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Old 05-06-2012, 10:58 AM   #1
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New construction of second floor, would 2x8' be okay to use instread of 2x12'?


We have bought a high school gym and we are making it our home. It has great bones. We are going to build a second floor and was thinking that it would be ok to use 2x8 floor joist instead of 2x12 floor joist, What do you think?

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Old 05-06-2012, 11:04 AM   #2
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New construction of second floor, would 2x8' be okay to use instread of 2x12'?


It totally depends on the span and the load on those joists.

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Old 05-06-2012, 11:08 AM   #3
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New construction of second floor, would 2x8' be okay to use instread of 2x12'?


if you hae to question it then go bigger, why not 2x10?
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Old 05-06-2012, 11:09 AM   #4
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New construction of second floor, would 2x8' be okay to use instread of 2x12'?


Span will be 14 ft to 14 1/2ft and it will have 2 bedrooms 3/4 bath and a sitting area.
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Old 05-06-2012, 11:20 AM   #5
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New construction of second floor, would 2x8' be okay to use instread of 2x12'?


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Originally Posted by wesshe69
Span will be 14 ft to 14 1/2ft and it will have 2 bedrooms 3/4 bath and a sitting area.
You designing this yourself and drawing it up to bring to the building department for permits and inspections?
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Old 05-06-2012, 11:20 AM   #6
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New construction of second floor, would 2x8' be okay to use instread of 2x12'?


We have had contractor tell us that he would use 2x12 even at the 14ft span, then We have had another contractor tell us that 2x8 would be good with 14ft span. We dont mind going with 2x12 if that is what is needed however if 2x8 is going to the same as a 2x12, why spend the extra money....We feel sure that we will be going with the 2x10. What is the rule of thumb for the size of the floor joist for the span?
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Old 05-06-2012, 11:24 AM   #7
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New construction of second floor, would 2x8' be okay to use instread of 2x12'?


We live in an unincorporated town...We dont have to have a building inspector. We are not changing the existing structure, it is the shell. We will be adding walls...The only permit that is need in the town and state is electrical. We have been talking with several building contractors and their advise differ.
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Old 05-06-2012, 11:28 AM   #8
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New construction of second floor, would 2x8' be okay to use instread of 2x12'?


2x8 for a 14' span will make a bouncy floor, I would advise against it. Stop talking to the guy who suggested 2x8's he doesn't have a clue.

My personal recommendation is to use TJI or BCI engineered floor joists, they are far superior to dimensional lumber.
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Old 05-06-2012, 11:29 AM   #9
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New construction of second floor, would 2x8' be okay to use instread of 2x12'?


JOE, We live in an unincorporated town...We dont have to have a building inspector. We are not changing the existing structure, it is the shell. We will be adding walls...The only permit that is need in the town and state is electrical. We have been talking with several building contractors and their advise differ.
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Old 05-06-2012, 11:30 AM   #10
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New construction of second floor, would 2x8' be okay to use instread of 2x12'?


Thinking about that as well.
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Old 05-06-2012, 11:34 AM   #11
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New construction of second floor, would 2x8' be okay to use instread of 2x12'?


2x8's are going to be very bouncy....and that is if you do it 12" OC.

If your worried about the cost difference between 2x8 vs 2x12....then you should not be doing the project.

I'm doing a 2-story addition right now....the upstairs is 2x12 12" OC....the original house is 2x8 12" OC...BIG difference....

Additionally, I used 1 1/8" T&G upstairs.....I've had several people comment that it almost feels like they are walking on concrete.....yea...it's that firm...

Do all the work yourself and save a lot of money....

If you want to see what mine looks like....click on the link in my signature....
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Old 05-06-2012, 11:35 AM   #12
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New construction of second floor, would 2x8' be okay to use instread of 2x12'?


Quote:
Originally Posted by wesshe69 View Post
We have bought a high school gym and we are making it our home. It has great bones. We are going to build a second floor and was thinking that it would be ok to use 2x8 floor joist instead of 2x12 floor joist, What do you think?

We will be adding walls...

Span will be 14 ft to 14 1/2ft and it will have 2 bedrooms 3/4 bath and a sitting area.
So you have a big open area that is most likely on a slab and you will be framing walls on top of this slab around 14'-14' 6" supporting a second floor. What do you intend to do about footings underneath these walls that will be supporting the second floor?
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Old 05-06-2012, 11:36 AM   #13
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New construction of second floor, would 2x8' be okay to use instread of 2x12'?


If not permitted/inspected and it fails, people can die.
Is it worth your life and/or the lives of your loved ones to not have it drawn up and the proper calculations run?

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Old 05-06-2012, 11:46 AM   #14
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New construction of second floor, would 2x8' be okay to use instread of 2x12'?


We do want to make this a solid safe and sound house. We are talking and getting our options down on paper to make the very best choice for us and our investment.
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Old 05-06-2012, 11:51 AM   #15
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New construction of second floor, would 2x8' be okay to use instread of 2x12'?


Okay, so you do not need a permit. You still need to decide the basis of design. There are only five ways I know of to determine the basis of design for a structure. Here they are, not in any particular order:

1. Build to code. If there is a particular code for your area, you use that. If there is no code for your area, you select a reasonable code such as the International Residential Code, and go by the requirements of that code.

2. Build according to architectural and engineering plans. This requires you to hire an architect and engineer. This may be necessary if you are building a structure that is beyond standard code, for example you are building an underground house and code does not address such a structure. Also, if you go this method, you can design using materials not discussed in code, so you have more flexibility than strict code design.

3. Build by copying another structure. You examine another structure that is similar to the one you propose, and attempt to duplicate the construction technique.

4. Build by experience. Many contractors are familiar with construction practice based on their personal experience, so they build that way. No code, no engineering calculations, this is kind of a variant on technique 3. The problem with this approach is that any flaws in the design are repeated on the next project.

5. Build by guesswork. This is the technique of last resort. You have no idea how to build based on code, calculations, experience, and there is no similar structure to copy, so you just guess. Very dangerous approach.

My suggestion to you is to decide on which code you would like to base your design on. I suggest the International Residential Code, latest edition. There are tables in the code that should allow your contractor to select an appropriate sized joist for your application. If for some reason you want to deviate from code, or code is not applicable to your specific situation, I suggest hiring an architect to help you through the design process. I have seen may structures built by methods 3, 4 and 5, I do not recommend those approaches.

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