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Bonus room floor joists - checking with the experts

Bonus room floor joists - checking with the experts


  #1  
Old 05-09-06, 05:49 PM
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Bonus room floor joists - checking with the experts

Hello all,

Searched around the forum, checked my building codes, and did some more research online... but wanted to have one more sanity check from the experts on this forum.

I am finishing a bonus room above my garage. It is 23.5' x 23.5' supported by an I beam underneath. It has attached stairs and has been used as storage since the house was built. I have pulled up the plywood floor (1/2" plywood) to insulate. The floor joists are 2x8 16"-OC that span 12' from either side and overlap at above the I-beam. The floor joists have the following stamped on them - "Northwood Kiln Dried 2." According to my NC building codes: Joist Span I should be fine.

I am writing to just confirm three things:
1) Am I interpreting the codes correctly and am okay without any joist modification?
2) Am I okay laying back down the 1/2" plywood subfloor or should I go with thicker? (It is not spongy at all due to 16"-OC)
3) There used to be a pull-down staircase before they built the permanent one and it was framed in with headers. When they closed it up, they ran a 2x8 across the middle of the opening where the joist would have been that was cut out to accomodate the pull down steps. Is this sufficient?

Obviously, I have my building permit and am going to get all the appropriate inspections. Just wanted to quatdruple check .

Thanks in advance,
Charles
 
  #2  
Old 05-09-06, 07:49 PM
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Charles: welcome to the forums. What part of NC are you in?
Taking in order: 1) I do some work in NC, and it seems the span versus the size of joisting is well within parameters, especially with 16oc.
2) I believe I would go ahead with Advantek subflooring, since it is tongue and groove. What type of final flooring are you planning. If it is full 3/4" hardwood, you may very well be ok with the 1/2", but marginally. With carpeting or laminates, you won't be satisfied with the thinner subflooring.
3)You will be spanning this space with the subflooring, so the repair piece will give adequate support.
 
  #3  
Old 05-10-06, 07:59 AM
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Chandler,

Thanks very much for your answers!

I am in Cary, NC.

I was originally thinking carpet for this room due to ease of installation but since it will be an office, hardwoods might be a nicer touch. Changing the subflooring will be a real bummer since the stairs are a bit tight getting 4x8 sheet up there. They fit but it is difficult (hence why I am going to contract out the drywall ). Anyway, you feel that carpet over my existing flooring even with 16-OC is not the way to go huh?

Thanks,
Charles
 
  #4  
Old 05-12-06, 06:04 AM
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"2) Am I okay laying back down the 1/2" plywood subfloor or should I go with thicker? (It is not spongy at all due to 16"-OC)"

I think you need to have a chat with your local building official
regarding the structure and function of a diaphragm.
Your 1/2" ply as sub-flooring is substantially insufficient for meeting the live and dead load requirements for any occupancy, other than lite storage.
The floor diaphragm requires the sub-flooring to extend to, AND be
correctly fastened to the rim joist and blocking.
Diaphragm shear is the resistance to twisting or racking FROM the action generated by the effects of both live and dead loading.
If you cut the ply at the inside of the perimeter walls to remove, you should expect to be required to install blocking and teco clips to reestablish the diaphragms connection to the structural perimeter.

Regarding your stairway. There are specific min. requirements for egress based upon occupancy.
Apparently you do not meet them.
 
  #5  
Old 05-12-06, 05:01 PM
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Snoonyb,

I appreciate the response. Regarding the stairwell... I have over 90" vertical clearance through the entire slope and greater than 36" width including handrail, over 32" inside handrail. From my interpretation, this meets NC building codes.

After reading your response and reading through the NC codes, I still have one question regarding the subfloor...

After insulating under the floor and getting it inspected (which our inspectors said they would do)..

can I:

- nail back down the 1/2 ply
- frame up the knee walls and partition walls
- install tounge and groove subflooring in the inhabitable space over the 1/2 ply

That would only leave the storage space behind the knee walls with the 1/2 ply.

Thanks,
Charles
 
  #6  
Old 05-12-06, 07:26 PM
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I have a moral and ethical obligation to caution you against what I know from practical experience to be an unsafe practice,
so I have elected to reiterate my previous comments.
If they are still not clear to you, you'll notice that I've also suggested that you have a conversation with your local building official.

Please, do not build an unsafe structure!

"can I:

- nail back down the 1/2 ply

I think you need to have a chat with your local building official
regarding the structure and function of a diaphragm.

The floor diaphragm requires the sub-flooring to extend to, AND be correctly fastened to the rim joist and blocking.

- frame up the knee walls and partition walls

Diaphragm shear is the resistance to twisting or racking FROM the action generated by the effects of both live and dead loading.
If you cut the ply at the inside of the perimeter walls to remove, you should expect to be required to install blocking and teco clips to reestablish the diaphragms connection to the structural perimeter.

