Double-up floor joist?

[geraldthehamster]

My first floor joists are 7in x 2in, at 400mm centres. They span about

2.4m. Counting from one side of the room, the first joist is 3in from the wall - if I remove the second joist, to create a stair well, in principle does the third joist, which is now at the edge of the stair well, need to be doubled up, and if so why? Would it make a difference if a cast iron bath were to be placed in that part of the room?

Regards Richard

[Jules]

Speculation follows, IANASE etc. :-)

Is a vertical support at the top of the stairs running to the floor below an option? Depends what the implications are of transmitting load to that floor below, but if it's solid beneath I suspect that'd do the job.

Presumably some load on the floor is spread to the walls 'sideways' at right-angles to the joists, so cutting out a big hole for stairs does weaken things a bit, but by how much I'm not sure.

(Interesting question, anyway - I'm thinking about putting in some proper stairs for the first floor in our barn, so would have the same issues)

cheers

Jules

[geraldthehamster]

Yes, I'm interested in the theory as well as the practice. I can see that a new stud wall built onto what is now the "edge joist" might necessitate doubling up to support it, but is it necessary in any case because the joist is at the edge? If so, I don't understand the physics ;-)

Regards Richard

[John Rumm]

----------------------------------------- Wall ========================================= Joist

========================================= Joist

========================================= Joist

========================================= Joist

========================================= Joist

And you want:

----------------------------------------- Wall ========================================= Joist

Stair well

========================================= Extra Joist ========================================= Joist

========================================= Joist

========================================= Joist

There are a number or reasons why its often doubled. One would certainly be of you wanted a wall on the top of it running its length. Another would be (depending on design) it may need to carry a proportion of the load of the staircase. Another possibility is when you don't want to take the full length of a joist out, and need a "trimmer" to support the the cut end:

----------------------------------------- Wall ========================================= Joist # # #==================== Cut Joist #

[george (dicegeorge)]

there will be a lot more stress and strain with people running up and down the stairs, lugging heavy things up and down etc, you dont want to finish it off beautiful and have the building inspector tell you to do it again, or it to come loose after a few years use and abuse.

[g]

[geraldthehamster]

The building what, sorry? ;-)

Regards Richard

Regards Richard