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StructuralEng, Consultant
Category: Structural Engineering
Satisfied Customers: 7260
Experience:  Structural Engineer
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I am looking at existing construction on 1960's to 1970's

Customer Question

I am looking at existing construction on 1960's to 1970's era house.
A second story sleeping area, the sleeping area is 15' 10" by 14' 9", the floor is covered in 3/4 T&G plywood, and the joists are also carrying 5/8 sheetrock of the ceiling below.
2"x10" Doug-fir #1 joists span the 15" 10".
On one end the the 2x10's are carried by the exterior wall (which also carries the high end of a shed roof).
On the other end a 4"x12" beam, spanning 14' 9", carries the 2x10's on joist hangers, and on top of the bean is a 4' stem wall the carries the low side of the shed roof.
This is sunny, no winter snow, west coast location. Assume the shed roof to be 5 in 12 or 6 in 12.
From what I can tell the 2x10 span of 15' 10" is "okay" for 30lbs live load residential sleeping area (I could probably add blocking to help stiffen the floor).
My main question is the sizing and load on the 4"x12" beam, under this senerio. Is this beam undersized for a 14' 9" span which is carrying half the floor load and half the roof load?
With a laser level, after 45-years, there appears to be a 5/8's sag about 5' (~1/3) into the 4x12 beam's span but no obvious sign of crack or failure. It could just be an original twist in the beam?
Secondly what would the load be on the post at the end of the beam be. One end of the beam is not well supported and we are looking at beefing that up.
Submitted: 2 years ago.
Category: Structural Engineering
Expert:  StructuralEng replied 2 years ago.
That beam is very undersized for both strength and deflection. For strength, it is overstressed by 200% under a full design load. Deflection is over 1.25" under a full design load. The load on one post is approximately 4500 pounds.
Customer: replied 2 years ago.

What live loads did you use for res sleeping, roof, and dead?

Expert:  StructuralEng replied 2 years ago.
I use 40 psf live load. The code allows you to use 30 psf for sleeping areas, but it's limited to sleeping areas, not closets, bathrooms, or hallways. The extra 10 psf is not going to make any significant difference. The roof live load is 20 psf, but when combining the two, you only use 75% of each. The dead load is 15 psf for floor and roof.