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Subfloor over joists hung from beam/header

AdamE | Posted in Construction Techniques on April 24, 2024 11:17pm

I’ll do my best to explain this; 

I have an 8′ opening in a 16′ wall between my living room and dining room with a doubled up 2×12 header supprting that span. The joists in both the living room and dining room run perpendicular  to this header for that 8′ span. The joists sit in joist hangers where they meet the header, and on the wall otherwise. I would like to add some usable space in the attic (above these joists) and want to put a subfloor over the joists. Assuming the joists are thick enough to handle the weight (they are) do I have anything to worry about across this span? Am I correct in assuming that this header would support a wall on top of it? (I want to create a bedroom over the dining room, and a great room over the living room)

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  1. User avater
    unclemike42 | Apr 25, 2024 06:21am | #1

    You have to run the numbers, (or check some tables)

    Need the lumber grade and the width of the building.

    https://codes.iccsafe.org/s/IRC2021P2/chapter-6-wall-construction/IRC2021P2-Pt03-Ch06-SecR602.7

    1. User avater
      AdamE | Apr 25, 2024 07:50am | #2

      Thanks!

      Since this is an interior wall, I’m assuming that I am in the second table. Am I looking at “one floor only” or “two floors”?

      Is this referring to what is above the header? If so, it looks like I’m good to 10’-9” ?

      1. User avater
        unclemike42 | Apr 26, 2024 06:41am | #4

        That column applies if the distance between exterior walls is 12 feet.

        How wide is this part of your house?

        (which is another way of asking what total span length of the floor joists on both sides of your header)

        If the floor joists are ten feet long on one side of your header, and 8 feet on the other, 18 feet would be the building width, and note 3 (which says you can interpolate) would lead to an acceptable span length of up to 9'2'' for the header made of #2 2x12 in one of the species listed. Probably need the pair of jack studs on each end. (check my math. It is your house..)

        1. User avater
          AdamE | Apr 26, 2024 09:03am | #5

          I appreciate the help.

          Looking at it from the attic, this header does not appear to be supporting anything but the joists butted into it. It rests on two load bearing walls itself, but appears to be in place to support the joists and allow for the 8' opening between the two rooms. Nothing rests on top of it.

          There are 5 joists hung from either side of it, joists over the living room span 15', joists over the dining room span 13'

          My intent was to add a room above the dining room with a wall running parallel to this header, but extending beyond it either side. Looks like with a 28' span I may be about a foot over spanned for this header though

          Would there be any way to beef it up?

  2. sana234 | Apr 25, 2024 11:51am | #3

    thank you

  3. User avater
    tvasteconstructions | Apr 29, 2024 05:19am | #6

    Given the doubled up 2x12 header and the perpendicular joists in both rooms, adding a subfloor over the joists should be structurally sound. Ensure proper weight distribution for safety. Yes, the header should support a wall above it, allowing for additional rooms as planned.

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