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StructuralEng
StructuralEng, Structural Engineer-expert
Category: General
Satisfied Customers: 4829
Experience:  Licensed Structural Engineer
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what size header do I need for a 16 foot span, it is on an

Customer Question

what size header do I need for a 16 foot span, it is on an exterior wall with a shed porch above
Submitted: 3 years ago.
Category: Structural Engineer
Expert:  StructuralEng replied 3 years ago.

StructuralEng :

Hi, I can help you

StructuralEng :

What is the length of the joists that is supports?

StructuralEng :

Where are you located so I can look at snow load.

Customer:

Im in Lubbock Texas

StructuralEng :

And the length of joist that it supports?

Customer:

Yhe porch is about 12 feet deep and the porch joists extend above the roof line for about a 4/12 pitch

StructuralEng :

You can get away with a triple 2x12. Doug-Fir No.1 or equivalent grade/species combination.

StructuralEng :

If you've found my answer helpful, please "accept" it. I'll be happy to answer additional questions on the topic. If you could provide feedback, I would appreciate it.

Customer:

the header is across one of those jeldwen sliding glass doors that has an 8 foot opening when fully extended, does that make any difference? also we have a pier and beam foundation, any special shoring up required for that?

StructuralEng :

Ok. I'll hold a more stiff deflection criteria because of the sliders.

StructuralEng :

You'll want a quadruple 2x12, or you can use engineered lumber (which will be much smaller)

StructuralEng :

3-1/2" x 11-1/4" LVL with the following minimum properties: Fb=2600 psi, Fv=285 psi, E=1900 ksi.

Customer:

Thanks so much, my installers cut about 30% of the existing header away to make the door "fit" I told them that would not fly especially with the addition of the porch added to the structure.

StructuralEng :

Is there joists framing in from both sides to this beam?

StructuralEng :

30% is huge. I hate when contractors take such liberties!

Customer:

I'm not sure I understand what that means,

StructuralEng :

I initially thought that one side had joists and the other side didnt't (i.e. that it was supporting load from one side only), but one of your recent statements made me think otherwise.

Customer:

the framer that built the porch called it a cripple so it is supported from the roof and from the adjoining side of the structure

StructuralEng :

It's supporting the porch roof (8' joists), correct? Is it also supporting the house roof? If so, what is the length of the rafters of the house?

Customer:

the main house rafters are about 16 feet in length

StructuralEng :

Ok, that will change my recommendation.

StructuralEng :

Give me just a minute

StructuralEng :

One more question. I just need to make sure I'm giving you the right advice. Is the 16' the distance from the beam to the ridge? Do you know if you have a ridge beam or a ridge board? If you don't know the ridge beam or ridge board question, I just assume a ridge board, since that is conservative.

Customer:

the main house roof has a scissor truss framing if that helps

StructuralEng :

Gotcha. Is the 16' the total length of the scissor truss or half the length (from eave to ridge)?

Customer:

I think its more like 16 feet from eave to ridge

StructuralEng :

ok

StructuralEng :

Give me a min

StructuralEng :

5-1/4" x 14" deep LVL with the same properties listed above. This will hold L/400 deflection to ensure it doesn't interfere with the performance of the sliders.

StructuralEng :

If you've found my answer helpful, please "accept" it. I'll be happy to answer additional questions on the topic. If you could provide feedback, I would appreciate it.

Customer:

can I sister on to the existing header as replacing it will entail an extensive demo of the brand new lovely stucco job we could bolt onto the existing header with some support posts on either side, maybe not ideal but is that a possibility?

StructuralEng :

I don't like that idea.

StructuralEng :

You'll have to bolt completely through anyway.

StructuralEng :

If you want to take that approach, I suggest using a steel channel.

Customer:

I'll talk it over with the installers as they are responsible for fixing the mess they made. I want to be reasonable but I also dont want the door or my walls to fail. any other suggestions as to how to fix it without diturbing the outer shell any more than necessary, would a steel channel be installed between 2by 12 or go directly over the existing header'

StructuralEng :

The channel would get installed on the inside of the existing header.

Customer:

how thick and how wide would that need to be?

StructuralEng :

Give me a minute to size it

StructuralEng :

C10x20. It's a 10" deep channel and weighs 20 pounds per foot.

Customer:

ok I think I understand. Thanks so much for your help. how would you apprach this problem if it was your house

StructuralEng :

If it were my home, I would make them completely take out the affect member and replace it. They took action that they shouldn't have and I would want the fix that makes me feel most comfortable.

Customer:

thanks have a great day

StructuralEng, Structural Engineer-expert
Satisfied Customers: 4829
Experience: Licensed Structural Engineer
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