Stairwell opening

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Old 08-13-19, 11:58 AM
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Stairwell opening

HI Everyone,
I want to cutout a stairwell opening with actual stairs that lead from the main living space to the basement, as the current entry to the basement is pretty much a ladder thru a trap door. I have attached a picture that represents my project. Additional info: My house is a small 800 feet ranch built in the 50s. Next to the stairwell will be a bedroom with a queen bed and a closet . So the floor will be essentially supporting the weight of a bedroom. From my research online this is what i understand. Support the floor with a temp wall wall made of 2 by 4s . Cut the subfloor and the joists. Sister up joist along the opening represented by the green lines on the picture. Connect the floor joist with joist hangers where they connect perpendicularly and Support with lally column underneath.Considering i Will be cutting 6 joists should i put 2 lally colums at the ends or just one in the middle? Im looking at the concrete filled non-adjustable kind for added support. . Should i do a footing or just let the lally colum rest on the concrete slab of the basement considering its just supporting a 10 by 12 bedroom ? . Lastly, I feel pretty confident in doing this and im farily handy but I have never undertaken a project of this magnitude . Are there things I should be aware of or is it better to hire a professional ? All help will be greatly appreciated.
Thanks
Sean
 
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Old 08-13-19, 05:17 PM
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The answers to your questions get into structural engineering, which we do not usually provide for free sight unseen... its something you usually need a permit for, the changes need to be approved by your local building inspector, and he will usually only approve them if they are acompanied by plans that are authorized by a structural engineer in writing (who has looked at it in person). Occasionally they will approve plans if you seem to know what you are doing, present it well with a clear plan that meets all codes and you have span tables and references to back yourself up. In that case you will need to be able to present your facts clearly yourself.

So in short, you should really have a structural engineer approve your plan.

From what I can see, and I'm just your run of the mill carpenter, TABLE R602.7(2) indicates that a triple 2x8 header supporting floor only, can only span 7'2". Not enough for your 9' opening. Is there some reason you can't build a load bearing wall under that triple header? Because that would be much easier than columns. And yes, since the concrete floor would be load bearing you would need to cut the floor open, excavate deeper, and pour a rebar reinforced footing. A load bearing wall cannot just sit on an existing floor unless a structural engineer says it can.

Just some advice, you will want to present your inspector with a drawing that is to scale. Top view and side view.

You will also want to draw a side view of your stairs and verify your headroom on the stairs before you even begin. Stairways require a minimum of 80" headroom vertically as measured from any stair nosing to the finished ceiling above / bottom of your joist. That might affect the length of your opening if your basement is not deep enough, 9' may not be enough opening.
 
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Old 08-14-19, 05:33 PM
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Hi there,
Firstly let me just say that I appreciate your time and help in this matter. I want to at least have a solid perspective before I approach a structural engineer . That way i can draw up a reasonably plan before consulting and consequently keep the consultation as minimal as possible .
My basement has low ceiling , its about 88 inches . From what i researched online( pdf of irc code for stairs in NJ) I found the Min tread has to be 9" and Max rise is 8.25" with clearance of 80".( Unless this is wrong then perhaps i will need to have a L shaped stairwell) . So with a rise of 8 inch i will need 11 risers/10 treads .And the stairwell opening is 9ft 4 inches to be exact. I plan to do 8 treads of 10 inch each (9 +1 for nose) which comes to a total run of 80 inches and rise of 64 inches .The last 2 steps will be winders in a 34 inch square. Head room will not be an issue throughout the steps.
About the spans , I plan to use LVL 2 by 8 for the header . The entire floor of my house is build with 2 by 8s and they span 15 ft everywhere. Thats the reason I chose 2 by 8. But if putting 2 by 8s wont do then perhaps i can consider putting a metal I beam. I chose a column instead of a load bearing wall because My basement can get pretty damp and humid so I figured painted metal would deteriorate at a slower rate than wood. But if i go this route then I suppose the rebar reinforced footing will be throughout the entire area where the wall comes in contact with the basement floor ?
Again thanks for your insight.
Best
Sean
 
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Old 08-14-19, 05:37 PM
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Your maximum rise is probably 7 3/4". Stairways also shall not be less than 36" wide, so no 34" winders... See link Yes, the footing would be under the entire length of the wall, unless they grant you an exception. Your bottom plate will be pressure treated, rest of wall should be SPF.

With that ceiling height, it sound likes your opening needs to be as long as the entire stringer is. And your stair height will be 88/12, or 7.33".
 
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