Does Sistering Joist Short of Wall Support Increase Floor Load Capacity?
zink88
| Posted in General Discussion on
I am in the middle of a bathroom renovation project. Original floor joists from 1994 home build are 2×10 stamped as SPF #2 with a 13′-5″ span. I have sistered them with 12′ 2x10s of SYP #2 stopping ~ 8″ short of the wall plate supports at each end. The sistered joists have been attached using Great Stuff construction adhesive and (3) 3″ screws every 12″. The joists are now noticeably stiffer. Does sistering the joists in this manner increase the design value in bending and load capacity…or has the floor load capacity actually been decreased by the weight of the new joists?
Replies
Your original joists were adequate for the loads, Shear and bending. You have not increased the shear strength, but as you notice they are stiffer so you have helped with deflection and bending. The increased dead load of the sistered joists is insignificant.
The shower will be 8' x 3.5' = 28 square feet.
I estimate the weight of materials to be...
cement board & tile on left & right walls not directly over support walls (56 sq ft * 8.5 lbs/sq ft)= 476 pounds
2 layers of plywood (3/4 & 5/8) = 4 lbs/sq ft * 28 sq ft = 112 pounds
mud base for shower (10) 50 lb bags = 500 pounds
Shower floor tile = 6 lbs / sq ft * 28 sq ft = 168 pounds
Frameless glass = 4.9 lbs / sq ft * 40 sq ft (8'x5') = 196 pounds
For total of 1452 pounds not including the framing weight of the two interior walls to be tiled nor the weight of the thinset. This equates to just under 52 pounds/sq foot in the footprint of the shower and also does not include the weight of the person in the shower.
Since most residential homes are built at 40 lbs/sq foot live load and 10 lbs/sq foot dead load, how are large showers being supported? Does my floor really need to be sized to handle 60 lbs/sq ft?
Joists are running parallel to the length of the shower. Instead of looking at the weight in the area of the shower, do I need to look at the total weight across the entire joist span (13'4") and shower width (3.5') which is an area of 46.66 sq ft?
In 50 years of construction I have never once seen the dead weight of a shower figured into engineering calcs. Hot tubs yes.
I need help..I got a 120 gallon fish tank..4x2 so 1200lbs of water,rock,sand..so 1500-1700lbs to be on safe side...only place I can put it would be over basement not on outside wall..so it would be basically over center of basement so I can't put posts under it..and it would be sitting on 2 joists..I wonderd if I could sister up the 2x8 joists in basement and make the 2 joists into 6...the basement is 12 foot..I might be able to get 13 foot 2x8's and put one end in the wall on brick foundation and other end on existing I beam..at this point I would lag bolt 10 2x8's together if it ment not putting tank in basement...I was going to but a 13 foot steel i beam and use that under tank..but I don't think I can maneuver in into house and into place..I might be able to put it on diff wall and have half the tank sitting on I beam and over 4 joists..but not sure if I would still need posts under front half of tank(and thats last place I want it its a small living room)...any real help i can find to pull this off..or should I just cut my losses and put in basement