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StructuralEng
StructuralEng, Consultant
Category: Structural Engineering
Satisfied Customers: 7184
Experience:  Structural Engineer
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I have a midcentury modern home built in 1961 with a large

Customer Question

I have a midcentury modern home built in 1961 with a large open living room and a flat roof. The ceiling joists are 23'5" long. Actual size is 2.5" x 9.25 inches. 16" on center. The carpenter notched seven joists .75 inch on bottom. DO I have a problem?
JA: OK. Is there anything else important you think the Structural Engineer should know?
Customer: Notches are about 3.5 inches wide
Submitted: 12 months ago.
Category: Structural Engineering
Expert:  StructuralEng replied 12 months ago.
Hello
Expert:  StructuralEng replied 12 months ago.
I can help
Customer: replied 12 months ago.
I live in the Northeast
Expert:  StructuralEng replied 12 months ago.
What is above these joists? An attic? A floor?
Customer: replied 12 months ago.
Flat roof. The house is a one story midcentury modern
Expert:  StructuralEng replied 12 months ago.
What is the city and state so I can look at snow loading?
Expert:  StructuralEng replied 12 months ago.
Where along the span was the notch made?
Customer: replied 12 months ago.
NY. About 9 feet in from right side
Expert:  StructuralEng replied 12 months ago.
What city in NY. The location has a big impact on the snow load.
Customer: replied 12 months ago.
Customer: replied 12 months ago.
Pound Ridge, NY. Near Mt. Kisco
Expert:  StructuralEng replied 12 months ago.
You have a problem on two fronts. 23' - 5" is too long of a span for that loading on 2x10s and the notch is in a location that is unacceptable
Expert:  StructuralEng replied 12 months ago.
Even without the notch the joists are over stressed significantly
Customer: replied 12 months ago.
That span was original to the house so it is grandfathered in.
Customer: replied 12 months ago.
The beams are actually 2.5 inches wide
Customer: replied 12 months ago.
It is a historic house
Expert:  StructuralEng replied 12 months ago.
It may be grandfathered in, but once you make any modification, it's required to meet the current building code criteria
Customer: replied 12 months ago.
Is there a way to reinforce the notched beams?
Customer: replied 12 months ago.
Would adding engineered beams be a solution?
Customer: replied 12 months ago.
As I originally wrote the beams are 9.25" by a true 2.5" wide
Customer: replied 12 months ago.
They are NOT 1.5"
Customer: replied 12 months ago.
Some are doubled as well.
Customer: replied 12 months ago.
I suppose you'd call these 10x3? They are not standard beams.
Expert:  StructuralEng replied 12 months ago.
there is. A beam perpendicular?
Expert:  StructuralEng replied 12 months ago.
I know. The actual bending stress in the unnotched beam is about 1500 psi, which is too high
Expert:  StructuralEng replied 12 months ago.
You can sister the existing joists with new 2x10
Expert:  StructuralEng replied 12 months ago.
Full length
Customer: replied 12 months ago.
Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from you: Live Phone Call. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Customer: replied 12 months ago.
Does that add too much weight to the structure. If you look at the picture these joists are all on steel hangars. It's a pavilion style.
Customer: replied 12 months ago.
Would we just sister 2x10 to the notched beams?
Customer: replied 12 months ago.
Must be full length?
Expert:  StructuralEng replied 12 months ago.
The weight of the additional structure is nothing compared to the snow load on the roof or to the additional capacity the sisters will add
Customer: replied 12 months ago.
Must they be on hangers as well? This might be difficult because of the existing hangars which wrap around the end beams.
Is it okay to attach the sisters without using hangers on the ends?
Customer: replied 12 months ago.
The existing joists all have hangers already
Expert:  StructuralEng replied 12 months ago.
You can use a Simpson light gauge framing clip on the exposed sides of the sister
Customer: replied 12 months ago.
What about snugging it up to the existing beam where the existing hangers are? Don't want to thin the sister at the ends to accommodate the old hangers?
Expert:  StructuralEng replied 12 months ago.
Are the existing hangers wider than the existing joists?
Customer: replied 12 months ago.
They flare. I've attached a photo.
Expert:  StructuralEng replied 12 months ago.
There is no space to add a new joist in the old hanger
Customer: replied 12 months ago.
No
Expert:  StructuralEng replied 12 months ago.
Then I would stop it just short of the existing hanger and make sure there enough fasteners to transfer the load from the sister, through shear, back into the origina joist to be supported by the hanger
Customer: replied 12 months ago.
What types of fasters and what spacing? Are screws acceptable? Lag bolts? I don't want to drill through the beams unless necessary.
Expert:  StructuralEng replied 12 months ago.
3 - 1/4" Simpson SDS screws at the end and every 12" along the length
Customer: replied 12 months ago.
Is there any advantage to hanging engineered beams between the existing joists instead?
Expert:  StructuralEng replied 12 months ago.
Then you still have the issue of the existing joist notches. I suppose there is an option where you install a light gauge strap to the bottom, full length. That would be easier installation
Expert:  StructuralEng replied 12 months ago.
I would need to submit an additional service offer, though, to design the strap and the fastening pattern to the joists
Customer: replied 12 months ago.
sistering the seven notched joists will strengthen the notched beams but also add additional load capacity to the flat roof?
Expert:  StructuralEng replied 12 months ago.

It will lessen the impact of the notch.

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