- install tounge and groove subflooring in the inhabitable space over the 1/2 ply

Your 1/2" ply as sub-flooring is substantially insufficient for meeting the live and dead load requirements for any occupancy, other than lite storage.

You can add 10' of thickness to your 1/2" NONCONFORMING subfloor and it will DO NOTHING to reestablish the REQUIRED
diaphragm shear mandated by your change in occupancy.

That would only leave the storage space behind the knee walls with the 1/2 ply."

The floor diaphragm requires the sub-flooring to extend, uninterupted, to, AND be correctly fastened to the rim joist and blocking.
 
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Old 05-13-06, 06:28 AM
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Thanks for the response. I will make sure I speak with a builder friend of mine regarding the subfloor. He has been building houses around here for almost 20 years. I appreciate your concern regarding an unsafe structure and that is precisely why I am asking questions on this forum and conforming to all local codes and inspections. I thought that was the purpose of this forum... to obtain advice and knowledge from others.

Thanks again,
Charles
 
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Old 05-13-06, 07:07 AM
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Originally Posted by zx7king
I thought that was the purpose of this forum... to obtain advice and knowledge from others.
And you haven't?
Because you "don't like it", and it doesn't fit your, "interpretation" of the code you are reading, doesn't mean that the advice isn't sound.

Yet, even though you have been advised to consult with your local building official, who, by the way, is the GOVERNING authority, you have elected to,
Originally Posted by zx7king
I will make sure I speak with a builder friend of mine regarding the subfloor.
, who probably has no legal authority, at all.

Originally Posted by zx7king
I appreciate your concern regarding an unsafe structure and that is precisely why I am asking questions on this forum and conforming to all local codes and inspections.
Again, have a chat with your local building official, BEFORE, you nail your 1/2" ply.
 
  #9  
Old 05-13-06, 10:37 AM
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I have abandoned the idea of keeping the 1/2 ply and will be replacing it with the correct subfloor material and fastening it to NC code standards.

Regarding your comment:
And you haven't?
Because you "don't like it", and it doesn't fit your, "interpretation" of the code you are reading, doesn't mean that the advice isn't sound.
Yes, I have received advice and do appreciate it. When did I once say I did not like the advice? Read through the thread, I have been nothing but thankful for the responses. I do not appreciate the tone of your response above.
 
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Old 05-13-06, 02:52 PM
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Bonus room floor joists - checking with the experts

It is hard to be a building code inspector until you have seen the project.

If not seeing it, you are interpreting one person's opinion (DIYer) of what he sees from an observational viewpoint and may not be able to added the important information that may be relevent.

The building official is in the best position to evaluate the project.

As a structural engineer, diaphragms and similar structural features are rarely required unless you are in some seismic areas. Often there are other factors that seem unimportant like other bracing and aspect ratios that offer the required structural needs.

I would never try to out-guess an official unless I had seen the project or was not an engineer.

Dick
 
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Old 05-13-06, 06:57 PM
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"When did I once say I did not like the advice? Read through the thread, I have been nothing but thankful for the responses."

"I thought that was the purpose of this forum... to obtain advice and knowledge from others."

Would that be a bit of sarcasm?

Yes, you have been appreciative, however, you were also insistent upon using the 1/2" ply as sub-flooring. So much so that your response led me to believe that you had not read my response.

I do not appreciate the tone of your response above.

That's your choice, however, if I have caused you think, to consider, to ask an authority if your interpretations are correct or need some clarification, and in doing so cause you to gain the knowledge to build a safe building, save you a potential loss, then, by all means, be insulted.

By the way, there are several of us contributors in here, that
when we started building, your friend with 20yrs experience, was a twinkle in his daddy's eye.
 
  #12  
Old 05-13-06, 07:32 PM
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Originally Posted by Concretemasonry
The building official is in the best position to evaluate the project.

As a structural engineer, diaphragms and similar structural features are rarely required unless you are in some seismic areas. Often there are other factors that seem unimportant like other bracing and aspect ratios that offer the required structural needs.
I learned early on that all floor systems are diaphragms and transfer the effects of live loading to the perimeter of the diaphragm, to the foundation.

The OP is working on 2 story structure which he intends to change the occupancy from that of lite storage to an office.
Live loads will be dramatically increased.

An example of what I believe he has created would be like cutting a square out of a sheet of paper, laying them on a flat surface assembled, placing your hand on the inner square and twisting back and forth, while holding the outer square fixed.

Assuming that in a residential structure exceeding 8' in height,
wind, not seismic governs. That floor diaphragm, whose integrity has been compromised, is a key component in the structures ability to resist the racking forces of the wind.
 
 

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