luck.
I’ve got the footings and stems figured out at 135# per cubic foot.
I’m going to figure 15/30 for a total of 45 psf on the roof and use half the span.
So how say you to a 2×6 frame wall with 5/8″ FireRock on the inside, OSB and stucco on the outside? Figure 10′ tall walls. Stucco is probably about 130# per cubic foot, so about 11# per square foot.
Floor is partly slab on grade, partly joisted. Joisted section figure TJI and plywood with Hardibacker and tile.
What is up here is I need to check some engineering assumptions for bearing competence of soils.
Thanks.
The best politics is right action. -Mohandas K. Gandhi (1869-1948)
Replies
For rule of thumb go 15psf dead load plus 50 psf live load for each floor/roof (and up the live load for the roof if your snow load is more than 50 psf). Add extra to the dead load for the stucco. That should get you pretty darn close, and 15 psf should be pretty conservative for the dead load.
"A job well done is its own reward. Now would you prefer to make the final payment by cash, check or Master Card?"
Exactly what I was looking for. Thank you.The best politics is right action. -Mohandas K. Gandhi (1869-1948)
Not sure about the house, but now I know what is a henway.
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
my house weight 1400 lbs per lineral foot.. 2+3=7on the light side that will be 98 tons.
Edited 3/15/2006 9:53 pm by brownbagg
98tons!
dang it brownbagg, now yer scarin' me.
be isn't a henway where they race cars and stuff?
'Nemo me impune lacesset'No one will provoke me with impunity
Edited 3/18/2006 4:12 pm ET by razzman
rememeber its a concrete house.. 2+3=7
Whew!
be relaxed
'Nemo me impune lacesset'No one will provoke me with impunity
Hey think about it, its cheaper than chikin! Jim Devier
I knew that would end up here, I just didn't know from who. <G>
The best politics is right action. -Mohandas K. Gandhi (1869-1948)
What's a henway? :-OIs it kinda sorta like a dickfir?
16 ounces to the pound...
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming
WOW!!! What a Ride!
Forget the primal scream, just ROAR!!!
I lifted my house a few years ago. It's two stories with about 950 sq ft per floor, wood siding. The raisers looked at their gauges and told me it weighed around 100 tons.
my house weights 98 tons. it is 40x30 my footers are 18 inches wide. thats a 140 feet of footer divide by 98 tons. thats 1400 lbs per lineral foot. 1400 diveide by 18 inches. that 933 lbs per lineral square foot. 933 divide by 144 inches. my house weights 6.48 lbs per square inch On soil thats good for 2800 lbs per square foot.. 2+3=7
933 divide by 144 inches. my house weights 6.48 lbs per square inch On soil thats good for 2800 lbs per square foot
Thanks for the numbers, particularly the last one. Assuming that my roof load is equal on front and rear walls, my front wall exerts 2860 lbs/sq ft under the footing.
Even though I paid for 2 engineers, it wasn't until I came here that I'd heard of soil bearing capacity. It's working, so what's under my footing must be adequate. Same deal for the client house, which weighs considerably more.PAHS Designer/Builder- Bury it!
I can see it now, beating the Joneses--"My house weighs more than your house, nya, nya, nya-nya, nya!" (Along with "My Vulcan range can burn more burgers per minute than your GE")
Well maybe your house DOES weigh more. We try to tread lightly on this planet. <g>Tipi, Tipi, Tipi!
http://www.asmallwoodworkingcompany.com
Good response. BTW, a tipi weighs very little. Did you read the latest issue of FHB where the guy criticized open plans and said the best example of such was a wigwam!? Not too PC I guess!
