Is a torsion box the best solution?

[iublue]

I'm suggesting relocating the basement entrance, not putting the metal door in the room.
It's only "overly melodramatic" until someone gets hurt.  Just trying to help.

I appreciate the help.  I brought up your concerns to the homeowner.  To relocate the opening to the outside would be a major job costing thousands for dollars.  Moving the stairs was an option that the homeowner looked into.  IIRC, the price he was given was 5K.

I see virtually no scenario where anyone could get hurt.  The door will be as stiff as the floor and will be support on all four sides.  Where is the danger?

Codes are wonderful guides to go by but they are not the end all and be all and generally they are the minimum acceptable standard.  Is L/360 still code for a floor span?  If it is, have you ever walked on a L/360 floor?  Way to much give for my taste.

I have built everything from furniture to 1800 Sq Ft ranch homes to a 4000 Sq Ft 5 level home to a multi-million dollar movie theater so I am supremely confident that I can build a door that will not pose ANY risk to anyone.  But you could very well be right and if they sell the home, the inspector might very well flag it and it will have to be addressed at that time but there is a very good chance that it will be the homeowners kids that will have to deal with it.

[NickNC]

I appreciate the help.  I brought up your concerns to the homeowner.  To relocate the opening to the outside would be a major job costing thousands for dollars.  Moving the stairs was an option that the homeowner looked into.  IIRC, the price he was given was 5K.

I see virtually no scenario where anyone could get hurt.  The door will be as stiff as the floor and will be support on all four sides.  Where is the danger?

Codes are wonderful guides to go by but they are not the end all and be all and generally they are the minimum acceptable standard.  Is L/360 still code for a floor span?  If it is, have you ever walked on a L/360 floor?  Way to much give for my taste.

I have built everything from furniture to 1800 Sq Ft ranch homes to a 4000 Sq Ft 5 level home to a multi-million dollar movie theater so I am supremely confident that I can build a door that will not pose ANY risk to anyone.  But you could very well be right and if they sell the home, the inspector might very well flag it and it will have to be addressed at that time but there is a very good chance that it will be the homeowners kids that will have to deal with it.

Honestly iublue, I’m not trying to be difficult.  I found the thread interesting and always enjoy a unique solution to an issue, which is why I got into this business.
 
As I drew your solution up in my head, several flags went up.  My biggest heartburn is that plywood isn’t structural lumber.  My immediate thought went to “why not simply use 2x6’s” like the rest of the floor system.  My brain went immediately to a “hay drop hatch” similar to the hatch used in hay lofts or what has been described as this “through-loft”.  A simpler design would be like this trap door or this one.  Of course there’s also several commercial solutions as well that have been presented.
 
The other thing that hit me was that while it may be “stiff”, there’s a big difference between stiffness and strength.  Plywood has no structural span rating, and as sure as I thought I could do it, I couldn’t find a load table that proved me right.  JE Gordon’s book “Structures: Or Why Things Don't Fall Down” has a lot of insight into this difference.
 
In the end, thinking of our own permit and inspection process here – I live in the big city where they consider codes the minimum you will comply with, not simply a guide – I figured they wouldn’t let me do it anyway.
 
Whatever you come up with, post pictures.  I’m always interested in the unique solution.  And yes, I agree, the L/360 limit is a bit squishy.  I think that’s been changed to 1/360, but I’ve been working in concrete and steel for the last decade or so and my limits are 1/720.