"Even though I paid for 2 engineers, it wasn't until I came here that I'd heard of soil bearing capacity"Yeah, typically soil bearing capacity is mentioned in the general structural specifications, which are usually submitted by the engineer with the drawings. It will probably say something like, (taken from an actual set I had on hand) "2. Footing design based on the assumption of an allowance soil bearing pressure equal to 2 tons per square foot. All footings shall be a minimum of 4’-0” below finish grade or on clean undisturbed ledge, if applicable.Keyword, assumption. In this case the engineer is saying that the builder of the home is responsible for verifying feild conditions."Oh, this is the worst-looking hat I ever saw. What, when you buy a hat like this I bet you get a free bowl of soup, huh? Oh, it looks good on you though."
"2. Footing design based on the assumption of an allowance soil bearing pressure equal to 2 tons per square foot. All footings shall be a minimum of 4’-0” below finish grade or on clean undisturbed ledge, if applicable.
Keyword, assumption. In this case the engineer is saying that the builder of the home is responsible for verifying feild conditions.
Makes sense to me.
I'd feel better if either of my engineers had bothered to bring up the subject. All I got was a design for reinforced concrete, no mention that there should be something substantial under it, or that it was a question or assumption. Nor did our building dept have anything to say.
Well, my building dept did have something to say, but it was about the reinforcing. Upon hearing which engineers were involved I was told that if I eliminated half the rebar I'd be about right. To which I said "great- which half?". Their response was that it was my choice. Good, the person who knows nothing makes the decision. I bought the rebar, wasting $750 in their estimation.PAHS Designer/Builder- Bury it!
<<Even though I paid for 2 engineers, it wasn't until I came here that I'd heard of soil bearing capacity>>That's exactly what this exercise is about.The engineers are designing the foundation for 1 to 2 ksf. So far so good, that's got quite a safety factor.[edit -- for comparison, using Brownbagg's figures he's right at .9 ksf, and his house is pretty heayy.]Ordinarily, even soils that aren't too good will hold 3 to 5 ksf. Compact gravel is good to around 14 ksf for the sake of comparison.I'm looking at some really, really bad expansive clay that appears to go down deeper than anyone cares to dig. I fired 4,000 gallons of water into the hole on Friday and watched the site grow. It actually cracked rock in about three hours. We're talking rock that an 18,000# track hoe would not even rattle, by the end of the day what appeared to be ledge was split into layers.In various places around the site there is also a bunch of white clay that is dessicated and obviously collapsible. This stuff is under 5% moisture and I'd bet over 80% would pass a #200 sieve.Then we have shale and decomposed granite and limestone. Pieces coming up out of the ground two tons to a chunk.My recommendation to the homeowner-builder is to overex 2' below the footing and 2' beyond and replace with suitable soil. like an e-fill or base course blended with dirty pit run. I may also recommend placing the material over geotextile.Typically soil failures happen in shear. Two feet of suitable material over fabric pretty much takes care of that. I'm going to give the architect and the engineer a courtesy call and invite them to visit the site. I think a shear failure is only part of our problem here.The best politics is right action. -Mohandas K. Gandhi (1869-1948)
Edited 3/19/2006 11:52 pm by Catskinner
Thanks. That's lighter than I would have guessed.The best politics is right action. -Mohandas K. Gandhi (1869-1948)
Mine's two story stucco, 3124 sq. ft. I figured it out once from the mudsills up, and got 175 tons.
-- J.S.
Thanks.Any idea how that translates into pounds per linear foot on the footings?The best politics is right action. -Mohandas K. Gandhi (1869-1948)
More than one way to skin a cat, right?
To translate the weight of the house into plf, you actually have to look at the design to see how the loads are distributed. Quick simple example, assume 15' wide by 50' long simple rectangular house. All bearing members are across the 15' width (thus bearing on the 50' long wall). Take the weight of the house (actually the entire design load of the house -- a lot more than it actually weighs) and divide by two -- two bearing walls. Take that and divide by 50' of wall = plf on the foundation. Add the weight of the foundation and footings in plf = weight on the soil in plf. Take width of footing and calculate psf on the soil (simple example, if footing is 1' wide, obviously weight in plf = pressure in psf on the soil).
This method isn't exact (technically can subtract the weight of the gable walls in the above example), but it's conservative and will get you close enough to know if you're too close on the soil bearing. If you find the soil can't support what you come up with this way, then you really have to get into the nitty gritty of calculating the actual dead load, the actual required live load design loads, the distribution on each area of the footing, etc. Can be tedious.
As a side note, to figure out if the foundation can handle the weight, you may need to get into calculating loads on sepecific areas of the foundation if there are high concentrated loads in the design. But your question is soil bearing and the assumption is the foundation is made strong enough to distribute concentrated loads.
"A job well done is its own reward. Now would you prefer to make the final payment by cash, check or Master Card?"
then lets go one more step. the strength of the concrete and the amount of rebar in the footing. you can have a strong concrete mix and bridge over bad soil in the footing area. settlement is not the only thing in factor here but also the bending moment of the footing itself by overloading.. BOB thinks I,m an idiot
>>"then lets go one more step. the strength of the concrete and the amount of rebar in the footing. you can have a strong concrete mix and bridge over bad soil in the footing area. settlement is not the only thing in factor here but also the bending moment of the footing itself by overloading."
Absolutely agreed. If the soil can't handle the calculated load, have to do something. Widening the footing (and making sure it is reinforced well enough to handle the load) is one way to tackle it.
"A job well done is its own reward. Now would you prefer to make the final payment by cash, check or Master Card?"
<<then lets go one more step. the strength of the concrete and the amount of rebar in the footing. you can have a strong concrete mix and bridge over bad soil in the footing area. settlement is not the only thing in factor here but also the bending moment of the footing itself by overloading.>>Yep, that's where the engineer comes in.We've got two issues here -- the bearing competence of the native material overall and the potential for differential settlement.<<. BOB thinks I,m an idiot>>Unlikely. He may differ with your political conclusions (as do I on occasion also <G>) but I seriously doubt if your intelligence will ever be called into question here. At least not by anyone who could be taken seriously.The best politics is right action. -Mohandas K. Gandhi (1869-1948)
<<More than one way to skin a cat, right?>>Yes, indeed. My (at the time teenage) daughter once suggested with a perfectly straight face that the preferred method was "Bottle caps and an orbital sander."Normally the soil failure that most folks are worried about is a localized shear failure. I think this situation is worse than that. I want to learn as much as I can from you guys about the weight of houses so the engineer or architect doesn't do something bizzarre to cover their butts. The homeowner pays for it, and as the excavation sub I do feel a certain obligation to protect him from those excesses. I want a good job at least as much as anyone, but I don't want to spend a bunch of his money for no good reason.Thank you for all of the good info.
The best politics is right action. -Mohandas K. Gandhi (1869-1948)
>>"I want a good job at least as much as anyone, but I don't want to spend a bunch of his money for no good reason."
Good deal.
I know what you mean about the archineers. Don't know about foundations specifically but published wood frame tables and engineering values already have a safety factor of between 8 and 10 (like a joist can actually hold 8 to 10 times design load in 90% of all cases -- we all use the wood we use for that 10% where bad things could happen). Of course we all understand why we need that but when some archy or engineer who thinks even more is always better for no reason other than lazy and CYA, end up with a tank of a house that costs more than it should with no real benefit.
Anyway, I've been in the thick of it with a pair of archys since November. Still don't have stamped plans or permit. Would have been quicker for me to do my own plans and use my own engineer for the stamp. Don't get me started.
Oh, I almost forgot. Yeah, localized shear failure. Two choices, no? Up the size (footprint) of the footings to spread the load enough to reduce localized shear, or bond beam footing made to hold it all to bridge soft spots. Let me guess, your guy wants both?
"A job well done is its own reward. Now would you prefer to make the final payment by cash, check or Master Card?"
Edited 3/21/2006 2:19 am ET by philarenewal
Edited 3/21/2006 2:22 am ET by philarenewal
<<Two choices, no? Up the size (footprint) of the footings to spread the load enough to reduce localized shear, or bond beam footing made to hold it all to bridge soft spots. Let me guess, your guy wants both?>>Don't know yet. I have not called the architect yet to break the news. But within reason, "both" might be a good answer.The house is drawn with 24" wide footings. I need to go back and look at the details on the stemwalls and see what's to be in them for rebar.Last time I did one on a site this bad we overexed 2' below the footing, procesed to optimal and replaced, and switched the foundation to a monoslab with a bunch of rebar in the turndown and a #4 mat 16" o.c.e.w. Then we ran #4 2' o.c. up into the ICF to the top plate and two #5 each side of every opening, and a #5 continuous around the top. The building was rebar from the bottom of the footings to the top plate, and the monoslab would support light truck traffic.That way if the soil gives out either nothing will happen or the whole house will tip over. <G>But I don't think that's an option this time.On this one I see at least a 2' overex below the footing, replace with something that has a Proctor better than 124 with plenty of fractured component, maybe widen the footings a little bit, turn the stemwall into a grade beam (I'm thinking about #5 grade 60 top, middle, and bottom, with #3 shear bars between the top and middle bar.)I'll let you know what the archy says. I think he's probably pretty good, but I'm still not calling him until after I meet with the engineer.The best politics is right action. -Mohandas K. Gandhi (1869-1948)
Wow! I can't see a 24" footing out here except under some retaining wall that uses it for lateral resistance. We put three stories of masonry on 18". I think as built can go as skinny as 10". You weren't kidding about that dirt.
Does drive home the point that dirt is not just dirt.
"A job well done is its own reward. Now would you prefer to make the final payment by cash, check or Master Card?"
No, I don't have the paper calculations any more, I just remembered the final number. It's perimeter footing with pier and post inside, so I'd have to figure out how much weight goes where. The piers under internal bearing walls look to have settled about equally with the perimeter footings, leaving a slight "whaleback" hump in the middles of the big rooms downstairs. Even if most of the weight were on the perimeter, it would be well under a ton per foot.
Otto Service Co. in Burbank sells the Norco bottle jacks with the pressure gauge accessory. Unfortunately, I didn't spend the extra money....
-- J.S.
now here is a question, take the 40 x 30 house that weighs in at around 100 tons, assume a central beam in the middle of the house carrying the 2nd floor joists. what's the distribution of weight on the sill and the central beam that sits on the wall that sits on posts in the basement? does the central span carry the peak of the roof and it's weight solely, or do the walls carry some of the central weight because the joists are "lapped"?
i know it's a crazy question, too many variables, but is reminiscent of my house and i'm curious.
thanks everyone!
If it's a truss roof, its weight could all be on the outside walls on the sides with the eaves. If it's a structural ridge beam, half of it could be point loads in the middles of the gable ends. There are lotsa possibilities.
-- J.S.
oh i see....if there's a truss, the weight of the roof is carried on the outer walls, and the beam under the 2nd floor carries the weight of the 2nd floor but not the roof. otherwise, the distribution is very site specific?no reason i'm asking, i was just curious how the weight that everyone is talking about is distributed. thank you
While trusses are often -- even usually -- used that way, they can be designed to be supported at any number of points. The more points of support you can put under a truss, the easier and cheaper it can be made. But mostly they're chosen for their ability to span long distances cost effectively, allowing you to build "open" floorplans. That's why they're mostly supported at two points, one very near each end.
For an education in trusses, search this site for messages from Boss Hog. He's our long time resident truss expert.
-- J.S.
thank you very much!!
check out "Contractor's Guide to the Building Code" by Jack M. Hageman
It has the info you need including typical soil bearing capacity numbers, assumed load numbers etc.
http://www.amazon.com/gp/product/1572180587/qid=1142913031/sr=1-3/ref=sr_1_3/103-6026628-3079000?s=books&v=glance&n=283155